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Recombinant CHO-K1 cells stably overexpress Mus musculus cytotoxic T-lymphocyte-associated protein 4 (CTLA4) on the surface. The surface expression of mouse CTLA4 is validated by FACS analysis. This cell line is designed for cell-based binding for screening antibodies binding with mouse CTLA4 and for evaluating target binding affinity.

HVEM is found on the surface of various cell types, including hematopoietic and non-hematopoietic cells, and is expressed mainly in spleen, thymus, bone marrow, lung and intestines. It has been identified as a canonical TNF receptor, signaling through the TNF receptor-associated factors (TRAFs) leading to NFκB activation. Furthermore, in addition to acting as a signaling receptor, in binding to Ig superfamily members it acts as a ligand for these inhibitory receptors. Therefore, bidirectional signaling is possible for the HVEM-mediated signaling network, which can be involved in positive or negative immunological reactions under different contexts.

Programmed death-ligand 1 (PD-L1) also known as cluster of differentiation 274 (CD274) or B7 homolog 1 (B7-H1) is a protein that in humans is encoded by the CD274 gene. The formation of PD-1 receptor / PD-L1 or B7.1 receptor /PD-L1 ligand complex transmits an inhibitory signal which reduces the proliferation of these CD8+ T cells at the lymph nodes. After that PD-1 is also able to control the accumulation of foreign antigen specific T cells in the lymph nodes through apoptosis, which is further mediated by a downregulation of the Bcl-2 gene.

TIGIT (also called T cell immunoreceptor with Ig and ITIM domains) is one newly discovered immune receptor on some percentage of T cells and Natural Killer Cells (NK). It is also identified as WUCAM and Vstm3. TIGIT binds to CD155 (PVR) on dendritic cells (DCs), macrophages, etc. with high affinity, and also to CD112 (PVRL2) with lower affinity. Research has shown that TIGIT-Fc fusion proteins interact with PVR on dendritic cells and increase IL-10 secretion, while decreasing IL-12 secretion under LPS stimulation. TIGIT-Fc fusion proteins also inhibit T cell activation in vivo. TIGIT’s inhibition of NK cytotoxicity can be blocked by antibodies against its interaction with PVR, which is directed through its ITIM domain.

V-domain Ig suppressor of T cell activation (VISTA) is a potent negative regulator of T-cell function that is expressed on hematopoietic cells. VISTA levels are heightened within the tumor microenvironment, in which its blockade can enhance antitumor immune responses in mice. In humans, blockade of the related programmed cell death 1 (PD-1) pathway has shown great potential in clinical immunotherapy trials.

Recombinant CHO-K1 cells stably overexpress mas-related G-protein coupled receptor member X2 (MRGPRX2). MRGPRX2 couples to both Gi and Gq alpha subunits in mast cells naturally, so that the PLC signaling can be triggered within the cells by agonist binding. This cell line is recommended for agonist screening and functional validations with calcium flux assay.

Melatonin binds to two specific G-protein coupled receptors (GPCR), MT1 (MTNR1A/MEL1A) and MT2 (MTNR1B/MEL1B). MT1 receptors signal via inhibitory G proteins (Gα_i and Gα_o) leading to adenylate cyclase inhibition and possibly inositol phosphate stimulation in recombinant systems. In certain native tissues (e.g. sheep pars tuberalis, rat cerebral and caudal arteries) melatonin responses are presumably mediated through activation of MT1 receptors. The hypothalamic suprachiasmatic nucleus appears to be involved in circadian rhythm while the hypophysial pars tuberalis may be responsible for the reproductive effects of melatonin.

Melatonin is a neurohormone that plays a key role in the synchronisation of circadian and seasonal functions with cyclic environmental variations. In mammals, two melatonin receptors, MT1 and MT2, have been cloned. Activation of MT2 melatonin receptors phase shift circadian rhythms of neuronal firing in the suprachiasmatic nucleus, inhibit dopamine release in retina, induce vasodilation and inhibition of leukocyte rolling in arterial beds, and enhance immune responses.

The motilin receptor (MTLR) represents a clinically useful pharmacological target, as agonists binding to the MTLR have gastroprokinetic properties. Motilin is a 22 amino acid peptide that potently stimulates gastrointestinal contractility. The biological effects of motilin are mediated by a G_q-coupled seven transmembrane protein, currently termed motilin receptor (MR) that shares significant sequence similarity with the ghrelin receptor. The motilin receptor is also activated by the antibiotic erythromycin; this interaction appears to mediate some of the gastrointestinal side effects of erythromycin. Although motilides (non-antibiotic derivatives of erythromycin) such as ABT-229 have been investigated for treatment of diabetic gastroporesis, the effectiveness has been limited by tachyphylaxis (decreased response to ligand) resulting from receptor downregulation. Agonists of the motilin receptor with reduced densensitization activity remain a potential treatment for disorders of gastric motility.

GPR109A is a high affinity receptor for nicotinic acid (niacin) and is a member of the nicotinic acid receptor family of G protein-coupled receptors (the other identified member being GPR109B). GPR109A is a G_i/o protein-coupled receptor with high affinity for nicotinic acid. In GPR109A knockout mice, the effects of niacin on both lipids and flushing are eliminated. Furthermore in arrestin beta 1 knockout mice, niacin’s effect on flushing is greatly reduced while the lipid modifying effects are maintained. GPR109A is believed to be an important biomolecular target of niacin which is a widely prescribed drug for the treatment of dyslipidemia and to increase HDL cholesterol but whose therapeutic use is limited by flushing.

Tachykinins are peptides sharing the common C-terminal amino acid sequence Phe-X-Gly-Leu-Met-NH₂. This neuropeptide family is composed of substance P, neurokinin A, and neurokinin B, which are widely distributed in mammalian central and peripheral nervous systems. It plays a role as both a neurotransmitter and a neuromodulator. Their actions are mediated by binding with three distinct receptors, namely, NK1, NK2, and NK3. NK1 has high affinity with substance P. In the CNS, NK1 has been implicated to play a role in regulating neuronal survival and degeneration. In the cardiovascular system, NK1 mediates endothelium-dependent vasodilatation and plasma protein extravasations. In the gastrointestinal system, NK1 receptors mediate intestinal motility, secretion, and vascular functions. SP-NK1 receptor communication is also involved in glioma development and progression. NK1 receptor antagonists may have several therapeutic applications in diseases mediated by tachykinins, such as pulmonary disorders, gut disorders, and the pathophysiology of depression.

Tachykinins are peptides sharing a common C-terminal amino acid sequence: Phe-X-Gly-Leu-Met-NH₂. This neuropeptide family is composed of substance P, neurokinin A, and neurokinin B, which are widely distributed in mammalian central and peripheral nervous systems. These three molecules serve as both neurotransmitters and neuromodulators. Their actions are mediated by binding with three distinct receptors, namely NK1, NK2, and NK3. In particular, NK2 is expressed in gastrointestinal tract. Activation of NK2 is chiefly responsible for the regulation of intestinal motor functions (both excitatory and inhibitory), secretions, inflammation, and visceral sensitivity. Antagonists of NK2 may be useful in the treatment of irritable bowel syndrome.

Tachykinins are peptides sharing a common C-terminal amino acid sequence: Phe-X-Gly-Leu-Met-NH₂. This neuropeptide family is composed of substance P, neurokinin A, and neurokinin B, which are widely distributed in mammalian central and peripheral nervous systems. These three molecules serve as both neurotransmitters and neuromodulators. Their actions are mediated by binding with three distinct receptors, namely NK1, NK2, and NK3. NK3 receptors show affinity for neurokinin B. They are predominantly expressed in both the peripheral and central nervous systems. NK3 receptors appear to modulate monoaminergic and amino acid neurotransmission. Studies show that manipulating modulation of NK3 receptor activity may have therapeutic utility in psychiatric diseases such as schizophrenia and affective disorders.

Neuromedin U receptor 1 (NMUR1) is a member of G-protein coupled receptor family A and is the most abundant in peripheral tissue, particularly in small intestines and stomach. This protein is a receptor for Neuromedin U (NMU-25). The first biological activity ascribed to NmU was smooth muscle contraction. Neuromedin U has also been reported to increase arterial blood pressure and modify ion transport in the intestinal tract. Finally, NmU injected subcutaneously into rats has been reported to result in a short term increase in circulating ACTH levels and a long term increase in serum corticosterone levels, suggesting a role in regulation of the hypothalamo-pituitary-adrenal axis.

The neuropeptide S receptor isoform a (NPS1a) is G_q/11 and Gs-coupled GPCRs expressed in the bronchial smooth muscle cells, basally in colon epithelium and in occasional basal keratinocytes in skin. An Asn107->Ile mutation is significantly up-regulated in a mouse model of ovalbumen-induced lung inflammation supporting a role in the pathogenesis of asthma.

The NPS receptor is a typical GPCR, also known as GPR154, vasopressin-receptor related receptor 1 (VRR1), or GPRA. NPSR was found mainly expressed in the central nervous system of rats by using in-situ hybridization. NPS receptor mRNA is widely distributed in many brain areas with high expression levels in cortex, hypothalamus, amygdala and multiple midline thalamic nuclei. Many of these areas have been functionally associated with arousal and processing of emotional behavior. In 2004, the NPS receptor was identified as an asthma susceptibility gene in a genome wide screen in Finnish and Canadian patients. The study showed that a number of polymorphic variants of the NPS receptor exist in human and that particular sets of these variants (haplotypes) are associated with an increased risk of asthma and possibly allergic diseases characterized by high IgE serum levels. A carboxy-terminal splice variant of human NPS receptor was found to be over-expressed in asthmatic airway tissue. Expression of NPS receptor mRNA was also found upregulated in a mouse model of airway inflammation.

The NPY family consists of three 36-amino acid peptides, neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP), which bind to the NPY receptors. At present five distinct NPY receptors, Y1, Y2, Y4, Y5, and y6, have been established by receptor cloning studies and all of them are G_i-coupled GPCRs. Activation of NPY receptors mediate a variety physiological effects including stimulation of food intake, inhibition of anxiety in the CNS, presynaptic inhibition of neurotransmitter release in the CNS and periphery, modulation of circadian rhythm, release of pituitary hormones, modulation of hippocampal activity, pain transmission, vasoconstriction, inhibition of insulin release and modulation of renal function. With regard to endogenous agonists, the receptors Y2 preferentially bind NPY and PYY.

The NPY family consists of three 36-amino acid peptides, neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP), which bind to the NPY receptors. At present five distinct NPY receptors, Y1, Y2, Y4, Y5, and y6, have been established by receptor cloning studies and all of them are G_i-coupled GPCRs. Activation of NPY receptors mediate a variety physiological effects including stimulation of food intake, inhibition of anxiety in the CNS, presynaptic inhibition of neurotransmitter release in the CNS and periphery, modulation of circadian rhythm, release of pituitary hormones, modulation of hippocampal activity, pain transmission, vasoconstriction, inhibition of insulin release and modulation of renal function. Y4 receptor preferentially binds PP, with significant binding to NPY and PYY.

Neurotensin receptor 1 (NTS1) is a member of G-protein coupled receptor family A and is a receptor for Neurotensin (NT). Neurotensin (NT) exerts its intracellular effect by interacting with 3 different receptors. Two of these receptors (NTR1 and NTR2) belong to the G protein-coupled receptor family, whereas the third one (NTR3) is a type I receptor with a single transmembrane domain. The NTS1 is expressed in CNS such as cerebral cortex, basal ganglia, limbic areas, vestibular system, and esophageal smooth muscle.

Opioid receptor family includes three classic receptors, μ, δ, and κ, also known as OP1, OP2 and OP3, respectively. The receptors are G_i/o-coupled GPCRs which will reduce intracellular cAMP levels after activation. δ-opioid receptor modulates many kinase cascades including ERKs, Akts, JNKs, STAT3, P38 involving Src, Ras, Rac, Raf-1, Cdc42, RTKs. In addition, δ-opioid receptor has also been proposed to interact with μ receptors. The observed pharmacological cross-talk may partially arise from agonist cross-reactivity.

Opioid receptors and their endogenous peptide ligands play important roles in the reward and reinforcement of drugs such as heroin, cocaine, and alcohol. The κ-opioid receptor is a type of opioid receptor which binds the peptide opioid dynorphin as the primary endogenous ligand. κ-opioid receptors are widely distributed in the brain, spinal cord, and in pain neurons. They are associated with the risk for alcohol dependence.

Following the cloning of the classical opioid receptors (mu, delta and kappa), the opiate receptor like-1 (ORL1) was identified as a G-protein coupled receptor (GPCR) with 65% structure homology to the other members of the opioid family. OPRL1 is a receptor for the 17 aa neuropeptide nociceptin/orphanin FQ and may be involved in the regulation of numerous brain activities, particularly instinctive and emotional behaviors. Recently, new study results are consistent with the reported high density of ORL1 receptor mRNA in dorsal raphe nucleus and with inhibitory actions of nociceptin in cells expressing ORL1.

The µ-opioid receptor (oprm1) is the principal site of action in the brain by which morphine, other opiate drugs of abuse, and endogenous opioid peptides effect analgesia and alter mood. Opioid receptors belong to the rhodopsin family of G protein-coupled receptors (GPCRs). The three types of opioid receptors (μ, δ, and κ) have been shown to associate with each other in a homotypic or heterotypic fashion when expressed in heterologous cells. A member of the seven-transmembrane domain (TM) G protein-coupled receptor (GPCR) superfamily, the µ-opioid receptor modulates ion channels and second messenger effectors in an opioid agonist-dependent fashion that is reversible by the classic opiate antagonist naloxone.

OX40L is the ligand for CD134 and is expressed on such cells as DC2s (a subtype of dendritic cells) enabling amplification of Th2 cell differentiation. OX40L has also been designated CD252 (cluster of differentiation 252). Various single nucleotide polymorphisms (SNPs) of the OX40L gene have been identified. For some of them association with systemic lupus erythematosus has been reported.

The orexin/hypocretin peptides orexin A and orexin B (also known as hcrt-1 and hcrt-2) are 33- and 28-amino acid peptides, respectively. They are preferentially expressed in hypothalamus. The orexins have a range of physiological functions including feeding control, energy metabolism, neuroendocrine function modulation, and sleep-wake cycle regulation. The two orexin receptor subtypes OX1 and OX2 both mediate the action of orexin-A and orexin-B and couple efficiently through Gq/11 to activate phospholipase C and lead to elevation of intracellular calcium.

Hypocretin (orexin) receptor 2, also known as OX2, is a human protein encoded by the HCRTR2 gene. Orexin A and orexin B are neuropeptides originally identified as endogenous ligands for OX2. Orexin neuropeptides are produced by a small group of neurons in the lateral hypothalamic and perifornical areas, a region that is classically implicated with the control of mammalian feeding behavior. Orexin neurons that project throughout the central nervous system to nuclei are known to be important in the control of feeding, sleep-wakefulness, neuroendocrine homeostasis, and autonomic regulation.

OX40 (CD134) is a member of the TNFR/TNF superfamily. Costimulatory signals from OX40 to a conventional T cell promotes division and survival, augmenting the clonal expansion of effector and memory populations as they are being generated to antigens. OX40 additionally suppresses the differentiation and activity of Treg, further amplifying this process.

Oxytocin is an abundant neuropeptide that exerts a wide spectrum of central and peripheral effects. In the context of human reproduction, oxytocin promotes uterine contractions and lactation. It is the most commonly used drug for labor induction. Oxytocin receptors are expressed in the uterus and in mammary glands, where they mediate functions related to partutition, such as contraction of the uterine myometrium during labor and milk letdown. In addition, oxytocin receptors are expressed in a variety of other peripheral tissues and in the brain, where oxytocin mediates a variety of functions. OXTR antagonists may be promising candidates to prevent preterm labor and dysmenorrheal and its agonists may also be useful for treatment of psychiatric illnesses such as anxiety, drug abuse, sexual dysfunctions, eating disorders, and autism.

The Vasoactive intestinal Peptide/Pituitary Adenylate Cyclase Activating Polypeptide (VPAC) receptor is G protein-coupled and has been divided into at least three types: PAC1, VPAC1, and VPAC2. High expression of PAC1 is observed in CNS and the adrenal medulla. Several splice variants of PAC1 result in proteins that differ at the N-terminus and third intracellular loop; these variants differ in their affinities for PACAP and abilities to activate Gq and Gs. This manual describes establishment of a cell line and a protocol of pharmacologically validated human PAC1 GPCR receptor (Genebank Accession Number: NM_003382).

Proteinase-activated receptors (PAR) are a subfamily of G-protein coupled, seven-transmembrane domain receptors, which are cleaved within the aminoterminal exodomain by certain serine proteinases at a specific peptide bond. Trypsin and mast cell tryptase, and more recently, the activated coagulation factors VIIa and Xa, have been identified as serine proteinases able to activate mammalian PAR-2. As already indicated, PAR-2 is believed to be involved in inflammation. This role for PAR-2 implies that elastase and cathepsin G would paradoxically display an anti-inflammatory property by disarming PAR-2.

Protease-activated receptor (PAR)-4 is a member of a unique family of GPCRs. The protease-activated receptors (PARs) that are activated by proteolytic cleavage of the N-terminal domain of the receptor reveal a tethered ligand. The PAR family consists of 4 receptors; PAR1 and PAR3 are activated by thrombin, and PAR2 and PAR4 are activated by several serine proteases (Macfarlane et al., 2001). PAR4 is a recently identified low-affinity thrombin receptor that plays a pathophysiological role in many types of tissues including the lung. Mice lacking PAR4 are protected from mesenteric arteriole thrombosis, indicating that PAR4 is a potential target for treatment of thrombosis in humans.

Programmed cell death protein 1, also known as PD-1 and CD279 (cluster of differentiation 279), is a protein that in humans is encoded by the PDCD1 gene. PD-1, functioning as an immune checkpoint, plays an important role in down regulating the immune system by preventing the activation of T-cells, which in turn reduces autoimmunity and promotes self-tolerance. The inhibitory effect of PD-1 is accomplished through a dual mechanism of promoting apoptosis (programmed cell death) in antigen specific T-cells in lymph nodes while simultaneously reducing apoptosis in regulatory T cells (suppressor T cells).

Recombinant CHO-K1 cells stably overexpress Homo sapiens programmed death-ligand 1 (PD-L1) on the cell surface. The surface expression is validated by FACS analysis. This cell line is recommended for cell-based binding assay to screen antibodies against PD-L1 or to measure binding affinity between PD-L1 and anti-PD-L1 antibodies.

Programmed cell death 1 ligand 2 (PD-L2) is a protein that in humans is encoded by the PDCD1LG2 gene. PDCD1LG2 has also been designated as CD273 (cluster of differentiation 273). Inhibitory molecules of the B7/CD28 family play a key role in the induction of immune tolerance in the tumor microenvironment. The programmed death-1 receptor (PD-1), with its ligands PD-L1 and PD-L2, constitutes an important member of these inhibitory pathways. PD-L2 expression was initially thought to be restricted to antigen-presenting cells such as macrophages and dendritic cells (DCs). PD-L2 expression can be induced on a wide variety of other immune cells and nonimmune cells depending on microenvironmental stimuli.

The prolactin releasing hormone receptor PRLHR also named PrRP receptor is a G-protein coupled receptor that binds the prolactin releasing hormone. RT-PCR analysis showed expression of PRLHR in the human brain, pituitaries, normal portions of adrenal glands and various tumor tissues. Northern blot analysis showed high expression of PRLHR only in tumor tissues of pheochromocytomas, indicating that PRLHR expression is high in pheochromocytomas. The present study has shown that PRLHR mRNA was widely expressed in the brain tissues, pituitaries, adrenal glands and various tumors. The high expression of PRLHR receptor in pheochromocytomas suggests potential pathophysiological roles of PRLHR in these tumors

The platelet-activating factor (PAF) receptor (PTAFR) is a G protein coupled receptor that signals through multiple pathways and mediates several cellular responses including cell motility, smooth muscle contraction, and releases of cytokine and leukotriene (Stafforini et al., 2003). In humans, various diseases have been associated with PAF, such as allergic asthma, endotoxic shock, atherosclerosis and psoriasis.

Parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor (PTHR1) is a G protein coupled receptor which mediates the actions of both amino-terminal PTH and PTHrP fragments. The most abundant expression of PTHR1 is found in renal tubular cells and in osteoblasts, where the PTH/PTHrP receptor mediates the endocrine actions of PTH, and in prehypertrophic chondrocytes of the metaphyseal growth plate, where it mediates the autocrine/paracrine actions of PTHrP. Intact PTH (PTH 1-84) is compounded by a peptide of 84 amino acids (AA), the amino-terminal sequence, constituted by the first 34 AA (N-terminal structure), is necessary for its action.

Recombinant CHO-K1 cells stably overexpress human SARS-CoV-2 spike protein on their surface. The surface expression of SARS-CoV-2 spike protein is validated by FACS analysis. This stable cell line product is designed for screening antibodies against the SARS-CoV-2 spike protein, as well as measuring binding affinity and stability of antibody-based biologics that bind with spike protein. GenScript also offers spike protein expressing HEK293T stable cell line (Cat. No. M00804) for SARS-CoV-2 study.

Somatostatin acts at many sites to inhibit the release of many hormones and other secretory proteins. The biologic effects of somatostatin are probably mediated by a family of G protein-coupled receptors that are expressed in a tissue-specific manner. SST1 receptor is a Gi/Go-coupled GPCR which is expressed in pancreatic islets, pituitary, Cerebellum (Purkinje cells), frontal cortex (pyramidal cells), hippocampus (CA1-4 subfields and some granule cells of the dentate gyrus). It inhibits cAMP accumulation and stimulates tyrosine phosphatase activity, it also can antiproliferation.
GenScript’s SST1-expressing stable cell line was made in CHO-K1/Gqi5 host cell and optimized for calcium assays.

Somatostatin acts at many sites to inhibit the release of many hormones and other secretory proteins. The biologic effects of somatostatin are probably mediated by a family of G protein-coupled receptors that are expressed in a tissue-specific manner. SST2 is a member of the superfamily of receptors having seven transmembrane segments and is expressed in highest levels in cerebrum and kidney. Studies showed the involvement of the SST2 receptor in the inhibition of glucagon secretion.

Somatostatin receptors (SSTRs), a family of seven transmembrane (TM) domain G-protein-coupled receptors having five distinct subtypes (termed SSTR1-5), are activated by somatostatin secreted from the nerve and endocrine cells. SSTRs are widely expressed in many tissues, frequently as multiple subtypes that coexist in the same cell. With expressions in a tissue-specific manner, SSTRs are involved in the regulation of secretion of insulin, glucagon, and growth hormone as well as cell growth induced by neuronal excitation in both the central and peripheral nervous systems. The five receptors share common signaling pathways such as the inhibition of adenylyl cyclase, activation of phosphotyrosine phosphatase (PTP), and modulation of mitogen-activated protein kinase (MAPK) through G-protein-dependent mechanisms. Aberrant expression of somatostatin receptors is known to be involved in a large number of human tumors. The human medullary thyroid carcinoma cell line TT expresses all SSTR subtypes. SSTR3 mRNA is detected in the brain and pancreatic islets. SSTR3 uniquely triggers PTP-dependent apoptosis accompanied by the activation of p53 and pro-apoptotic protein Bax, and displays acute desensitization of adenylyl cyclase coupling.

Somatostatin acts at many sites to inhibit the release of many hormones and other secretory proteins. The biologic effects of somatostatin are probably mediated by a family of G protein-coupled receptors that are expressed in a tissue-specific manner. SST4 is a member of the superfamily of receptors having seven transmembrane segments and is expressed in highest levels in fetal and adult brain and lung. SST4 enhances AMPA receptor-mediated currents in the hippocampus, and interacts with the SST2 receptor.

Somatostatin receptors (SSTRs), a family of seven transmembrane (TM) domain G-protein-coupled receptors having five distinct subtypes (termed SSTR1–5), are activated by somatostatin secreted from the nerve and endocrine cells. SSTRs are widely expressed in many tissues, frequently as multiple subtypes that coexist in the same cell. With expressions in a tissue-specific manner, SSTRs are involved in the regulation of secretion of insulin, glucagon and growth hormone as well as cell growth induced by neuronal excitation in both the central and peripheral nervous systems. The five receptors share common signaling pathways such as the inhibition of adenylyl cyclase, activation of phosphotyrosine phosphatase (PTP), and modulation of mitogen-activated protein kinase (MAPK) through G-protein-dependent mechanisms. Aberrant expression of somatostatin receptors is known to be involved in a large number of human tumors. The human medullary thyroid carcinoma cell line TT expresses all SSTR subtypes. SSTR5 induces cell cycle arrest via PTP-dependent modulation of MAPK, which is associated with the induction of the retinoblastoma tumor suppressor protein and p21. In addition, SSTR 5 displays acute desensitization of adenylyl cyclase coupling and undergoes rapid agonist-dependent endocytosis.

TIGIT (T cell immunoreceptor with Ig and ITIM domains) was recently characterized as an inhibitory receptor, which is expressed mainly on NK, Treg, CD8+ T, and CD4+ T cells. TIGIT harbors an immunoglobulin tail tyrosine (ITT)-like phosphorylation motif and an ITIM (immunoreceptor tyrosine-based inhibition motif) in its cytoplasmic tail. The poliovirus receptor (PVR or CD155) was identified as the physical ligand of TIGIT with high affinity, and PVRL2 (Nectin2 or CD112) also binds to TIGIT with a weaker binding capacity. TIGIT/PVR engagement suppresses T cell activation through IL-10 secretion mediated by dendritic cells. Furthermore, TIGIT also exerts an intrinsic inhibitory function to T cell activation.

T cell immunoglobulin mucin-3 (TIM-3) is a member of the T-cell Immunoglobulin- and Mucin-domain-containing family of type I membrane glycoproteins that regulate autoimmune and allergic disease. TIM-3 is selectively expressed on Th1 cells and interacts with galectin-9. It negatively regulates Th1 responses and affects macrophage activation. The 280 amino acid mature human TIM-3 contains a V-type Ig-like domain that shows multiple polymorphisms, followed by a mucin-like domain in the 171 amino acid extracellular region, which shares 60% amino acid identity with mouse TIM-3 ECD.

Thyrtropin-releasing hormone receptor1 (TRH1) is a member of G-protein coupled receptor family A. This protein is a receptor for Thyrtropin-releasing hormone (TRH). Human TRH1 is expressed in lymphocytes, pituitary gland and CNS. It can stimulate the releasing of prolactin (PRL), thyrotropin (TSH). TRH1 receptor knockout mice exhibit a slightly reduced growth rate, considerable decrease in serum T₃, T₄, and prolactin levels but no alteration of thyroid-stimulating hormone levels.

The Urotensin II receptor (UT2), also named UTS2R, GPR14, which is expressed in endothelium, smooth muscle, heart and pancreas. Pharmacological inhibition of urotensin II receptor interactions prevents renal insufficiency following renal artery ligation. .

The antidiuretic hormone arginine vasopressin (AVP) receptors are G protein-coupled receptors which consists of at least three types: V1A (vascular/hepatic) and V1B (anterior pituitary) receptors, which act through phosphatidylinositol hydrolysis to mobilize intracellular Ca²⁺; and V2 (kidney) receptor, which is coupled to adenylate cyclase. V1B receptors are expressed in anterior pituitary where they mediate the release of ACTH . Its peripheral actions, such as antidiuresis, contraction of vascular smooth muscle, and stimulation of hepatic glycogenolysis are well characterized.

Arginine vasopressin (AVP) is a cyclic nonapeptide that acts by binding to a family of vasopressin receptors that includes V1a, V1b, and V2 receptors. In particular, V2 receptors are expressed in kidney where vasopressin exerts its antidiuretic action. V1a and V1b couple to Gq and calcium release, whereas V2 couples to Gs. Mutations in V2 result in X-linked nephrogenic diabetes insipidus, a syndrome in which the kidney is unable to concentrate urine, leading to dehydration and hypernatremia. Conversely, elevated levels of AVP lead to hyponatremia in the syndrome of inappropriate antidiuretic hormone secretion (SIADH), congestive heart failure or cirrhosis, and V2 selective antagonists have been developed to treat these conditions.

Recombinant CHO-K1 cells stably overexpress V-domain Ig suppressor of T cell activation (VISTA) on the cell surface. The surface expression of VISTA is validated by FACS analysis. This cell line is designed for cell-based binding for screening antibodies binding with VISTA and evaluating target binding affinity.