Epidermal growth factor enhances [125I]iodo-follicle-stimulating hormone binding by cultured porcine granulosa cells.
Epidermal growth factor (EGF) has been shown to have diverse effects on granulosa cells (GC). Although a potent mitogen for GC from several species, EGF attenuates many FSH-mediated processes associated with GC differentiation, suggesting that EGF promotes cell proliferation at the expense of cell differentiation. The extent to which EGF effects involve modulation of the FSH receptor level in proliferating GC has not been established. Accordingly, we investigated the effect of EGF on [125I]iodo-FSH binding by porcine GC isolated from small follicles maintained in monolayer cultures. Relative to cells cultured in medium with insulin alone, EGF treatment increased total monolayer [125I]iodo-FSH binding (per culture) 120% (P less than 0.005). This was due to a 40-50% (P less than 0.01) increase in binding per U protein and/or per U cell and a 40-60% (P less than 0.005) increase in both monolayer cell and protein contents. EGF stimulated GC hyperplasia, but not hypertrophy. Optimum EGF doses for increased total monolayer [125I]iodo-FSH binding and binding normalized per U protein or cell were 0.5 and 0.1 ng/ml, respectively. Fibroblast growth factor was 20- to 100-fold less potent than EGF, and thrombin was without effect. Whereas [125I]iodo-FSH binding per U protein or cell was not affected by the serum concentration of the culture medium, the EGF effects on total monolayer binding and cell proliferation were directly related to the serum concentration (P less than 0.005). Thus, EGF-mediated increases in total monolayer [125I]iodo-FSH binding were paralleled by increases in cell number. The equilibrium dissociation constants (Kd) for [125I]iodo-FSH binding to cells cultured with and without EGF were 5.3 and 2.5 X 10(-10) M, respectively. Thus, EGF treatment significantly increased FSH receptor number, but significantly decreased receptor-binding affinity (P less than 0.05). Chronic FSH treatment during monolayer culture decreased total monolayer [125I]iodo-FSH binding and binding per U protein or per cell and attenuated EGF-stimulated cell proliferation, but markedly stimulated cell hypertrophy. Thus, concomitant treatment with EGF and FSH stimulated cell hypertrophy rather than hyperplasia. EGF and FSH each would appear capable of modulating the action of the other with respect to GC function. Our results indicate that EGF-mediated GC proliferation is associated with the expression of FSH-binding sites. This appears to be due to both an increase in FSH receptors among the cell population and an increase in the monolayer cell population.(ABSTRACT TRUNCATED AT 400 WORDS)
May, JV; Buck, PA; Schomberg, DW
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