The effects of epidermal growth factor/transforming growth factor alpha on the expression of placental lactogen I and II mRNAs in a rat choriocarcinoma cell line.

Pregnancy in the rat and mouse is characterized by a developmental switch in expression at midgestation between the related placental lactogens I and II (PLI, PLII) suggesting that these proteins have important but different roles. The factors that control this differential gene expression are poorly understood. In this paper we describe experiments which investigate the effects of EGF and TGFalpha on rPLI and rPLII mRNA levels in the rat choriocarcinoma cell line, Rcho. This cell line has been widely used as a model system for studying genes expressed in the rodent placental giant cell. We find that in these cultures both growth factors produce a two fold increase in endogenous rPLI mRNA levels, and a two fold decrease in rPLII mRNA levels. Using DNA transfection assays we have tested the effects of TGFalpha on the expression of hybrid rPLI and rPLII 5'flanking/luciferase reporter constructs in Rcho cells. The transfected rPLI/luciferase reporter constructs produce a similar two fold increase in reporter expression to that seen for the endogenous mRNA, suggesting that EGF/TGFalpha positively regulate rPLI mRNA levels by effects on gene transcription. Unlike the endogenous gene, however, the rPLII/ luciferase constructs show a five fold increase in rPLII-directed luciferase expression in the presence of TGFalpha. The effect of EGF/TGFalpha on placental rPLII mRNA levels appears to involve negative response element(s) located elsewhere in the gene to those regions tested.