Cyclin D1 inhibits peroxisome proliferator-activated receptor gamma-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)gamma-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 PPARgamma function. Herein, murine embryonic fibroblast (MEF) differentiation by PPARgamma 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 PPARgamma-mediated adipogenesis. PPARgamma activity was enhanced in cyclin D1-/- cells. Reintroduction of cyclin D1 inhibited basal and ligand-induced PPARgamma activity and enhanced HDAC repression of PPARgamma 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 PPARgamma-mediated adipocyte differentiation through recruitment of HDACs to regulate PPAR response element local chromatin structure and PPARgamma function.     

Tight function zonula occludens-3 regulates cyclin D1-dependent cell proliferation

Coordinated regulation of cell proliferation is vital for epithelial tissue homeostasis, and uncontrolled proliferation is a hallmark of carcinogenesis. A growing body of evidence indicates that epithelial tight junctions (TJs) play a role in these processes, although the mechanisms involved are poorly understood. In this study, we identify and characterize a novel plasma membrane pool of cyclin D1 with cell-cycle regulatory functions. We have determined that the zonula occludens (ZO) family of TJ plaque proteins sequesters cyclin D1 at TJs during mitosis, through an evolutionarily conserved class II PSD-95, Dlg, and ZO-1 (PDZ)-binding motif within cyclin D1. Disruption of the cyclin D1/ZO complex through mutagenesis or siRNA-mediated suppression of ZO-3 resulted in increased cyclin D1 proteolysis and G(0)/G(1) cell-cycle retention. This study highlights an important new role for ZO family TJ proteins in regulating epithelial cell proliferation through stabilization of cyclin D1 during mitosis.     

Analysis of HDAC1-mediated regulation of Runx2-induced osteopontin gene expression in C3h10t1/2 cells

Histone deacetylases (HDACs) deacetylate lysine residues of histone and non-histone proteins and thereby regulate the cell-cycle, gene expression, and several other processes. We have analyzed the effects of HDAC1 on Runx2-mediated regulation of osteopontin (OPN) promoter activation and gene expression in mesenchymal progenitor C3h10t1/2 cells and show that co-expression of HDAC1 along with Runx2 results in down-regulation of Runx2-induced OPN mRNA expression during both the proliferation and differentiation stages of C3h10t1/2 cells. Luciferase assay results revealed that HDAC1 efficiently down-regulated Runx2-stimulated OPN promoter activity in a dose-dependent manner whereas TSA relieved the HDAC1-mediated repression and up-regulated the Runx2-induced OPN promoter activity and mRNA expression. In vivo HDAC1 co-localized and physically interacted with Runx2 and associated with the OPN promoter. Thus, HDAC1 not only plays a critical role in regulation of Runx2-stimulated expression of osteogenic genes, like OPN, but also regulate the proliferation and differentiation stages of mesenchymal progenitor cells, such as C3h10t1/2.