Identification and Characterization of SAP25, a Novel Component of the mSin3 Corepressor Complex

Abstract

The transcriptional corepressor mSin3 is associated with histone deacetylases (HDACs) and is utilized by many DNA-binding transcriptional repressors. We have cloned and characterized a novel mSin3A-binding protein, SAP25. SAP25 binds to the PAH1 domain of mSin3A, associates with the mSin3A-HDAC complex in vivo, and represses transcription when tethered to DNA. SAP25 is required for mSin3A-mediated, but not N-CoR-mediated, repression. SAP25 is a nucleocytoplasmic shuttling protein, actively exported from the nucleus by a CRM1-dependent mechanism. A fraction of SAP25 is located in promyelocytic leukemia protein (PML) nuclear bodies, and PML induces a striking nuclear accumulation of SAP25. An isotope-coded affinity tag quantitative proteomic analysis of the SAP25 complex revealed that SAP25 is associated with several components of the mSin3 complex, nuclear export machinery, and regulators of transcription and cell cycle. These results suggest that SAP25 is a novel core component of the mSin3 corepressor complex whose subcellular location is regulated by PML.

We thank Yoshiro Maru, Ed Seto, and Roel van Driel for antibodies and Shaun Cowley for estrogen receptor constructs. We are grateful to Ishwar Radhakrishnan for discussions and prepublication information.

This work was supported by NIH grant R37CA057138 (R.N.E.); by federal funding from the National Heart, Blood, and Lung Institute under contract N01-HV-28179 (R.A.); by the NCI-Japanese Foundation for Cancer Research Training Program in the U.S.-Japan Cooperative Cancer Committee (Y.S.); by the Interdisciplinary Research Training Fellowship from the Fred Hutchinson Cancer Research Center (Y.S.); and by a gift from Merck and Co. to the ISB. R.N.E. is a Research Professor of the American Cancer Society.