Fra-1: a novel target for retinoid action

Using a cDNA gene expression array system, we identified fra-1 as a novel target molecule for retinoid action in the human pancreatic carcinoma cell line Dan-G. Retinoid treatment resulted in a significant and time-dependent induction of the fra-1 expression on the post-transcriptional level. Supershift assays revealed that fra-1 participates in the activator protein 1 complex together with c-fos, c-jun and junB. Transient transfection experiments using a reporter plasmid containing an activator protein site upstream of the CAT reporter gene revealed that the phorbolester-induced CAT activity was suppressed by retinoids. Since fra-1 lacks a transactivation function, we therefore suggest that the retinoid-mediated induction of fra-1 might function as a negative regulator of the activator protein 1 activity in human pancreatic carcinoma cells.