Identification of two testosterone-responsive testicular proteins in Sertoli cell-enriched culture medium whose secretion is suppressed by cells of the intact seminiferous tubule.

Of 30 proteins identified in medium from primary Sertoli cell-enriched cultures, five of these proteins appear to increase primarily in response to testosterone. Using high performance liquid chromatography, two of these proteins, designated CMB-22 and CMB-23, were purified to apparent homogeneity from medium. Both are monomeric proteins with apparent molecular weights of Mr 37,000 and Mr 40,000, respectively. Both interact with concanavalin A and wheat germ agglutinin on lectin blots. CMB-22 has a pI of 5.8; CMB-23 has two distinctive isoelectric variants with pIs of 5.4 and 5.2, the latter variant was designated CMB-23 Isoform. Polyvalent antisera raised against purified CMB-22 and CMB-23 in rabbits cross-reacted with one another. Removal of carbohydrate from these proteins by either enzymatic or chemical treatments reduced their apparent molecular weights but did not abolish their size differences on sodium dodecyl sulfate-polyacrylamide gels. Peptide maps generated by Staphylococcus aureus protease V8 and visualized by silver staining and immunoblots suggest that CMB-22 and CMB-23 are similar but distinctive proteins that share almost identical epitopes. A radioimmunoassay was developed and used to measure total immunoreactive CMB-22-like material (CMB-22 plus CMB-23 immunoreactivity) in culture media, biological fluids, and tissue extracts. The results of these studies showed that the secretion of CMB-22-like material is unique with regard to other proteins that have been identified in Sertoli cell-enriched cultures. That is, CMB-22-like material is secreted by Sertoli cell-enriched cultures, but cannot be detected in media from cultures of intact tubular segments in vitro. In addition, immunoreactive material is also not detected in the testicular fluids from interstitium, tubule, or rete testis. This is in striking contrast to other Sertoli cell proteins which are present in substantial concentrations in these fluids. These observations suggest that the secretion and possibly the hormone responsiveness of CMB-22 and CMB-23 are normally suppressed in the intact tubule both in vivo and in vitro. We propose that studies of CMB-22 and CMB-23 will provide important insights into cell-cell interactions in the seminiferous epithelium.