RETINOIC ACID RECEPTORS AND MUSCLE B-HLH PROTEINS - PARTNERS IN RETINOID-INDUCED MYOGENESIS

The results reported here indicate that retinoic acid (RA) induces gro wth arrest and differentiation only in MyoD-expressing muscle cells. T ransient transfection assays reveal a functional interaction between M yoD, a key myogenic regulator and RA-receptors, principal mediators of RA actions, Interestingly, we demonstrate that RXR-MyoD-containing co mplexes are recruited at specific MyoD DNA-binding sites in muscle cel ls, Furthermore, we also demonstrate that RA-receptors and the muscle basic helix-loop-helix (b-HLH) proteins interact physically. Mutationa l analysis suggests that this interaction occurs via the basic region of muscle b-HLH proteins and the DIVA-binding domain of RA-receptors a nd is important for functional interactions between these two families of transcription factors. In conclusion, these results highlight nove l interactions between two distinct groups of regulatory proteins that influence cell growth and differentiation.