mSin3A Regulates Murine Erythroleukemia Cell Differentiation through Association with the TAL1 (or SCL) Transcription Factor

Abstract

Activation of the TAL1 (or SCL) gene is the most frequent gain-of-function mutation in T-cell acute lymphoblastic leukemia (T-ALL). TAL1 belongs to the basic helix-loop-helix (HLH) family of transcription factors that bind as heterodimers with the E2A and HEB/HTF4 gene products to a nucleotide sequence motif termed the E-box. Reported to act both as an activator and as a repressor of transcription, the mechanisms underlying TAL1-regulated gene expression are poorly understood. We report here that the corepressor mSin3A is associated with TAL1 in murine erythroleukemia (MEL) and human T-ALL cells. Interaction mapping showed that the basic-HLH domain of TAL1 was both necessary and sufficient for TAL1-mSin3A interaction. TAL1 was found, in addition, to interact with the histone deacetylase HDAC1 in vitro and in vivo, and a specific histone deacetylase inhibitor, trichostatin A (TSA), relieved TAL1-mediated repression of an E-box-containing promoter and a GAL4 reporter linked to a thymidine kinase minimal promoter. Further, TAL1 association with mSin3A and HDAC1 declined during dimethyl sulfoxide-induced differentiation of MEL cells in parallel with a decrease in mSin3A abundance. Finally, TSA had a synergistic effect with enforced TAL1 expression in stimulating MEL cells to differentiate, while constitutive expression of mSin3A inhibited MEL cell differentiation. These results demonstrate that a corepressor complex containing mSin3A and HDAC1 interacts with TAL1 and restricts its function in erythroid differentiation. This also has implications for this transcription factor's actions in leukemogenesis.

ACKNOWLEDGMENTS

We thank Scott Hiebert for many helpful discussions and for reviewing the manuscript; Bart Lutterbach and Rebecca Shattuck-Brandt for their suggestions on the manuscript; Yubin Shi for assistance with expression of GST fusion proteins; Robert Eisenman, Edward Seto, Garry Nolan, Arthur Nienhuis, Richard Baer, Scott Hiebert, Mark Koury, Maurice Bondurant, Roland Stein, and Sanford Krantz for providing reagents; and Victoria Richon for advice on purification of radiolabeled histones and HDAC assays.

This work was supported by National Institutes of Health grant R01 HL49118 (to S.J.B.), a Merit Review Award from the Department of Veterans Affairs (to S.J.B.), and an American Society of Hematology Fellow Scholar Award (to S.H.). Photomicroscopy was carried out in the Vanderbilt University Medical Center Imaging Resource supported by National Institutes of Health grants CA68485 and DK20593.