INHIBITORY EFFECTS OF A TUMOR-PROMOTING PHORBOL ESTER ON LUTEINIZING HORMONE-STIMULATED RENIN AND PRORENIN PRODUCTION BY CULTURED BOVINE THECA CELLS

In this report, we have described a serum free culture method for culturing bovine theca cells in vitro. These cultured cells could be stimulated with LH to produce renin and prorenin. Though intracellular prorenin as well as renin was increased by LH, no renin was found to be released into the extracellular medium. The extracellular medium contained prorenin exclusively. The stimulatory effect of LH could be mimicked by 8-bromo-cAMP (8-Br-cAMP) and forskolin, suggesting cAMP to be the second messenger involved. Induction of renin and prorenin production by LH in cultured theca cells was dependent upon de novo protein synthesis, since the action of LH could be completely blocked by the protein synthesis inhibitor, cycloheximide. The stimulatory effects of LH, 8-Br-cAMP, or forskolin were also blocked by 4β-phorbol 12-myristate 13- acetate (PMA), via putative activation of protein kinase C. However, to completely block the stimulatory effect of LH or 8- Br-cAMP, it was necessary to add PMA either before LH/8-BrcAMP was added or simultaneously with the agonists. With progressive delay in addition of PMA after LH/8-Br-cAMP was added, the extent of inhibition decreased gradually and if PMA was added anytime after 4 h of LH/8-Br-cAMP addition, no inhibitory effect could be observed. Thus we have shown that renin/prorenin production by theca cells in vitro can be directly regulated by LH in a cAMP-dependent manner. Prorenin is preferentially released from the cells. Activation of protein kinase C appears to inhibit some very early steps in the induction of prorenin/renin production which however is distal to cAMP formation. © 1990 by The Endocrine Society.