Silencing mediator for retinoid and thyroid hormone receptors (SMRT) – nuclear receptor complex (SMRT–NR complex)

The Silencing Mediator for Retinoid and Thyroid hormone receptors (SMRT), also known as Nuclear Receptor Corepressor 2 (NCOR2), is a critical transcriptional coregulator that forms complexes with various nuclear receptors to mediate gene silencing [1]. In the absence of ligands or the presence of antagonists, SMRT binds to the ligand-binding domain of nuclear receptors, such as the thyroid hormone receptor (TR) and retinoic acid receptor (RAR), and recruits a corepressor complex containing histone deacetylase 3 (HDAC3) [2]. This enzymatic activity leads to the deacetylation of histones, resulting in a compact, transcriptionally inactive chromatin structure [2]. The SMRT–nuclear receptor complex plays a pivotal role in human disease, most notably in Acute Promyelocytic Leukemia (APL), where the PML-RARα fusion protein abnormally recruits SMRT to repress genes essential for myeloid differentiation [3]. Additionally, SMRT levels and its interaction with the estrogen receptor are key determinants of the therapeutic response and resistance to tamoxifen in breast cancer patients [4]. Because of its central role in epigenetic regulation and hormone signaling, the SMRT–nuclear receptor complex is a significant target for developing HDAC inhibitors and selective nuclear receptor modulators [1, 2]. Sources: [1] UniProt (Q9Y6Q9); [2] Privalsky, M. L. (2004) Annu Rev Physiol; [3] Lin, R. J., et al. (1998) Nature; [4] Girault, I., et al. (2003) Clinical Cancer Research.

Other names

NCOR2-nuclear receptor complexNuclear receptor corepressor 2 complexTRAC-nuclear receptor complexT3 receptor-associating cofactor complexSMRT-HDAC3 complex

Recruitment of histone deacetylase 3 (HDAC3) and other chromatin-modifying enzymes to the promoter regions of target genes, leading to transcriptional silencing through histone deacetylation.