Tissue-specific distribution of a novel C-terminal truncation retinoic acid receptor mutant which acts as a negative repressor in a promoter- and cell-type-specific manner.

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A cDNA clone which encodes a truncation form of the gamma subtype of the retinoic acid receptor (RAR gamma) has been isolated. The mutant RAR gamma (RAR gamma Bm382) has lost its 65 C-terminal amino acids, thus truncating a part of the dimerization and activation domains. By using a reverse transcription-coupled PCR technique, it was shown that RAR gamma Bm382 is expressed at different levels in various mouse tissues and that the level of its expression does not correlate with that of normal RAR gamma B. Cotransfection studies revealed that RAR gamma Bm382 acts as a repressor of normal RARs in a promoter- and cell-type-specific manner. Transcription of beta RARE and TREinv promoters was inhibited by RAR gamma Bm382 in both HeLa and F9 cells. Unlike these two promoters, however, RAR gamma Bm382 did not inhibit transcription of the TREpal promoter in HeLa cells but did so in F9 cells. Moreover, while transcription of the lamRARE promoter was inhibited by RAR gamma Bm382 in both HeLa and F9 cells, the inhibition was not observed when F9 cells were induced to differentiate with retinoic acid and dibutyryl cyclic AMP. DNA-binding analysis revealed that RAR gamma Bm382 is able to form a heterodimer with the retinoid X receptor and bind to the different types of retinoic acid response elements with almost the same efficiency as normal RAR. By comparison with effects of other truncation mutants created in vitro, it was suggested that the C-terminal end of the ligand binding domain of RAR is crucial for determining the specificity of transactivation by RAR. Given these observations, we discuss the possibility that protein factors which mediate retinoic acid response element- and cell-type-specific transactivation by RAR are present.

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