Hsu SY, et al 2000 reported the classification of three subfamilies of leucine-rich repeat-containing G protein-coupled receptors (LGR) and the identification of LGR6 and LGR7 and the signaling mechanism for LGR7.
Glycoprotein hormone receptors, including LH receptor, FSH receptor, and TSH
receptor, belong to the large G protein-coupled receptor (GPCR) superfamily but
are unique in having a large ectodomain important for ligand binding. The authors identified two new
paralogs, LGR6 and LGR7, for glycoprotein hormone receptors. Phylogenetic
analysis showed that there are three LGR subgroups: the known glycoprotein
hormone receptors; LGR4 to 6; and a third subgroup represented by LGR7. LGR6
has a subgroup-specific hinge region after leucine-rich repeats whereas LGR7,
like snail LGR, contains a low density lipoprotein (LDL) receptor cysteine-rich
motif at the N terminus. Similar to LGR4 and LGR5, LGR6 and LGR7 mRNAs are
expressed in multiple tissues, including the ovary. Although the putative ligands for LGR6 and LGR7
are unknown, studies on single amino acid mutants of LGR7, with a design based
on known LH and TSH receptor gain-of-function mutations, indicated that the
action of LGR7 is likely mediated by the protein kinase A but not the
phospholipase C pathway. Thus, mutagenesis of conserved residues to allow
constitutive receptor activation is a novel approach for the characterization of
signaling pathways of selective orphan GPCRs. The present study also defines the
existence of three subclasses of leucine-rich repeat-containing, G protein-coupled
receptors in the human genome and allows future studies on the physiological
importance of this expanding subgroup of GPCR.
/////////////////Identification and optimization of small-molecule agonists of the human relaxin hormone receptor RXFP1. Xiao J et al. The anti-fibrotic, vasodilatory and pro-angiogenic therapeutic properties of recombinant relaxin peptide hormone have been investigated in several diseases, and recent clinical trial data has shown benefit in treating acute heart failure. However, the remodelling capacity of these peptide hormones is difficult to study in chronic settings because of their short half-life and the need for intravenous administration. Here we present the first small-molecule series of human relaxin/insulin-like family peptide receptor 1 agonists. These molecules display similar efficacy as the natural hormone in several functional assays. Mutagenesis studies indicate that the small molecules activate relaxin receptor through an allosteric site. These compounds have excellent physical and in vivo pharmacokinetic properties to support further investigation of relaxin biology and animal efficacy studies of the therapeutic benefits of relaxin/insulin-like family peptide receptor 1 activation.
General function
Receptor
Comment
Identification of Small-Molecule Agonists of Human Relaxin Family Receptor 1 (RXFP1) by Using a Homogenous Cell-Based cAMP Assay. Chen CZ et al. The relaxin hormone is involved in a variety of biological functions, including female reproduction and parturition, as well as regulation of cardiovascular, renal, pulmonary, and hepatic functions. It regulates extracellular matrix remodeling, cell invasiveness, proliferation, differentiation, and overall tissue homeostasis. The G protein-coupled receptor (GPCR) relaxin family receptor 1 (RXFP1) is a cognate relaxin receptor that mainly signals through cyclic AMP second messenger. Although agonists of the receptor could have a wide range of pharmacologic utility, until now there have been no reported small-molecule agonists for relaxin receptors. Here, we report the development of a quantitative high-throughput platform for an RXFP1 agonist screen based on homogenous cell-based HTRF cyclic AMP (cAMP) assay technology. Two small molecules of similar structure were independently identified from a screen of more than 365 677 compounds. Neither compound showed activity in a counterscreen with HEK293T cells transfected with an unrelated GPCR vasopressin 1b receptor. These small-molecule agonists also demonstrated selectivity against the RXFP2 receptor, providing a basis for future medicinal chemistry optimization of selective relaxin receptor agonists.
Cellular localization
Plasma membrane
Comment
Ovarian function
Primary follicle growth
Comment
Early Human Preantral Follicles Have Relaxin and Relaxin Receptor (LGR7) and Relaxin Promotes their Development.
Shirota K, et al .
The regulatory mechanisms of early follicle development are not clearly understood. Although relaxin is a peptide that controls cell proliferation and differentiation in many tissues, its role in human follicular development is unclear. In this study we cultured slices of human ovarian cortical tissue in the presence and absence of recombinant human relaxin. Ovarian tissue was obtained by biopsy during gynecological laparotomy or laparoscopy (14 women, mean age +/- SEM: 29.0 +/- 6.1 yr, range: 17-37 yr). A significantly higher proportion of secondary follicles (14.5% vs. 5.0% in the control group, P < 0.01) and a significantly decreased proportion of primordial follicles (30.1% vs. 47.4% in the control group, P < 0.05) were found in tissues cultured with relaxin for 7 days. Immunocytochemical studies with the anti-C-peptide of prorelaxin and anti-relaxin antibodies revealed the localization of relaxin in the oocyte, flat pre-granulosa and granulosa cells of primordial, primary and secondary follicles. The presence of the relaxin receptor LGR7 was observed in flat pre-granulosa and granulosa cells of primordial, primary and secondary follicles by immunocytochemical and in situ hybridization analyses. These results suggest that relaxin plays a role through its receptor during the early stage of follicle development.
Expression regulated by
Comment
Ovarian localization
Granulosa, Luteal cells
Comment
Hsu SY, et al 2000 reported LGR7 is present in the ovary detected by Northern blotting assay.
Expression of LGR7 in the primate corpus luteum implicates the corpus luteum as a relaxin target organ. Maseelall PB et al. In women, the corpus luteum is the source of circulating relaxin. No previous studies have addressed whether the corpus luteum is also a relaxin target organ. We determined relaxin receptor LGR7 mRNA expression in human term pregnancy corpora lutea and nonhuman primate corpora lutea obtained during the menstrual cycle. Real-time reverse transcription-PCR demonstrated the expression of LGR7 mRNA in both human and rhesus monkey corpora lutea. Rhesus monkey corpora lutea were obtained from naturally cycling animals following documented luteinizing hormone (LH) surges at early, mid-, mid-late, and late luteal phases. Luteal expression of LGR7 mRNA did not show temporal variation. Since the primate corpus luteum is LH dependent, we assessed LGR7 mRNA expression in corpora lutea from rhesus monkeys treated with a gonadotropin-releasing hormone (GnRH) antagonist, which significantly suppressed pituitary LH levels. GnRH antagonist treatment, which also inhibits both progesterone and relaxin production, resulted in a fivefold increase in luteal LGR7 mRNA expression. These data suggest that luteal LGR7 mRNA expression may be regulated by relaxin and/or LH and that the primate corpus luteum is a target organ for relaxin.
Follicle stages
Primordial, Primary, Secondary, Corpus luteum
Comment
Expression of LGR7 in the primate corpus luteum implicates the corpus luteum as a relaxin target organ. Maseelall PB et al. In women, the corpus luteum is the source of circulating relaxin. No previous studies have addressed whether the corpus luteum is also a relaxin target organ. We determined relaxin receptor LGR7 mRNA expression in human term pregnancy corpora lutea and nonhuman primate corpora lutea obtained during the menstrual cycle. Real-time reverse transcription-PCR demonstrated the expression of LGR7 mRNA in both human and rhesus monkey corpora lutea. Rhesus monkey corpora lutea were obtained from naturally cycling animals following documented luteinizing hormone (LH) surges at early, mid-, mid-late, and late luteal phases. Luteal expression of LGR7 mRNA did not show temporal variation. Since the primate corpus luteum is LH dependent, we assessed LGR7 mRNA expression in corpora lutea from rhesus monkeys treated with a gonadotropin-releasing hormone (GnRH) antagonist, which significantly suppressed pituitary LH levels. GnRH antagonist treatment, which also inhibits both progesterone and relaxin production, resulted in a fivefold increase in luteal LGR7 mRNA expression. These data suggest that luteal LGR7 mRNA expression may be regulated by relaxin and/or LH and that the primate corpus luteum is a target organ for relaxin.
Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: subfertile Comment: Impaired Nipple Development and Parturition in LGR7 Knockout Mice.
Krajnc-Franken MA, et al .
LGR7 is a G-protein coupled receptor with structural homology to the gonadotrophin and thyrotrophin receptors. Recently, LGR7 was deorphanized, and it was shown that relaxin is the ligand for LGR7. To further study the function of this receptor, mice deficient for LGR7 were generated by replacing part of the transmembrane-encoding region with a LacZ reporter cassette. Here we show that LGR7 is expressed in various tissues, including the uterus, heart, brain, and testis. Fertility studies using female LGR7(-/-) mice showed normal fertility and litter size. However, some females were incapable of delivering their pups, and several pups were found dead. Moreover, all offspring died within 24 to 48 h after delivery because female LGR7(-/-) mice were unable to feed their offspring due to impaired nipple development. In some male LGR7(-/-) mice, spermatogenesis was impaired, leading to azoospermia and a reduction in fertility. Interestingly, these phenomena were absent in mutant mice at older ages or in later generations. Taken together, results from LGR7 knockout mice indicate an essential role for the LGR7 receptor in nipple development during pregnancy. Moreover, a defect in parturition was observed, suggesting a role for LGR7 in the process of cervical ripening.
Species: mouse
Mutation name: None
type: null mutation fertility: fertile Comment: Relaxin (RLN) is a small peptide hormone that affects a variety of biological processes. Rln1 knockout mice exhibit abnormal nipple development, prolonged parturition, age-related pulmonary fibrosis, and abnormalities in the testis and prostate. Kamat AA, et al 2004 describe here relaxin receptor Lgr7 deficient mice. Mutant females have grossly underdeveloped nipples and are unable to feed their progeny. Some Lgr7(-/-) females were unable to deliver their pups. Histological analysis of Lgr7 mutant lung tissues demonstrates increased collagen accumulation and fibrosis surrounding the bronchioles and the vascular bundles, absent in wild-type animals. However, Lgr7 deficient males do not exhibit abnormalities in the testes or prostate as seen in Rln1 knockout mice. Lgr7 deficient females with additional deletion of Lgr8 (Great), another putative receptor for relaxin, are fertile and have normal sized litters. Double mutant males have normal sized prostate and testes, suggesting that Lgr8 does not account for differences in Rln1-/- and Lgr7-/- phenotypes. Transgenic overexpression of Insl3, the cognate ligand for Lgr8, does not rescue the mutant phenotype of Lgr7 deficient female mice indicating non-overlapping functions of the two receptors. Our data indicate that neither Insl3 nor Lgr8 contribute to the relaxin signaling pathway. We conclude that the Insl3/Lgr8 and Rln1/Lgr7 actions do not overlap in vivo.