Retinoic acid induces proteasome-dependent degradation of retinoic acid receptor alpha (RARalpha) and oncogenic RARalpha fusion proteins.

Analyzing the pathways by which retinoic acid (RA) induces promyelocytic leukemia/retinoic acid receptor alpha (PML/RARalpha) catabolism in acute promyelocytic leukemia (APL), we found that, in addition to caspase-mediated PML/RARalpha cleavage, RA triggers degradation of both PML/RARalpha and RARalpha. Similarly, in non-APL cells, RA directly targeted RARalpha and RARalpha fusions to the proteasome degradation pathway. Activation of either RARalpha or RXRalpha by specific agonists induced degradation of both proteins. Conversely, a mutation in RARalpha that abolishes heterodimer formation and DNA binding, blocked both RARalpha and RXRalpha degradation. Mutations in the RARalpha DNA-binding domain or AF-2 transcriptional activation region also impaired RARalpha catabolism. Hence, our results link transcriptional activation to receptor catabolism and suggest that transcriptional up-regulation of nuclear receptors by their ligands may be a feedback mechanism allowing sustained target-gene activation.