The involvement of the phosphorylatable and nonphosphorylatable transcription factor CREB-1 in the control of human ovarian cell functions

Abstract

The objective of our study was to elucidate the role of the transcription factor CREB-1 in controlling ovarian cell proliferation, apoptosis, and hormone release and the significance of CREB-1 phosphorylation in these processes. Human ovarian granulosa cells were transfected with a gene construct encoding wild-type CREB-1 (CREB-1 WT) or CREB-1 nonphosphorylatable mutant (CREB-1 M1). The expression of total and phosphorylated CREB-1, markers of proliferation (PCNA) and apoptosis (bax), as well as the release of progesterone, oxytocin, prostaglandin F2 alpha (PGF2), prostaglandin E2 (PGE2), and insulin-like growth factor I (IGF-I) were compared by immunocytochemistry, enzyme immunoassay (EIA), and immunoradiometric assay (IRMA). Transfection with CREB-1 WT or CREB-1 M1 increased total CREB-1 expression and proliferation and decreased the release of oxytocin, PGE2, and IGF-I by ovarian cells. CREB-1 M1, not CREB-1 WT, promoted apoptosis and inhibited progesterone output. PGF2 release was inhibited by CREB-1 WT but stimulated by CREB-1 M1 construct. Phosphorylated CREB-1 was undetected in any cell group. These observations confirm the involvement of CREB-1 in the control of ovarian cell proliferation, apoptosis, and steroid hormone release. This is the first demonstration of the involvement of CREB-1 in the regulation of the ovarian non-steroidal hormones such as oxytocin, PGF2, PGE2, and IGF-I. The absence of CREB-1 phosphorylation, similar effects exerted by CREB-1 WT and CREB-1 M1 on cell proliferation and release of oxytocin, PGE2, and IGF-I, and the influence of CREB-1 M1 on apoptosis and progesterone suggest that phosphorylation plays no role in the action of CREB-1 on the majority of analyzed functions of human ovarian cells.