FOLLICLE-STIMULATING-HORMONE INCREASES GUANINE NUCLEOTIDE-BINDING REGULATORY PROTEIN SUBUNIT ALPHA-I-3 MESSENGER-RNA BUT DECREASES ALPHA-I-1 AND ALPHA-I-2 MESSENGER-RNA IN SERTOLI CELLS

FSH interacts with a guanine nucleotide-binding protein (G-protein)-coupled receptor, which in turn modulates signal transduction via the G-protein subunit alpha(s). However, it is unknown whether FSH regulates alpha-subunit gene expression and whether G-protein alpha-subunit genes other than alpha(s) are modulated in FSH-stimulated signal transduction. Regulation of mRNA for alpha(s) and alpha(i-2) was studied in primary cultures of rat Sertoli cells because these proteins are linked to the control of adenylyl cyclase. In addition, mRNA for alpha(i-1) and alpha(i-3) were quantified because these proteins are putatively linked to ion channels but have not been well characterized in the Sertoli cell. Northern blot analyses demonstrated that FSH induced a dose-dependent increase in steady state levels of alpha(i-3) mRNA. In contrast, FSH caused a dose-dependent decrease in levels of alpha(i-1) and alpha(i-2) mRNA. No significant effect of FSH on alpha(s) mRNA levels was detectable. The time course of FSH effects showed a 75% decrease in alpha(i-1) mRNA levels, a 50% decrease in alpha(i-2) mRNA levels and a nearly 3-fold increase in levels of alpha(i-3) mRNA between 4-6 h of treatment with 100 ng/ml FSH. Steady state levels of alpha(i-1) and alpha(i-2) mRNA returned to pretreatment levels after 10 h FSH treatment, while alpha(i-3) mRNA returned to a new steady state level approximately 50% greater than the pretreatment level. These data suggest that FSH differentially regulates mRNA coding for structurally related inhibitory G-protein alpha-subunits. Treatment of Sertoli cells with 8-bromo-cAMP induced a 75% decrease in levels of alpha(i-1) MRNA, a 40% decrease in alpha(i-2) mRNA, and a 2-fold increase in alpha(i-3) mRNA levels after 6 h, similar to the patterns observed in the presence of FSH. The altered expression of alpha(i-1), alpha(i-2), and alpha(i-3) mRNA in the presence of 8-bromo-cAMP was maintained for up to 24 h and did not return to pretreatment levels. In contrast, alpha(s) mRNA levels decreased nearly 50% after only 2 h of treatment with 8-bromo-cAMP and returned to control values at 6 h. These data suggest that FSH actions on G-protein alpha-subunit gene expression were mediated by cAMP. Thus, FSH down-regulates gene expression of a component of the inhibitory signal transduction pathway, namely alpha(i-2). We propose that FSH may also influence alternative signal transduction pathways by controlling the expression of genes for G-protein alpha-subunits alpha(i-1), and alpha(i-3).