Regulation of parathyroid hormone-related protein gene expression in murine keratinocytes by E1A isoforms: a role for basal promoter and Ets-1 site.

PTHrP gene expression was evaluated in a murine keratinocyte line, Pam 212K, transformed with E1A and ras. We found that the 12S-E1A oncogene, with or without ras transformation, markedly reduced PTHrP mRNA expression. Using transient transfection assays, we found that the 12S isoform repressed activity from a 5'PTHrP-driven reporter gene. E1A-induced repression of PTHrP reporter constructs appears to be mediated by sequences within minimal promoter region. The 13S-E1A isoform did not repress PTHrP reporter gene activity, and a 13S-deletion mutant that lacked the repressor domains activated a subset of reporter constructs. Mutation of an Ets-1 binding site upstream of the basal promoter substantially decreased activation of reporter constructs by this 13S-deletion mutant. These findings suggest that the E1A oncoprotein may serve as a model for both activation and repression of PTHrP gene expression.