Abstract
Nuclear receptors (NRs) regulate gene transcription by recruiting coregulators, involved in chromatin remodeling and assembly of the basal transcription machinery. The NR-associated protein ligand-dependent corepressor (LCoR) has previously been shown to suppress hepatic lipogenesis by decreasing the binding of steroid receptor coactivators to thyroid hormone receptor. However, the role of LCoR in adipogenesis has not been established. Here, we show that LCoR expression is reduced in the early stage of adipogenesis in vitro LCoR overexpression inhibited 3T3-L1 adipocyte differentiation, whereas LCoR knockdown promoted it. Using an unbiased affinity purification approach, we identified CCAAT/enhancer-binding protein β (C/EBPβ), a key transcriptional regulator in early adipogenesis, and corepressor C-terminal binding proteins as potential components of an LCoR-containing complex in 3T3-L1 adipocytes. We found that LCoR directly interacts with C/EBPβ through its C-terminal helix-turn-helix domain, required for LCoR's inhibitory effects on adipogenesis. LCoR overexpression also inhibited C/EBPβ transcriptional activity, leading to inhibition of mitotic clonal expansion and transcriptional repression of C/EBPα and peroxisome proliferator-activated receptor γ2 (PPARγ2). However, LCoR overexpression did not affect the recruitment of C/EBPβ to the promoters of C/EBPα and PPARγ2 in 3T3-L1 adipocytes. Of note, restoration of PPARγ2 or C/EBPα expression attenuated the inhibitory effect of LCoR on adipogenesis. Mechanistically, LCoR suppressed C/EBPβ-mediated transcription by recruiting C-terminal binding proteins to the C/EBPα and PPARγ2 promoters and by modulating histone modifications. Taken together, our results indicate that LCoR negatively regulates early adipogenesis by repressing C/EBPβ transcriptional activity and add LCoR to the growing list of transcriptional corepressors of adipogenesis.
Highlights
Nuclear receptors (NRs) regulate gene transcription by recruiting coregulators, involved in chromatin remodeling and assembly of the basal transcription machinery
Similar to the ligand-dependent corepressor (LCoR) expression pattern that was observed during 3T3-L1 adipocyte differentiation, the mRNA levels of LCoR were reduced in the early stage and increased gradually afterward during the adipogenesis of stromal vascular fraction (SVF) cells (Fig. 1C)
In agreement with the current notion that C/EBP is recruited to the promoters of C/EBP␣ and peroxisome proliferator-activated receptor ␥2 (PPAR␥2) after adipogenic induction, we found that C/EBP was enriched in the promoter region of C/EBP␣ and peroxisome proliferator-activated receptor ␥ (PPAR␥)2 at 24 h after adipogenic induction (Fig. 5, A and B)
Summary
Nuclear receptors (NRs) regulate gene transcription by recruiting coregulators, involved in chromatin remodeling and assembly of the basal transcription machinery. The role of LCoR during early adipogenesis been shown to interact with transcriptional factor Krüppel-like factor 6 (KLF6) and repress KLF6 target gene transcription [8]. These findings suggest that different mechanisms are involved in the regulation of transcription by LCoR. As the master transcriptional regulators, peroxisome proliferator-activated receptor ␥ (PPAR␥) and CCAAT/enhancer-binding protein ␣ (C/EBP␣) control almost all of the genes involved in the morphological changes and lipid accumulation during adipocyte differentiation and lipid droplet formation. C/EBP and C/EBP␦, two transcription factors induced in the early stage of adipogenesis, play crucial roles in the initiation of the differentiation program by activating the expression of PPAR␥ and C/EBP␣, which leads to terminal adipogenic differentiation. Our results provided novel insights into the molecular mechanism involved in the regulation of early adipogenesis
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