MacDougald O A, Cornelius P, Liu R, Lane M D
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
J Biol Chem. 1995 Jan 13;270(2):647-54. doi: 10.1074/jbc.270.2.647.
The effect of insulin on expression of CCAAT/enhancer binding protein (C/EBP) alpha, beta, and delta was investigated in fully-differentiated 3T3-L1 adipocytes. Treatment of adipocytes with insulin stimulated rapid dephosphorylation of C/EBP alpha, and repressed the expression of C/EBP alpha within 2-4 h, with > 90% suppression occurring at 24 h. While insulin induced expression of C/EBP beta and C/EBP delta 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/EBP alpha while increasing binding of nuclear C/EBP beta and C/EBP delta. 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/EBP alpha and/or its dephosphorylation.
在完全分化的3T3-L1脂肪细胞中研究了胰岛素对CCAAT/增强子结合蛋白（C/EBP）α、β和δ表达的影响。用胰岛素处理脂肪细胞可刺激C/EBPα快速去磷酸化，并在2 - 4小时内抑制C/EBPα的表达，24小时时抑制率超过90%。虽然胰岛素在1小时内诱导C/EBPβ和C/EBPδ的表达，4小时时使其增加超过20倍，但到24小时时表达又回到接近预处理水平。这些效应的胰岛素浓度依赖性与胰岛素受体的参与一致。凝胶迁移分析显示，胰岛素处理6小时可降低核C/EBPα的结合，同时增加核C/EBPβ和C/EBPδ的结合。胰岛素对C/EBP转录因子稳态水平的相反作用在动力学和定量上可由其mRNA水平的变化来解释，而mRNA水平的变化又可由对基因转录的影响来解释。胰岛素对脂肪细胞基因转录（如GLUT4）的影响可能至少部分是由C/EBPα的下调和/或其去磷酸化介导的。
