In humans, failure of testicular descent (cryptorchidism) is one of the most frequent congenital malformations, affecting 1-3% of newborn boys. The clinical consequences of this abnormality are infertility in adulthood and a significantly increased risk of testicular malignancy. Recently, we described a mouse transgene insertional mutation, crsp, causing high intraabdominal cryptorchidism in homozygous males. A candidate gene Great (G-protein-coupled receptor affecting testis descent), was identified within the transgene integration site. Great encodes a seven-transmembrane receptor with a close similarity to the glycoprotein hormone receptors. The Great gene is highly expressed in the gubernaculum, the ligament that controls testicular movement during development, and therefore may be responsible for mediating hormonal signals that affect testicular descent. Here we show that genetic targeting of the Great gene in mice causes infertile bilateral intraabdominal cryptorchidism. The mutant gubernaculae fail to differentiate, indicating that the Great gene controls their development. Mutation screening of the human GREAT gene was performed using DHPLC analysis of the genomic DNA from 60 cryptorchid patients. Nucleotide variations in GREAT cDNA were found in both the patient and the control populations. A unique missense mutation (T222P) in the ectodomain of the GREAT receptor was identified in one of the patients. This mutant receptor fails to respond to ligand stimulation, implicating the GREAT gene in the etiology in some cases of cryptorchidism in humans.

During male development testes descend from their embryonic intraabdominal position into the scrotum. Two genes, encoding the insulin-like 3 peptide (INSL3) and the GREAT/LGR8 G protein-coupled receptor, control the differentiation of gubernaculum, the caudal genitoinguinal ligament critical for testicular descent. It was established that the INSL3 peptide activates GREAT/LGR8 receptor in vitro. Mutations of Insl3 or Great cause cryptorchidism (undescended testes) in mice. Overexpression of the transgenic Insl3 causes male-like gubernaculum differentiation, ovarian descent into lower abdominal position, and reduced fertility in females. To address the question whether Great deletion complements the mutant female phenotype caused by the Insl3 overexpression, we have produced Insl3 transgenic mice deficient for Great. Such females had a wild-type phenotype, demonstrating that Great was the only cognate receptor for Insl3 in vivo. We have established that pancreatic HIT cells, transfected with the INSL3 cDNA, produce functionally active peptide. Analysis of five INSL3 mutant variants detected in cryptorchid patients showed that P49S substitution renders functionally compromised peptide. Therefore, mutations in INSL3 might contribute to the etiology of cryptorchidism. We have also showed that synthetic insulin-like peptides (INSL4 and INSL6) were unable to activate LGR7 or GREAT/LGR8.

Relaxin (RLN) is a small peptide hormone that affects a variety of biological processes. Rln1 knockout mice exhibit abnormal nipple development, prolonged parturition, agerelated pulmonary fibrosis, and abnormalities in the testes and prostate. We describe here RLN 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 RLN, 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 nonoverlapping functions of the two receptors. Our data indicate that neither Insl3 nor Lgr8 contribute to the RLN signaling pathway. We conclude that the Insl3/Lgr8 and Rln1/Lgr7 actions do not overlap in vivo.

Relaxin (RLN) is a small peptide hormone expressed in several cancers of reproductive and endocrine organs. Increased expression of RLN in prostate cancer correlates with aggressive cancer. RLN G-protein-coupled receptor (RLN family peptide receptor 1, RXFP1) is expressed in both androgen receptor (AR)-positive and -negative prostate cancers as well as in prostate cancer cell lines. RLN behaves as a cell growth factor and increases invasiveness and proliferation of cancer cells in vitro and in vivo. The objective of this study is to determine whether downregulation of RXFP1 expression using small interfering RNA (siRNA) reduces cancer growth and metastasis in a xenograft model of prostate cancer. We used two well-characterized prostate adenocarcinoma cell lines, AR-positive LNCaP cells and AR-negative PC3 cells. The tumors were established in nude male mice by s.c. injections. Intratumoral injections of siRNAs loaded on biodegradable chitosan nanoparticles led to a downregulation of RXFP1 receptor expression and a dramatic reduction in tumor growth. In LNCaP tumors, the siRNA treatment led to an extensive necrosis. In PC3 xenografts treated with siRNA against RXFP1, the smaller tumor size was associated with the decreased cell proliferation and increased apoptosis. The downregulation of RXFP1 resulted in significant decrease in metastasis rate in PC3 tumors. Global transcriptional profiling of PC3 cells treated with RXFP1 siRNA revealed genes with significantly altered expression profiles previously shown to promote tumorigenesis, including the downregulation of MCAM, MUC1, ANGPTL4, GPI, and TSPAN8. Thus, the suppression of RLN/RXFP1 may have potential therapeutic benefits in prostate cancer.

Bogatcheva NV, Ferlin A, Feng S, Truong A, Gianesello L, Foresta C, Agoulnik AI. T222P mutation of the insulin-like 3 hormone receptor LGR8 is associated with testicular maldescent and hinders receptor expression on the cell surface membrane.