DOWN-REGULATION OF RETINOIC ACID RECEPTOR ACTIVITY ASSOCIATED WITH DECREASED ALPHA-ISOFORM AND GAMMA-ISOFORM EXPRESSION IN F9 EMBRYONAL CARCINOMA-CELLS DIFFERENTIATED BY RETINOIC ACID

F9 embryonal carcinoma cells differentiate in response to retinoic aci d (RA). To investigate the regulation of RA receptors (RARs) expressio n during this process, cDNA probes specific for the major RAR isoforms were used. In contrast to the level of RARbeta2 mRNA which was high i n cells treated 5 days with RA and below detection in untreated cells as previously described, the steady state levels of RARalpha1, alpha2, gamma1, and gamma2 mRNAs were markedly decreased in the RA-differenti ated cells as compared to untreated cells. The down-regulation of the RA-responsive system in differentiated cells was also evident in gel s hift assays as a marked decrease in binding capacity to a retinoid aci d response element (beta2RARE), as well as in chloramphenicol acetyltr ansferase (CAT) assays as a sixfold decrease in RA-mediated transactin g activity via this element. The down-regulation of RAR DNA-binding an d transacting activity coincided with the burst in tissue plasminogen activator secretion and thus, occurred at the hinge between early and late differentiation. The down-regulation of RA responsiveness may con stitute an important event in the transition between early and late di fferentiation stage in F9 cells. (C) 1993 Wiley-Liss, Inc.