Regulation of Protein Kinase Inhibitor by Follicle-Stimulating Hormone in Sertoli Cells in Vitro*

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Abstract
The heat-stable protein inhibitor of cAMP-dependent protein kinase is specifically regulated by hormones in cultures of rat Sertoli cells maintained under completely defined conditions. Hormones that are known to elevate Sertoli cell cAMP concentrations, namely FSH and isoproterenol, produce a 4- to 5-fold increase in the specific activity of protein kinase inhibitor, whereas testosterone and LH have no effect. The stimulatory effects of FSH or isoproterenol on protein kinase inhibitor are completely mimicked by dibutyryl cAMP. The ability of FSH to stimulate protein kinase inhibitor is dependent upon the age of the animals used as a source for the Sertoli cells. FSH stimulates protein kinase inhibitor activity in cells from 9- and 16-day-old animals, but not in cells from 32-day-old animals. On the other hand, isoproterenol or dibutyryl cAMP will stimulate protein kinase inhibitor in cells from both young and old animals. FSH can stimulate protein kinase inhibitor activity in older cells only in the added presence of the phosphodiesterase inhibitor, l-methyl-3-isobutyl xanthine. Using specific antibodies to protein kinase inhibitor, we have shown that this protein is regulated by hormones via preferential stimulation of de novo synthesis of the inhibitor. (Endocrinology108: 427, 1981)