Effects of Estrogen and Epidermal Growth Factor on Prolactin and Pit-1 mRNA in GH 3 Cells

Abstract

The effects of epidermal growth factor (EGF) and 17β-estradiol (E₂) on the expression of prolactin (PRL), the transcription factor Pit-1/GHF-1 (Pit-1), and on dopamine D₂ receptor mRNA in GH₃ cells were analyzed by immunocytochemistry, in situ hybridization, and Northern analysis in a defined serum-free cell culture medium. Radioimmunoassay was used to determine PRL secretion. Both EGF and E₂ stimulated PRL mRNA and PRL secretion, although the effects of EGF were more rapid than those of E₂. Pit-1 mRNA levels were not significantly changed in spite of the 2- to 8-fold increases in PRL mRNA levels and significant increases in PRL secretion. Analysis of dopamine D2 receptor mRNA by in situ hybridization and Northern hybridization detected expression of dopamine receptor in GH₃ cells, but the receptor mRNA levels were not modified by EGF or E₂ treatment in complete serum or in serum-free media. These observations suggest that EGF and E₂ modulate PRL mRNA levels and PRL secretion significantly in vitro, while the mRNA levels of Pit-1 do not change significantly in GH₃ cells cultured in a defined culture medium.