Brd2 Inhibits Adipogenesis via the ERK1/2 Signaling Pathway in 3T3-L1 Adipocytes

Abstract

Bromodomain-containing protein 2 (Brd2) is a nuclear serine/threonine kinase involved in transcriptional regulation. In 3T3-L1 adipocytes, Brd2 normally co-represses PPARγ (peroxisome proliferator-activated receptor gamma) and inhibits adipogenesis. Here, we show that Brd2 over-expression in preadipocytes inhibits their differentiation into adipocytes, while Brd2 knockdown promotes adipogenic differentiation in vitro and forces cells to undergo adipogenesis independent of the MDI (methyisobutylxanthane, dexamethasone and insulin) induction. In this study, the two key transcription factors for adipogenesis, PPARγ and C/EBPα (CCAAT/enhancer binding protein-α) were persistently expressed during the differentiation of preadipocytes to mature adipocytes in Brd2 knockdown 3T3-L1 cells, but their expression was inhibited in cells in which Brd2 was overexpressed. To investigate the role of Brd2 in signal transduction we examined the expression of several signaling molecules involved in the regulation of gene expression and cell differentiation by immunoblotting assay. Down-regulation of Brd2 expression in 3T3-L1 cells led to a decrease in extracellular signal-regulated kinase1/2 (ERK1/2) activity and, conversely, the up-regulation of Brd2 leads to increase in ERK1/2 phosphorylation. Nevertheless, changes in Brd2 expression do not affect the activities of JNK and p38 MAPK. In addition, the phosphorylation of Rafs is not affected by changes in Brd2 expression in 3T3-L1 cells. MEK inhibitor UO126 partly restores differentiation of 3T3-L1 cells that overexpress Brd2. In conclusion, these results indicate that Brd2 regulates ERK1/2 activity independently of Raf signaling in 3T3-L1 adipocytes.

The suppression of bromodomain and extra‐terminal domain inhibits vascular inflammation by blocking NF‐κB and MAPK activation

“…In this study, we found that treatment with the BET inhibitor JQ1 or specific shRNA for Brd2 or Brd4 reduced the TNFα‐induced activation of p38 and JNK, but not ERK in HUVECs, suggesting the effects of BET bromodomain on endothelial inflammation are mediated by the activation of p38 and JNK. However, in contrast to our findings, a recent study showed that Brd2 is involved in regulating ERK1/2 phosphorylation but does not affect the activities of JNK and p38MAPK in 3T3‐L1 cells (Zang et al, ). This suggests a the effects of BET bromodomain on the MAPK pathway are cell type‐specific.…”

Bromodomain and extra-terminal domain (BET) proteins regulate melanocyte differentiation

“…Our studies determined that both BRD4 and BRD2 are required for expression of two critical melanogenic genes, Tyr and Tyrp1, indicating a role for both BRD2 and BRD4 in melanocyte differentiation. Similarly, BRD2 and BRD4 are required for erythroid gene activation [48], but play opposing roles during adipogenesis [46,47,62].…”

I-BET151 selectively regulates IL-6 production

“…These actions of I-BET151 may be particularly due to its interaction with BRD4, although it also binds other BRD proteins, because as described in Belkina et al, 2013, BRD4 does not bind to the promoter of TNFα, and we found no change in the production of TNF in the presence of I-BET151, suggesting that I-BET151 may preferentially regulate BRD4 to also inhibit IL-6 production. As suggested by Zang et al 2013, signal transduction may also regulate the actions of the BET proteins through kinase cascades.…”