HUMAN GROWTH-HORMONE AUGMENTATION OF EPIDERMAL GROWTH-FACTOR BINDING-SITES ON RAT GRANULOSA-CELLS

The effect of human GH (hGH) on the regulation of epidermal growth fac tor (EGF) receptor was investigated during differentiation of FSH-trea ted rat granulosa cells, which has been reported to be mediated by a c AMP-dependent mechanism. By measuring the binding of [I-125]iodo-EGF t o the intact cells, FSH was shown to cause increases in the number of EGF binding sites after culture for 72 h. When granulosa cells were cu ltured with hGH, the number of FSH-induced EGF binding sites was augme nted, with a half-maximal effect at about 10 mu g hGH/l and a maximal stimulatory concentration of 100 mu g/l. The stimulatory effect of hGH was absolutely dependent on insulin which by itself showed stimulator y effects on EGF binding sites. Scatchard analysis of EGF binding site s indicated that treatment with hGH increased the number of EGF bindin g sites (17 200 sites/cell after treatment with FSH; 31 700 sites/cell after FSH plus hGH), but did not alter the binding affinity. The augm entation was observed after culturing for 48 h and increased progressi vely with time, reaching 280% of the level after FSH treatment by 120 h. Although progesterone synthesis was increased by hGH, the markers o f cell differentiation such as cAMP synthesis and LH binding sites wer e suppressed, indicating hGH inhibition of the cAMP-mediated signal. T he action of hGH on the EGF binding sites was not accompanied by cell proliferation. These findings indicate that hGH has a novel action on the regulation of rat granulosa cell EGF binding sites and that the gr anulosa cell may possess both cAMP-dependent and -independent mechanis ms for expression of EGF binding sites.