IUPHAR/BPS Guide to Pharmacology CITE
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Neuropeptide FF/neuropeptide AF receptors in GtoPdb v.2023.1
Get PDFThe Neuropeptide FF receptor family contains two subtypes, NPFF1 and NPFF2 (provisional nomenclature [12]), which exhibit high affinities for neuropeptide FF (NPFF, O15130) and RFamide related peptides (RFRP: precursor gene symbol NPVF, Q9HCQ7). NPFF1 is broadly distributed in the central nervous system with the highest levels found in the limbic system and the hypothalamus. NPFF2 is present in high density in the superficial layers of the mammalian spinal cord where it is involved in nociception and modulation of opioid functions
QRFP receptor in GtoPdb v.2023.1
Get PDFThe human gene encoding the QRFP receptor (nomenclature as agreed by the NC-IUPHAR Subcommittee on the QRFP receptor [19]; QRFPR, formerly known as the Peptide P518 receptor), previously designated as an orphan GPCR receptor was identified in 2001 by Lee et al. from a hypothalamus cDNA library [17]. However, the reported cDNA (AF411117) is a chimera with bases 1-127 derived from chromosome 1 and bases 155-1368 derived from chromosome 4. When corrected, QRFPR (also referred to as SP9155 or AQ27) encodes a 431 amino acid protein that shares sequence similarities in the transmembrane spanning regions with other peptide receptors. These include neuropeptide FF2 (38%), neuropeptide Y2 (37%) and galanin Gal1 (35%) receptors. QRFP receptor was identified as a Gs-coupled GPCR [6, 14] that\u27s activated by the endogenous peptides QRFP43 (43RFa) and QRFP26 (26RFa) [6, 14, 11]. However, Gq- and Gi/o-mediated signaling was also reported [11, 25]. Two naturally occurring mutations in the human QRFP receptor lead to distinct and opposite 26RFa-evoked signaling bias [20]
Trace amine receptor in GtoPdb v.2023.1
Get PDFTrace amine-associated receptors were discovered from a search for novel 5-HT receptors [9], where 15 mammalian orthologues were identified and divided into two families. The TA1 receptor (nomenclature as agreed by the NC-IUPHAR Subcommittee for the Trace amine receptor [58]) has affinity for the endogenous trace amines tyramine, β-phenylethylamine and octopamine in addition to the classical amine dopamine [9]. Emerging evidence suggests that TA1 is a modulator of monoaminergic activity in the brain [94] with TA1 and dopamine D2 receptors shown to form constitutive heterodimers when co-expressed [30]. In addition to trace amines, receptors can be activated by amphetamine-like psychostimulants, and endogenous thyronamines
Urotensin receptor in GtoPdb v.2023.1
Get PDFThe urotensin-II (U-II) receptor (UT, nomenclature as agreed by the NC-IUPHAR Subcommittee on the Urotensin receptor [26, 36, 94]) is activated by the endogenous dodecapeptide urotensin-II, originally isolated from the urophysis, the endocrine organ of the caudal neurosecretory system of teleost fish [7, 93]. Several structural forms of U-II exist in fish and amphibians [94]. The goby orthologue was used to identify U-II as the cognate ligand for the predicted receptor encoded by the rat gene gpr14 [2, 20, 63, 69, 72]. Human urotensin-II, an 11-amino-acid peptide [20], retains the cyclohexapeptide sequence of goby U-II that is thought to be important in ligand binding [61, 53, 10]. This sequence is also conserved in the deduced amino-acid sequence of rat urotensin-II (14 amino-acids) and mouse urotensin-II (14 amino-acids), although the N-terminal is more divergent from the human sequence [19]. A second endogenous ligand for the UT has been discovered in rat [86]. This is the urotensin II-related peptide, an octapeptide that is derived from a different gene, but shares the C-terminal sequence (CFWKYCV) common to U-II from other species. Identical sequences to rat urotensin II-related peptide are predicted for the mature mouse and human peptides [32]. UT exhibits relatively high sequence identity with somatostatin, opioid and galanin receptors [94]. The urotensinergic system displays an unprecedented repertoire of four or five ancient UT in some vertebrate lineages and five U-II family peptides in teleost fish [91]
Lanosterol biosynthesis pathway in GtoPdb v.2023.1
Get PDFLanosterol is a precursor for cholesterol, which is synthesized primarily in the liver in a pathway often described as the mevalonate or HMG-CoA reductase pathway. The first two steps (formation of acetoacetyl CoA and the mitochondrial generation of (S)-3-hydroxy-3-methylglutaryl-CoA) are also associated with oxidation of fatty acids
Epithelial sodium channel (ENaC) in GtoPdb v.2023.1
Get PDFOverviewThe epithelial sodium channels (ENaC) are located on the apical membrane of epithelial cells in the kidney tubules, lung, respiratory tract, male and female reproductive tracts, sweat and salivary glands, placenta, colon, and some other organs [10, 48, 14, 23, 22]. In these epithelia, Na+ ions flow from the extracellular fluid into the cytoplasm of epithelial cells via ENaC and are then pumped out of the cytoplasm into the interstitial fluid by the Na+/K+ ATPase located on the basolateral membrane [42]. As Na+ is one of the major electrolytes in the extracellular fluid (ECF), osmolarity change initiated by the Na+ flow is accompanied by a flow of water [7]. Thus, ENaC has a central role in regulating ECF volume and blood pressure, primarily via its function in the kidney [43]. The expression of ENaC subunits, hence its activity, is regulated by the renin-angiotensin-aldosterone system, and other factors involved in electrolyte homeostasis [43, 32]. The genetics of the hereditary systemic pseudohypoaldosteronism type-I revealed that the activity of ENaC is dependent on three subunits encoded by three genes [23, 12]. Within the protein superfamily that includes ENaC, the crystal structure of ASIC was determined first, revealing a trimeric structure with a large extracellular domain anchored in the membrane with a bundle of six TM helices (two TM helices/subunit) [3, 26]. The first 3D structure of human ENaC was determined by single-particle cryo-electron microscopy at a resolution of 3.7 Å [38]. A recent study improved the resolution to 3 Å [39]. These structures confirmed that ENaC has a 3D quaternary structure similar to ASIC. ENaC is assembled as a hetero-trimer with a clockwise order of α-γ-β subunit viewed from the top, as shown previously [13]. In contrast to ASIC1 which can assemble into a functional homotrimer, ENaC activity can be reconstituted fully only as a heterotrimer with an αβγ or a δβγ composition [29]. In the respiratory tract and female reproductive tract, large segments of the epithelia are composed of multi-ciliated cells. In these cells, ENaC is located along the entire length of the cilia that cover the cell surface [16]. Cilial location greatly increases ENaC density per cell surface and allows ENaC to serve as a sensitive regulator of osmolarity of the periciliary fluid throughout the whole depth of the fluid bathing the cilia [16]. In contrast to ENaC, CFTR (ion transporter defective in cystic fibrosis) is located on the non-cilial cell surface [16]. In the vas deferens segment of the male reproductive tract, the luminal surface is covered by microvilli and stereocilia projections with backbones composed of actin filament bundles [48]. In these cells, both ENaC and the water channel aquaporin AQP9 are localized on these projections and also in the basal and smooth muscle layers [48]. Thus, ENaC function regulates the volume of fluid lining epithelia essential for mucociliary clearance of respiratory airways, transport of germ cells, fertilization, implantation, and cell migration [37, 16, 23]. Genes and PhylogenyIn the human genome, there are four homologous genes (SCNN1A, SCNN1B, SCNN1D, and SCNN1G) that encode four proteins, α-, β-, γ-, and δ-ENaC that may be involved in the assembly of ENaC [11, 34, 47, 53]. These four subunits share 23-34% sequence identity and <20% identity with ASIC subunits [23]. The genes coding for all four ENaC subunits are present in all bony vertebrates with the exception of ray-finned fish genomes that have lost all ENaC genes. The mouse genome has lost the gene SCNN1D that codes for δ-ENaC [18, 23, 23]. The α-, β-, and γ-ENaC genes are also present in jawless vertebrates (e.g., lampreys) and cartilaginous fishes (e.g., sharks) [23]. Examination of the methylation patterns of the 5\u27-flanking region of SCNN1A, SCNN1B, and SCNN1G genes in human cells showed an inverse correlation between gene expression and DNA methylation, suggesting epigenetic transcriptional control of ENaC genes [41]. Channel biogenesis, assembly and functionThe expression of ENaC subunits is regulated primarily by aldosterone and many additional extracellular and intracellular factors [43, 31, 40]. Most of the studies indicate that the expression of the three subunits is not coordinated [9]. However, the transport of the subunits to the membrane is dependent on three intact subunits. Even a missense mutation in one subunit reduces the concentration of assembled channels on the cell surface [15]. ENaC is a constitutively active channel, i.e., the flow of Na+ ions is not dependent on an activating factor. Hence, heterologous cells expressing ENaC (e.g., Xenopus oocytes), must be maintained in a solution that contains amiloride to keep ENaC inhibited. To measure ENaC activity, the bath solution is switched to a solution without amiloride. ENaC has two major states: 1) Open, and 2) Closed. The probability of ENaC being in the open state is called ENaC open probability (Po). ENaC activity is regulated by a diverse array of factors that exert their effects by modifying, directly or indirectly, two major parameters: 1) The density of ENaC in the membrane; and 2) The channel open probability [27, 29]. The Po of ENaC is greatly decreased by external Na+ and this response is called Na+ self-inhibition [49, 4, 25].An important aspect of ENaC regulation is that the α and the γ subunits have conserved serine protease cleavage sites in the extracellular segment [23]. Cleavage of these subunits by proteases such as furin and plasmin leads to the activation of ENaC [44, 30, 1].Diseases associated with ENaC mutationsMutations in any of the three genes (SCNN1A, SCNN1B, and SCNN1G) may cause partial or complete loss of ENaC activity, depending on the mutation [12, 20]. Such loss-of-function mutations are associated with a syndrome named "systemic" or "multi-system" autosomal recessive pseudohypoaldosteronism type I (PHA1B) [19, 12, 23, 16, 55, 46]. So far, no mutation has been found in the SCNN1D gene that causes PHA. PHA patients suffer from severe salt loss from all aldosterone target organs expressing ENaC, including kidney, sweat and salivary glands and respiratory tract. During infancy and early childhood, the severe electrolyte disturbances, dehydration and acidosis may require recurrent hospitalizations. The severity and frequency of salt-wasting episodes improve with age [21]. PHA1B is also associated with a dysfunctional female reproductive system [16, 6]. The carboxy-terminal of ENaC includes a short consensus sequence called the PY motif. Mutations in this motif in SCNN1B and SCNN1G are associated with Liddle syndrome, which is characterized by early-onset hypertension [5, 50]. The PY motif is recognized by Nedd4-2 that is a ubiquitin ligase. Thus, mutations in the PY motif reduce ubiquitylation of ENaC leading to the accumulation of ENaC in the membrane, consequently enhance the activity of ENaC [45].ENaC expression in tumorsThe observation that [Na+] is higher in many cancerous cells as compared to non-cancerous cells has led to the suggestion that enhanced expression of ENaC may be responsible for increased metastasis [33]. However, analysis of RNA sequencing data of ENaC-encoding genes, and clinical data of cervical cancer patients from The Cancer Genome Atlas showed a negative correlation with histologic grades of tumor [51]. Similarly, studies on breast cancer cells that altered α-ENaC levels by over-expression or siRNA-mediated knockdown showed that increased α-ENaC expression was associated with decreased breast cancer cell proliferation [54]. In contrast, analysis of RNA sequencing data from The Cancer Genome Atlas showed that high expression of SCNN1A was correlated with poor prognosis in patients with ovarian cancer [35]. These findings indicate that the association of ENaC levels with tumorigenesis varies depending on the tissue.COVID-19The surface of SARS-CoV-2 virions that cause COVID-19 is covered by many glycosylated S (spike) proteins. These S proteins bind to the membrane-bound angiotensin-converting enzyme 2 (ACE2) as a first step in the entry of the virion into the host cell. Viral entry into the cell is dependent on the cleavage of the S protein (at Arg-667/Ser-668) by a serine-protease. Anand et al. showed that this cleavage site has a sequence motif that is homologous to the furin cleavage site in α-ENaC [2]. A comprehensive review on the pathological consequences of COVID-19 suggests a role for ENaC in the early phases of COVID-19 infection in the respiratory tract epithelia [17]
SLC36 family of proton-coupled amino acid transporters in GtoPdb v.2023.1
Get PDFMembers of the SLC36 family of proton-coupled amino acid transporters are involved in membrane transport of amino acids and derivatives [29, 30]. The four transporters show variable tissue expression patterns and are expressed in various cell types at the plasma-membrane and in intracellular organelles. PAT1 is expressed at the luminal surface of the small intestine and absorbs amino acids and derivatives [4]. In lysosomes, PAT1 functions as an efflux mechanism for amino acids produced during intralysosomal proteolysis [2, 26]. PAT2 is expressed at the apical membrane of the renal proximal tubule [7] and at the plasma-membrane in brown/beige adipocytes [31]. PAT1 and PAT4 are involved in regulation of the mTORC1 pathway [12, 28]. More comprehensive lists of substrates can be found within the reviews under Further Reading and in the references [3]
Phosphodiesterases, 3\u27,5\u27-cyclic nucleotide (PDEs) in GtoPdb v.2023.1
Get PDF3\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
Tumour necrosis factor (TNF) receptor family in GtoPdb v.2023.1
Get PDFDysregulated TNFR signalling is associated with many inflammatory disorders, including some forms of arthritis and inflammatory bowel disease, and targeting TNF has been an effective therapeutic strategy in these diseases and for cancer immunotherapy [5, 6, 49]
Aquaporins in GtoPdb v.2023.3
Get PDFAquaporins and aquaglyceroporins are membrane channels that allow the permeation of water and certain other small solutes across the cell membrane, or in the case of AQP6, AQP11 and AQP12A, intracellular membranes, such as vesicles and the endoplasmic reticulum membrane [16]. Since the isolation and cloning of the first aquaporin (AQP1) [20], 12 additional mammalian members of the family have been identified, although little is known about the functional properties of one of these (AQP12A; Q8IXF9) and it is thus not tabulated. The other 12 aquaporins can be broadly divided into three families: orthodox aquaporins (AQP0,-1,-2,-4,-5, -6 and -8) permeable mainly to water, but for some additional solutes [4]; aquaglyceroporins (AQP3,-7 -9 and -10), additionally permeable to glycerol and for some isoforms urea [14], and superaquaporins (AQP11 and 12) located within cells [12]. Some aquaporins also conduct ammonia and/or H2O2 giving rise to the terms \u27ammoniaporins\u27 (\u27aquaammoniaporins\u27) and \u27peroxiporins\u27, respectively. Aquaporins are impermeable to protons and other inorganic and organic cations, with the possible exception of AQP1, although this is controversial [14]. One or more members of this family of proteins have been found to be expressed in almost all tissues of the body [reviewed in Yang (2017) [26]]. AQPs are involved in numerous processes that include systemic water homeostasis, adipocyte metabolism, brain oedema, cell migration and fluid secretion by epithelia. Loss of function mutations of some human AQPs, or their disruption by autoantibodies further underscore their importance [reviewed by Verkman et al. (2014) [23], Kitchen et al. (2105) [14]]. Functional AQPs exist as homotetramers that are the water conducting units wherein individual AQP subunits (each a protomer) have six TM helices and two half helices that constitute a seventh \u27pseudotransmembrane domain\u27 that surrounds a narrow water conducting channel [16]. In addition to the four pores contributed by the protomers, an additional hydrophobic pore exists within the center of the complex [16] that may mediate the transport through AQP1. Although numerous small molecule inhibitors of aquaporins, particularly APQ1, have been reported primarily from Xenopus oocyte swelling assays, the activity of most has subsequently been disputed upon retesting using assays of water transport that are less prone to various artifacts [5] and they are therefore excluded from the tables [see Tradtrantip et al. (2017) [22] for a review]