SHARP1/DEC2 inhibits adipogenic differentiation by regulating the activity of C/EBP

Abstract

SHARP1, a basic helix-loop-helix transcription factor, is expressed in many cell types; however, the mechanisms by which it regulates cellular differentiation remain largely unknown. Here, we show that SHARP1 negatively regulates adipogenesis. Although expression of the early marker CCAAT/enhancer binding protein b (C/EBPb) is not altered, its crucial downstream targets C/EBPa and peroxisome proliferator-activated receptor c (PPARc) are downregulated by SHARP1. Protein interaction studies confirm that SHARP1 interacts with and inhibits the transcriptional activity of both C/EBPb and C/EBPa, and enhances the association of C/EBPb with histone deacetylase 1 (HDAC1). Consistently, in SHARP1-expressing cells, HDAC1 and the histone methyltransferase G9a are retained at the C/EBP regulatory sites on the C/EBPa and PPARc2 promoters during differentiation, resulting in inhibition of their expression. Interestingly, treatment with troglitazone results in displacement of HDAC1 and G9a, and rescues the differentiation defect of SHARP1-overexpressing cells. Our data indicate that SHARP1 inhibits adipogenesis through the regulation of C/EBP activity, which is essential for PPARc-ligand-dependent displacement of co-repressors from adipogenic promoters.

Differentiated Embryo Chondrocyte 1 (DEC1) Represses PPARγ2 Gene through Interacting with CCAAT/Enhancer Binding Protein β (C/EBPβ)

“…Although DEC1 prevents neither C/EBPβ nor RXR from binding to its target gene, DEC1 prevents bHLH domain containing transactivators such as BMAL1, MyoD and SREBP-1c, from binding to their target DNA by either protein-protein interaction or by directly binding to their responsive elements containing an E-box (Azmi et al, 2004;Choi et al, 2008;Li et al, 2004). Recently, Gulbagci et al demonstrated that DEC2, isoform of DEC1, also interacts with C/EBPβ and increases the recruitment of histone methyltransferase G9a to the promoter of PPARγ2 (Gulbagci et al, 2009). Our results suggested the fact that not only DEC2 but also DEC1 is involved in repression of PPARγ2 gene.…”

Small Ubiquitin-like Modifier (SUMO) Protein-specific Protease 1 De-SUMOylates Sharp-1 Protein and Controls Adipocyte Differentiation

“…Sharp-1, a member of the transcriptional repressor subfamily of basic helix-loop-helix transcription factors, has been shown to be one of the negative regulators in control of C/EBP and PPAR␥ activity. Taneja and co-workers (8) reported that Sharp-1, as a corepressor, inhibits C/EBP activity by retaining HDAC1 and G9a on the C/EBP␣ and PPAR␥2 promoter to inhibit PPAR␥ expression and adipogenesis. Furthermore, Sharp-1 has been shown to be a SUMOylated protein.…”

“…This medium was changed every 2 days until the end of differentiation. Oil Red O (Sigma) staining and quantification were performed as described previously (8).…”

“…However, this regulation is modulated by negative regulators such as Sharp-1, a member of the transcriptional repressor subfamily of basic helix-loop-helix transcription factors (7). Sharp-1 has been shown to be a corepressor to retain HDAC1 and G9a on the C/EBP␣ and PPAR␥2 promoter to inhibit PPAR␥ expression in adipogenesis (8). Sharp-1 has been reported to be a SUMOylated protein (21).…”

“…Sharp-1 binds to class B E-box sites with high affinity to repress the transcription of target genes and also associates with distinct corepressors, including HDAC1, SIRT1, and the histone methyltransferase G9a, to inhibit gene transcription (7). Taneja and co-workers (8) found that Sharp-1 interacts with and inhibits the transcriptional activity of both C/EBP␤ and C/EBP␣ by retaining HDAC1 and G9a at the C/EBP regulatory sites on the C/EBP␣ and PPAR␥2 promoters to inhibit their expression and, thus, adipogenesis, identifying Sharp-1 function as a negative regulator during adipogenesis.…”