The Rho family of small guanine nucleotide binding proteins is one of five generally recognized branches of the Ras superfamily. Like most Ras superfamily members, typical Rho proteins function as binary switches controlling a variety of biological processes. They perform this function by cycling between active GTP-bound and inactive GDP-bound conformations. Mammalian Rho GTPases include RhoA, RhoB and RhoC (Rho proteins), Rac1 3 (Rac proteins), Cdc42, TC10, TCL, Wrch1, Chp/Wrch2, RhoD and RhoG, to name some. The family also includes RhoH and Rnd1-3, which lack GTPase activity and are predicted to exist in a constitutively active state.
Members of the Rho family have been identified in all eukaryotes. Including the atypical RHOBTB1-3 and RHOT1-2 proteins, 24 Rho family members have been identified in mammals (Jaffe and Hall, 2005; Bernards, 2005; Ridley, 2006). Among Rho GTPases, RhoA, Rac1 and Cdc42 have been most extensively studied. These proteins are best known for their ability to induce dynamic rearrangements of the plasma membrane-associated actin cytoskeleton (Aspenstrom et al, 2004; Murphy et al, 1999; Govek et al, 2005). Beyond this function, Rho GTPases also regulate actomyosin contractility and microtubule dynamics. Rho mediated effects on transcription and membrane trafficking are believed to be secondary to these functions. At the more macroscopic level, Rho GTPases have been implicated in many important cell biological processes, including cell growth control, cytokinesis, cell motility, cell cell and cell extracellular matrix adhesion, cell transformation and invasion, and development (Govek et al., 2005). The illustration below lists Rho GTPase effectors implicated in actin and microtubule dynamics (courtesy: Govek et al., 2005, Genes and Development, CSHL Press). Detailed annotations of various biological processes regulated by Rho GTPases will be available in future releases.
View original pathway at:Reactome.</div>
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Zheng Y, Fischer DJ, Santos MF, Tigyi G, Pasteris NG, Gorski JL, Xu Y.; ''The faciogenital dysplasia gene product FGD1 functions as a Cdc42Hs-specific guanine-nucleotide exchange factor.''; PubMedEurope PMCScholia
Zhou H, Kramer RH.; ''Integrin engagement differentially modulates epithelial cell motility by RhoA/ROCK and PAK1.''; PubMedEurope PMCScholia
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Kim C, Dinauer MC.; ''Rac2 is an essential regulator of neutrophil nicotinamide adenine dinucleotide phosphate oxidase activation in response to specific signaling pathways.''; PubMedEurope PMCScholia
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Takahashi M, Mukai H, Toshimori M, Miyamoto M, Ono Y.; ''Proteolytic activation of PKN by caspase-3 or related protease during apoptosis.''; PubMedEurope PMCScholia
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Berthold J, Schenkova K, Rivero F.; ''Rho GTPases of the RhoBTB subfamily and tumorigenesis.''; PubMedEurope PMCScholia
Vignal E, Blangy A, Martin M, Gauthier-Rouvière C, Fort P.; ''Kinectin is a key effector of RhoG microtubule-dependent cellular activity.''; PubMedEurope PMCScholia
Hart MJ, Maru Y, Leonard D, Witte ON, Evans T, Cerione RA.; ''A GDP dissociation inhibitor that serves as a GTPase inhibitor for the Ras-like protein CDC42Hs.''; PubMedEurope PMCScholia
Sudo K, Ito H, Iwamoto I, Morishita R, Asano T, Nagata K.; ''Identification of a cell polarity-related protein, Lin-7B, as a binding partner for a Rho effector, Rhotekin, and their possible interaction in neurons.''; PubMedEurope PMCScholia
Lancaster CA, Taylor-Harris PM, Self AJ, Brill S, van Erp HE, Hall A.; ''Characterization of rhoGAP. A GTPase-activating protein for rho-related small GTPases.''; PubMedEurope PMCScholia
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Hart MJ, Sharma S, elMasry N, Qiu RG, McCabe P, Polakis P, Bollag G.; ''Identification of a novel guanine nucleotide exchange factor for the Rho GTPase.''; PubMedEurope PMCScholia
Yuan BZ, Miller MJ, Keck CL, Zimonjic DB, Thorgeirsson SS, Popescu NC.; ''Cloning, characterization, and chromosomal localization of a gene frequently deleted in human liver cancer (DLC-1) homologous to rat RhoGAP.''; PubMedEurope PMCScholia
Brill S, Li S, Lyman CW, Church DM, Wasmuth JJ, Weissbach L, Bernards A, Snijders AJ.; ''The Ras GTPase-activating-protein-related human protein IQGAP2 harbors a potential actin binding domain and interacts with calmodulin and Rho family GTPases.''; PubMedEurope PMCScholia
Pasteris NG, Cadle A, Logie LJ, Porteous ME, Schwartz CE, Stevenson RE, Glover TW, Wilroy RS, Gorski JL.; ''Isolation and characterization of the faciogenital dysplasia (Aarskog-Scott syndrome) gene: a putative Rho/Rac guanine nucleotide exchange factor.''; PubMedEurope PMCScholia
Soltau M, Richter D, Kreienkamp HJ.; ''The insulin receptor substrate IRSp53 links postsynaptic shank1 to the small G-protein cdc42.''; PubMedEurope PMCScholia
Ueyama T, Geiszt M, Leto TL.; ''Involvement of Rac1 in activation of multicomponent Nox1- and Nox3-based NADPH oxidases.''; PubMedEurope PMCScholia
Govek EE, Newey SE, Van Aelst L.; ''The role of the Rho GTPases in neuronal development.''; PubMedEurope PMCScholia
Ren Y, Li R, Zheng Y, Busch H.; ''Cloning and characterization of GEF-H1, a microtubule-associated guanine nucleotide exchange factor for Rac and Rho GTPases.''; PubMedEurope PMCScholia
Bächner D, Sedlacek Z, Korn B, Hameister H, Poustka A.; ''Expression patterns of two human genes coding for different rab GDP-dissociation inhibitors (GDIs), extremely conserved proteins involved in cellular transport.''; PubMedEurope PMCScholia
Suzuki K, Takahashi K.; ''Regulation of lamellipodia formation and cell invasion by CLIP-170 in invasive human breast cancer cells.''; PubMedEurope PMCScholia
Fukata M, Watanabe T, Noritake J, Nakagawa M, Yamaga M, Kuroda S, Matsuura Y, Iwamatsu A, Perez F, Kaibuchi K.; ''Rac1 and Cdc42 capture microtubules through IQGAP1 and CLIP-170.''; PubMedEurope PMCScholia
Miralles F, Posern G, Zaromytidou AI, Treisman R.; ''Actin dynamics control SRF activity by regulation of its coactivator MAL.''; PubMedEurope PMCScholia
Tcherkezian J, Lamarche-Vane N.; ''Current knowledge of the large RhoGAP family of proteins.''; PubMedEurope PMCScholia
Miki H, Yamaguchi H, Suetsugu S, Takenawa T.; ''IRSp53 is an essential intermediate between Rac and WAVE in the regulation of membrane ruffling.''; PubMedEurope PMCScholia
Maesaki R, Ihara K, Shimizu T, Kuroda S, Kaibuchi K, Hakoshima T.; ''The structural basis of Rho effector recognition revealed by the crystal structure of human RhoA complexed with the effector domain of PKN/PRK1.''; PubMedEurope PMCScholia
Amano M, Ito M, Kimura K, Fukata Y, Chihara K, Nakano T, Matsuura Y, Kaibuchi K.; ''Phosphorylation and activation of myosin by Rho-associated kinase (Rho-kinase).''; PubMedEurope PMCScholia
Watanabe T, Hosoya H, Yonemura S.; ''Regulation of myosin II dynamics by phosphorylation and dephosphorylation of its light chain in epithelial cells.''; PubMedEurope PMCScholia
Wang S, Watanabe T, Noritake J, Fukata M, Yoshimura T, Itoh N, Harada T, Nakagawa M, Matsuura Y, Arimura N, Kaibuchi K.; ''IQGAP3, a novel effector of Rac1 and Cdc42, regulates neurite outgrowth.''; PubMedEurope PMCScholia
Camera P, da Silva JS, Griffiths G, Giuffrida MG, Ferrara L, Schubert V, Imarisio S, Silengo L, Dotti CG, Di Cunto F.; ''Citron-N is a neuronal Rho-associated protein involved in Golgi organization through actin cytoskeleton regulation.''; PubMedEurope PMCScholia
Pelikan-Conchaudron A, Le Clainche C, Didry D, Carlier MF.; ''The IQGAP1 protein is a calmodulin-regulated barbed end capper of actin filaments: possible implications in its function in cell migration.''; PubMedEurope PMCScholia
Neudauer CL, Joberty G, Macara IG.; ''PIST: a novel PDZ/coiled-coil domain binding partner for the rho-family GTPase TC10.''; PubMedEurope PMCScholia
Metzger E, Müller JM, Ferrari S, Buettner R, Schüle R.; ''A novel inducible transactivation domain in the androgen receptor: implications for PRK in prostate cancer.''; PubMedEurope PMCScholia
Adra CN, Manor D, Ko JL, Zhu S, Horiuchi T, Van Aelst L, Cerione RA, Lim B.; ''RhoGDIgamma: a GDP-dissociation inhibitor for Rho proteins with preferential expression in brain and pancreas.''; PubMedEurope PMCScholia
Metzger E, Wissmann M, Yin N, Müller JM, Schneider R, Peters AH, Günther T, Buettner R, Schüle R.; ''LSD1 demethylates repressive histone marks to promote androgen-receptor-dependent transcription.''; PubMedEurope PMCScholia
Ramos-Morales F, Romero F, Schweighoffer F, Bismuth G, Camonis J, Tortolero M, Fischer S.; ''The proline-rich region of Vav binds to Grb2 and Grb3-3.''; PubMedEurope PMCScholia
Reid T, Bathoorn A, Ahmadian MR, Collard JG.; ''Identification and characterization of hPEM-2, a guanine nucleotide exchange factor specific for Cdc42.''; PubMedEurope PMCScholia
Knaus UG, Heyworth PG, Evans T, Curnutte JT, Bokoch GM.; ''Regulation of phagocyte oxygen radical production by the GTP-binding protein Rac 2.''; PubMedEurope PMCScholia
Flynn P, Mellor H, Casamassima A, Parker PJ.; ''Rho GTPase control of protein kinase C-related protein kinase activation by 3-phosphoinositide-dependent protein kinase.''; PubMedEurope PMCScholia
Lane J, Martin T, Weeks HP, Jiang WG.; ''Structure and role of WASP and WAVE in Rho GTPase signalling in cancer.''; PubMedEurope PMCScholia
Hutchinson CL, Lowe PN, McLaughlin SH, Mott HR, Owen D.; ''Differential binding of RhoA, RhoB, and RhoC to protein kinase C-related kinase (PRK) isoforms PRK1, PRK2, and PRK3: PRKs have the highest affinity for RhoB.''; PubMedEurope PMCScholia
Bassi ZI, Audusseau M, Riparbelli MG, Callaini G, D'Avino PP.; ''Citron kinase controls a molecular network required for midbody formation in cytokinesis.''; PubMedEurope PMCScholia
DerMardirossian C, Bokoch GM.; ''GDIs: central regulatory molecules in Rho GTPase activation.''; PubMedEurope PMCScholia
Watanabe G, Saito Y, Madaule P, Ishizaki T, Fujisawa K, Morii N, Mukai H, Ono Y, Kakizuka A, Narumiya S.; ''Protein kinase N (PKN) and PKN-related protein rhophilin as targets of small GTPase Rho.''; PubMedEurope PMCScholia
Gruneberg U, Neef R, Li X, Chan EH, Chalamalasetty RB, Nigg EA, Barr FA.; ''KIF14 and citron kinase act together to promote efficient cytokinesis.''; PubMedEurope PMCScholia
Kuroda S, Fukata M, Nakagawa M, Fujii K, Nakamura T, Ookubo T, Izawa I, Nagase T, Nomura N, Tani H, Shoji I, Matsuura Y, Yonehara S, Kaibuchi K.; ''Role of IQGAP1, a target of the small GTPases Cdc42 and Rac1, in regulation of E-cadherin- mediated cell-cell adhesion.''; PubMedEurope PMCScholia
Hart MJ, Eva A, Zangrilli D, Aaronson SA, Evans T, Cerione RA, Zheng Y.; ''Cellular transformation and guanine nucleotide exchange activity are catalyzed by a common domain on the dbl oncogene product.''; PubMedEurope PMCScholia
Parrini MC, Lei M, Harrison SC, Mayer BJ.; ''Pak1 kinase homodimers are autoinhibited in trans and dissociated upon activation by Cdc42 and Rac1.''; PubMedEurope PMCScholia
Richnau N, Aspenström P.; ''Rich, a rho GTPase-activating protein domain-containing protein involved in signaling by Cdc42 and Rac1.''; PubMedEurope PMCScholia
Leung DW, Rosen MK.; ''The nucleotide switch in Cdc42 modulates coupling between the GTPase-binding and allosteric equilibria of Wiskott-Aldrich syndrome protein.''; PubMedEurope PMCScholia
Jyoti A, Singh AK, Dubey M, Kumar S, Saluja R, Keshari RS, Verma A, Chandra T, Kumar A, Bajpai VK, Barthwal MK, Dikshit M.; ''Interaction of inducible nitric oxide synthase with rac2 regulates reactive oxygen and nitrogen species generation in the human neutrophil phagosomes: implication in microbial killing.''; PubMedEurope PMCScholia
Robbe K, Otto-Bruc A, Chardin P, Antonny B.; ''Dissociation of GDP dissociation inhibitor and membrane translocation are required for efficient activation of Rac by the Dbl homology-pleckstrin homology region of Tiam.''; PubMedEurope PMCScholia
Ohashi K, Nagata K, Maekawa M, Ishizaki T, Narumiya S, Mizuno K.; ''Rho-associated kinase ROCK activates LIM-kinase 1 by phosphorylation at threonine 508 within the activation loop.''; PubMedEurope PMCScholia
Leung T, Chen XQ, Manser E, Lim L.; ''The p160 RhoA-binding kinase ROK alpha is a member of a kinase family and is involved in the reorganization of the cytoskeleton.''; PubMedEurope PMCScholia
Sumi T, Matsumoto K, Nakamura T.; ''Specific activation of LIM kinase 2 via phosphorylation of threonine 505 by ROCK, a Rho-dependent protein kinase.''; PubMedEurope PMCScholia
Peck JW, Oberst M, Bouker KB, Bowden E, Burbelo PD.; ''The RhoA-binding protein, rhophilin-2, regulates actin cytoskeleton organization.''; PubMedEurope PMCScholia
Fukata M, Kuroda S, Fujii K, Nakamura T, Shoji I, Matsuura Y, Okawa K, Iwamatsu A, Kikuchi A, Kaibuchi K.; ''Regulation of cross-linking of actin filament by IQGAP1, a target for Cdc42.''; PubMedEurope PMCScholia
Govind S, Kozma R, Monfries C, Lim L, Ahmed S.; ''Cdc42Hs facilitates cytoskeletal reorganization and neurite outgrowth by localizing the 58-kD insulin receptor substrate to filamentous actin.''; PubMedEurope PMCScholia
Van Aelst L, D'Souza-Schorey C.; ''Rho GTPases and signaling networks.''; PubMedEurope PMCScholia
Tan YC, Wu H, Wang WN, Zheng Y, Wang ZX.; ''Characterization of the interactions between the small GTPase RhoA and its guanine nucleotide exchange factors.''; PubMedEurope PMCScholia
Hage B, Meinel K, Baum I, Giehl K, Menke A.; ''Rac1 activation inhibits E-cadherin-mediated adherens junctions via binding to IQGAP1 in pancreatic carcinoma cells.''; PubMedEurope PMCScholia
Zong H, Raman N, Mickelson-Young LA, Atkinson SJ, Quilliam LA.; ''Loop 6 of RhoA confers specificity for effector binding, stress fiber formation, and cellular transformation.''; PubMedEurope PMCScholia
Abdul-Manan N, Aghazadeh B, Liu GA, Majumdar A, Ouerfelli O, Siminovitch KA, Rosen MK.; ''Structure of Cdc42 in complex with the GTPase-binding domain of the 'Wiskott-Aldrich syndrome' protein.''; PubMedEurope PMCScholia
Swart-Mataraza JM, Li Z, Sacks DB.; ''IQGAP1 is a component of Cdc42 signaling to the cytoskeleton.''; PubMedEurope PMCScholia
Schmidt A, Hall A.; ''Guanine nucleotide exchange factors for Rho GTPases: turning on the switch.''; PubMedEurope PMCScholia
Bashour AM, Fullerton AT, Hart MJ, Bloom GS.; ''IQGAP1, a Rac- and Cdc42-binding protein, directly binds and cross-links microfilaments.''; PubMedEurope PMCScholia
Ho HY, Rohatgi R, Lebensohn AM, Le Ma, Li J, Gygi SP, Kirschner MW.; ''Toca-1 mediates Cdc42-dependent actin nucleation by activating the N-WASP-WIP complex.''; PubMedEurope PMCScholia
Torbett NE, Casamassima A, Parker PJ.; ''Hyperosmotic-induced protein kinase N 1 activation in a vesicular compartment is dependent upon Rac1 and 3-phosphoinositide-dependent kinase 1.''; PubMedEurope PMCScholia
Hamaguchi T, Ito M, Feng J, Seko T, Koyama M, Machida H, Takase K, Amano M, Kaibuchi K, Hartshorne DJ, Nakano T.; ''Phosphorylation of CPI-17, an inhibitor of myosin phosphatase, by protein kinase N.''; PubMedEurope PMCScholia
Miyano K, Ueno N, Takeya R, Sumimoto H.; ''Direct involvement of the small GTPase Rac in activation of the superoxide-producing NADPH oxidase Nox1.''; PubMedEurope PMCScholia
Madaule P, Furuyashiki T, Reid T, Ishizaki T, Watanabe G, Morii N, Narumiya S.; ''A novel partner for the GTP-bound forms of rho and rac.''; PubMedEurope PMCScholia
Manser E, Chong C, Zhao ZS, Leung T, Michael G, Hall C, Lim L.; ''Molecular cloning of a new member of the p21-Cdc42/Rac-activated kinase (PAK) family.''; PubMedEurope PMCScholia
Fujita A, Nakamura K, Kato T, Watanabe N, Ishizaki T, Kimura K, Mizoguchi A, Narumiya S.; ''Ropporin, a sperm-specific binding protein of rhophilin, that is localized in the fibrous sheath of sperm flagella.''; PubMedEurope PMCScholia
Hutchinson CL, Lowe PN, McLaughlin SH, Mott HR, Owen D.; ''Mutational analysis reveals a single binding interface between RhoA and its effector, PRK1.''; PubMedEurope PMCScholia
Lei M, Lu W, Meng W, Parrini MC, Eck MJ, Mayer BJ, Harrison SC.; ''Structure of PAK1 in an autoinhibited conformation reveals a multistage activation switch.''; PubMedEurope PMCScholia
Sun J, Barbieri JT.; ''ExoS Rho GTPase-activating protein activity stimulates reorganization of the actin cytoskeleton through Rho GTPase guanine nucleotide disassociation inhibitor.''; PubMedEurope PMCScholia
Cheng J, Wang H, Guggino WB.; ''Regulation of cystic fibrosis transmembrane regulator trafficking and protein expression by a Rho family small GTPase TC10.''; PubMedEurope PMCScholia
Reynaud C, Fabre S, Jalinot P.; ''The PDZ protein TIP-1 interacts with the Rho effector rhotekin and is involved in Rho signaling to the serum response element.''; PubMedEurope PMCScholia
Daniels RH, Bokoch GM.; ''p21-activated protein kinase: a crucial component of morphological signaling?''; PubMedEurope PMCScholia
Kuroda S, Fukata M, Kobayashi K, Nakafuku M, Nomura N, Iwamatsu A, Kaibuchi K.; ''Identification of IQGAP as a putative target for the small GTPases, Cdc42 and Rac1.''; PubMedEurope PMCScholia
Zhang B, Chernoff J, Zheng Y.; ''Interaction of Rac1 with GTPase-activating proteins and putative effectors. A comparison with Cdc42 and RhoA.''; PubMedEurope PMCScholia
Ishizaki T, Maekawa M, Fujisawa K, Okawa K, Iwamatsu A, Fujita A, Watanabe N, Saito Y, Kakizuka A, Morii N, Narumiya S.; ''The small GTP-binding protein Rho binds to and activates a 160 kDa Ser/Thr protein kinase homologous to myotonic dystrophy kinase.''; PubMedEurope PMCScholia
Roberts AW, Kim C, Zhen L, Lowe JB, Kapur R, Petryniak B, Spaetti A, Pollock JD, Borneo JB, Bradford GB, Atkinson SJ, Dinauer MC, Williams DA.; ''Deficiency of the hematopoietic cell-specific Rho family GTPase Rac2 is characterized by abnormalities in neutrophil function and host defense.''; PubMedEurope PMCScholia
Metzger E, Yin N, Wissmann M, Kunowska N, Fischer K, Friedrichs N, Patnaik D, Higgins JM, Potier N, Scheidtmann KH, Buettner R, Schüle R.; ''Phosphorylation of histone H3 at threonine 11 establishes a novel chromatin mark for transcriptional regulation.''; PubMedEurope PMCScholia
Watanabe S, De Zan T, Ishizaki T, Narumiya S.; ''Citron kinase mediates transition from constriction to abscission through its coiled-coil domain.''; PubMedEurope PMCScholia
Fainstein E, Marcelle C, Rosner A, Canaani E, Gale RP, Dreazen O, Smith SD, Croce CM.; ''A new fused transcript in Philadelphia chromosome positive acute lymphocytic leukaemia.''; PubMedEurope PMCScholia
RHO GTPases regulate cell behaviour by activating a number of downstream effectors that regulate cytoskeletal organization, intracellular trafficking and transcription (reviewed by Sahai and Marshall 2002).
One of the best studied RHO GTPase effectors are protein kinases ROCK1 and ROCK2, which are activated by binding RHOA, RHOB or RHOC. ROCK1 and ROCK2 phosphorylate many proteins involved in the stabilization of actin filaments and generation of actin-myosin contractile force, such as LIM kinases and myosin regulatory light chains (MRLC) (Amano et al. 1996, Ishizaki et al. 1996, Leung et al. 1996, Ohashi et al. 2000, Sumi et al. 2001, Riento and Ridley 2003, Watanabe et al. 2007).
PAK1, PAK2 and PAK3, members of the p21-activated kinase family, are activated by binding to RHO GTPases RAC1 and CDC42 and subsequent autophosphorylation and are involved in cytoskeleton regulation (Manser et al. 1994, Manser et al. 1995, Zhang et al. 1998, Edwards et al. 1999, Lei et al. 2000, Parrini et al. 2002; reviewed by Daniels and Bokoch 1999, Szczepanowska 2009).
RHOA, RHOB, RHOC and RAC1 activate protein kinase C related kinases (PKNs) PKN1, PKN2 and PKN3 (Maesaki et al. 1999, Zong et al. 1999, Owen et al. 2003, Modha et al. 2008, Hutchinson et al. 2011, Hutchinson et al. 2013), bringing them in proximity to the PIP3-activated PDPK1 (PDK1) and thus enabling PDPK1-mediated phosphorylation of PKN1, PKN2 and PKN3 (Flynn et al. 2000, Torbett et al. 2003). PKNs play important roles in cytoskeleton organization (Hamaguchi et al. 2000), regulation of cell cycle (Misaki et al. 2001), receptor trafficking (Metzger et al. 2003) and apoptosis (Takahashi et al. 1998). PKN1 is also involved in the ligand-dependent transcriptional activation by the androgen receptor (Metzger et al. 2003, Metzger et al. 2005, Metzger et al. 2008).
Citron kinase (CIT) binds RHO GTPases RHOA, RHOB, RHOC and RAC1 (Madaule et al. 1995), but the mechanism of CIT activation by GTP-bound RHO GTPases has not been elucidated. CIT and RHOA are implicated to act together in Golgi apparatus organization through regulation of the actin cytoskeleton (Camera et al. 2003). CIT is also involved in the regulation of cytokinesis through its interaction with KIF14 (Gruneberg et al. 2006, Bassi et al. 2013, Watanabe et al. 2013).
RHOA, RHOG, RAC1 and CDC42 bind kinectin (KTN1), a kinesin anchor protein involved in kinesin-mediated vesicle motility (Vignal et al. 2001, Hotta et al. 1996). The effect of RHOG activity on cellular morphology, exhibited in the formation of microtubule-dependent cellular protrusions, depends both on RHOG interaction with KTN1, as well as on the kinesin activity (Vignal et al. 2001). RHOG and KTN1 also cooperate in microtubule-dependent lysosomal transport (Vignal et al. 2001).
IQGAP proteins IQGAP1, IQGAP2 and IQGAP3, bind RAC1 and CDC42 and stabilize them in their GTP-bound state (Kuroda et al. 1996, Swart-Mataraza et al. 2002, Wang et al. 2007). IQGAPs bind F-actin filaments and modulate cell shape and motility through regulation of G-actin/F-actin equilibrium (Brill et al. 1996, Fukata et al. 1997, Bashour et al. 1997, Wang et al. 2007, Pelikan-Conchaudron et al. 2011). Binding of IQGAPs to F-actin is inhibited by calmodulin (Bashour et al. 1997, Pelikan-Conchaudron et al. 2011). IQGAP1 is involved in the regulation of adherens junctions through its interaction with E-cadherin (CDH1) and catenins (CTTNB1 and CTTNA1) (Kuroda et al. 1998, Hage et al. 2009). IQGAP1 contributes to cell polarity and lamellipodia formation through its interaction with microtubules (Fukata et al. 2002, Suzuki and Takahashi 2008).
RHOQ (TC10) regulates the trafficking of CFTR (cystic fibrosis transmembrane conductance regulator) by binding to the Golgi-associated protein GOPC (also known as PIST, FIG and CAL). In the absence of RHOQ, GOPC bound to CFTR directs CFTR for lysosomal degradation, while GTP-bound RHOQ directs GOPC:CFTR complex to the plasma membrane, thereby rescuing CFTR (Neudauer et al. 2001, Cheng et al. 2005).
RAC1 and CDC42 activate WASP and WAVE proteins, members of the Wiskott-Aldrich Syndrome protein family. WASPs and WAVEs simultaneously interact with G-actin and the actin-related ARP2/3 complex, acting as nucleation promoting factors in actin polymerization (reviewed by Lane et al. 2014).
RHOA, RHOB, RHOC, RAC1 and CDC42 activate a subset of formin family members. Once activated, formins bind G-actin and the actin-bound profilins and accelerate actin polymerization, while some formins also interact with microtubules. Formin-mediated cytoskeletal reorganization plays important roles in cell motility, organelle trafficking and mitosis (reviewed by Kuhn and Geyer 2014).
Rhotekin (RTKN) and rhophilins (RHPN1 and RHPN2) are effectors of RHOA, RHOB and RHOC and have not been studied in detail. They regulate the organization of the actin cytoskeleton and are implicated in the establishment of cell polarity, cell motility and possibly endosome trafficking (Sudo et al. 2006, Watanabe et al. 1996, Fujita et al. 2000, Peck et al. 2002, Mircescu et al. 2002). Similar to formins (Miralles et al. 2003), cytoskeletal changes triggered by RTKN activation may lead to stimulation of SRF-mediated transcription (Reynaud et al. 2000).
RHO GTPases RAC1 and RAC2 are needed for activation of NADPH oxidase complexes 1, 2 and 3 (NOX1, NOX2 and NOX3), membrane associated enzymatic complexes that use NADPH as an electron donor to reduce oxygen and produce superoxide (O2-). Superoxide serves as a secondary messenger and also directly contributes to the microbicidal activity of neutrophils (Knaus et al. 1991, Roberts et al. 1999, Kim and Dinauer 2001, Jyoti et al. 2014, Cheng et al. 2006, Miyano et al. 2006, Ueyama et al. 2006).
GDP dissociation inhibitors or GDIs confer an additional but important layer of Rho GTPase regulation along with GEFs and GAPs. GDIs mainly inhibit the dissociation of bound guanine nucleotide (usually GDP) from their partner GTPases. So far, three human GDIs with proven biological functions have been found: RhoGDI/GDIalpha/GDI1, hematopoietic cell selective Ly/D4GDI/GDIbeta/GDI2, and Rho GDIgamma/GDI3 (DerMardirossian and Bokoch, 2005). Three specific biochemical functions of GDIs have been established: inhibiting the dissociation of GDP from Rho proteins, maintaining the GTPases in an inactive form, and preventing GTPase activation by GEFs (Olofsson, 1999). Detailed annotations of GDIs will be available in future releases.
To transduce signals, the activated, GTP-bound Rho GTPases interact with specific effector molecules. It has been observed that GEFs contribute to the signaling specificity of their downstream target GTPase via association with scaffolding molecules that link them and the GTPase to specific GTPase effectors (Govek et al., 2005). Some of the effector molecules implicated in actin and microtubule dynamics include diaphanous-related formins, Toca 1, WIP, WASP, Pak, p35/Cdk5, Wave, Nap125, MLCK, MLC, IRSp53. Detailed annotations of the downstream events stimulated by activated, GTP bound Rho GTPases will be available in future releases.
Guanine nucleotide exchange factors (GEFs) activate GTPases by enhancing the exchange of bound GDP for GTP. Much evidence points to GEFs being critical mediators of Rho GTPase activation (Schmidt and Hall, 2002). Many GEFs are known to be highly specific for a particular GTPase, e.g. Fgd1/Cdc42 and p115RhoGEF/Rho (Hart et al., 1996, Zheng et al., 1996). Others have a broader spectrum and activate several GTPases, e.g. Vav1 for Rac, Rho, and Cdc42 (Hart et al, 1994).
The human genome includes approximately 70 genes that are predicted to encode Rho-specific GTPase Activating Proteins (RhoGAPs). As in the case of GEFs, some RhoGAPs are believed to be highly specific, whereas others are more promiscuous with respect to their target GTPases. Increasing evidence suggests that GAPs are also regulated by external cues in addition to being signal terminators leading to Rho GTPase inactivation. These proteins play important role in many Rho mediated signaling pathways.
Some known GAPs include p190 A, cdGAP, ARAP3, MgcRacGAP, Chimaerin, Nadrin, TCGAP, DLC 1, 2, ArhGAP6, Myosin IXA. These and other GAPs have been implicated in many processes, such as exocytosis, endocytosis, cytokinesis, cell differentiation, migration, neuronal morphogenesis, angiogenesis and tumor suppression. Detailed annotations of the biological role of GAPs in Rho mediated signaling will be available in future releases.
GDIs sequester the inactive GTPases, preventing the dissociation of GDP and interactions with regulatory and effector molecules. They maintain Rho GTPases as soluble cytosolic proteins by forming high affinity complexes. In these complexes, the geranylgeranyl membrane targeting moiety present at the C terminus of the Rho GTPases is shielded from the solvent by its insertion into the hydrophobic pocket formed by the immunoglobulin like beta sandwich of the GDI (DerMardirossian and Bokoch, 2005).
Rho proteins, when released from the sequestering cytosolic GDIs, insert into the lipid bilayer of the plasma membrane with their isoprenylated C termini. The membrane bound GEFs activate these free RhoGTPases and thereby trigger the downstream signaling events via respective effector proteins on the membrane (Robbe et al., 2003). Detailed annotation of the activities of farnesyltransferase / geranylgeranyltransferases on prenylation of Rho GTPases thereby enabling their subsequent localization to plasma membrane will be available in future releases.
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RhoGTPase:GDP:GDI
complexOne of the best studied RHO GTPase effectors are protein kinases ROCK1 and ROCK2, which are activated by binding RHOA, RHOB or RHOC. ROCK1 and ROCK2 phosphorylate many proteins involved in the stabilization of actin filaments and generation of actin-myosin contractile force, such as LIM kinases and myosin regulatory light chains (MRLC) (Amano et al. 1996, Ishizaki et al. 1996, Leung et al. 1996, Ohashi et al. 2000, Sumi et al. 2001, Riento and Ridley 2003, Watanabe et al. 2007).
PAK1, PAK2 and PAK3, members of the p21-activated kinase family, are activated by binding to RHO GTPases RAC1 and CDC42 and subsequent autophosphorylation and are involved in cytoskeleton regulation (Manser et al. 1994, Manser et al. 1995, Zhang et al. 1998, Edwards et al. 1999, Lei et al. 2000, Parrini et al. 2002; reviewed by Daniels and Bokoch 1999, Szczepanowska 2009).
RHOA, RHOB, RHOC and RAC1 activate protein kinase C related kinases (PKNs) PKN1, PKN2 and PKN3 (Maesaki et al. 1999, Zong et al. 1999, Owen et al. 2003, Modha et al. 2008, Hutchinson et al. 2011, Hutchinson et al. 2013), bringing them in proximity to the PIP3-activated PDPK1 (PDK1) and thus enabling PDPK1-mediated phosphorylation of PKN1, PKN2 and PKN3 (Flynn et al. 2000, Torbett et al. 2003). PKNs play important roles in cytoskeleton organization (Hamaguchi et al. 2000), regulation of cell cycle (Misaki et al. 2001), receptor trafficking (Metzger et al. 2003) and apoptosis (Takahashi et al. 1998). PKN1 is also involved in the ligand-dependent transcriptional activation by the androgen receptor (Metzger et al. 2003, Metzger et al. 2005, Metzger et al. 2008).
Citron kinase (CIT) binds RHO GTPases RHOA, RHOB, RHOC and RAC1 (Madaule et al. 1995), but the mechanism of CIT activation by GTP-bound RHO GTPases has not been elucidated. CIT and RHOA are implicated to act together in Golgi apparatus organization through regulation of the actin cytoskeleton (Camera et al. 2003). CIT is also involved in the regulation of cytokinesis through its interaction with KIF14 (Gruneberg et al. 2006, Bassi et al. 2013, Watanabe et al. 2013).
RHOA, RHOG, RAC1 and CDC42 bind kinectin (KTN1), a kinesin anchor protein involved in kinesin-mediated vesicle motility (Vignal et al. 2001, Hotta et al. 1996). The effect of RHOG activity on cellular morphology, exhibited in the formation of microtubule-dependent cellular protrusions, depends both on RHOG interaction with KTN1, as well as on the kinesin activity (Vignal et al. 2001). RHOG and KTN1 also cooperate in microtubule-dependent lysosomal transport (Vignal et al. 2001).
IQGAP proteins IQGAP1, IQGAP2 and IQGAP3, bind RAC1 and CDC42 and stabilize them in their GTP-bound state (Kuroda et al. 1996, Swart-Mataraza et al. 2002, Wang et al. 2007). IQGAPs bind F-actin filaments and modulate cell shape and motility through regulation of G-actin/F-actin equilibrium (Brill et al. 1996, Fukata et al. 1997, Bashour et al. 1997, Wang et al. 2007, Pelikan-Conchaudron et al. 2011). Binding of IQGAPs to F-actin is inhibited by calmodulin (Bashour et al. 1997, Pelikan-Conchaudron et al. 2011). IQGAP1 is involved in the regulation of adherens junctions through its interaction with E-cadherin (CDH1) and catenins (CTTNB1 and CTTNA1) (Kuroda et al. 1998, Hage et al. 2009). IQGAP1 contributes to cell polarity and lamellipodia formation through its interaction with microtubules (Fukata et al. 2002, Suzuki and Takahashi 2008).
RHOQ (TC10) regulates the trafficking of CFTR (cystic fibrosis transmembrane conductance regulator) by binding to the Golgi-associated protein GOPC (also known as PIST, FIG and CAL). In the absence of RHOQ, GOPC bound to CFTR directs CFTR for lysosomal degradation, while GTP-bound RHOQ directs GOPC:CFTR complex to the plasma membrane, thereby rescuing CFTR (Neudauer et al. 2001, Cheng et al. 2005).
RAC1 and CDC42 activate WASP and WAVE proteins, members of the Wiskott-Aldrich Syndrome protein family. WASPs and WAVEs simultaneously interact with G-actin and the actin-related ARP2/3 complex, acting as nucleation promoting factors in actin polymerization (reviewed by Lane et al. 2014).
RHOA, RHOB, RHOC, RAC1 and CDC42 activate a subset of formin family members. Once activated, formins bind G-actin and the actin-bound profilins and accelerate actin polymerization, while some formins also interact with microtubules. Formin-mediated cytoskeletal reorganization plays important roles in cell motility, organelle trafficking and mitosis (reviewed by Kuhn and Geyer 2014).
Rhotekin (RTKN) and rhophilins (RHPN1 and RHPN2) are effectors of RHOA, RHOB and RHOC and have not been studied in detail. They regulate the organization of the actin cytoskeleton and are implicated in the establishment of cell polarity, cell motility and possibly endosome trafficking (Sudo et al. 2006, Watanabe et al. 1996, Fujita et al. 2000, Peck et al. 2002, Mircescu et al. 2002). Similar to formins (Miralles et al. 2003), cytoskeletal changes triggered by RTKN activation may lead to stimulation of SRF-mediated transcription (Reynaud et al. 2000).
RHO GTPases RAC1 and RAC2 are needed for activation of NADPH oxidase complexes 1, 2 and 3 (NOX1, NOX2 and NOX3), membrane associated enzymatic complexes that use NADPH as an electron donor to reduce oxygen and produce superoxide (O2-). Superoxide serves as a secondary messenger and also directly contributes to the microbicidal activity of neutrophils (Knaus et al. 1991, Roberts et al. 1999, Kim and Dinauer 2001, Jyoti et al. 2014, Cheng et al. 2006, Miyano et al. 2006, Ueyama et al. 2006).
Annotated Interactions
RhoGTPase:GDP:GDI
complexRhoGTPase:GDP:GDI
complexSome known GAPs include p190 A, cdGAP, ARAP3, MgcRacGAP, Chimaerin, Nadrin, TCGAP, DLC 1, 2, ArhGAP6, Myosin IXA. These and other GAPs have been implicated in many processes, such as exocytosis, endocytosis, cytokinesis, cell differentiation, migration, neuronal morphogenesis, angiogenesis and tumor suppression. Detailed annotations of the biological role of GAPs in Rho mediated signaling will be available in future releases.
Rho proteins, when released from the sequestering cytosolic GDIs, insert into the lipid bilayer of the plasma membrane with their isoprenylated C termini. The membrane bound GEFs activate these free RhoGTPases and thereby trigger the downstream signaling events via respective effector proteins on the membrane (Robbe et al., 2003). Detailed annotation of the activities of farnesyltransferase / geranylgeranyltransferases on prenylation of Rho GTPases thereby enabling their subsequent localization to plasma membrane will be available in future releases.