TISSUE-SPECIFIC DISTRIBUTION OF A NOVEL C-TERMINAL TRUNCATION RETINOIC ACID RECEPTOR MUTANT WHICH ACTS AS A NEGATIVE REPRESSOR IN A PROMOTER-TYPE AND CELL-TYPE SPECIFIC MANNER

A cDNA clone which encodes a truncation form of the gamma subtype of t he retinoic acid receptor (RAR gamma) has been isolated. The mutant RA R gamma (RAR gamma Bm382) has lost its 65 C-terminal amino acids, thus truncating a part of the dimerization and activation domains. By usin g 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 Bm3 82 acts as a repressor of normal RARs in a promoter- and cell-type-spe cific manner. Transcription of beta RARE and TREinv promoters was inhi bited by RaR gamma Bm382 in both HeLa and F9 cells. Unlike these two p romoters, however, RAR gamma Bm382 did not inhibit transcription of th e TREpal promoter in HeLa cells but did so in F9 cells. Moreover, whil e transcription of the lamRARE promoter was inhibited by RAR gamma Bm3 82 in both HeLa and F9 tells, the inhibition was not observed when F9 cells were induced to differentiate with retinoic acid and dibutyryl c yclic AMP. DNA binding analysis revealed that RAR gamma Bm382 is able to form a heterodimer with the retinoid X receptor and bind to the dif ferent types of retinoic acid response elements with almost the same e fficiency as normal RAR. By comparison with effects of other truncatio n mutants created in vitro, it was suggested that the C-terminal end o f the ligand binding domain of RAR is crucial for determining the spec ificity of transactivation by RAR. Given these observations, we discus s the possibility that protein factors which mediate retinoic acid res ponse element- and cell-type-specific transactivation bg RAR are prese nt.