Constitutively Active Protein Kinase A Qualitatively Mimics the Effects of Follicle-Stimulating Hormone on Granulosa Cell Differentiation

Abstract

Activation of the protein kinase A (PKA) signaling system is necessary for FSH-induced granulosa cell differentiation, but it is not known whether activation of PKA is sufficient to account for the complex pattern of gene expression that occurs during this process. We addressed this question by infecting granulosa cells with a lentiviral vector that directs the expression of a constitutively active mutant of PKA (PKA-CQR) and compared the cellular responses to PKA-CQR with cells stimulated by FSH. Expression of PKA-CQR in undifferentiated granulosa cells resulted in the induction of both estrogen and progesterone production in the absence of cAMP. The stimulatory effects of both PKA-CQR and FSH on estrogen and progesterone production were suppressed by the PKA inhibitor H-89 and were mimicked by PKA-selective cAMP agonists. mRNA levels for P450scc and 3beta-HSD were induced to a similar extent by FSH and PKA-CQR, whereas mRNA levels for P450arom and the LHr were induced to a greater extent by FSH. Microarray analysis of gene expression profiles revealed that the majority of genes appeared to be comparably regulated by FSH and PKA-CQR but that some genes appear to be induced to a greater extent by FSH than by PKA-CQR. These results indicate that the PKA signaling pathway is sufficient to account for the induction of most genes (as identified by microarray analysis), including those of the progesterone biosynthetic pathway during granulosa cell differentiation. However, optimal induction of aromatase, the LHr, and other genes by FSH appears to require activation of additional signaling pathways.