Retinoic Acid Blocks Adipogenesis by Inhibiting C/EBPβ-Mediated Transcription

Abstract

Adipocyte differentiation is thought to involve sequential induction of the transcription factors C/EBP␤, peroxisome proliferator-activated receptor ␥ (PPAR␥), and C/EBP␣. C/EBP␣ expression is both necessary and sufficient for adipocyte differentiation. Here we report that ectopic expression of either C/EBP␣ or C/EBP␤ induces PPAR␥ expression and adipogenesis and that retinoic acid (RA) completely inhibits adipogenesis by either form of C/EBP. In studies of normal preadipocytes, RA does not prevent C/EBP␤ induction but blocks induction of PPAR␥, C/EBP␣, and adipogenesis. In transient transfection studies, liganded RA receptor (RAR) specifically blocks transcriptional activation by either C/EBP␣ or C/EBP␤. These results strongly suggest that C/EBP␣ substitutes for C/EBP␤ to induce adipocyte differentiation and that liganded RAR inhibits adipogenesis by blocking C/EBP␤-mediated induction of downstream genes.

Peroxisome Proliferator Activated Receptor γ, CCAAT/ Enhancer-binding Protein α, and Cell Cycle Status Regulate the Commitment to Adipocyte Differentiation

“…For experiments involving RA, retrovirally infected cells were studied in the following two protocols: 1) cells were maintained in the constant presence of 10 M RA from the time of infection and then exposed to the presence or absence of 1 M BRL49653 at day 0, or 2) cells were grown in the absence of RA until day 0 and then exposed to RA and various conditions. The first of these two conditions corresponds to that described previously (13).…”

“…Indeed, during normal 3T3-L1 differentiation, RA loses effectiveness at times when PPAR␥ and C/EBP␣ are simultaneously expressed in the cells (23). Since C/EBP␣ (13) and C/EBP␤ induce PPAR␥ (12, 13), we considered the possibility that PPAR␥ and C/EBP␣ may induce each other, leading after some time to a state that is refractory to RA inhibition of adipogenesis. To determine whether PPAR␥ is able to activate C/EBP␣ gene expression, L1-PPAR␥ cells were collected prior to differentiation and subjected to Western analysis.…”

“…Liganded RAR blocks C/EBPstimulated gene transcription, and RA also prevents adipogenesis due to ectopic expression of C/EBP␣ or -␤ (13). However, during normal adipogenesis RA exerts its inhibitory function only when added in the first 24 -48 h after exposure to differentiating stimuli that are applied postconfluence.…”

“…7). Enforced expression of PPAR␥ (8), C/EBP␣ (9 -11), or C/EBP␤ (10,12,13) stimulates adipogenesis in NIH 3T3 fibroblasts, suggesting the essential roles of these transcription factors in regulating adipogenesis. Furthermore, combined expression of PPAR␥ and C/EBP␣ has synergistic effects on promoting fat cell conversion in myoblasts (14).…”

JDP2 suppresses adipocyte differentiation by regulating histone acetylation

“…11 Once PPARg2 and C/EBPa have been activated, 'cross-talk' between PPARg2 and C/EBPa maintains the expression of each protein during adipocyte differentiation, even in the absence of C/EBPb and C/EBPd. 12,13 Jun dimerization protein 2 (JDP2) is a DNA-binding protein that forms homodimers or heterodimers with c-Jun, ATF2 and C/EBPg. [14][15][16] JDP2 can function not only as a transcriptional repressor but also as a coactivator in various types of cell, 15,[17][18][19][20] and it is involved in a variety of biological phenomena such as proliferation and differentiation of cells and apoptosis.…”