INSL5 Is a High Affinity Specific Agonist for GPCR142 (GPR100)

Abstract

Insulin-like peptide 5 (INSL5) is a peptide that belongs to the relaxin/insulin family, and its receptor has not been identified. In this report, we demonstrate that INSL5 is a specific agonist for GPCR142. Human INSL5 displaces the binding of 125 I-relaxin-3 to GPCR142 with a high affinity (K i ‫؍‬ 1.5 nM). In a saturation binding assay, 125 The relaxin/insulin family peptides include insulin (1), IGF1 1 (2), IGF2 (3), relaxin (4, 5), INSL3 (6), INSL4 (7), INSL5 (8), INSL6 (9), and relaxin-3/INSL7 (10). Except for IGF1 and IGF2, which are single chain peptides, each member of the family consists of two peptide subunits (an A-chain and a B-chain) that are linked by three disulfide bonds (4 -14). Insulin, IGF1, and IGF2 are known to be involved in the regulation of glucose metabolism (15) and signal through tyrosine kinase/ growth factor receptors, which are single transmembrane receptors (16, 17). Relaxin plays multifunctional roles including uterus relaxation, reproductive tissue growth, and collagen remodeling in females (18). In addition, relaxin has been reported to play important roles in nonreproductive functions including wound healing, cardiac protection, and allergic responses (19). The receptor for relaxin has been identified recently as a leucine-rich repeat containing the G-protein-coupled receptor (LGR) LGR7 (20). Although relaxin also activates LGR8 in vitro (20), recent studies show that LGR8 is likely the endogenous receptor for INSL3 and is involved in testis descent (21,22). To date, the receptors for INSL4, INSL5, and INSL6 have not been identified. Relaxin-3 (also known as INSL7), the most recently identified member of the family, was reported to be an additional ligand for LGR7 (23). We recently identified relaxin-3 as a ligand for two orphan G-protein-coupled receptors GPCR135 (14) and GPCR142 (24). The predominant brain expression for both 14,25, 26) and GPCR135 (14,26), coupled with their high affinity interaction, strongly suggests that relaxin-3 is the endogenous ligand for GPCR135. The tissue expression pattern of GPCR142 (also known as GPR100), which is primarily in peripheral tissues (24), is drastically different from that of relaxin-3, suggesting that GPCR142 may have an endogenous ligand other than relaxin-3. Furthermore, despite the high conservation of relaxin-3 in different species, GPCR142 is less conserved in the mouse and is a pseudogene in the rat (26), suggesting that GPCR142 may have a diminished role in rodents and may function as a receptor for a different ligand (other than relaxin-3) in other mammals. Sequence analysis among insulin/relaxin family members indicates that INSL5 shares high homology to relaxin-3 (Fig. 1A), suggesting that it may be an additional ligand for GPCR135, GPCR142, LGR7, or LGR8. In this report, we demonstrate that INSL5 is an agonist for GPCR142 but not for GPCR135, LGR7, or LGR8.

Insulin-like peptide 5 is an orexigenic gastrointestinal hormone

“…By contrast, Insl5 does not stimulate the related Rxfp3, unlike relaxin-3, which is an agonist at both receptors (15,16). The pairing of receptor and ligand is further supported by the observation that both Insl5 and Rxfp4 are inactivated in tandem by pseudogenization in some species such as rat and dog (17).…”

The A-chain of Human Relaxin Family Peptides Has Distinct Roles in the Binding and Activation of the Different Relaxin Family Peptide Receptors

“…The native receptor for H3 relaxin is the unrelated receptor GPCR135, also known as the somatostatin-and angiotensin-like peptide receptor (6). H3 relaxin also has high affinity for the related receptor GPCR142, which is the receptor for INSL5 (7). Both receptors are classic peptide ligand GPCRs and lack a large ectodomain.…”

An insulin-like peptide regulates egg maturation and metabolism in the mosquito Aedes aegypti

“…Insulin is the only ILP that binds with high affinity to a homodimer receptor tyrosine kinase (RTK) (Ϸ500 kDa) called the insulin receptor (IR) and stimulates a signaling pathway that includes phosphoinositide 3-kinase (PI3K) and serine/threonine kinase (AKT). IGFs preferentially bind a related RTK [IGF receptor (IGFR)] and activate the MAPK pathway, and relaxins bind G protein-coupled receptors (GPCRs) (4)(5)(6). Together, these hormones mediate a diversity of processes with insulin primarily regulating metabolism, IGFs regulating cell proliferation and survival, and relaxins mediating vasodilation.…”