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) 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.

Insulin and Sterol-regulatory Element-binding Protein-1c (SREBP-1C) Regulation of Gene Expression in 3T3-L1 Adipocytes

“…Two protein products are synthesized from the single C/EBP␤ messenger RNA: a transcriptionally active LAP form and a shorter naturally occurring dominant negative LIP that lacks the N-terminal transactivating domain of the protein. In agreement with the work of MacDougald et al (34), which first described the stimulatory effect of insulin on C/EBP␤, we observed a 4-fold stimulation in total C/EBP␤ content (LIP and LAP) in cells treated for 24 h with insulin. A similar effect, although of higher magnitude, was obtained by infection of the cell with Ad SREBP-1c, showing that SREBP-1c, like insulin, was able to increase the intracellular levels of C/EBP␤ proteins.…”

Adipocyte-specific Expression of Murine Resistin Is Mediated by Synergism between Peroxisome Proliferator-activated Receptor γ and CCAAT/Enhancer-binding Proteins

“…Furthermore, the presence of C/EBP␣ and C/EBP␤ in multiple complexes suggests that they may interact with these sites as both homo-and heterodimers. These data agree with earlier in vitro studies demonstrating that C/EBP isoforms are capable of binding to the same site as homo-and heterodimers in all intrafamilial combinations and that the majority of the binding activity in 3T3-L1 adipocytes is associated with C/EBP␣ and C/EBP␤ (59,60).…”

PPARγ and C/EBP factors orchestrate adipocyte biology via adjacent binding on a genome-wide scale

“…6B; Christy et al 1989;Park et al 2004). We hypothesized that this may be due to compensation by C/EBP␤, which has been reported to be present and active in differentiated adipocytes (MacDougald et al 1995). Indeed, ChIP-QPCR in mature adipocytes revealed C/EBP␤ binding to several newly discovered and previously known C/EBP targets (Supplemental Fig.…”