E1A FUNCTIONS AS A COACTIVATOR OF RETINOIC ACID-DEPENDENT RETINOIC ACID RECEPTOR-BETA-2 PROMOTER ACTIVATION

The retinoic acid (RA) receptor (RAR) beta2 promoter is strongly activ ated by RA in embryonal carcinoma (EC) cells. We examined this activat ion in the P19 EC-derived END-2 cell line and in E1A-expressing counte rparts and found strong RA-dependent RARbeta2 promoter activation in t he E1A-expressing cells, which was not observed in the parental cell l ine, indicating a possible role for E1A in RARbeta2 activation. In tra nsient transfection assays, E1A functioned as a coactivator of RA-depe ndent RARbeta2 promoter activation and, moreover, was able to restore this activation in cells lacking RARbeta2 activation. By deletion anal ysis, two regions in the RARbeta2 promoter were identified that mediat e the stimulatory effect of E1A: the RA response element and TATA box- containing region and a more up-stream region between -180 and -63, in which a cAMP response element-related motif was identified as a targe t element for E1A. In addition, determination of endogenous E1A-like a ctivity by measuring E2A promoter activity in transient transfection a ssays in EC and differentiated cells revealed a correlation between RA -dependent RARbeta2 promoter activation and the presence of this activ ity, suggesting an important role for the cellular equivalent of E1A i n regulation of the RARbeta2 promoter.