Role of PML and PML-RARα in Mad-mediated transcriptional repression

Fusion of the promyelocytic leukemia (PML) protein to the retinoic acid receptor-alpha (RAR alpha) generates the transforming protein of acute promyelocytic leukemias. PML appears to be involved in multiple functions, including apoptosis and transcriptional activation by RAR, whereas PML-RAR alpha blocks these functions of PML. However, the mechanisms of leukemogenesis by PML-RAR alpha remain elusive. Here we show that PML interacts with multiple corepressors (c-Ski, N-CoR, and mSin3A) and histone deacetylase 1, and that this interaction is required for transcriptional repression mediated by the tumor suppressor Mad. PML-RAR alpha has the two corepressor-interacting sites and inhibits Mad-mediated repression, suggesting that aberrant binding of PML-RAR alpha to the corepressor complexes may lead to abrogation of the corepressor function. These mechanisms may contribute to events leading to leukemogenesis.