Class II Histone Deacetylases Limit GLUT4 Gene Expression during Adipocyte Differentiation

Insulin-dependent glucose homeostasis is highly sensitive to the levels of insulin-responsive glucose transporter 4 (GLUT4) expression in adipocytes. The level of GLUT4 protein expression is highly dependent on the rate of GLUT4 gene transcription. GLUT4 gene transcription is decreased in a variety of physiologic states of insulin resistance including type 2 diabetes, obesity, and prolonged fasting. GLUT4 gene expression in adipocytes is differentiation-dependent, with full expression delayed until late in the differentiation program. In this paper, we have tested the hypothesis that differentiation-dependent GLUT4 gene expression in 3T3-L1 adipocytes is dependent on the nuclear concentration of a 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 alpha-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.