Although both promoter and enhancer sequences of the PRL gene 5'-flanking DNA are required for cell-specific, high level expression in transgenic animals, reports of the relative contributions of these elements determined in transient transfection experiments have varied. In this study we examined the transcriptional activities of proximal promoter (-422/+33) and distal enhancer (-1956/-1530) sequences of the rat (r) PRL gene by transient transfection of hybrid genes containing these sequences into two rat pituitary cell lines, GC and 235-1. These cell lines exhibit characteristics either of mammosomatotropes, which express both PRL and the evolutionarily related GH gene (GC), or lactotropes, which express only PRL (235-1). As lactotropes are thought to differentiate from a mammosomatotrope precursor cell, comparisons between these cell lines provide the opportunity to examine the mechanisms that activate PRL and GH genes during development. We show that the relative contributions of promoter and enhancer elements differ between GC and 235-1 cells. Although maximal enhancer-driven activity was similar between these cell lines, promoter sequences were more active in GC (5-10% maximal) than 235-1 cells (1-2% maximal). However, no apparent differences in factor binding to the rPRL promoter region could be correlated with differences in activity, suggesting that differential factor modification, rather than different factors, is involved. As the rGH promoter exhibited a similar pattern of activity in these cell lines, these observations suggest that promoter as well as enhancer elements contribute to the cell specificity of PRL and GH gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals DNA, Neoplasm