EPIDERMAL GROWTH-FACTOR INDUCES PROLACTIN MESSENGER-RNA IN GH4C1 CELLS VIA A PROTEIN SYNTHESIS-DEPENDENT PATHWAY

Prolactin (PRL) gene expression is regulated through a complex network of signal transduction pathways activated by various hormones and growth factors. Estrogens regulate PRL gene transcription in vivo through both direct and indirect, protein synthesis-dependent, mechanisms. Therefore, we hypothesized that other stimulators of PRL gene transcription might also act via protein synthesis-dependent mechanisms. To test this hypothesis, we examined, in GH4C1 rat pituitary tumor cells, the effects of protein synthesis inhibitors on the induction of PRL mRNA by known stimulators of PRL gene transcription. Whereas induction by epidermal growth factor (EGF) was abolished by cycloheximide and puromycin, increases in PRL mRNA caused by thyrotropin releasing hormone, 12-O-tetradecanoylphorbol 13-acetate, forskolin, or dibutyryl cyclic AMP were unaffected. These data suggest that the induction of PRL mRNA by EGF may require the induced synthesis of an intermediary regulatory protein.