Thenumber signindicates a statistically significant difference from knocking down all three class II HDACs and the addition of transactivating factors (p< 0.05) over all other conditions.D, preadipocytes or adipocytes 6 days after differentiation were transiently transfected with either scrambled siRNA or HDAC-specific siRNA as indicated by +. class II histone deacetylase (HDAC) protein, HDAC5. We have tested this hypothesis by reducing the levels of class II HDACs in the nuclear compartment of 3T3-L1 preadipocytes using two experimental approaches. First, preadipocytes were treated with phenylephrine, an -adrenergic receptor agonist, to drive HDACS out of the nuclear compartment. Also, the class II HDAC concentrations were reduced using siRNA knockdown. In each case, reduction of nuclear class II HDAC concentration resulted in increased expression of endogenous GLUT4 mRNA in preadipocytes. Together, our data indicate that class II HDAC expression is the major regulatory mechanism for inhibiting GLUT4 expression in the predifferentiated state. Keywords:Adipocyte, Differentiation, Gene Regulation, Glucose Transport, Histone Deacetylase, GLUT4 == Introduction == The facilitative glucose transporter 4 (GLUT4)2is responsible, in part, for insulin-mediated glucose uptake in skeletal muscle, heart, and adipose tissues (1). Several studies have demonstrated that insulin-dependent glucose homeostasis is highly sensitive to changes in GLUT4 protein expression (24). GLUT4 expression is altered in different physiological and pathological states including fasting, insulin resistance, and type 2 diabetes (59). Therefore, it is of great importance to understand how GLUT4 is properly regulated to understand the significant changes that result in insulin resistance, and ultimately, type 2 diabetes. We have previously shown that the human GLUT4 promoter, when expressed in transgenic mice, is governed by twocis-acting domains: a MEF2-binding Valsartan domain (10) and Domain I (11,12). Using both transgenic and cultured cell models, we have shown that maximal GLUT4 transcriptional activation is achieved when MEF2 proteins are bound to the MEF2 domain and GLUT4 enhancer factor (GEF) is bound to Domain I (1012). GEF proteins form a complex with MEF2 Valsartan proteins that, in turn, serves as a binding site for other transcriptional mediators. It is well established that class II HDACs (HDAC4, HDAC5, HDAC7, and HDAC9) down-regulate MEF2 dependent gene transcription (1316). GLUT4, like other MEF2-dependent genes, is regulated by recruitment of the class II histone deacetylase, HDAC5 (17). The class II HDACs possess an N-terminal domain that has been found to mediate its interactions with other proteins, including the MEF2 proteins (13,14,18). We have shown that HDAC5 can also form a protein complex with GEF informing us of the molecular basis by which MEF2, GEF, and HDAC5 regulate the GLUT4 promoter (17). Several lines of evidence support the role of a class II HDAC, HDAC5, in transcriptional regulation of the GLUT4 promoter in adipocytes. First, it has been shown that constitutive localization of HDAC5 into the nucleus in cardiac tissue has resulted in a significant (3-fold) decrease in GLUT4 expression (19). Also, an increase in GLUT4 expression during exercise correlates with a decreased association between MEF2 and HDAC5, suggesting that HDAC5 mediates the repression of GLUT4 through MEF2 interactions (20). We have observed that the expression of HDAC5 during adipocyte differentiation is inversely correlated with GLUT4 expression (17). Usingin vitrotranscription assays, we have shown that HDAC5 specifically represses transcriptional activation of the GLUT4 promoter.In vivo, ChIP assays demonstrate that HDAC5 associates with the GLUT4 promoter in preadipocytes. In the current study, we tested the hypothesis that nuclear HDAC5 levels in preadipocytes are responsible for repression of GLUT4 gene transcription prior to differentiation. Using a variety of techniques to reduce nuclear HDAC expression, we were able to induce GLUT4 mRNA expression in preadipocytes, a state in which GLUT4 is not normally expressed, confirming that HDAC-mediated repression of the GLUT4 promoter is a major mechanism responsible for regulation of differentiation-dependent GLUT4 gene Rabbit Polyclonal to PPIF expression. == MATERIALS AND METHODS == == == == == == Cell Culture and Transfections == 3T3-L1 cells were maintained and transfected via electroporation as described previously (21). Briefly, 10-cm plates on day 5 after differentiation 3T3-L1 adipocytes or preadipocyte fibroblasts were washed with PBS and incubated in Valsartan trypsin/EDTA, PBS, and collagenase. The cells were resuspended and pelleted at 500 gfor 5 min. The cells were resuspended in DMEM containing 25 mmglucose. Five hundred microliters of cell suspension was transferred to a 0.4-cm electroporation cuvette (Bio-Rad), and 50 g of each of the indicated plasmids were added. Empty vector (pcDNA3) was used to normalize the total DNA added in all of the experiments. The cells were electroporated using a Gene Pulser II (Bio-Rad) at 0.18 kV and 950 microfarads. The cells were allowed to recover for 10 min at room temperature. Equivalent amounts of cell suspension and fresh media were added together and plated according to the intended experiment. COS-7 cells were transiently transfected using.
HDACs