Mitotic G2 (gap 2) phase is the second growth phase during eukaryotic mitotic cell cycle. G2 encompasses the interval between the completion of DNA synthesis and the beginning of mitosis. During G2, the cytoplasmic content of the cell increases. At G2/M transition, duplicated centrosomes mature and separate and CDK1:cyclin B complexes become active, setting the stage for spindle assembly and chromosome condensation that occur in the prophase of mitosis (O'Farrell 2001, Bruinsma et al. 2012, Jiang et al. 2014).
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Bublik DR, Scolz M, Triolo G, Monte M, Schneider C.; ''Human GTSE-1 regulates p21(CIP1/WAF1) stability conferring resistance to paclitaxel treatment.''; PubMedEurope PMCScholia
Chiyoda T, Sugiyama N, Shimizu T, Naoe H, Kobayashi Y, Ishizawa J, Arima Y, Tsuda H, Ito M, Kaibuchi K, Aoki D, Ishihama Y, Saya H, Kuninaka S.; ''LATS1/WARTS phosphorylates MYPT1 to counteract PLK1 and regulate mammalian mitotic progression.''; PubMedEurope PMCScholia
Chan EH, Santamaria A, Silljé HH, Nigg EA.; ''Plk1 regulates mitotic Aurora A function through betaTrCP-dependent degradation of hBora.''; PubMedEurope PMCScholia
Strausfeld U, Labbé JC, Fesquet D, Cavadore JC, Picard A, Sadhu K, Russell P, Dorée M.; ''Dephosphorylation and activation of a p34cdc2/cyclin B complex in vitro by human CDC25 protein.''; PubMedEurope PMCScholia
Kruiswijk F, Labuschagne CF, Vousden KH.; ''p53 in survival, death and metabolic health: a lifeguard with a licence to kill.''; PubMedEurope PMCScholia
Källström H, Lindqvist A, Pospisil V, Lundgren A, Rosenthal CK.; ''Cdc25A localisation and shuttling: characterisation of sequences mediating nuclear export and import.''; PubMedEurope PMCScholia
Bonnet J, Mayonove P, Morris MC.; ''Differential phosphorylation of Cdc25C phosphatase in mitosis.''; PubMedEurope PMCScholia
Seki A, Coppinger JA, Du H, Jang CY, Yates JR, Fang G.; ''Plk1- and beta-TrCP-dependent degradation of Bora controls mitotic progression.''; PubMedEurope PMCScholia
Parker LL, Piwnica-Worms H.; ''Inactivation of the p34cdc2-cyclin B complex by the human WEE1 tyrosine kinase.''; PubMedEurope PMCScholia
Macůrek L, Lindqvist A, Lim D, Lampson MA, Klompmaker R, Freire R, Clouin C, Taylor SS, Yaffe MB, Medema RH.; ''Polo-like kinase-1 is activated by aurora A to promote checkpoint recovery.''; PubMedEurope PMCScholia
Strausfeld U, Fernandez A, Capony JP, Girard F, Lautredou N, Derancourt J, Labbe JC, Lamb NJ.; ''Activation of p34cdc2 protein kinase by microinjection of human cdc25C into mammalian cells. Requirement for prior phosphorylation of cdc25C by p34cdc2 on sites phosphorylated at mitosis.''; PubMedEurope PMCScholia
Hirota T, Kunitoku N, Sasayama T, Marumoto T, Zhang D, Nitta M, Hatakeyama K, Saya H.; ''Aurora-A and an interacting activator, the LIM protein Ajuba, are required for mitotic commitment in human cells.''; PubMedEurope PMCScholia
Seki A, Coppinger JA, Jang CY, Yates JR, Fang G.; ''Bora and the kinase Aurora a cooperatively activate the kinase Plk1 and control mitotic entry.''; PubMedEurope PMCScholia
Bruinsma W, Raaijmakers JA, Medema RH.; ''Switching Polo-like kinase-1 on and off in time and space.''; PubMedEurope PMCScholia
Alvarez-Fernández M, Halim VA, Aprelia M, Laoukili J, Mohammed S, Medema RH.; ''Protein phosphatase 2A (B55α) prevents premature activation of forkhead transcription factor FoxM1 by antagonizing cyclin A/cyclin-dependent kinase-mediated phosphorylation.''; PubMedEurope PMCScholia
McGowan CH, Russell P.; ''Human Wee1 kinase inhibits cell division by phosphorylating p34cdc2 exclusively on Tyr15.''; PubMedEurope PMCScholia
Xu M, Sheppard KA, Peng CY, Yee AS, Piwnica-Worms H.; ''Cyclin A/CDK2 binds directly to E2F-1 and inhibits the DNA-binding activity of E2F-1/DP-1 by phosphorylation.''; PubMedEurope PMCScholia
Jang YJ, Ma S, Terada Y, Erikson RL.; ''Phosphorylation of threonine 210 and the role of serine 137 in the regulation of mammalian polo-like kinase.''; PubMedEurope PMCScholia
Xing Y, Li Z, Chen Y, Stock JB, Jeffrey PD, Shi Y.; ''Structural mechanism of demethylation and inactivation of protein phosphatase 2A.''; PubMedEurope PMCScholia
Kumagai A, Dunphy WG.; ''Purification and molecular cloning of Plx1, a Cdc25-regulatory kinase from Xenopus egg extracts.''; PubMedEurope PMCScholia
Krek W, Ewen ME, Shirodkar S, Arany Z, Kaelin WG, Livingston DM.; ''Negative regulation of the growth-promoting transcription factor E2F-1 by a stably bound cyclin A-dependent protein kinase.''; PubMedEurope PMCScholia
Laoukili J, Alvarez M, Meijer LA, Stahl M, Mohammed S, Kleij L, Heck AJ, Medema RH.; ''Activation of FoxM1 during G2 requires cyclin A/Cdk-dependent relief of autorepression by the FoxM1 N-terminal domain.''; PubMedEurope PMCScholia
Yu D, Jing T, Liu B, Yao J, Tan M, McDonnell TJ, Hung MC.; ''Overexpression of ErbB2 blocks Taxol-induced apoptosis by upregulation of p21Cip1, which inhibits p34Cdc2 kinase.''; PubMedEurope PMCScholia
Mailand N, Podtelejnikov AV, Groth A, Mann M, Bartek J, Lukas J.; ''Regulation of G(2)/M events by Cdc25A through phosphorylation-dependent modulation of its stability.''; PubMedEurope PMCScholia
Voges D, Zwickl P, Baumeister W.; ''The 26S proteasome: a molecular machine designed for controlled proteolysis.''; PubMedEurope PMCScholia
Sakchaisri K, Asano S, Yu LR, Shulewitz MJ, Park CJ, Park JE, Cho YW, Veenstra TD, Thorner J, Lee KS.; ''Coupling morphogenesis to mitotic entry.''; PubMedEurope PMCScholia
Liu D, Liao C, Wolgemuth DJ.; ''A role for cyclin A1 in the activation of MPF and G2-M transition during meiosis of male germ cells in mice.''; PubMedEurope PMCScholia
Scolz M, Widlund PO, Piazza S, Bublik DR, Reber S, Peche LY, Ciani Y, Hubner N, Isokane M, Monte M, Ellenberg J, Hyman AA, Schneider C, Bird AW.; ''GTSE1 is a microtubule plus-end tracking protein that regulates EB1-dependent cell migration.''; PubMedEurope PMCScholia
Mailand N, Falck J, Lukas C, Syljuâsen RG, Welcker M, Bartek J, Lukas J.; ''Rapid destruction of human Cdc25A in response to DNA damage.''; PubMedEurope PMCScholia
Teixidó-Travesa N, Villén J, Lacasa C, Bertran MT, Archinti M, Gygi SP, Caelles C, Roig J, Lüders J.; ''The gammaTuRC revisited: a comparative analysis of interphase and mitotic human gammaTuRC redefines the set of core components and identifies the novel subunit GCP8.''; PubMedEurope PMCScholia
Hagting A, Karlsson C, Clute P, Jackman M, Pines J.; ''MPF localization is controlled by nuclear export.''; PubMedEurope PMCScholia
Nakajima H, Toyoshima-Morimoto F, Taniguchi E, Nishida E.; ''Identification of a consensus motif for Plk (Polo-like kinase) phosphorylation reveals Myt1 as a Plk1 substrate.''; PubMedEurope PMCScholia
Fu Z, Malureanu L, Huang J, Wang W, Li H, van Deursen JM, Tindall DJ, Chen J.; ''Plk1-dependent phosphorylation of FoxM1 regulates a transcriptional programme required for mitotic progression.''; PubMedEurope PMCScholia
Lindqvist A, Källström H, Karlsson Rosenthal C.; ''Characterisation of Cdc25B localisation and nuclear export during the cell cycle and in response to stress.''; PubMedEurope PMCScholia
Scrofani J, Sardon T, Meunier S, Vernos I.; ''Microtubule nucleation in mitosis by a RanGTP-dependent protein complex.''; PubMedEurope PMCScholia
Takizawa CG, Weis K, Morgan DO.; ''Ran-independent nuclear import of cyclin B1-Cdc2 by importin beta.''; PubMedEurope PMCScholia
Xu X, Wang X, Xiao Z, Li Y, Wang Y.; ''Two TPX2-dependent switches control the activity of Aurora A.''; PubMedEurope PMCScholia
Honda R, Ohba Y, Nagata A, Okayama H, Yasuda H.; ''Dephosphorylation of human p34cdc2 kinase on both Thr-14 and Tyr-15 by human cdc25B phosphatase.''; PubMedEurope PMCScholia
Maxwell CA, Keats JJ, Belch AR, Pilarski LM, Reiman T.; ''Receptor for hyaluronan-mediated motility correlates with centrosome abnormalities in multiple myeloma and maintains mitotic integrity.''; PubMedEurope PMCScholia
Mayor T, Stierhof YD, Tanaka K, Fry AM, Nigg EA.; ''The centrosomal protein C-Nap1 is required for cell cycle-regulated centrosome cohesion.''; PubMedEurope PMCScholia
Yamashiro S, Yamakita Y, Totsukawa G, Goto H, Kaibuchi K, Ito M, Hartshorne DJ, Matsumura F.; ''Myosin phosphatase-targeting subunit 1 regulates mitosis by antagonizing polo-like kinase 1.''; PubMedEurope PMCScholia
Vousden KH, Prives C.; ''Blinded by the Light: The Growing Complexity of p53.''; PubMedEurope PMCScholia
Jackman M, Firth M, Pines J.; ''Human cyclins B1 and B2 are localized to strikingly different structures: B1 to microtubules, B2 primarily to the Golgi apparatus.''; PubMedEurope PMCScholia
Dodson CA, Bayliss R.; ''Activation of Aurora-A kinase by protein partner binding and phosphorylation are independent and synergistic.''; PubMedEurope PMCScholia
Taniguchi E, Toyoshima-Morimoto F, Nishida E.; ''Nuclear translocation of plk1 mediated by its bipartite nuclear localization signal.''; PubMedEurope PMCScholia
Shi P, Zhu S, Lin Y, Liu Y, Liu Y, Chen Z, Shi Y, Qian Y.; ''Persistent stimulation with interleukin-17 desensitizes cells through SCFβ-TrCP-mediated degradation of Act1.''; PubMedEurope PMCScholia
Sen I, Veprintsev D, Akhmanova A, Steinmetz MO.; ''End binding proteins are obligatory dimers.''; PubMedEurope PMCScholia
Johnson EO, Chang KH, de Pablo Y, Ghosh S, Mehta R, Badve S, Shah K.; ''PHLDA1 is a crucial negative regulator and effector of Aurora A kinase in breast cancer.''; PubMedEurope PMCScholia
Petretti C, Savoian M, Montembault E, Glover DM, Prigent C, Giet R.; ''The PITSLRE/CDK11p58 protein kinase promotes centrosome maturation and bipolar spindle formation.''; PubMedEurope PMCScholia
De Baere I, Derua R, Janssens V, Van Hoof C, Waelkens E, Merlevede W, Goris J.; ''Purification of porcine brain protein phosphatase 2A leucine carboxyl methyltransferase and cloning of the human homologue.''; PubMedEurope PMCScholia
Wang G, Jiang Q, Zhang C.; ''The role of mitotic kinases in coupling the centrosome cycle with the assembly of the mitotic spindle.''; PubMedEurope PMCScholia
Liu Y, Lear T, Zhao Y, Zhao J, Zou C, Chen BB, Mallampalli RK.; ''F-box protein Fbxl18 mediates polyubiquitylation and proteasomal degradation of the pro-apoptotic SCF subunit Fbxl7.''; PubMedEurope PMCScholia
Hutterer A, Berdnik D, Wirtz-Peitz F, Zigman M, Schleiffer A, Knoblich JA.; ''Mitotic activation of the kinase Aurora-A requires its binding partner Bora.''; PubMedEurope PMCScholia
Hutchins JR, Toyoda Y, Hegemann B, Poser I, Hériché JK, Sykora MM, Augsburg M, Hudecz O, Buschhorn BA, Bulkescher J, Conrad C, Comartin D, Schleiffer A, Sarov M, Pozniakovsky A, Slabicki MM, Schloissnig S, Steinmacher I, Leuschner M, Ssykor A, Lawo S, Pelletier L, Stark H, Nasmyth K, Ellenberg J, Durbin R, Buchholz F, Mechtler K, Hyman AA, Peters JM.; ''Systematic analysis of human protein complexes identifies chromosome segregation proteins.''; PubMedEurope PMCScholia
Timofeev O, Cizmecioglu O, Hu E, Orlik T, Hoffmann I.; ''Human Cdc25A phosphatase has a non-redundant function in G2 phase by activating Cyclin A-dependent kinases.''; PubMedEurope PMCScholia
Monte M, Benetti R, Buscemi G, Sandy P, Del Sal G, Schneider C.; ''The cell cycle-regulated protein human GTSE-1 controls DNA damage-induced apoptosis by affecting p53 function.''; PubMedEurope PMCScholia
Takahashi M, Yamagiwa A, Nishimura T, Mukai H, Ono Y.; ''Centrosomal proteins CG-NAP and kendrin provide microtubule nucleation sites by anchoring gamma-tubulin ring complex.''; PubMedEurope PMCScholia
Casenghi M, Meraldi P, Weinhart U, Duncan PI, Körner R, Nigg EA.; ''Polo-like kinase 1 regulates Nlp, a centrosome protein involved in microtubule nucleation.''; PubMedEurope PMCScholia
Dynlacht BD, Flores O, Lees JA, Harlow E.; ''Differential regulation of E2F transactivation by cyclin/cdk2 complexes.''; PubMedEurope PMCScholia
O'Farrell PH.; ''Triggering the all-or-nothing switch into mitosis.''; PubMedEurope PMCScholia
Galaktionov K, Beach D.; ''Specific activation of cdc25 tyrosine phosphatases by B-type cyclins: evidence for multiple roles of mitotic cyclins.''; PubMedEurope PMCScholia
Kachaner D, Filipe J, Laplantine E, Bauch A, Bennett KL, Superti-Furga G, Israël A, Weil R.; ''Plk1-dependent phosphorylation of optineurin provides a negative feedback mechanism for mitotic progression.''; PubMedEurope PMCScholia
Pines J, Hunter T.; ''Human cyclins A and B1 are differentially located in the cell and undergo cell cycle-dependent nuclear transport.''; PubMedEurope PMCScholia
Graves PR, Lovly CM, Uy GL, Piwnica-Worms H.; ''Localization of human Cdc25C is regulated both by nuclear export and 14-3-3 protein binding.''; PubMedEurope PMCScholia
Coon TA, Glasser JR, Mallampalli RK, Chen BB.; ''Novel E3 ligase component FBXL7 ubiquitinates and degrades Aurora A, causing mitotic arrest.''; PubMedEurope PMCScholia
Sullivan C, Liu Y, Shen J, Curtis A, Newman C, Hock JM, Li X.; ''Novel interactions between FOXM1 and CDC25A regulate the cell cycle.''; PubMedEurope PMCScholia
Laoukili J, Kooistra MR, Brás A, Kauw J, Kerkhoven RM, Morrison A, Clevers H, Medema RH.; ''FoxM1 is required for execution of the mitotic programme and chromosome stability.''; PubMedEurope PMCScholia
Bayliss R, Sardon T, Vernos I, Conti E.; ''Structural basis of Aurora-A activation by TPX2 at the mitotic spindle.''; PubMedEurope PMCScholia
Goda T, Ishii T, Nakajo N, Sagata N, Kobayashi H.; ''The RRASK motif in Xenopus cyclin B2 is required for the substrate recognition of Cdc25C by the cyclin B-Cdc2 complex.''; PubMedEurope PMCScholia
Chen X, Müller GA, Quaas M, Fischer M, Han N, Stutchbury B, Sharrocks AD, Engeland K.; ''The forkhead transcription factor FOXM1 controls cell cycle-dependent gene expression through an atypical chromatin binding mechanism.''; PubMedEurope PMCScholia
Jascur T, Brickner H, Salles-Passador I, Barbier V, El Khissiin A, Smith B, Fotedar R, Fotedar A.; ''Regulation of p21(WAF1/CIP1) stability by WISp39, a Hsp90 binding TPR protein.''; PubMedEurope PMCScholia
Monte M, Benetti R, Collavin L, Marchionni L, Del Sal G, Schneider C.; ''hGTSE-1 expression stimulates cytoplasmic localization of p53.''; PubMedEurope PMCScholia
Draviam VM, Orrechia S, Lowe M, Pardi R, Pines J.; ''The localization of human cyclins B1 and B2 determines CDK1 substrate specificity and neither enzyme requires MEK to disassemble the Golgi apparatus.''; PubMedEurope PMCScholia
Desai D, Wessling HC, Fisher RP, Morgan DO.; ''Effects of phosphorylation by CAK on cyclin binding by CDC2 and CDK2.''; PubMedEurope PMCScholia
Timofeev O, Cizmecioglu O, Settele F, Kempf T, Hoffmann I.; ''Cdc25 phosphatases are required for timely assembly of CDK1-cyclin B at the G2/M transition.''; PubMedEurope PMCScholia
Bellanger S, de Gramont A, Sobczak-Thépot J.; ''Cyclin B2 suppresses mitotic failure and DNA re-replication in human somatic cells knocked down for both cyclins B1 and B2.''; PubMedEurope PMCScholia
Watanabe N, Arai H, Nishihara Y, Taniguchi M, Watanabe N, Hunter T, Osada H.; ''M-phase kinases induce phospho-dependent ubiquitination of somatic Wee1 by SCFbeta-TrCP.''; PubMedEurope PMCScholia
Major ML, Lepe R, Costa RH.; ''Forkhead box M1B transcriptional activity requires binding of Cdk-cyclin complexes for phosphorylation-dependent recruitment of p300/CBP coactivators.''; PubMedEurope PMCScholia
Toyoshima-Morimoto F, Taniguchi E, Nishida E.; ''Plk1 promotes nuclear translocation of human Cdc25C during prophase.''; PubMedEurope PMCScholia
Yang J, Bardes ES, Moore JD, Brennan J, Powers MA, Kornbluth S.; ''Control of cyclin B1 localization through regulated binding of the nuclear export factor CRM1.''; PubMedEurope PMCScholia
Liu XS, Li H, Song B, Liu X.; ''Polo-like kinase 1 phosphorylation of G2 and S-phase-expressed 1 protein is essential for p53 inactivation during G2 checkpoint recovery.''; PubMedEurope PMCScholia
Takizawa CG, Morgan DO.; ''Control of mitosis by changes in the subcellular location of cyclin-B1-Cdk1 and Cdc25C.''; PubMedEurope PMCScholia
Groen AC, Cameron LA, Coughlin M, Miyamoto DT, Mitchison TJ, Ohi R.; ''XRHAMM functions in ran-dependent microtubule nucleation and pole formation during anastral spindle assembly.''; PubMedEurope PMCScholia
Wei SJ, Williams JG, Dang H, Darden TA, Betz BL, Humble MM, Chang FM, Trempus CS, Johnson K, Cannon RE, Tennant RW.; ''Identification of a specific motif of the DSS1 protein required for proteasome interaction and p53 protein degradation.''; PubMedEurope PMCScholia
Hagting A, Jackman M, Simpson K, Pines J.; ''Translocation of cyclin B1 to the nucleus at prophase requires a phosphorylation-dependent nuclear import signal.''; PubMedEurope PMCScholia
Golsteyn RM, Mundt KE, Fry AM, Nigg EA.; ''Cell cycle regulation of the activity and subcellular localization of Plk1, a human protein kinase implicated in mitotic spindle function.''; PubMedEurope PMCScholia
Liu F, Stanton JJ, Wu Z, Piwnica-Worms H.; ''The human Myt1 kinase preferentially phosphorylates Cdc2 on threonine 14 and localizes to the endoplasmic reticulum and Golgi complex.''; PubMedEurope PMCScholia
All known myosin phosphatases consist of PP1 beta and both a large and a small myosin phosphatase targetting (Mypt) subunit. The large Mypt targets PP1 beta to myosin and determines the substrate specifity of the phosphatase. The Large Mypt subunit is encoded by one of three human genes, PPP1R12A (MYPT1), PPP1R12B (MYPT2) and PPP1R12C. Only MYPT1 is represented here. The small subunit is an alternative transcript of MYPT2. The function of the small Mypt subunit remains unclear, but because it is known to interact directly with myosin and the large Mypt it is thought to have an unspecified regulatory role.
The tumor suppressor TP53 (encoded by the gene p53) is a transcription factor. Under stress conditions, it recognizes specific responsive DNA elements and thus regulates the transcription of many genes involved in a variety of cellular processes, such as cellular metabolism, survival, senescence, apoptosis and DNA damage response. Because of its critical function, p53 is frequently mutated in around 50% of all malignant tumors. For a recent review, please refer to Vousden and Prives 2009 and Kruiswijk et al. 2015.
A current model of the arrangement of subunits within the TuRC postulates that 6-7 TuSC subcomplexes are held together by the other Grip proteins, which together form the cap subunits(Reviewed in Wiese and Zheng, 2006).
PLK1 phosphorylates CDC25C on serine residue S198. In addition to catalytically activating CDC25C, PLK1-mediated phosphorylation also results in the nuclear accumulation of CDC25C (Toyoshima-Morimoto et al. 2002). It has been shown that Xenopus polo homolog, Plx1, directly phosphorylates and activates Cdc25C, which in turn dephosphorylates and activates Cdc2. This step is critical for the onset of mitosis. Since Plx1-dependent Cdc25C phosphorylation occurs in the absence of Cdc2 activity, it is likely that Plx1 is a triggering kinase, which leads to the activation of Cdc2 and therefore the normal onset of mitosis (Kumagai and Dunphy 1996).
*Plk1 is shown to phosphorylate Wee1A, an event that is likely critical for recognition and ubiquitination of Wee1A by SCF and therefore for the subsequent degradation of Wee1A . **Plk1 phosphorylates Wee1A at S53, creating the second phosphodegron, PD53. ** Evidence also exists in budding yeast that the budding yeast polo homolog Cdc5 directly phosphorylates and down-regulate the budding yeast Wee1 ortholog Swe1. Thus, polo kinase-dependent phosphorylation and degradation of Wee1A (or Swe1) is likely conserved throughout evolution and is critical for normal mitotic entry.
At mitotic entry Plk1 phosphorylates and inhibits Myt1 activity. Cyclin B1-bound Cdc2, which is the target of Myt1, functions in a feedback loop and phosphorylates and further inhibits Myt1.
During interphase, cyclin B1:Cdc2 shuttles continuously in and out of the nucleus. Cyclin B1:Cdc2 is transported into the nucleus by an unusual mechanism that requires importin b but not importin a or Ran. Dissociation of the cyclin-B1:Cdc2:importin complex in the nucleus requires ATP and involves
other yet unidentified nuclear factors (Takizawa et al.,1991).
Cyclin dependent kinases are themselves catalytically inactive due to the fact that their active site is blocked by a portion of the Cdk molecule itself. Binding to their corresponding cyclin partner results in conformational change that partially exposes the active site. The two B-type cyclins localize to different regions within the cell and and are thought to have specific roles as CDK1-activating subunits (see Bellanger et al., 2007). Cyclin B1 is primarily cytoplasmic during interphase and translocates into the nucleus at the onset of mitosis (Jackman et al., 1995; Hagting et al., 1999). Cyclin B2 colocalizes with the Golgi apparatus and contributes to its fragmentation during mitosis (Jackman et al., 1995; Draviam et al., 2001).
WEE1, a nuclear kinase, phosphorylates cyclin B1:Cdc2 (CCNB1:CDK1) on tyrosine 15 (Y15), inactivating the complex (Parker and Piwnica-Worms 1992, McGowan and Russell 1993). The complex of cyclin B2 and Cdc2 (CCNB2:CDK1) is also phosphorylated on Y15 (Galaktionov and Beach 1991).
During interphase, cyclin B1 shuttles continuously in and out of the nucleus. The cyclin B cytoplasmic retention sequence (CRS), which is responsible for its interphase cytoplasmic localization, functions as a nuclear export sequence (Yang et al., 1998).
Full activity of most CDKs is dependent on CAK mediated phosphorylation at a conserved residue (Thr161 in Cdc2). This modification is thought to improve substrate binding. Cyclin B:Cdc2 complexes have considerably low activity in the absence of CAK mediated phosphorylation (Desai et al 1995).
Cyclin A is synthesized and associates with Cdc2 in G1. Cyclin dependent kinases are themselves catalytically inactive due to the fact that their active sites are blocked by a portion of the CDK molecule itself. Binding to their corresponding cyclin partner results in a conformational change that partially exposes the active site.
Full activity of most CDKs is dependent on CAK mediated phosphorylation at a conserved residue (Thr 161 in Cdc2). This modification is thought to improve substrate binding. High affinity binding of Cyclin A within the Cyclin A:Cdc2 complex requires this phosphorylation (Desai et al 1995).
Cdc25B shuttles between the nucleus and the cytoplasm. Translocation out of the nucleus involves a nuclear export sequence in the N-terminus of Cdc25B (Lindqvist et al., 2004).
At the onset of mitosis, cyclin B is phosphorylated in the CRS sequence which creates a nuclear import signal in the amino terminus. The kinase(s) responsible for this phosphorylation are not yet known (Hagting et al., 1999).
The rapid translocation of cyclin B1:Cdc2 from the cytoplasm to the nucleus at the onset of mitosis is a result of an increase in the rate of import and, likely, a
decreased rate of export. The increased rate of nuclear import is dependent upon phosphorylation of the CRS which creates a nuclear import signal in the amino terminus of cyclin B1 (Hagting et al, 1999).
During interphase, CDC25C, phosphorylated on serine residue 216, is associated with 14-3-3 proteins, preventing nuclear import. At the onset of mitosis, dephosphorylation of S216 of Cdc25C and dissociation of 14-3-3, with phosphorylation of CDC25C on S198 by activated PLK1 promotes nuclear import (Takizawa and Morgan 2000, Toyoshima-Morimoto et al. 2002, Bonnet et al. 2008). Activating CDC25C phosphorylation and nuclear translocation may further be enhanced by activated CCNB:CDK1 complexes (Bonnet et al. 2008).
Activation of the cyclin A:Cdc2 complexes at mitosis requires the removal of the inhibitory phosphate groups on Cdc2 (CDK1). This dephosphorylation is achieved by the activity of the CDC25A phosphatase (Timofeev et al. 2009). CDC25A, CDC25B, and CDC25C are kept inactive during interphase and are activated at the G2/M transition (see Wolfe and Gould 2004).
The localization of the Cdc25A, B and C proteins is dynamic involving the shuttling of these proteins between the nucleus and the cytoplasm. Sequences in these proteins mediate both nuclear export and import (Kallstrom et al., 2005; Lindqvist et al., 2004; Graves et al, 2001; Takizawa and Morgan, 2000).
Activation of the mitotic cyclinB:Cdc2 (CCNB:CDK1) complexes at mitosis requires the removal of the inhibitory phosphate groups on Cdc2 (CDK1). This dephosphorylation is achieved by the activity of the CDC25 family of phosphatases, which act on both CCNB1 and CCNB2-bound CDK1 (Galaktionov and Beach 1991, Goda et al. 2003, Timofeev et al. 2010). The CDC25 members, CDC25A, CDC25B, and CDC25C are kept inactive during interphase and are activated at the G2/M transition. CCNB:CDK1 complexes appear to participate in the full activation of CDC25 in a process that involves an amplification loop (see Wolfe and Gould, 2004). The initial activation of the CCNB:CDK1 (cyclin B1:Cdc2 and cyclin-B2:Cdc2) complexes occurs in the cytoplasm in prophase (Jackman et al., 2003). CDC25B, which is present at highest concentrations in the cytoplasm at this time, is thought to trigger the activation of CCNB1:CDK1 (Lindqvist et al. 2004; Honda et al., 1993). Active CCNB1:CDK1 then phosphorylates CDC25C (contributing to its PLK1-mediated activation) and stabilizes CDC25A (Strausfeld et al., 1994; Hoffman et al.,1993; Mailand et al, 2002). This creates positive feedback loops that allows CDC25A and CDC25C to dephosphorylate and further activate CDK1. As active CDC25C is nuclear, it presumably predominantly contributes to activation of nuclear CDK1 (Strausfeld et al. 1994, Toyoshima-Morimoto et al. 2002, Bonnet, Coopman et al. 2008, Bonnet Mayonove et al. 2008).
In G2 Cdk2, in association with cyclin A, phosphorylates E2F1 and E2F3 resulting in the inactivation and possibly degradation of these two transcription factors (Dynlacht et al., 1994; Krek et al., 1994).
AURKA (Aurora A kinase) activation through autophosphorylation of threonine T288 is facilitated by AJUBA binding. AJUBA is also phosphorylated by AURKA on an unidentified serine or threonine residue (Hirota et al. 2003).
AJUBA, a LIM domain-containing protein, binds centrosome-associated AURKA (Aurora A kinase) through interaction of LIM-2 and LIM-3 domains of AJUBA with the N-terminus of AURKA (Hirota et al. 2003).
AURKA (Aurora A kinase) phosphorylates PLK1 on threonine residue T210 that lies in the conserved aurora kinase consensus site (Seki et al. 2008). PLK1 needs to be phosphorylated on T210 to become catalytically active (Jang et al. 2002). BORA, but not other AURKA co-activators, facilitate PLK1 phosphorylation by AURKA (Macurek et al. 2008, Seki et al. 2008).
BORA is able to interact with both AURKA (Aurora A kinase) and PLK1. Binding of BORA to PLK1 increases the accessibility of PLK1 threonine residue T210 and also brings PLK1 in proximity to AURKA, enabling AURKA to phosphorylate T210 of PLK1 and thereby activate PLK1 (Seki et al. 2008). While BORA is required for mitotic activation of AURKA in Drosophila (Hutterer et al. 2006), it does not significantly activate AURKA in human cells (Seki et al. 2008). AURKA is able to phosphorylate BORA in vitro, but the functional significance of this modification has not been determined (Hutterer et al. 2006).
PLK1 phosphorylates BORA on serine residue S497 and threonine residue T501 that both lie in the DSGYNT degron recognized by beta-TrCP F-box proteins (Seki et al. 2008).
SCF-beta-TrCP ubiquitin ligases promote ubiquitination and degradation of BORA phosphorylated by PLK1, and this is required for timely mitotic progression (Seki et al. 2008).
The substrate recognition subunits beta-TrCP (BTRC) and beta-TrCP2 (FBXW11) of SCF-beta-TrPC1 and SCF-beta-TrPC2 ubiquitin ligases, respectively, bind the phosphorylated DSGYNT motif of BORA (Seki et al. 2008).
PLK1 is induced in S phase and can be find in both cytosol and nucleus in S and G2 phases of the cell cycle. PLK1 possesses a bipartite nuclear localization signal (NLS) that enables it to enter the nucleus (Taniguchi et al. 2002).
The myosin phosphatase complex can dephosphorylate PLK1 threonine residue T210 and inactivate PLK1 (Yamashiro et al. 2008). Myosin phosphatase is activated through phosphorylation of its PPP1R12A (MYPT1) subunit. Several kinases, including CDK1 (Yamashiro et al. 2008) and LATS1 (Chiyoda et al. 2012) have been implicated in myosin phosphatase activation, but the position and temporal order of key PPP1R12A phosphorylations need to be investigated further. Phosphorylated OPTN (optineurin) is able to bind PPP1R12A (MYPT1) and positively regulates PLK1 dephosphorylation by myosin phosphatase, posibly by facilitating PPP1R12A phosphorylation and myosin phosphatase activation (Kachaner et al. 2012).
Microtubule nucleation at the centrosome is mediated by the gamma tubulin ring complex (gamma TuRC) (reviewed in Raynaud-Messina and Merdes, 2006; Wiese and Zheng, 2006). In humans, this large complex contains the tubulin superfamily member gamma-tubulin, five gamma complex proteins (GCP2-GPC6) and NEDD1/GCP-WD. A current model of the arrangement of subunits within the gamma-TuRC proposes that 6-7 TuSC subcomplexes are held together by the other Grip proteins (at an unknown stoichiometry), which together form the cap subunits.
In many animal cells, the recruitment of gamma-tubulin complexes to the centrosome rapidly increases (3–5 fold ) before mitosis to support the formation of new spindle microtubules (Khodjakov and Rieder 1999). NEDD1/GCP-WD plays an essential role in recruitment of these complexes to the centrosomes (Haren et al., 2006; Luders et al., 2006) and to the mitotic spindle (Luders et al., 2006). GCP-WD/NEDD1 associates directly with the gamma-TuRC. The carboxy-terminal half binds to the gamma-TuRC whereas the amino-terminal half, corresponding to the WD-repeat domain, is responsible for its attachment to the centrosome (Haren et al., 2006). Additional centrosomal proteins have also been implicated in the docking of gamma-TuRC to the centrosomes. CG-NAP/AKAP450 and kendrin are necessary for the initiation of microtubule nucleation and interact with GCP2/GCP3 and GCP2, respectively (Takahashi et al., 2002). Pericentrin plays an important role in microtubule organization in mitotic cells and anchors gamma- TuRC through domains that bind GCP2 and GCP3 (Zimmerman et al. 2004). Ninein localizes to the centriole via its C-terminus and interacts with gamma-tubulin-containing complexes via its N-terminus.
The centrosomal protein C-Nap1 is thought to play an important role in centrosome cohesion during interphase (Fry et al.,1998). At the onset of mitosis, when centrosomes separate to form the bipolar spindle, C-Nap1 dissociates (Mayor et al., 2000). Dissociation of C-Nap1 from mitotic centrosomes appears to be regulated by phosphorylation (Mayor et al. 2002).
CDK11p58 is a kinase that is active during mitosis when it associates with centrosomes, and has a crucial role in centrosome maturation and bipolar spindle formation (Petretti et al., 2006). CDK11p58 facilitates microtubule nucleation and is required for the recruitment of Aurora and Plk1 to the centrosome (Petretti et al., 2006).
CDK1 phosphorylates both human and Drosophila BORA protein (Hutterer et al. 2006) on an evolutionarily conserved serine residue - S252 in human BORA (Chan et al. 2008), providing a docking site for PLK1.
In the G2 phase of the cell cycle, cyclin A (CCNA) and B (CCNB)-dependent kinases CDK1 and CDK2 phosphorylate FOXM1 transcription factor, increasing its transcriptional activity. Threonine residue T611 (corresponds to T596 in FOXM1B isoform) was shown to be phosphorylated by both CCNA:CDK1/2 and CCNB:CDK1 complexes and its functional relevance is best establshed (Major et al. 2004, Laoukili et al. 2008, Fu et al. 2008). CCNA:CDK1/2 may also phosphorylate FOXM1 on T600 (Laoukili et al. 2008), while CCNB:CDK1 may phosphorylate it on S693 (S678 in FOXM1B isoform) (Fu et al. 2008). The phosphorylation of FOXM1 threonine residue T611 relieves the N-terminal domain-mediated autoinhibition of FOXM1 transcriptional activity (Laoukili et al. 2008), likely enabling interaction with transcriptional co-activators (Major et al. 2004), and creates a docking site for the Polo-box domain (PBD) of PLK1 (Fu et al. 2008).
PLK1 polo-box domain (PBD) binds a consensus sequence S-pS/pT-P/X in the transactivation domain (TAD) of FOXM1 after the threonine T611 (T596 in FOXM1B isoform) in this sequence is phosphorylated by cyclin-dependent kinase(s). PLK1 may also bind to another consensus site in the TAD of FOXM1, which involves CDK-phosphorylated serine S693 (S678 in FOXM1B isoform) (Fu et al. 2008).
PLK1 phosphorylates FOXM1 on serine residues S730 and S739 (S715 and S724 in FOXM1B isoform) in the C-terminal transactivation domain (TAD). PLK1-mediated phosphorylation of FOXM1 upregulates FOXM1 transcriptional activity and is crucial for FOXM1 function at G2/M transition (Fu et al. 2008).
FOXM1 can bind the regulatory subunit B55-alpha (PPP2R2A) of serine/threonine-protein phosphatase 2A (PP2A). PP2A dephosphorylates FOXM1, preventing its premature activation (Alvarez-Fernandez et al. 2011).
Phosphorylated FOXM1 transcription factor binds the promoter of CDC25A gene and also recruits EP300 (p300) transcriptional coactivator to the promoter (Sullivan et al. 2012). While FOXM1 DNA binding may not depend on phosphorylation, the phosphorylation of the threonine residue T611 (T596 in FOXM1B isoform) is necessary for EP300 recruitment (Major et al. 2004).
FOXM1 bound to the MuvB complex (consisting of LIN9, LIN37, LIN52, LIN54 and RBBP4) and MYBL2 (B-MYB) stimulates CCNB1 (cyclin B1) transcription (Laoukili et al. 2005, Sadasivam et al. 2012).
FOXM1, bound to the MuvB complex (consisting of LIN9, LIN37, LIN52, LIN54 and RBBP4) and MYBL2 (B-MYB), stimulates CCNB2 (cyclin B2) transcription (Chen et al. 2013).
FOXM1 bound to the MuvB complex (consisting of LIN9, LIN37, LIN52, LIN54 and RBBP4) and MYBL2 (B-MYB) stimulates PLK1 transcription. This creates a positive feedback loop, where PLK1 phosphorylates and activates FOXM1 (Fu et al. 2008), while FOXM1 transcriptional activity results in increased PLK1 levels. MuvB and FOXM1 may persist on the PLK1 promoter throughout G2, while MYBL2 may gradually dissociate from the PLK1 promoter due to proteasome-mediated degradation initiated when MYBL2 is phosphorylated by CCNA (cyclin A)-associated CDKs (Sadasivam et al. 2012).
MuvB complex, consisting of LIN9, LIN37, LIN52, LIN54 and RBBP4, together with MYBL2 (B-MYB), recruits FOXM1 to CHR (cell cycle genes homology regions) motifs in the promoter of PLK1 gene (Sadasivam et al. 2012, Chen et al. 2013).
The MuvB complex (consisting of LIN9, LIN37, LIN52, LIN54 and RBBP4), together with MYBL2 (B-MYB), recruits FOXM1 to CHR motifs in the promoter of the CCNB1 (cyclin B1) gene (Sadasivam et al. 2012, Chen et al. 2013).
MuvB complex (consisting of LIN9, LIN37, LIN52, LIN54 and RBBP4), together with MYBL2 (B-MYB) recruits FOMX1 to the CCNB2 (cyclin B2) promoter (Chen et al. 2013).
FOXM1 stimulates the transcription of the kinetochore protein CENPF. FOXM1-depleted cells have reduced CENPF levels, leading to the misalignment of mitotic chromosomes (Laoukili et al. 2005).
At the beginning of this reaction, 1 molecule of 'ATP', and 1 molecule of 'G2/M transition protein' are present. At the end of this reaction, 1 molecule of 'ADP', and 1 molecule of 'phospho-G2/M transition protein' are present.
This reaction takes place in the 'nucleoplasm' and is mediated by the 'cyclin-dependent protein kinase activity' of 'Cyclin A1:Cdc2' (Liu et al. 2000).
At the beginning of this reaction, 1 molecule of 'ATP', and 1 molecule of 'G2/M transition protein' are present. At the end of this reaction, 1 molecule of 'ADP', and 1 molecule of 'phospho-G2/M transition protein' are present.
This reaction takes place in the 'nucleoplasm' and is mediated by the 'cyclin-dependent protein kinase activity' of 'Cyclin A2:Cdc2'.
During interphase, GTSE1 localizes to the growing plus-end tip of microtubules by binding to the microtubule plus end protein MAPRE1 (EB1). This interaction involves two SKIP-like EB1-interaction motifs of GTSE1 and the C-terminal EB-homology (EBH) domain of MAPRE1. The interaction between GTSE1 and MAPRE1 is evolutionarily conserved. The interaction between GTSE1 and MAPRE1 at growing microtubule plus ends promotes cell migration, likely through microtubule-induced disassembly of focal adhesions. GTSE1 expression levels in G1 phase correlate with invasiveness of breast cancer cell lines (Scolz et al. 2012).
Starting in mitotic prometaphase, GTSE1 becomes phosphorylated at threonine residues T513 and T526 (and possibly other sites), located adjacent to the two SKIP-like motifs involved in binding to MAPRE1 (EB1). Mitotic phosphorylation of GTSE1 inhibits its association with microtubule plus ends. CDK1 activity inhibits the association of recombinant human GTSE1 with microtubule plus ends in Xenopus extracts, but it is not certain whether CDK1 or another mitotic kinase phosphorylates GTSE1 (Scolz et al. 2012).
Activated PLK1 phosphorylates GTSE1 on serine residue S435, located in immediate vicinity of the GTSE1 nuclear localization signal (NLS) R431RR433 (Arg431Arg432Arg433). PLK1-mediated phosphorylation promotes GTSE1 nuclear translocation, possibly by exposing the NLS of GTSE1 to the nuclear import machinery. PLK1 can also phosphorylate human GTSE1 on serine residue S233. S233 is not evolutionarily conserved and is therefore not shown (Liu et al. 2010).
PLK1-mediated phosphorylation of GTSE1 is needed for nuclear accumulation of GTSE1, probably because it exposes the nuclear localization signal (NLS) of GTSE1 to the nuclear import machinery. Nuclear localization of GTSE1 is not needed for normal G2 phase progression, but is needed for the G2 checkpoint recovery (cell cycle re-entry after G2 checkpoint arrest) (Liu et al. 2010).
Since MDM2-mediated ubiquitination of TP53 promotes translocation of TP53 to the cytosol, and since GTSE1-facilitated translocation of TP53 to the cytosol depends on the functional MDM2 (with no reported interaction between GTSE1 and MDM2) (Monte et al. 2004), it is plausible that GTSE1 binds to TP53 polyubiquitinated by MDM2. The interaction between TP53 and GTSE1 involves the C-terminal regulatory domain of TP53 and the C-terminus of GTSE1 (Monte et al. 2003).
Binding of GTSE1 to TP53 (p53) in the nucleus promotes translocation of TP53 to the cytosol. This process is dependent on the nuclear export signal (NES) of GTSE1 (Monte et al. 2004).
GTSE1 promotes down-regulation of TP53 in a proteasome-dependent way. Nuclear export of TP53 facilitated by GTSE1 and MDM2likely makes ubiquitinated TP53 available to the proteasome machinery. GTSE1-mediated decrease of TP53 levels is needed for the G2 checkpoint recovery (cell cycle re-entry after DNA damage induced G2 arrest) and rescues cells from DNA damage induced apoptosis during S/G2 phase (Monte et al. 2003, Monte et al. 2004).
Stabilization of the newly synthesized protein product of the CDKN1A (p21) gene, a CDK inhibitor and a TP53 (p53) transcriptional target, requires binding of CDKN1A to FKBPL (WISp39). FKBPL simultaneously interacts with CDKN1A and a chaperone protein HSP90, forming a ternary complex (Jascur et al. 2005). GTSE1 was identified as another component of the complex of CDKN1A, FKBPL and HSP90. GTSE1 directly interacts with CDKN1A and FKBPL and contributes to CDKN1A stabilization (Bublik et al. 2010). Increased CDKN1A levels delay G2/M onset and rescue cells from G2 checkpoint-induced apoptosis, thus causing resistance to taxol induced cytotoxicity (Yu et al. 1998, Bublik et al. 2010).
TPX2 binds to aurora kinase A (AURKA) at centrosomes. The first 43 amino acids at the N-terminus of TPX2 are needed for binding to AURKA (Bayliss et al. 2003). HMMR (RHAMM) binds to TPX2 (Groen et al. 2004, Maxwell et al. 2005) and is involved in the proper localization of TPX2 to centrosomes and TPX2-mediated AURKA activation (Chen et al. 2014, Scrofani et al. 2015).
TPX2 binding to Aurora A protects premature AURKA degradation by APC/C-mediated proteolysis during early mitosis. TPX2 differentially regulates AURKA stability, activity and localization. While amino acids 1-43 in TPX2 facilitate complex formation between AURKA and TPX2 and promote kinase activation, they are insufficient for AURKA targeting to the mitotic spindle (Giubettini et al. 2011).
TPX2 promotes aurora kinase A (AURKA) activation via autophosphorylation of AURKA on threonine residue T288. Continuous association of TPX2 with AURKA facilitates active state conformation of AURKA and may prevent inactivation of AURKA by protein phosphatases (Bayliss et al. 2003).
Molecular dynamic simulations suggest the existence of two TPX2-dependent switches for Aurora A activation. 1) TPX2 binding to Aurora A forces lysine residue K143 of AURKA into an “open� state, which pulls ADP out of the ATP binding site in AURKA to promote kinase activation. 2) Arginine residue R180 of AURKA undergoes a “closed� movement upon TPX2 binding, thus capturing phosphorylated threonine T288 of AURKA into a buried position and locking AURKA in its active conformation. The existence of two TPX2-dependent switches in AURKA activation was further verified by the analysis of two AURKA mutants (K143A and R180A) (Xu et al. 2011).AURKA activation is enabled through phosphorylation and TPX2 binding; these two activating switches act synergistically and withough a predefined order (Dodson and Bayliss 2012).
Aurora kinase A binds PHLDA1 (TDAG51) and the two proteins co-localize in the cytosol (Johnson et al. 2011). Although phosphorylation of AURKA at threonine residue T288 within the catalytic loop of AURKA is needed for AURKA kinase activity (Walter et al. 2000), AURKA phosphorylation has not been specifically examined in the context of AURKA interaction with PHLDA1 and AURKA is therefore shown as unphosphorylated.
Aurora kinase A (AURKA) phosphorylates PHLDA1 on serine residue S95. This residue is conserved in mouse and matches S98 in the recombinant mouse protein used for identification of the AURKA target site in PHLDA1. Although phosphorylation of AURKA on threonine residue T288 within the catalytic loop is needed for AURKA kinase activity (Walter et al. 2000), AURKA phosphorylation has not been specifically examined in the context of PHLDA1 phosphorylation and AURKA is therefore shown as unphosphorylated. AURKA-mediated phosphorylation promotes PHLDA1 ubiquitination by an unknown ubiquitin ligase, which triggers degradation of PHLDA1 and may contribute to the oncogenic role of AURKA in breast cancer. Unphosphorylated PHLDA1 contributes to AURKA ubiquitination and degradation but the identity of the ubiquitin ligase and cell cycle timing have not been determined (Johnson et al. 2011).
PHLDA1 is implicated as both a tumor suppressor and an oncogene. As a putative tumor suppressor, PHLDA1 may act by promoting cell death (Park et al. 1996, Neef et al. 2002, Hossain et al. 2003, Hayashida et al. 2006, Oberst et al. 2008) or inhibiting protein synthesis (Hinz et al. 2001). Higher levels of PHLDA1 in ERBB2 (HER2) positive breast tumors correlate with increased sensitivity to ERBB2 inhibitor, lapatinib (Li et al. 2014).
In estrogen receptor positive tumors, higher levels of PHLDA1 correlate with increased risk of cancer recurrence and distant metastases after hormone therapy, which may depend on the concomitant up-regulation of the NF-kappa B (NFKB) complex activity (Kastrati et al. 2015).
PHLDA1 has also been reported as a mediator of anti-apoptotic effect of IGF1 (Toyoshima et al. 2004). These studies suggest that PHLDA1 may have an oncogenic role in some settings.
Regulation of PHLDA1 expression has not been fully elucidated. PHLDA1 transcription may be directly stimulated by the activated estrogen receptor (Marchiori et al. 2008, Kastrati et al. 2015), possibly in cooperation with the NFKB complex (Kastrati et al. 2015). Indirectly, downregulation of microRNAs miR-181a and miR-181b in an estrogen and NFKB-dependent manner, increases stability of the PHLDA1 mRNA (Kastrati et al. 2015). Activation of ERK1 (MAPK3) or ERK2 (MAPK1) in response to ERBB2 or EGFR activation may also be involved in PHLDA1 up-regulation, possibly through a route that also involves JAK2 and STAT3 (Oberst et al. 2008, Li et al. 2014, Lyu et al. 2016). PHLDA1 may also be up-regulated in response to cellular stress such as heat shock (Hayashida et al. 2006), endoplasmic reticulum stress (Hossain et al. 2003) and oxidative stress (Park et al. 2013).
The SCF-FBXL7 E3 ubiquitin ligase complex, composed of SKP1, CUL1, RBX1 and FBXL7, ubiquitinates aurora kinase A (AURKA), targeting it for degradation (Coon et al. 2012).
FBXL18, a substrate recognition subunit of the SCF E3 ubiquitin ligase complex can bind to the FQ motif of FBXL7. The E3 ubiquitin ligase complex SCF-FBXL18 (SKP1:CUL1:RBX1:FBXL18) polyubiquitinates FBXL7 on lysine residue K109, targeting it for proteasome-mediated degradation (Liu et al. 2015).
Reversible methylation of the PP2A C subunit is a highly conserved and essential regulatory mechanism (Lee et al. 1996). Methylation of the carboxy-termius of PP2A C enhances the affinity of the PP2A core enzyme for some regulatory subunits (Xing et al. 2008). Changes in PP2A methylation appear to regulate formation of PP2A complexes and alter the specificity of PP2A phosphatase activity (Mumby 2001). Blockade of PP2A methylation in yeast causes a set of phenotypes that are consistent with decreased formation of PP2A holoenzymes (Wu et al. 2000). Reversible methylation of PP2A is catalyzed by two highly conserved enzymes, a 38 kDa leucine carboxyl methyltransferase (LCMT1) (De Baere et al. 1999, Lee & Stock 1993) and a 42 kDa methylesterase (PPME1) (Lee et al. 1996, Ogris et al. 1999). PP2A carboxy-methylation by LCMT1 requires an active PP2A conformation and is significantly facilitated by the PP2A scaffold (or A) subunit (Stanevich et al. 2011, Stanevich et al. 2014). LCMT1 also methylates the PP2A-like phosphatases PP4 and PP6 (Hwang et al. 2016). PPME1 catalyzes removal of the methyl group, thus reversing the activity of LCMT1 (Lee et al. 1996). Overexpression of yeast PPME caused phenotypes similar to those associated with loss of the methyltransferase gene (Wu et al. 2000).
The reversible methylation of the PP2A C subunit is a highly conserved and essential regulatory mechanism (Lee et al. 1996). Methylation of the carboxy-termius of PP2A C enhances the affinity of the PP2A core enzyme for some regulatory subunits (Xing et al. 2008). Changes in PP2A methylation appear to regulate formation of PP2A complexes and alter the specificity of PP2A phosphatase activity (Mumby 2001). Blockade of PP2A methylation in yeast causes a set of phenotypes that are consistent with decreased formation of PP2A holoenzymes (Wu et al. 2000). Reversible methylation of PP2A is catalyzed by two highly conserved enzymes, a 38 kDa leucine carboxyl methyltransferase (LCMT1) (De Baere et al. 1999, Lee & Stock 1993) and a 42 kDa methylesterase (PPME1) (Lee et al. 1996, Ogris et al. 1999). PP2A carboxy-methylation by LCMT1 requires an active PP2A conformation and is significantly facilitated by the PP2A scaffold (or A) subunit (Stanevich et al. 2011, Stanevich et al. 2014). LCMT1 also methylates the PP2A-like phosphatases PP4 and PP6 (Hwang et al. 2016). PPME1 catalyzes removal of the methyl group, thus reversing the activity of LCMT1 (Lee et al. 1996). Overexpression of yeast PPME caused phenotypes similar to those associated with loss of the methyltransferase gene (Wu et al. 2000).
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containing
recruited CDK11p58phosphorylated G2/M
transition proteinphosphorylated G2/M
transition proteinenriched in gamma-TURC
complexesB1
(CRS):phospho-Cdc2(Thr 161)containing
phosphorylated NlpAnnotated Interactions
containing
recruited CDK11p58phosphorylated G2/M
transition proteinphosphorylated G2/M
transition proteinenriched in gamma-TURC
complexesB1
(CRS):phospho-Cdc2(Thr 161)This reaction takes place in the 'nucleoplasm' and is mediated by the 'cyclin-dependent protein kinase activity' of 'Cyclin A1:Cdc2' (Liu et al. 2000).
This reaction takes place in the 'nucleoplasm' and is mediated by the 'cyclin-dependent protein kinase activity' of 'Cyclin A2:Cdc2'.
TPX2 binding to Aurora A protects premature AURKA degradation by APC/C-mediated proteolysis during early mitosis. TPX2 differentially regulates AURKA stability, activity and localization. While amino acids 1-43 in TPX2 facilitate complex formation between AURKA and TPX2 and promote kinase activation, they are insufficient for AURKA targeting to the mitotic spindle (Giubettini et al. 2011).
Molecular dynamic simulations suggest the existence of two TPX2-dependent switches for Aurora A activation. 1) TPX2 binding to Aurora A forces lysine residue K143 of AURKA into an “open� state, which pulls ADP out of the ATP binding site in AURKA to promote kinase activation. 2) Arginine residue R180 of AURKA undergoes a “closed� movement upon TPX2 binding, thus capturing phosphorylated threonine T288 of AURKA into a buried position and locking AURKA in its active conformation. The existence of two TPX2-dependent switches in AURKA activation was further verified by the analysis of two AURKA mutants (K143A and R180A) (Xu et al. 2011).AURKA activation is enabled through phosphorylation and TPX2 binding; these two activating switches act synergistically and withough a predefined order (Dodson and Bayliss 2012).
PHLDA1 is implicated as both a tumor suppressor and an oncogene. As a putative tumor suppressor, PHLDA1 may act by promoting cell death (Park et al. 1996, Neef et al. 2002, Hossain et al. 2003, Hayashida et al. 2006, Oberst et al. 2008) or inhibiting protein synthesis (Hinz et al. 2001). Higher levels of PHLDA1 in ERBB2 (HER2) positive breast tumors correlate with increased sensitivity to ERBB2 inhibitor, lapatinib (Li et al. 2014).
In estrogen receptor positive tumors, higher levels of PHLDA1 correlate with increased risk of cancer recurrence and distant metastases after hormone therapy, which may depend on the concomitant up-regulation of the NF-kappa B (NFKB) complex activity (Kastrati et al. 2015).
PHLDA1 has also been reported as a mediator of anti-apoptotic effect of IGF1 (Toyoshima et al. 2004). These studies suggest that PHLDA1 may have an oncogenic role in some settings.
Regulation of PHLDA1 expression has not been fully elucidated. PHLDA1 transcription may be directly stimulated by the activated estrogen receptor (Marchiori et al. 2008, Kastrati et al. 2015), possibly in cooperation with the NFKB complex (Kastrati et al. 2015). Indirectly, downregulation of microRNAs miR-181a and miR-181b in an estrogen and NFKB-dependent manner, increases stability of the PHLDA1 mRNA (Kastrati et al. 2015). Activation of ERK1 (MAPK3) or ERK2 (MAPK1) in response to ERBB2 or EGFR activation may also be involved in PHLDA1 up-regulation, possibly through a route that also involves JAK2 and STAT3 (Oberst et al. 2008, Li et al. 2014, Lyu et al. 2016). PHLDA1 may also be up-regulated in response to cellular stress such as heat shock (Hayashida et al. 2006), endoplasmic reticulum stress (Hossain et al. 2003) and oxidative stress (Park et al. 2013).
Methylation and demethylation are spatially separated within mammalian cells, as the majority of LCMT1 is cytoplasmic and PPME1 predominantly localizes in the nucleus (Longin et al. 2008). In mammalian cells, LCMT1 knockdown results in apoptotic cell death (Longin et al. 2007). In mice, LCMT1 or PPME1 knockout are lethal (Lee & Pallas 2007, Ortega-Gutiérrez et al. 2008). Methylation levels of PP2A change during the cell cycle, suggesting a critical role of methylation in cell-cycle regulation (Turowski et al. 1995, Lee & Pallas 2007). Regulation of PP2A methylation by LCMT1 and PPME1 plays a critical role in differentiation of neuroblastoma cells (Sontag et al. 2010). Decreased PP2A methylation in Alzheimer’s and Parkinson’s disease patients contributes to PP2A inactivation and increased phosphorylation of tau and alpha-synuclein (Sontag & Sontag 2014, Park et al. 2016). PPME1 may also inhibit PP2A by sequestration (Longin et al. 2004) and/or by evicting catalytic metal ions from the PP2A active site (Xing et al. 2008). As such, increased PPME1 expression suppresses PP2A tumor suppressive function and promotes oncogenic MAPK/ERK and AKT pathway activities in various cancer types (Kaur & Westermarck 2016). PPME1 may also protect PP2A from ubiquitin/proteasome degradation (Yabe et al. 2015).
Methylation and demethylation are spatially separated within mammalian cells, as the majority of LCMT1 is cytoplasmic and PPME1 predominantly localizes in the nucleus (Longin et al. 2008). In mammalian cells, LCMT1 knockdown results in apoptotic cell death (Longin et al. 2007). In mice, LCMT1 or PPME1 knockout are lethal (Lee & Pallas 2007, Ortega-Gutiérrez et al. 2008). Methylation levels of PP2A change during the cell cycle, suggesting a critical role of methylation in cell-cycle regulation (Turowski et al. 1995, Lee & Pallas 2007). Regulation of PP2A methylation by LCMT1 and PPME1 plays a critical role in differentiation of neuroblastoma cells (Sontag et al. 2010). Decreased PP2A methylation in Alzheimer’s and Parkinson’s disease patients contributes to PP2A inactivation and increased phosphorylation of tau and alpha-synuclein (Sontag & Sontag 2014, Park et al. 2016). PPME1 may also inhibit PP2A by sequestration (Longin et al. 2004) and/or by evicting catalytic metal ions from the PP2A active site (Xing et al. 2008). As such, increased PPME1 expression suppresses PP2A tumor suppressive function and promotes oncogenic MAPK/ERK and AKT pathway activities in various cancer types (Kaur & Westermarck 2016). PPME1 may also protect PP2A from ubiquitin/proteasome degradation (Yabe et al. 2015).
containing
phosphorylated Nlpcontaining
phosphorylated Nlp