IUPHAR/BPS Guide to Pharmacology CITE
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Somatostatin receptors in GtoPdb v.2025.3
Somatostatin (somatotropin release inhibiting factor) is an abundant neuropeptide, which acts on five subtypes of somatostatin receptor (SST1-SST5; nomenclature as agreed by the NC-IUPHAR Subcommittee on Somatostatin Receptors [101]). Activation of these receptors produces a wide range of physiological effects throughout the body including the inhibition of secretion of many hormones. Endogenous ligands for these receptors are somatostatin-14 (SRIF-14) and somatostatin-28 (SRIF-28). cortistatin-14 has also been suggested to be an endogenous ligand for somatostatin receptors [62]
Type X RTKs: HGF (hepatocyte growth factor) receptor family in GtoPdb v.2025.3
The hepatocyte growth factor (HGF) receptor family - MET and Ron - regulate maturation of the liver in the embryo, as well as having roles in the adult, for example, in the innate immune system. HGF is synthesized as a single gene product, which is post-translationally processed to yield a heterodimer linked by a disulphide bridge. The maturation of HGF is enhanced by a serine protease, HGF activating complex, and inhibited by HGF-inhibitor 1, a serine protease inhibitor. MST1, the ligand of Ron, is two disulphide-linked peptide chains generated by proteolysis of a single gene product
Type XV RTKs: RYK in GtoPdb v.2025.3
The \u27related to tyrosine kinase receptor\u27 (Ryk) is structurally atypical of the family of RTKs, particularly in the activation and ATP-binding domains, lacking kinase activity akin to ROR1/2. Similarly, however, there is evidence that RTK is involved in Wnt signalling [2]
Blood coagulation components in GtoPdb v.2025.3
Coagulation as a process is interpreted as a mechanism for reducing excessive blood loss through the generation of a gel-like clot local to the site of injury. The process involves the activation, adhesion (see Integrins), degranulation and aggregation of platelets, as well as proteins circulating in the plasma. The coagulation cascade involves multiple proteins being converted to more active forms from less active precursors (for example, prothrombin [Factor II] is converted to thrombin [Factor IIa]), typically through proteolysis (see Proteases). Listed here are the components of the coagulation cascade targeted by agents in current clinical usage or at an advanced level of development
Type IX RTKs: MuSK in GtoPdb v.2025.3
The muscle-specific kinase MuSK is associated with the formation and organisation of the neuromuscular junction from the skeletal muscle side. agrin forms a complex with low-density lipoprotein receptor-related protein 4 to activate MuSK [5]. MuSK-mediated phosphorylation of downstream targets is involved in stabilised neuromuscular function. It is the target of pathogenic autoantibodies in myasthenia gravis, an autoimmune neuromuscular disease
Receptor guanylyl cyclase (RGC) family in GtoPdb v.2025.3
The mammalian genome encodes seven guanylyl cyclases, GC-A to GC-G, that are homodimeric transmembrane receptors activated by a diverse range of endogenous ligands. These enzymes convert guanosine-5\u27-triphosphate to the intracellular second messenger cyclic guanosine-3\u27,5\u27-monophosphate (cyclic GMP). GC-A, GC-B and GC-C are expressed predominantly in the cardiovascular system, skeletal system and intestinal epithelium, respectively. GC-D and GC-G are found in the olfactory neuropepithelium and Grueneberg ganglion of rodents, respectively. GC-E and GC-F are expressed in retinal photoreceptors
Class A Orphans in GtoPdb v.2025.4
The class A orphan GPCRs have been organised into the subfamilies listed below, to better segregate them based on evidence (or lack of evidence) for endogenous ligand or surrogate ligand interactions, and potential for deorphanization
Ionotropic glutamate receptors in GtoPdb v.2025.4
The ionotropic glutamate receptors comprise members of the NMDA (N-methyl-D-aspartate), AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid) and kainate receptor classes, named originally according to their preferred, synthetic, agonist [60, 99, 163]. Receptor heterogeneity within each class arises from the homo-oligomeric, or hetero-oligomeric, assembly of distinct subunits into cation-selective tetramers. Each subunit of the tetrameric complex comprises an extracellular amino terminal domain (ATD), an extracellular ligand binding domain (LBD), 3 TM domains (M1, M3 and M4), a channel lining re-entrant \u27p-loop\u27 (M2) located between M1 and M3 and an intracellular carboxy- terminal domain (CTD) [106, 74, 115, 163, 88]. The X-ray structure of a homomeric ionotropic glutamate receptor (GluA2- see below) has recently been solved at 3.6Å resolution [151] and although providing the most complete structural information current available may not be representative of the subunit arrangement of, for example, the heteromeric NMDA receptors [77]. It is beyond the scope of this supplement to discuss the pharmacology of individual ionotropic glutamate receptor isoforms in detail; such information can be gleaned from [60, 72, 34, 83, 44, 122, 27, 71, 163, 120, 121, 171]. Agents that discriminate between subunit isoforms are, where appropriate, noted in the tables and additional compounds that distinguish between receptor isoforms are indicated in the text below.The classification of glutamate receptor subunits has been re-addressed by NC-IUPHAR [31]. The scheme developed recommends a nomenclature for ionotropic glutamate receptor subunits that is adopted here.NMDA receptorsNMDA receptors assemble as obligate heteromers that may be drawn from GluN1, GluN2A, GluN2B, GluN2C, GluN2D, GluN3A and GluN3B subunits. Alternative splicing can generate eight isoforms of GluN1 with differing pharmacological properties. Various splice variants of GluN2B, 2C, 2D and GluN3A have also been reported. Activation of NMDA receptors containing GluN1 and GluN2 subunits requires the binding of two agonists, glutamate to the S1 and S2 regions of the GluN2 subunit and glycine to S1 and S2 regions of the GluN1 subunit [43, 28]. The minimal requirement for efficient functional expression of NMDA receptors in vitro is a di-heteromeric assembly of GluN1 and at least one GluN2 subunit variant, as a dimer of heterodimers arrangement in the extracellular domain [50, 106, 77]. However, more complex tri-heteromeric assemblies, incorporating multiple subtypes of GluN2 subunit, or GluN3 subunits, can be generated in vitro and occur in vivo. The NMDA receptor channel commonly has a high relative permeability to Ca2+ and is blocked, in a voltage-dependent manner, by Mg2+ such that at resting potentials the response is substantially inhibited.AMPA and Kainate receptorsAMPA receptors assemble as homomers, or heteromers, that may be drawn from GluA1, GluA2, GluA3 and GluA4 subunits. Transmembrane AMPA receptor regulatory proteins (TARPs) of class I (i.e. γ2, γ3, γ4 and γ8) act, with variable stoichiometry, as auxiliary subunits to AMPA receptors and influence their trafficking, single channel conductance gating and pharmacology (reviewed in [45, 110, 161, 70]). Functional kainate receptors can be expressed as homomers of GluK1, GluK2 or GluK3 subunits. GluK1-3 subunits are also capable of assembling into heterotetramers (e.g. GluK1/K2; [94, 127, 126]). Two additional kainate receptor subunits, GluK4 and GluK5, when expressed individually, form high affinity binding sites for kainate, but lack function, but can form heteromers when expressed with GluK1-3 subunits (e.g. GluK2/K5; reviewed in [127, 71, 126]). Kainate receptors may also exhibit \u27metabotropic\u27 functions [94, 139]. As found for AMPA receptors, kainate receptors are modulated by auxiliary subunits (Neto proteins, [126, 95]). An important function difference between AMPA and kainate receptors is that the latter require extracellular Na+ and Cl- for their activation [13, 128]. RNA encoding the GluA2 subunit undergoes extensive RNA editing in which the codon encoding a p-loop glutamine residue (Q) is converted to one encoding arginine (R). This Q/R site strongly influences the biophysical properties of the receptor. Recombinant AMPA receptors lacking RNA edited GluA2 subunits are: (1) permeable to Ca2+; (2) blocked by intracellular polyamines at depolarized potentials causing inward rectification (the latter being reduced by TARPs); (3) blocked by extracellular argiotoxin and joro spider toxins and (4) demonstrate higher channel conductances than receptors containing the edited form of GluA2 [147, 69]. GluK1 and GluK2, but not other kainate receptor subunits, are similarly edited and broadly similar functional characteristics apply to kainate receptors lacking either an RNA edited GluK1, or GluK2, subunit [94, 126]. Native AMPA and kainate receptors displaying differential channel conductances, Ca2+ permeabilities and sensitivity to block by intracellular polyamines have been identified [33, 69, 98]. GluA1-4 can exist as two variants generated by alternative splicing (termed ‘flip’ and ‘flop’) that differ in their desensitization kinetics and their desensitization in the presence of cyclothiazide which stabilises the nondesensitized state. TARPs also stabilise the non-desensitized conformation of AMPA receptors and facilitate the action of cyclothiazide [110]. Splice variants of GluK1-3 also exist which affects their trafficking [94, 126]
Hydrolases & Lipases in GtoPdb v.2025.2
Listed in this section are hydrolases not accumulated in other parts of the Concise Guide, such as monoacylglycerol lipase and acetylcholinesterase. Pancreatic lipase is the predominant mechanism of fat digestion in the alimentary system; its inhibition is associated with decreased fat absorption. CES1 is present at lower levels in the gut than CES2 (P23141), but predominates in the liver, where it is responsible for the hydrolysis of many aliphatic, aromatic and steroid esters. Hormone-sensitive lipase is also a relatively non-selective esterase associated with steroid ester hydrolysis and triglyceride metabolism, particularly in adipose tissue. Endothelial lipase is secreted from endothelial cells and regulates circulating cholesterol in high density lipoproteins
Phosphodiesterases, 3\u27,5\u27-cyclic nucleotide (PDEs) in GtoPdb v.2025.1
3\u27,5\u27-Cyclic nucleotide phosphodiesterases (PDEs, 3\u27,5\u27-cyclic-nucleotide 5\u27-nucleotidohydrolase), E.C. 3.1.4.17, catalyse the hydrolysis of a 3\u27,5\u27-cyclic nucleotide (usually cyclic AMP or cyclic GMP). isobutylmethylxanthine is a nonselective inhibitor with an IC50 value in the millimolar range for all isoforms except PDE 8A, 8B and 9A. A 2\u27,3\u27-cyclic nucleotide 3\u27-phosphodiesterase (E.C. 3.1.4.37 CNPase) activity is associated with myelin formation in the development of the CNS