Activation of p53 Transcriptional Activity by SMRT: a Histone Deacetylase 3-Independent Function of a Transcriptional Corepressor

Abstract

The silencing mediator of retinoic acid and thyroid hormone receptors (SMRT) is an established histone deacetylase 3 (HDAC3)-dependent transcriptional corepressor. Microarray analyses of MCF-7 cells transfected with control or SMRT small interfering RNA revealed SMRT regulation of genes involved in DNA damage responses, and the levels of the DNA damage marker γH2AX as well as poly(ADP-ribose) polymerase cleavage were elevated in SMRT-depleted cells treated with doxorubicin. A number of these genes are established p53 targets. SMRT knockdown decreased the activity of two p53-dependent reporter genes as well as the expression of p53 target genes, such as CDKN1A (which encodes p21). SMRT bound directly to p53 and was recruited to p53 binding sites within the p21 promoter. Depletion of GPS2 and TBL1, components of the SMRT corepressor complex, but not histone deacetylase 3 (HDAC3) decreased p21-luciferase activity. p53 bound to the SMRT deacetylase activation domain (DAD), which mediates HDAC3 binding and activation, and HDAC3 could attenuate p53 binding to the DAD region of SMRT. Moreover, an HDAC3 binding-deficient SMRT DAD mutant coactivated p53 transcriptional activity. Collectively, these data highlight a biological role for SMRT in mediating DNA damage responses and suggest a model where p53 binding to the DAD limits HDAC3 interaction with this coregulator, thereby facilitating SMRT coactivation of p53-dependent gene expression.

ACKNOWLEDGMENTS

We thank Lawrence Donehower, Mitchell Lazar, and Mengtao Li for providing plasmids and gratefully acknowledge the technical support of Cheryl Parker.

S.K. was supported by a postdoctoral fellowship award (PDF 0707868) from the Susan G. Komen for the Cure Foundation. This work was supported, in part, by the Genomic and RNA Profiling Core at the Baylor College of Medicine with funding from an NIH NCI grant (P30CA125123) and the expert assistance of Lisa D. White and by Public Health Service grant DK53002 to C.L.S. from the National Institute of Diabetes and Digestive and Kidney Diseases.