ACTIVATION OF PROTEIN-KINASE-C BETA-GENE EXPRESSION BY GONADOTROPIN-RELEASING-HORMONE IN ALPHA-T3-1 CELL-LINE - ROLE OF CA2-KINASE-C( AND AUTOREGULATION BY PROTEIN)

The gonadotroph-derived alpha T3-1 cell line was used to investigate t he effect of gonadotropin-releasing hormone (GnRH) upon conventional p rotein kinase C subtypes (cPKCs) gene expression. Addition of the stab le analog [D-Trp(6)]GnRH (GnRH-A, 0.1 nM) resulted in a rapid increase (30 min) of the steady state levels of PKC beta, but not PKC alpha, m RNA levels, while PKC gamma is not expressed in the cells. The rapid s timulatory effect of GnRH-A was blocked by pretreatment with actinomyc in D or with the GnRH antagonist (D-pGlu(1), pClPhe(2), D-Trp(3,6))GnR H and was not mimicked by thyrotropin-releasing hormone. Addition of t he PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted a lso in a rapid (30 min) and selective increase in PKC beta, but not PK C alpha, mRNA levels. In contrast, the calcium ionophore, ionomycin, i ncreased rapidly (30 min) both PKC alpha and PKC beta mRNA levels, and its stimulatory effect on PKC beta was not additive with that of TPA. The rapid stimulatory effect of GnRH-A was blocked by the PKC inhibit or bisindolylmaleimide (GF 109203X) or by down-regulation of endogenou s PKC. Similarly, the rapid effect of GnRH-A was abolished by the intr acellular Ca2+ chelator ,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraac etic acid (BAPTA) or by removal of extracellular Ca2+. Stimulation of PKC beta mRNA levels by ionomycin was only reduced by GF 109203X and w as not affected by down-regulation of PKC. In contrast the effect of T PA on PKC beta mRNA levels was reduced by BAPTA and abolished by remov al of Ca2+. We conclude that Ca2+ and PKC act sequentially during GnRH -A-induced PKC beta gene expression and that PKC beta gene expression induced by GnRH-A is autoregulated by PKC.