THE EFFECTS OF EPIDERMAL GROWTH-FACTOR TRANSFORMING-GROWTH-FACTOR-ALPHA ON THE EXPRESSION OF PLACENTAL-LACTOGEN-I AND PLACENTAL-LACTOGEN-IIMESSENGER-RNAS IN A RAT CHORIOCARCINOMA CELL-LINE

Pregnancy in the rat and mouse is characterized by a developmental swi tch in expression at midgestation between the related placental lactog ens 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 experiment s which investigate the effects of EGF and TGF alpha on rPLI and rPLII mRNA levels in the rat choriocarcinoma cell line, Rcho. This cell lin e has been widely used as a model system for studying genes expressed in the rodent placental giant cell. We find that in these cultures bot h growth factors produce a two fold increase in endogenous rPLI mRNA l evels, and a two fold decrease in rPLII mRNA levels. Using DNA transfe ction assays we have tested the effects of TGF alpha on the expression of hybrid rPLI and rPLII 5'flanking/luciferase reporter constructs in Rcho cells. The transfected rPLI/luciferase reporter constructs produ ce a similar two fold increase in reporter expression to that seen for the endogenous mRNA, suggesting that EGF/TGF alpha positively regulat e rPLI mRNA levels by effects on gene transcription. Unlike the endoge nous gene, however, the rPLII/ luciferase constructs show a five fold increase in rPLII-directed luciferase expression in the presence of TG F alpha. The effect of EGF/TGF alpha on placental rPLII mRNA levels ap pears to involve negative response element(s) located elsewhere in the gene to those regions tested.