Adenovirus-directed expression of a nonphosphorylatable mutant of CREB (cAMP response element-binding protein) adversely affects the survival, but not the differentiation, of rat granulosa cells

Although usually considered to be a constitutively expressed protein, in th e primate ovary the expression of CREB (cAMP response element-binding prote in) is extinguished after ovulation, and its loss is temporally associated with the cessation of proliferation of luteal cells and the ultimate commit ment of the corpus luteum to undergo regression. To determine the cellular consequences of the loss of CREB expression, we expressed a nonphosphorylat able mutant of CREB (CREB M1) in primary cultures of rat granulosa cells us ing a replication-defective adenovirus vector. Expression of CREB M1 did no t block granulosa cell differentiation as assessed by acquisition of the ab ility to produce estrogen and progesterone in response to FSH or forskolin. However, granulosa cells expressing CREB M1, but not adenovirus-directed b eta-galactosidase or enhanced green fluorescent protein, exhibited a 35% re duction in viability that was further reduced to 65% after stimulation with 10 mu M forskolin. These results demonstrate that the trophic effects of c AMP (proliferation and survival) on ovarian granulosa cells are functionall y separate from the effects of cAMP on differentiation and provide novel ev idence that CREB may function as a cell survival factor in the ovary. The s eparation of signaling pathways that govern differentiation and survival in the ovary thereby provides a mechanism by which progesterone production, w hich is absolutely essential for the maintenance of pregnancy, can continue despite the cessation of proliferation of luteal cells and their commitmen t to cell death (luteolysis).