This family is known as Family B (secretin-receptor family, family 2) G-protein-coupled receptors. Family B GPCRs include secretin, calcitonin, parathyroid hormone/parathyroid hormone-related peptides and vasoactive intestinal peptide receptors; all of which activate adenylyl cyclase and the phosphatidyl-inositol-calcium pathway (Harmar AJ, 2001).
View original pathway at Reactome.
Nelkin BD, Rosenfeld KI, de Bustros A, Leong SS, Roos BA, Baylin SB.; ''Structure and expression of a gene encoding human calcitonin and calcitonin gene related peptide.''; PubMedEurope PMCScholia
Usdin TB, Gruber C, Bonner TI.; ''Identification and functional expression of a receptor selectively recognizing parathyroid hormone, the PTH2 receptor.''; PubMedEurope PMCScholia
Aiyar N, Rand K, Elshourbagy NA, Zeng Z, Adamou JE, Bergsma DJ, Li Y.; ''A cDNA encoding the calcitonin gene-related peptide type 1 receptor.''; PubMedEurope PMCScholia
Pioszak AA, Parker NR, Suino-Powell K, Xu HE.; ''Molecular recognition of corticotropin-releasing factor by its G-protein-coupled receptor CRFR1.''; PubMedEurope PMCScholia
Runge S, Thøgersen H, Madsen K, Lau J, Rudolph R.; ''Crystal structure of the ligand-bound glucagon-like peptide-1 receptor extracellular domain.''; PubMedEurope PMCScholia
Hendy GN, Kronenberg HM, Potts JT, Rich A.; ''Nucleotide sequence of cloned cDNAs encoding human preproparathyroid hormone.''; PubMedEurope PMCScholia
Rall T, Harris BA.; ''Identification of the lesion in the stimulatory GTP-binding protein of the uncoupled S49 lymphoma.''; PubMedEurope PMCScholia
Donaldson CJ, Sutton SW, Perrin MH, Corrigan AZ, Lewis KA, Rivier JE, Vaughan JM, Vale WW.; ''Cloning and characterization of human urocortin.''; PubMedEurope PMCScholia
Schneider H, Feyen JH, Seuwen K.; ''A C-terminally truncated human parathyroid hormone receptor is functional and activates multiple G proteins.''; PubMedEurope PMCScholia
Kamitani S, Asakawa M, Shimekake Y, Kuwasako K, Nakahara K, Sakata T.; ''The RAMP2/CRLR complex is a functional adrenomedullin receptor in human endothelial and vascular smooth muscle cells.''; PubMedEurope PMCScholia
Mizuno N, Itoh H.; ''Functions and regulatory mechanisms of Gq-signaling pathways.''; PubMedEurope PMCScholia
Schipani E, Karga H, Karaplis AC, Potts JT, Kronenberg HM, Segre GV, Abou-Samra AB, Jüppner H.; ''Identical complementary deoxyribonucleic acids encode a human renal and bone parathyroid hormone (PTH)/PTH-related peptide receptor.''; PubMedEurope PMCScholia
Hamann J, Vogel B, van Schijndel GM, van Lier RA.; ''The seven-span transmembrane receptor CD97 has a cellular ligand (CD55, DAF).''; PubMedEurope PMCScholia
Whitmore TE, Holloway JL, Lofton-Day CE, Maurer MF, Chen L, Quinton TJ, Vincent JB, Scherer SW, Lok S.; ''Human secretin (SCT): gene structure, chromosome location, and distribution of mRNA.''; PubMedEurope PMCScholia
Koehler JA, Yusta B, Drucker DJ.; ''The HeLa cell glucagon-like peptide-2 receptor is coupled to regulation of apoptosis and ERK1/2 activation through divergent signaling pathways.''; PubMedEurope PMCScholia
Della Penna K, Kinose F, Sun H, Koblan KS, Wang H.; ''Tuberoinfundibular peptide of 39 residues (TIP39): molecular structure and activity for parathyroid hormone 2 receptor.''; PubMedEurope PMCScholia
Gaylinn BD, Harrison JK, Zysk JR, Lyons CE, Lynch KR, Thorner MO.; ''Molecular cloning and expression of a human anterior pituitary receptor for growth hormone-releasing hormone.''; PubMedEurope PMCScholia
Thorens B, Porret A, Bühler L, Deng SP, Morel P, Widmann C.; ''Cloning and functional expression of the human islet GLP-1 receptor. Demonstration that exendin-4 is an agonist and exendin-(9-39) an antagonist of the receptor.''; PubMedEurope PMCScholia
Roh J, Chang CL, Bhalla A, Klein C, Hsu SY.; ''Intermedin is a calcitonin/calcitonin gene-related peptide family peptide acting through the calcitonin receptor-like receptor/receptor activity-modifying protein receptor complexes.''; PubMedEurope PMCScholia
Kuwasako K, Cao YN, Nagoshi Y, Tsuruda T, Kitamura K, Eto T.; ''Characterization of the human calcitonin gene-related peptide receptor subtypes associated with receptor activity-modifying proteins.''; PubMedEurope PMCScholia
Patel DR, Kong Y, Sreedharan SP.; ''Molecular cloning and expression of a human secretin receptor.''; PubMedEurope PMCScholia
Kwakkenbos MJ, Pouwels W, Matmati M, Stacey M, Lin HH, Gordon S, van Lier RA, Hamann J.; ''Expression of the largest CD97 and EMR2 isoforms on leukocytes facilitates a specific interaction with chondroitin sulfate on B cells.''; PubMedEurope PMCScholia
Doyle ME, Egan JM.; ''Mechanisms of action of glucagon-like peptide 1 in the pancreas.''; PubMedEurope PMCScholia
Hansen IA, Jakob O, Wortmann S, Arzberger T, Allolio B, Blind E.; ''Characterization of the human and mouse genes encoding the tuberoinfundibular peptide of 39 residues, a ligand of the parathyroid hormone receptor family.''; PubMedEurope PMCScholia
Behan DP, De Souza EB, Lowry PJ, Potter E, Sawchenko P, Vale WW.; ''Corticotropin releasing factor (CRF) binding protein: a novel regulator of CRF and related peptides.''; PubMedEurope PMCScholia
Thomsen J, Kristiansen K, Brunfeldt K, Sundby F.; ''The amino acid sequence of human glucagon.''; PubMedEurope PMCScholia
Behar V, Pines M, Nakamoto C, Greenberg Z, Bisello A, Stueckle SM, Bessalle R, Usdin TB, Chorev M, Rosenblatt M, Suva LJ.; ''The human PTH2 receptor: binding and signal transduction properties of the stably expressed recombinant receptor.''; PubMedEurope PMCScholia
Gromada J, Rorsman P, Dissing S, Wulff BS.; ''Stimulation of cloned human glucagon-like peptide 1 receptor expressed in HEK 293 cells induces cAMP-dependent activation of calcium-induced calcium release.''; PubMedEurope PMCScholia
Morris HR, Panico M, Etienne T, Tippins J, Girgis SI, MacIntyre I.; ''Isolation and characterization of human calcitonin gene-related peptide.''; PubMedEurope PMCScholia
Runge S, Schimmer S, Oschmann J, Schiødt CB, Knudsen SM, Jeppesen CB, Madsen K, Lau J, Thøgersen H, Rudolph R.; ''Differential structural properties of GLP-1 and exendin-4 determine their relative affinity for the GLP-1 receptor N-terminal extracellular domain.''; PubMedEurope PMCScholia
Svoboda M, Tastenoy M, Van Rampelbergh J, Goossens JF, De Neef P, Waelbroeck M, Robberecht P.; ''Molecular cloning and functional characterization of a human VIP receptor from SUP-T1 lymphoblasts.''; PubMedEurope PMCScholia
Van Valen F, Piechot G, Jürgens H.; ''Calcitonin gene-related peptide (CGRP) receptors are linked to cyclic adenosine monophosphate production in SK-N-MC human neuroblastoma cells.''; PubMedEurope PMCScholia
Dillon JS, Tanizawa Y, Wheeler MB, Leng XH, Ligon BB, Rabin DU, Yoo-Warren H, Permutt MA, Boyd AE.; ''Cloning and functional expression of the human glucagon-like peptide-1 (GLP-1) receptor.''; PubMedEurope PMCScholia
Dallas-Yang Q, Shen X, Strowski M, Brady E, Saperstein R, Gibson RE, Szalkowski D, Qureshi SA, Candelore MR, Fenyk-Melody JE, Parmee ER, Zhang BB, Jiang G.; ''Hepatic glucagon receptor binding and glucose-lowering in vivo by peptidyl and non-peptidyl glucagon receptor antagonists.''; PubMedEurope PMCScholia
Kitamura K, Kangawa K, Kawamoto M, Ichiki Y, Nakamura S, Matsuo H, Eto T.; ''Adrenomedullin: a novel hypotensive peptide isolated from human pheochromocytoma.''; PubMedEurope PMCScholia
Mayo KE.; ''Molecular cloning and expression of a pituitary-specific receptor for growth hormone-releasing hormone.''; PubMedEurope PMCScholia
Gorn AH, Lin HY, Yamin M, Auron PE, Flannery MR, Tapp DR, Manning CA, Lodish HF, Krane SM, Goldring SR.; ''Cloning, characterization, and expression of a human calcitonin receptor from an ovarian carcinoma cell line.''; PubMedEurope PMCScholia
Lok S, Kuijper JL, Jelinek LJ, Kramer JM, Whitmore TE, Sprecher CA, Mathewes S, Grant FJ, Biggs SH, Rosenberg GB.; ''The human glucagon receptor encoding gene: structure, cDNA sequence and chromosomal localization.''; PubMedEurope PMCScholia
Ohkubo S, Kimura C, Ogi K, Okazaki K, Hosoya M, Onda H, Miyata A, Arimura A, Fujino M.; ''Primary structure and characterization of the precursor to human pituitary adenylate cyclase activating polypeptide.''; PubMedEurope PMCScholia
Munroe DG, Gupta AK, Kooshesh F, Vyas TB, Rizkalla G, Wang H, Demchyshyn L, Yang ZJ, Kamboj RK, Chen H, McCallum K, Sumner-Smith M, Drucker DJ, Crivici A.; ''Prototypic G protein-coupled receptor for the intestinotrophic factor glucagon-like peptide 2.''; PubMedEurope PMCScholia
Stone DM, Hynes M, Armanini M, Swanson TA, Gu Q, Johnson RL, Scott MP, Pennica D, Goddard A, Phillips H, Noll M, Hooper JE, de Sauvage F, Rosenthal A.; ''The tumour-suppressor gene patched encodes a candidate receptor for Sonic hedgehog.''; PubMedEurope PMCScholia
Tsukada T, Horovitch SJ, Montminy MR, Mandel G, Goodman RH.; ''Structure of the human vasoactive intestinal polypeptide gene.''; PubMedEurope PMCScholia
Lin HH, Stacey M, Saxby C, Knott V, Chaudhry Y, Evans D, Gordon S, McKnight AJ, Handford P, Lea S.; ''Molecular analysis of the epidermal growth factor-like short consensus repeat domain-mediated protein-protein interactions: dissection of the CD97-CD55 complex.''; PubMedEurope PMCScholia
Mikels AJ, Nusse R.; ''Purified Wnt5a protein activates or inhibits beta-catenin-TCF signaling depending on receptor context.''; PubMedEurope PMCScholia
Orskov C, Rabenhøj L, Wettergren A, Kofod H, Holst JJ.; ''Tissue and plasma concentrations of amidated and glycine-extended glucagon-like peptide I in humans.''; PubMedEurope PMCScholia
Gromada J, Brock B, Schmitz O, Rorsman P.; ''Glucagon-like peptide-1: regulation of insulin secretion and therapeutic potential.''; PubMedEurope PMCScholia
Aiyar N, Disa J, Pullen M, Nambi P.; ''Receptor activity modifying proteins interaction with human and porcine calcitonin receptor-like receptor (CRLR) in HEK-293 cells.''; PubMedEurope PMCScholia
Pal K, Swaminathan K, Xu HE, Pioszak AA.; ''Structural basis for hormone recognition by the Human CRFR2{alpha} G protein-coupled receptor.''; PubMedEurope PMCScholia
Behan DP, Potter E, Lewis KA, Jenkins NA, Copeland N, Lowry PJ, Vale WW.; ''Cloning and structure of the human corticotrophin releasing factor-binding protein gene (CRHBP)''; PubMedEurope PMCScholia
Bazarsuren A, Grauschopf U, Wozny M, Reusch D, Hoffmann E, Schaefer W, Panzner S, Rudolph R.; ''In vitro folding, functional characterization, and disulfide pattern of the extracellular domain of human GLP-1 receptor.''; PubMedEurope PMCScholia
Hsieh JC, Rattner A, Smallwood PM, Nathans J.; ''Biochemical characterization of Wnt-frizzled interactions using a soluble, biologically active vertebrate Wnt protein.''; PubMedEurope PMCScholia
Gubler U, Monahan JJ, Lomedico PT, Bhatt RS, Collier KJ, Hoffman BJ, Böhlen P, Esch F, Ling N, Zeytin F, Brazeau P, Poonian MS, Gage LP.; ''Cloning and sequence analysis of cDNA for the precursor of human growth hormone-releasing factor, somatocrinin.''; PubMedEurope PMCScholia
Moody AJ, Thim L, Valverde I.; ''The isolation and sequencing of human gastric inhibitory peptide (GIP).''; PubMedEurope PMCScholia
Nishi M, Sanke T, Seino S, Eddy RL, Fan YS, Byers MG, Shows TB, Bell GI, Steiner DF.; ''Human islet amyloid polypeptide gene: complete nucleotide sequence, chromosomal localization, and evolutionary history.''; PubMedEurope PMCScholia
Underwood CR, Garibay P, Knudsen LB, Hastrup S, Peters GH, Rudolph R, Reedtz-Runge S.; ''Crystal structure of glucagon-like peptide-1 in complex with the extracellular domain of the glucagon-like peptide-1 receptor.''; PubMedEurope PMCScholia
Schneider H, Feyen JH, Seuwen K, Movva NR.; ''Cloning and functional expression of a human parathyroid hormone receptor.''; PubMedEurope PMCScholia
Ogi K, Miyamoto Y, Masuda Y, Habata Y, Hosoya M, Ohtaki T, Masuo Y, Onda H, Fujino M.; ''Molecular cloning and functional expression of a cDNA encoding a human pituitary adenylate cyclase activating polypeptide receptor.''; PubMedEurope PMCScholia
Volz A, Göke R, Lankat-Buttgereit B, Fehmann HC, Bode HP, Göke B.; ''Molecular cloning, functional expression, and signal transduction of the GIP-receptor cloned from a human insulinoma.''; PubMedEurope PMCScholia
Sreedharan SP, Patel DR, Huang JX, Goetzl EJ.; ''Cloning and functional expression of a human neuroendocrine vasoactive intestinal peptide receptor.''; PubMedEurope PMCScholia
McLatchie LM, Fraser NJ, Main MJ, Wise A, Brown J, Thompson N, Solari R, Lee MG, Foord SM.; ''RAMPs regulate the transport and ligand specificity of the calcitonin-receptor-like receptor.''; PubMedEurope PMCScholia
Feldman DS, Zamah AM, Pierce KL, Miller WE, Kelly F, Rapacciuolo A, Rockman HA, Koch WJ, Luttrell LM.; ''Selective inhibition of heterotrimeric Gs signaling. Targeting the receptor-G protein interface using a peptide minigene encoding the Galpha(s) carboxyl terminus.''; PubMedEurope PMCScholia
Steenbergh PH, Höppener JW, Zandberg J, Lips CJ, Jansz HS.; ''A second human calcitonin/CGRP gene.''; PubMedEurope PMCScholia
Offermanns S, Iida-Klein A, Segre GV, Simon MI.; ''G alpha q family members couple parathyroid hormone (PTH)/PTH-related peptide and calcitonin receptors to phospholipase C in COS-7 cells.''; PubMedEurope PMCScholia
Suva LJ, Winslow GA, Wettenhall RE, Hammonds RG, Moseley JM, Diefenbach-Jagger H, Rodda CP, Kemp BE, Rodriguez H, Chen EY.; ''A parathyroid hormone-related protein implicated in malignant hypercalcemia: cloning and expression.''; PubMedEurope PMCScholia
The classic signalling route for G alpha (q) is activation of phospholipase C beta thereby triggering phosphoinositide hydrolysis, calcium mobilization and protein kinase C activation. This provides a path to calcium-regulated kinases and phosphatases, GEFs, MAP kinase cassettes and other proteins that mediate cellular responses ranging from granule secretion, integrin activation, and aggregation in platelets. Gq participates in many other signalling events including direct interaction with RhoGEFs that stimulate RhoA activity and inhibition of PI3K. Both in vitro and in vivo, the G-protein Gq seems to be the predominant mediator of the activation of platelets. Moreover, G alpha (q) can stimulate the activation of Burton tyrosine kinase (Ma Y C et al. 1998). Regulator of G-protein Signalling (RGS) proteins can regulate the activity of G alpha (z) (Soundararajan M et al. 2008).
The general function of the G alpha (s) subunit (Gs) is to activate adenylate cyclase (Tesmer et al. 1997), which in turn produces cAMP, leading to the activation of cAMP-dependent protein kinases (often referred to collectively as Protein Kinase A). The signal from the ligand-stimulated GPCR is amplified because the receptor can activate several Gs heterotrimers before it is inactivated. Another downstream effector of G alpha (s) is the protein tyrosine kinase c-Src (Ma et al. 2000).
Glucagon (Thomsen J et al, 1972) is an important peptide hormone produced by the pancreas. It is released when the glucose level in the blood is low (hypoglycemia), causing the liver to convert stored glycogen into glucose and release it into the bloodstream. The action of glucagon is thus opposite to that of insulin. Glucagon, together with glucagon-like peptide 1 (GLP-1) and glucagon-like peptide 2 (GLP-2), are peptide hormones encoded by a single common prohormone precursor, proglucagon.The glucagon receptor (Lok S et al, 1994) plays a central role in regulating the level of blood glucose by controlling the rate of hepatic glucose production and insulin secretion. The activity of this receptor is mediated by coupling to Gs and q, which stimulate adenylyl cyclase and a phosphatidylinositol-calcium second messenger system respectively.
The highly conserved Wnt signaling proteins play critical roles in guiding pattern formation, cell fate decision, and morphogenetic movement during animal development. They bind to the Frizzled (FZD) family of seven-pass transmembrane proteins and initiate at least three different intracellular signaling pathways. Historically they were considered to be family B GPCRs but more recent phylogenetic classifications put them into a class of their own (e.g. Schioth & Fredriksson 2005). FZD members have been demonstrated to signal via Gi/o (Slusarski et al. 1997) but this is not considered to be the primary signaling mechanism for these receptors (Hsieh 2004). Instead they signal through the canonical/beta-catenin pathway, the planar cell polarity (PCP) pathway and the Wnt/Ca2+ pathway. The canonical/beta-catenin pathway requires a co-receptor protein known as LDL5 or LDL6 (Tamai et al. 2000). Most Wnt signaling has been attributed to the activation of FZD receptors but there is evidence of FZD-independent signaling (Mikels & Nusse 2006). Much Wnt research has used indirect evidence to infer the involvement of FZD receptors (e.g. Gazit et al. 1999) but there is some direct evidence of Wnt-FZD binding (Hsieh et al. 1999; Mikels & Nusse 2006).
Glucagon-like Peptide-1 is synthesized in intestinal L-cells in response to the presence of glucose and fatty acids absorbed from the intestine. Most GLP-1 is the GLP-1 (7-36) amidated form; some GLP-1 is the GLP-1 (7-37) form. GLP-1 circulates to the pancreas where it binds the Glucagon-like Peptide-1 Receptor (GLP-1R), a G-protein coupled receptor located on the plasma membrane of beta cells. GLP-1R is a seven-pass transmembrane protein and a member of the B family of GPCRs, which have N-terminal extracellular domains of 100-150 amino acids. GLP-1 interacts with the extracellular N-terminal region of GLP-1R.
The CALC1 gene produces a prepropeptide from which calcitonin (CT) is a cleavage product (Nelkin BD et al, 1984). CT is a polypeptide hormone that is produced in the thyroid gland. It acts to reduce blood calcium, opposing the effects of parathyroid hormone. The CT receptor (Gorn AH et al, 1992) binds CT and mediates its actions. The ligand:receptor complex couples to the G protein alpha s subunit, which stimulates adenylyl cyclase and increases intracellular cAMP levels (Gorn AH et al, 1992).
Glucagon-like peptide 2 (GLP-2) (Drucker DJ 1999) is a 33-aa proglucagon-derived peptide produced by intestinal enteroendocrine cells. GLP-2 stimulates intestinal growth. The effects of GLP-2 are mediated by the GLP2 receptor (Munroe DG et al, 1999), which can couple with G protein alpha s subunit that activates adenylyl cyclase (Koehler JA et al, 2005).
The calcitonin gene-related peptides alpha-CGRP and beta-CGRP (Morris HR et al, 1984, Steenbergh PH et al, 1985 respectively) are members of the calcitonin family of peptides and are produced in both peripheral and central neurons. They are the most potent peptide vasodilators and can function in the transmission of pain. Their effects are mediated by binding to the CGRP1 receptor (CL) (Aiyar N et al, 1996). CGRP receptors are complexes between CL and receptor activity modifying protein 1 (RAMP1) (Kuwasako K et al, 2004). The activity of the receptor is mediated by coupling to the G protein alpha s subunit, which stimulates adenylyl cyclase which can increase intracellular cAMP levels (Van Valen et al, 1990).
The pituitary adenylate cyclase-activating peptide (PACAP) (Ohkubo S et al, 1992) is a peptide hormone similar to vasoactive intestinal peptide (VIP). PACAP functions as a hypophysiotropic hormone, neurotransmitter and neuromodulator. Three active peptides are cleaved from the precursor protein; PACAP-related peptide, PACAP-27 and PACAP-38. The effects of the PACAP peptides are mediated by the PACAP receptor (Ogi K et al, 1993). This receptor is predominantly expressed in the CNS. The activity of the receptor is mediated by coupling with the G protein alpha s subunit, which stimulates adenylyl cyclase which increases intracellular cAMP levels (Ogi K et al, 1993).
Corticoliberin (CRH, aka corticotropin-releasing factor CRF) is a 41-amino acid amino peptide which, together with CRH-related peptides such as the urocortins (UCNs), play a role in coordinating endocrine, autonomic and behavioural responses to stress. These peptides exert their effects through binding and activation of two class B/Secretin family of GPCRs, CRHR1 and CRHR2 (aka CRFR1 and CRFR2 respectively). The activity of these receptors is mediated by coupling to the G protein alpha s subunit, stimulating adenylyl cyclase which increases intracellular cAMP levels (Donaldson et al. 1996). CRH and UCN bind with highest affinity to both CRHR1 and CRHR2-alpha receptors (Donaldson et al. 1996, Pioszak et al. 2008, Pal et al. 2010).
Secretin (SCT) (Whitmore TE et al, 2000) is a peptide hormone belonging to the glucagon peptide hormone family and is produced in the duodenum. Its primary effect is to regulate the pH of the duodenal contents via the control of gastric acid secretion and buffering with bicarbonate. These effects are mediated by the SCT receptor (Patel DR et al, 1995). The receptor activity is mediated by coupling to G protein alpha s subunits, which stimulate adenylyl cyclase which increases intracellular cAMP levels (Patel DR et al, 1995).
Intermedin (AM2) (Roh J et al, 2004) and adrenomedullin (AM) (Kitamura K et al, 1993) belong to the calcitonin peptide hormone family and are important for cardiovascular and respiratory regulation. The functional adrenomedullin receptor AM1 is composed of the calcitonin gene-related peptide receptor (CGPR) and receptor activity modifying protein 2 (RAMP2) (Kamitani S et al, 1999). AM1 receptor can bind either of these peptide hormones and its activity is mediated by coupling with the G protein alpha s subunit which stimulates adenylyl cyclase and increases intracellular cAMP levels (Aiyar N et al, 2001). The function of the AM2 receptor (formed by the combination of CGPR and RAMP3) is very similar to that of AM1.
Vasoactive intestinal peptide (VIP) (Tsukada T et al, 1985) belongs to the glucagon hormone family and is expressed in many parts of the human body. VIP causes vasodilation, lowers arterial blood pressure, stimulates myocardial muscle contraction and increases glycogenolysis. It also relaxes the smooth muscle of trachea, stomach and gall bladder. The effects of VIP are mediated by the VIP receptors of which there are two, 1 and 2 (Sreedharan SP et al, 1993 and Svodoba M et al, 1994 respectively). The actions of the receptor are mediated by coupling with the G protein alpha s subunit, which stimulates adenylyl cyclase which increases intracellular cAMP levels (Sreedharan SP et al, 1993).
Growth hormone-releasing hormone (GHRH, somatocrinin, growth hormone-releasing factor) (Gubler U et al, 1983) is released from neurosecretory cells in the hypothalamus and along with the inhibitory peptide, somatostatin, mediates the neuroendocrine regulation of pituitary growth hormone synthesis and secretion. The GHRH receptor (Gaylinn BD et al, 1993) is expressed in the pituitary gland and mediates the activity of GHRH. Downstream signalling is mediated by coupling to the G protein alpha s subunit, which stimulates adenylyl cyclase which increases intracellular cAMP levels (Mayo KE, 1992).
Amylin (islet amyloid polypeptide, diabetes associated peptide) is a 37 amino acid peptide first purified from amyloid deposits in the pancreatic islets of type 2 diabetic patients (Nishi M et al, 1989). It is a product of the islet B-cell, along with insulin and probably has a hormonal role in the regulation of nutrient intake. Amylin receptors are multimeric complexes, formed by CT receptor (Gorn AH et al, 1992) interaction with receptor activity modifying proteins (RAMPs) (McLatchie LM et al, 1998). The CT receptor interacts with the three RAMPs, generating multiple subtypes of amylin receptor (AMY1-3).
Gastric inhibitory polypeptide (GIP, glucose-dependent insulinotropic peptide) (Moody AJ et al, 1984) is a member of the secretin family of hormones. It is synthesized and secreted from endocrine cells in the small intestine. GIP induces insulin secretion, which is primarily stimulated by hyperosmolarity of glucose in the duodenum. Gastric inhibitory polypeptide receptors are found on beta-cells in the pancreas (Volz A et al, 1995). Their effects are mediated by coupling to the G protein alpha s subunit, which stimulates adenylyl cyclase which can increase intracellular cAMP levels (Bollag RJ et al, 2000).
Parathyroid hormone (PTH) (Hendy GN et al, 1981), parathyroid hormone-related protein (PTHrP) (Suva LJ et al, 1987) and tuberoinfundibular peptide of thirty-nine residues (TIP39) (Hansen IA et al, 2002; Della Penna K et al, 2003) are endogenous ligands for the parathyroid hormone 1 and 2 receptors. These peptide hormones play a key role in controlling blood Ca(2+) concentration and endochondral bone formation. PTH1 is the classical PTH receptor 1 (Schipani E et al, 1993; Schneider H et al, 1993) and is expressed in high levels in bone and kidney. It regulates calcium ion homeostasis through activation of adenylate cyclase and phospholipase C. PTH receptor 2 (Usdin TB et al, 1995) is most abundant in brain and testes and potently activated by PTH. The activity of these receptors is mediated by G proteins which activate adenylyl cyclase (Schneider H et al, 1994; Offermanns S et al, 1996; Behar V et al, 1996).
The EGF-TM7 receptors are within the family B Adhesion (LNB) receptor subclass. They are characterised by long N-teminal extracellular domains containing multiple epidermal growth factor (EGF)-like domains. CD97 and EMR2 interact with the glycosaminoglycan chondroitin sulfate (CS).
Smoothened (Smo) is usually classified with family B GPCRs based on homology. There are indications that it can signal via G-proteins Gi and G12/13 (Ruiz-Gomez, 2007) but this role is poorly understood. It's better characterised physiological role is as the transducer of hedgehog (HH) signaling. In this capacity Smo is not acting as a receptor, but as part of a signaling cascade.
The Hedgehog(HH)/Smo signalling pathway was identified as a key component of Drosophila development and subsequently found to be conserved in all meatazoans. Most of the functions attributed to Smo are associated with development such as digit patterning in the chick limb bud and left–right asymmetry of vertebrate embryos. In addition, Smo appears to be involved in homeostasis; deregulated Smo signaling is implicated in tumorogenesis (Ruiz-Gomez, 2007).
The ligand of the 12 transmembrane-domain receptor Patched (Ptc) is Hedgehog(HH) but in the absence of HH, Ptc binds Smo (Stone et al. 1996) which consequently becomes internalised into endosomes, where it associates with Costal-2 (Cos2), and lysosomes, where it is degraded. This 'inactivates' Smo by preventing the formation of an active Smo signaling complex at the plasma membrane. Internalised Smo:Cos2 forms a complex with protein kinase A (PKA), casein kinase I (CKI) glycogen synthase kinase-3 (GSK3) and Cucurbitus interruptus (Ci), a transcriptional regulator, enabling phosphorylation of Ci and subsequent processing to a transcriptional repressor form (CiR). When HH binds to Ptc, it does not bind Smo, allowing Smo to undergo a conformational change, exposing a new surface in its cytoplasmic tail. This causes PKA, CKI and GSK3 to dissociate from Smo:Cos2 complexes, so that Ci is no longer phosphorylated or processed to CiR. Accumulating Smo is phosphorylated instead and assumes a third conformational state. Phosphorylated Smo trafficks to the plasma membrane (Denef et al. 2000) and assembles into a signalling complex that promotes the phosphorylation of Fused (Fu) and Cos2. Phosphorylated Cos2 dissociates from membranes and recruits Fu to Sufu (Suppressor of Fused), which produces the activated form of Ci (CiA), probably through phosphorylation of Sufu (Hooper & Scott, 2005).
CD55 (or Decay Accelerating Factor; DAF) is a member of the regulators of complement activation (RCA) family. It protects host cells from complement system attack by binding to C3b and C4b preventing formation of the membrane attack complex. CD97 is a member of the Adhesion class or LNB subfamily of family B GPCRs, characterized by long N-terminal regions containing domains contain multiple tandem epidermal growth factor (EGF)-like repeats in their N-termini (Foord et al. 2002). CD97 is constitutively expressed on granulocytes and monocytes and is rapidly up-regulated on activated T and B cells. It is known to have many splice forms containing different numbers of EGF domains, consequently binding CD55 with differing affinities. The highest affinity variant has three EGF domains. The leukocyte-restricted expression pattern of CD97, and the presence of both CD97 and CD55 in arthritic joints suggest a possible role in adhesion and signaling within the inflammatory and immune responses (Lin et al. 2001).
Corticoliberin (CRH, aka corticotropin-releasing factor CRF) is a 41-amino acid amino peptide which, together with CRH-related peptides such as the urocortins (UCNs), play a role in coordinating endocrine, autonomic and behavioural responses to stress. These peptides exert their effects through binding and activation of two class B/Secretin family of GPCRs, CRHR1 and CRHR2 (aka CRFR1 and CRFR2 respectively). The corticotropin-releasing factor-binding protein (CRHBP) can bind to CRH with high affinity, inactivating it. CRHBP is expressed in the brains of all species examined to date but is uniquely expressed in human liver and placenta. In the brain, CRHBP is located in pituitary corticotropes, where it is under positive glucocorticoid control, and is likely to locally modulate CRH-induced ACTH secretion (Behan et al. 1993, Behan et al. 1995).
Corticoliberin (CRH, aka corticotropin-releasing factor CRF) is a 41-amino acid amino peptide which, together with CRH-related peptides such as the urocortins (UCNs), plays a role in coordinating endocrine, autonomic and behavioral responses to stress. These peptides exert their effects through binding and activation of two class B/Secretin family of GPCRs, CRHR1 and CRHR2 (aka CRFR1 and CRFR2 respectively). The activity of these receptors is mediated by coupling to the G protein alpha s subunit, stimulating adenylyl cyclase which increases intracellular cAMP levels (Donaldson et al. 1996). CRH and UCN bind with highest affinity to both CRHR1 and CRHR2 receptors but CRHR2-beta receptors can also bind UCN2 and UCN3 (Pal et al. 2010).
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Annotated Interactions
Most Wnt signaling has been attributed to the activation of FZD receptors but there is evidence of FZD-independent signaling (Mikels & Nusse 2006). Much Wnt research has used indirect evidence to infer the involvement of FZD receptors (e.g. Gazit et al. 1999) but there is some direct evidence of Wnt-FZD binding (Hsieh et al. 1999; Mikels & Nusse 2006).
The ligand of the 12 transmembrane-domain receptor Patched (Ptc) is Hedgehog(HH) but in the absence of HH, Ptc binds Smo (Stone et al. 1996) which consequently becomes internalised into endosomes, where it associates with Costal-2 (Cos2), and lysosomes, where it is degraded. This 'inactivates' Smo by preventing the formation of an active Smo signaling complex at the plasma membrane. Internalised Smo:Cos2 forms a complex with protein kinase A (PKA), casein kinase I (CKI) glycogen synthase kinase-3 (GSK3) and Cucurbitus interruptus (Ci), a transcriptional regulator, enabling phosphorylation of Ci and subsequent processing to a transcriptional repressor form (CiR). When HH binds to Ptc, it does not bind Smo, allowing Smo to undergo a conformational change, exposing a new surface in its cytoplasmic tail. This causes PKA, CKI and GSK3 to dissociate from Smo:Cos2 complexes, so that Ci is no longer phosphorylated or processed to CiR. Accumulating Smo is phosphorylated instead and assumes a third conformational state. Phosphorylated Smo trafficks to the plasma membrane (Denef et al. 2000) and assembles into a signalling complex that promotes the phosphorylation of Fused (Fu) and Cos2. Phosphorylated Cos2 dissociates from membranes and recruits Fu to Sufu (Suppressor of Fused), which produces the activated form of Ci (CiA), probably through phosphorylation of Sufu (Hooper & Scott, 2005).The Hedgehog(HH)/Smo signalling pathway was identified as a key component of Drosophila development and subsequently found to be conserved in all meatazoans. Most of the functions attributed to Smo are associated with development such as digit patterning in the chick limb bud and left–right asymmetry of vertebrate embryos. In addition, Smo appears to be involved in homeostasis; deregulated Smo signaling is implicated in tumorogenesis (Ruiz-Gomez, 2007).