Abstract
Insulin suppresses growth hormone expression and induces prolactin (PRL) biosynthesis in MtT/S cells cultured in a medium supplemented with normal sera. Incorporation of [ 35S]amino acids into immunoprecipitable PRL became detectable at 15 h of culture with insulin (500 ng/ml) and increased up to 48 h. Northern blot hybridization demonstrated a concurrent induction of PRL mRNA. However, insulin failed to induce PRL in a medium supplemented with steroid-depleted sera. Either pre- or cocultivation of cells with 10 pM to 10 nM 17β-estradiol (E 2), which did not induce PRL by itself, restored the insulin-mediated PRL biosynthesis in a dose-dependent manner. Diethylstilbestrol was as effective as E 2, whereas testosterone, progesterone and corticosterone were without effect. The E 2 action was partially suppressed by tamoxifen. These results suggest that estrogen is required for the insulin-mediated induction of PRL biosynthesis in MtT/S cells.
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