Cyclic Adenosine Monophosphate and Phorbol Ester, like Gonadotropin-Releasing Hormone, Stimulate the Biosynthesis of Luteinizing Hormone Polypeptide Chains in a Nonadditive Manner

Abstract

We have previously reported that GnRH stimulates the synthesis of both the alpha- and beta-polypeptide chains of LH. In the present study, in order to investigate the mechanisms involved in the GnRH regulation of LH subunit synthesis, we have explored the effects of cAMP and a phorbol ester [12-O-tetradecanoyl phorbol 13-acetate (TPA)] using anterior pituitary cells in primary culture incubated in the presence of [35S]methionine. The radioactivity incorporated into alpha and LH beta immunologically related polypeptides was measured after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the labeled material immunoextracted from cells and media with specific antisera. The cAMP analog 8-Br-cAMP (at concentrations 0.25-2 mM), the cholera toxin (6-60 nM), and forskolin (10-100 microM) induced, like GnRH, an increase in the [35S]methionine incorporation into alpha- and LH beta-subunits. On the other hand, TPA (50-100 nM) also enhanced the synthesis of LH subunits. After a 5-h incubation in the presence of GnRH, 8-Br-cAMP, and TPA in different combinations, no cumulative effect was observed. These results demonstrate that intracellular cAMP and TPA are potent activators of both alpha- and LH beta-polypeptide chain synthesis, suggesting that cAMP as well as diacylglycerols may act as intracellular mediators of the GnRH effect on LH subunit synthesis.