Temporal Recruitment of Transcription Factors and SWI/SNF Chromatin-Remodeling Enzymes during Adipogenic Induction of the Peroxisome Proliferator-Activated Receptor γ Nuclear Hormone Receptor

Abstract

The peroxisome proliferator-activated receptor gamma (PPARγ) regulates adipogenesis, lipid metabolism, and glucose homeostasis, and roles have emerged for this receptor in the pathogenesis and treatment of diabetes, atherosclerosis, and cancer. We report here that induction of the PPARγ activator and adipogenesis forced by overexpression of adipogenic regulatory proteins is blocked upon expression of dominant-negative BRG1 or hBRM, the ATPase subunits of distinct SWI/SNF chromatin-remodeling enzymes. We demonstrate that histone hyperacetylation and the binding of C/EBP activators, polymerase II (Pol II), and general transcription factors (GTFs) initially occurred at the inducible PPARγ2 promoter in the absence of SWI/SNF function. However, the polymerase and GTFs were subsequently lost from the promoter in cells expressing dominant-negative SWI/SNF, explaining the inhibition of PPARγ2 expression. To corroborate these data, we analyzed interactions at the PPARγ2 promoter in differentiating preadipocytes. Changes in promoter structure, histone hyperacetylation, and binding of C/EBP activators, Pol II, and most GTFs preceded the interaction of SWI/SNF enzymes with the PPARγ2 promoter. However, transcription of the PPARγ2 gene occurred only upon subsequent association of SWI/SNF and TFIIH with the promoter. Thus, induction of the PPARγ nuclear hormone receptor during adipogenesis requires SWI/SNF enzymes to facilitate preinitiation complex function.

We are grateful to B. Spiegelman and S. Sif for providing reagents and to P. Pekala, R. Kingston, C. Peterson, and members of the Imbalzano and Peterson labs for suggestions, advice, and discussion.

This work was supported by the UMMS Diabetes Endocrine Research Center, by a Scholar Award from the Leukemia and Lymphoma Society, and by an NIH grant to A.N.I.