Involvement of transcription factor p53 and leptin in control of porcine ovarian granulosa cell functions.

The aim of our in vitro experiments was to examine the role of transcription factor p53 and the metabolic hormone leptin, in controlling basic functions (proliferation, apoptosis and secretory activity) of ovarian cells, as well as involvement of p53 in mediating or modulating actions of leptin, on ovarian cells. Porcine ovarian granulosa cells, transfected and non-transfected with a gene construct encoding p53, were cultured with leptin (at concentrations of 0, 1, 10 or 100 ng/ml). Accumulation of p53 and of apoptosis-related (bax) and proliferation-related (PCNA, cyclin B1) substances was evaluated by SDS-PAGE-western blotting. Secretion of progesterone (P4) was measured by RIA. Transfection with the p53 gene construct promoted accumulation of this transcription factor within cells. It also stimulated expression of bax (which can be thought of as a marker of apoptosis), and reduced accumulation of proliferation-related substances PCNA and cyclin B1. Overexpression of p53 resulted in reduced P4 secretion. Leptin, when added alone, increased accumulation of p53, bax and PCNA, decreased accumulation of cyclin B1 and had no effect on P4 secretion. Transfection of cells with p53 gene construct reversed effects of leptin on cyclin B1 and induced stimulatory effects of leptin on P4 release, but did not modify leptin action on p53, bax and PCNA. These multiple effects of the p53 gene construct on granulosa cells, cultured with and without leptin, (i) demonstrate that leptin can be involved in control of porcine ovarian cell proliferation, apoptosis and expression of p53, but not on P4 release; and (ii) confirm involvement of p53 in promoting apoptosis and suppression of proliferation and P4 secretion in these cells. (iii) The similarity of p53 and leptin's actions on bax and cyclin B1, and inability of p53 to further promote leptin action on this parameter suggest that p53 can be a mediator of leptin's action on ovarian cell apoptosis. (iv) On the other hand, p53 can modulate, but probably not mediate the effects of leptin on ovarian cell proliferation and P4 release.