Silencing mediator for retinoid and thyroid hormone receptors (SMRT) interaction with Promyelocytic leukemia-Retinoic acid receptor alpha (PML-RARα) (SMRT/PML-RARα interaction)

The interaction between the Silencing Mediator for Retinoid and Thyroid Hormone Receptors (SMRT, also known as NCOR2) and the Promyelocytic Leukemia-Retinoic Acid Receptor alpha (PML-RARα) fusion protein is a central molecular driver of Acute Promyelocytic Leukemia (APL) (Grignani et al., 1998). Under physiological conditions, SMRT acts as a corepressor that binds to Retinoic Acid Receptor alpha (RARα) and Thyroid Hormone Receptor (T3R) to recruit histone deacetylases (HDACs), maintaining genes in a transcriptionally silent state in the absence of ligands (Lin et al., 1998). In APL, the PML-RARα fusion protein binds SMRT with significantly higher affinity than wild-type receptors, resulting in the constitutive repression of genes required for myeloid cell maturation (UniProt: Q9Y6Q9). This interaction effectively blocks the differentiation of hematopoietic progenitor cells, leading to the accumulation of malignant promyelocytes. Therapeutic agents like All-trans retinoic acid (ATRA) and Arsenic trioxide (ATO) target this interaction by inducing conformational changes or degradation of the fusion protein, which triggers the release of the SMRT complex (Glass & Rosenfeld, 2000). The subsequent recruitment of transcriptional coactivators restores the expression of differentiation-related genes, allowing the leukemic cells to mature and eventually undergo apoptosis. Clinical challenges include the development of resistance mutations in the receptor's ligand-binding domain that prevent SMRT dissociation despite drug treatment (Zhu et al., 2001).

Other names

NCOR2-PML-RARA complexSMRT-RARα-T3R interactionNuclear receptor corepressor 2 interactionSMRT-HDAC complex recruitmentSilencing mediator for retinoid and thyroid hormone receptors

Ligand-induced dissociation of the SMRT/NCOR2 corepressor complex from the PML-RARα or RARα/T3R receptors, facilitating the recruitment of histone acetyltransferases (HATs) and transcriptional coactivators to restore gene expression (Glass & Rosenfeld, 2000; Lin et al., 1998).