Follicle-stimulating hormone and intracellular second messengers regulate steroidogenic acute regulatory protein messenger ribonucleic acid in luteinized porcine granulosa cells

Ligand-and second messenger-regulated expression of the gene for steroidogenic acute regulatory protein (StAR) was evaluated in luteinized porcine granulosa cells. For comparison, cytochrome P450 side-chain cleavage (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 P450(scc) band at 1.9 kb. FSH elevated both StAR and P450(scc) messages in a dose-dependent manner over 6 h and continually stimulated both over 24 h (p < 0.001). StAR message induction depended on transcription, as did that of P450(scc). Over 6 h, actinomycin D eliminated constitutive StAR message and reduced that of P450(scc) by two thirds, indicating briefer persistence of StAR. Pretreatment with cycloheximide prevented 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 their 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 steroid synthetic genes in luteinized granulosa cells.