Insulin regulates transcription of the CCAAT/enhancer binding protein (C/EBP) α, β, and δ genes in fully-differentiated 3T3-L1 adipocytes

Abstract

The effect of insulin on expression of CCAAT/enhancer binding protein (C/EBP) α, β, and δ was investigated in fully-differentiated 3T3-L1 adipocytes. Treatment of adipocytes with insulin stimulated rapid dephosphorylation of C/EBPα, and repressed the expression of C/EBPα within 2-4 h, with >90% suppression occurring at 24 h. While insulin induced expression of C/EBPβ and C/EBPδ within 1 h and caused a >20-fold increase by 4 h, expression returned to nearly pretreatment levels by 24 h. The insulin concentration dependence of these effects was consistent with involvement of the insulin receptor. Gel shift analysis revealed that 6 h of insulin treatment decreased the binding of nuclear C/EBPα while increasing binding of nuclear C/EBPβ and C/EBPδ. The reciprocal effects of insulin on the steady-state levels of C/EBP transcription factors can be accounted for kinetically and quantitatively by changes in their mRNA levels, which can be accounted for by effects on gene transcription. The effects of insulin on adipocyte gene transcription (e.g. GLUT4) may be mediated, at least in part, by down-regulation of C/EBPα and/or its dephosphorylation.