INDUCTION OF RETINOIC ACID RECEPTOR-BETA BY RETINOIC ACID IS CELL-SPECIFIC

The retinoic acid (RA) receptor-beta (RARbeta) gene is dramatically up-regulated by RA in F9 teratocarcinoma cells due to the presence of an RA-responsive element (RARE) in its promoter. Remarkably, however, RARbeta mRNA was essentially unaffected by RA in rat pituitary GH3 cells, even though the GH gene was induced by RA, and these cells express mRNAs specific for multiple RAR subtypes and for the potential RAR coactivators, retinoid X-receptors. The absence of RA induction of RARbeta was also observed in GH1 cells as well as in murine AtT20 pituitary cells and rat H35 hepatocarcinoma cells. The RA unresponsiveness of the RARbeta gene in GH3 and AtT20 cells was not due to a mutation in the RARE, which was identical to that in RA-responsive F9 cells. Furthermore, while AtT-20 and F9 cells both expressed multiple RARbeta isoforms, including RARbeta2, which was profoundly induced by RA in F9 cells, none of these was highly regulated by RA in AtT-20 cells. The failure of RA to induce RARbeta mRNA in certain murine and rat pituitary and nonpituitary cell lines indicates that target gene responsiveness to RA is cell type specific in some cases.