Gonadotropin induction of c-fos and c-myc expression and deoxyribonucleic acid synthesis in rat granulosa cells.

Although gonadotropins stimulate ovarian granulosa cells to proliferate and differentiate into steroidogenic cells, little is known about the molecular mechanisms by which gonadotropins induce these fundamentally different responses. In this study the acute effects of PMSG on protooncogene expression, DNA synthesis, and steroid secretion were examined. The levels of c-fos, c-myc, and beta-actin mRNA were measured in total RNA samples from granulosa cells by quantitative polymerase chain reaction. PMSG increased the mRNA levels of c-fos, c-myc, and beta-actin within 15 min. Fos and myc proteins were localized within granulosa cells by immunocytochemistry. Less than 10% of granulosa cells stained for c-fos or c-myc proteins in the control samples. In contrast, approximately 40% of the cells stained for these protooncogene proteins 30 min after PMSG injection (P less than 0.05). These values declined to about 10% of the cells 60 min after PMSG injection. DNA synthesis, as estimated by [3H]thymidine incorporation, increased 30 and 60 min after PMSG (P less than 0.05). 17 beta-Estradiol and progesterone synthesis did not change within 60 min of PMSG injection. These data demonstrate that 1) c-fos and c-myc are expressed in ovarian granulosa cells; 2) the expression of the genes encoding c-fos, c-myc, and beta-actin is rapidly increased by gonadotropin; and 3) the increase in the corresponding products of the c-fos and the c-myc genes precedes an increase in DNA synthesis and steroid production. These data suggest that the expression of c-fos and c-myc may be a part of the molecular mechanism through which gonadotropins regulate granulosa cell function.