Structure and Expression of a Membrane Component of the Inhibin Receptor System¹

Abstract

The purification and cloning of a membrane-anchored proteoglycan with affinity for inhibin A are described. Bovine pituitary membranes were isolated, and membrane-anchored proteins were solubilized and used as an enriched source of inhibin binding protein. The extract was passed over an inhibin A affinity column, and a protein, designated p120, was identified as an inhibin-binding moiety. A partial amino acid sequence was determined for the protein, which matched two human complementary DNAs (cDNAs) in the database. The full-length cDNA predicts a 1336-amino acid glycoprotein. Full-length p120-encoding cDNAs were isolated from human testis RNA and cloned into expression vectors. Two p120 messenger RNA transcripts of 4.6 kb and 2 kb are detected in rat pituitary by RNA blot analysis. Similar analysis of rat testis RNA revealed transcripts of identical molecular mass, albeit at lower abundance. To determine the cellular localization of p120 in pituitary and testis, an antibody directed against the predicted extracellular domain of the protein was generated and used in an immunohistochemical analysis of thin tissue sections. p120 immunostaining is coincident with FSHbeta immunopositive gonadotrope cells in rat pituitary. p120 staining is intense in the testicular Leydig cells, which bind iodinated inhibin but not iodinated activin. In summary, an inhibin-binding protein has been isolated that is produced in tissues that are targets of inhibin action.

Spatial and temporal expression of immunoglobulin superfamily member 1 in the rat

“…One study reported IGSF1 expression in human hepatocellular carcinoma, implying that the silenced expression of postnatal IGSF1 might be reversible in disease (Patil et al 2005). Although the fetal rat liver has not been investigated before, our results are in line with previous reports of Igsf1 mRNA expression in northern blots of fetal human liver (Frattini et al 1998, Mazzarella et al 1998 and its absence in the adult rat and human liver (Frattini et al 1998, Mazzarella et al 1998, Chong et al 2000, Bernard & Woodruff 2001.…”

Mechanisms of Inhibin Signal Transduction

“…We addressed this issue during more-extensive studies in rats. RNA blot analyses show a high level of InhBP expression in rat pituitary and a lower, but still detectable, level of expression in the testis (Chong et al, 2000). We since have observed high levels of InhBP expression in pituitaries of a variety of species, including mice, sheep, and cows.…”

“…Both inhibin A and activin A stimulate primate oocyte maturation in vitro and cytochrome P450t7, and LH receptor mRNA levels in porcine Leydig cells (Alak et al, 1996;Lejeune et al, 1997). Fourth, inhibin binding proteins have been identified in gonadal tumors from inhibin a-subunit knockout mice, bovine pituitaries, and human erythroleukemia cells (K562) (LeBrun and Vale, 1997;Draper et al, 1998;Chong et al, 2000). Thus, several pieces of data converge to indicate the presence of an inhibin receptor or binding protein distinct from the activin type II receptors.…”

“…With our third approach, we struck gold (Chong et al, 2000)! We used affinity chromatography to purify inhibin binding proteins.…”

“…In western blot analyses of bovine pituitary membrane proteins, these antisera detect a single protein of 142 kDa. In the original purification of proteins from the affinity column, we erroneously identified the protein to have a molecular mass of 120 kDa and referred to the protein as ~120 (Chong et al, 2000). Subsequent measurements confirmed a molecular mass of approximately 142 kDa.…”