SECRETION OF STEROIDS, GROWTH-FACTORS, AND CYTOKINES BY IMMORTALIZED MOUSE GRANULOSA-CELL LINES

The expression and function of gonadotropin receptors, and the secreti on of steroids, transferrin, and cytokines were investigated in three immortalized (single transfection with v-myc) mouse granulosa cell lin es (GRM01, GRM01L, and GRM02). A dose-dependent increase in progestero ne production was obtained in GRM01 and GRM02 cells after addition of LH, FSH, modulators of the adenylate cyclase enzyme system, and cAMP a nalogues. The LH-induced release of progesterone was already detectabl e in GRM02 cells after 8 h and was related to incubation time and cell number. Both epidermal growth th factor (EGF) and transforming growth factor a (TGF alpha) induced the secretion of progesterone in GRM02 c ells, while no effect was obtained with TGF beta. LH receptor concentr ation was highest in the GRM02 cell line. FSH receptor mRNA was visual ized in GRM01 and GRM02 cells. Aromatase activity in GRM02 cells was i nduced by androgens and inhibited by aromatase inhibitors. Whereas all cell lines were able to secrete transferrin, only in GRM01 cells was transferrin secretion increased significantly by LH. RH did not affect transferrin secretion in the three cell lines, in contrast to forskol in or 8-bromo-cAMP. The immortalized mouse granulosa cell lines were a ble to express and release several growth factors. The expression and secretion of activin, inhibin, TGF beta, EGF, TGF alpha, insulin-like growth factor II, fibroblast growth factor (acidic and basic), platele t-derived growth factor, and interleukin-6 suggest an autocrine or par acrine role for these factors in follicular differentiation and functi on. In conclusion, these cells, derived from mural granulosa cells and immortalized in a preovulatory state, can be used to study granulosa cell physiology or to study the role of granulosa cells and their deri vatives in the process of follicular maturation, fertilization, and ea rly embryonic development.