Cyclin D1 inhibits peroxisome proliferator-activated receptor γ-mediated adipogenesis through histone deacetylase recruitment

The cyclin D1 gene encodes the labile serum-inducible regulatory subunit of a holoenzyme that phosphorylates and inactivates the retinoblastoma protein. Overexpression of cyclin D1 promotes cellular proliferation and normal physiological levels of cyclin D1 function to inhibit adipocyte differentiation in vivo. We have previously shown that cyclin D1 inhibits peroxisome proliferator-activated receptor (PPAR)γ-dependent activity through a cyclin-dependent kinase- and retinoblastoma protein-binding-independent mechanism. In this study, we determined the molecular mechanism by which cyclin D1 regulated PPARγ function. Herein, murine embryonic fibroblast (MEF) differentiation by PPARγ ligand was associated with a reduction in histone deacetylase (HDAC1) activity. Cyclin D1^-/- MEFs showed an increased propensity to undergo differentiation into adipocytes. Genetic deletion of cyclin D1 reduced HDAC1 activity. Reconstitution of cyclin D1 into the cyclin D1^-/- MEFs increased HDAC1 activity and blocked PPARγ-mediated adipogenesis. PPARγ activity was enhanced in cyclin D1^-/- cells. Reintroduction of cyclin D1 inhibited basal and ligand-induced PPARγ activity and enhanced HDAC repression of PPARγ activity. Cyclin D1 bound HDAC in vivo and preferentially physically associated with HDAC1, HDAC2, HDAC3, and HDAC5. Chromatin immunoprecipitation assay demonstrated that cyclin D1 enhanced recruitment of HDAC1 and HDAC3 and histone methyltransferase SUV39H1 to the PPAR response element of the lipoprotein lipase promoter and decreased acetylation of total histone H3 and histone H3 lysine 9. Collectively, these studies suggest an important role of cyclin D1 in regulation of PPARγ-mediated adipocyte differentiation through recruitment of HDACs to regulate PPAR response element local chromatin structure and PPARγ function.