FOLLICLE-STIMULATING-HORMONE AND INTRACELLULAR 2ND-MESSENGER REGULATESTEROIDOGENIC ACUTE REGULATORY PROTEIN MESSENGER-RIBONUCLEIC-ACID IN LUTEINIZED PORCINE GRANULOSA-CELLS

Ligand-and second messenger-regulated expression of the gene for stero idogenic acute regulatory protein (StAR) was evaluated in luteinized p orcine granulosa cells. For comparison, cytochrome P450 side-chain cle avage (P450(scc)) was examined. Northern hybridization with homologous cDNA probes demonstrated three StAR mRNA species, of 2.7, 1.6, and 0. 8 kilobases (kb), with the smallest variably present, and a single P45 0(scc) band at 1.9 kb. FSH elevated both StAR and P450(scc) messages i n a dose-dependent manner over 6 h and continually stimulated both ove r 24 h (p < 0.001). StAR message induction depended on transcription, as did that of P450(scc). Over 6 h, actinomycin D eliminated constitut ive StAR message and reduced that of P450(scc) by two thirds, indicati ng briefer persistence of StAR. Pretreatment with cycloheximide preven ted FSH induction of StAR and P450(scc) mRNA, implicating intermediate protein synthesis in expression of both genes. Dibutyryl cAMP caused time-dependent increases in StAR and P450 mRNAs over 24 h (p < 0.001), indicating the importance of the protein kinase A (PKA) pathway in th eir gene expression. Activation of the protein kinase C (PKC) pathway by a phorbol ester eliminated FSH induction of StAR mRNA increases (p < 0.01) while only reducing P450(scc) induction (p < 0.05). Thus, StAR gene expression, as reflected in mRNA abundance, is regulated by FSH via the PKA pathway and is dependent on transcription and translation. Conversely, the PKC pathway inhibits induction of these important ste roid synthetic genes in luteinized granulosa cells.