scholarly journals Alternative Mechanisms by Which Mediator Subunit MED1/TRAP220 Regulates Peroxisome Proliferator-Activated Receptor γ-Stimulated Adipogenesis and Target Gene Expression

2007 ◽  
Vol 28 (3) ◽  
pp. 1081-1091 ◽  
Author(s):  
Kai Ge ◽  
Young-Wook Cho ◽  
Hong Guo ◽  
Teresa B. Hong ◽  
Mohamed Guermah ◽  
...  
Keyword(s):  
Gene Expression ◽  
Rna Polymerase Ii ◽  
Nuclear Receptor ◽  
Transcriptional Activity ◽  
Target Gene ◽  
Molecular Mechanisms ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Cultured Fibroblasts ◽  
Target Gene Expression

ABSTRACT Mediator is a general coactivator complex connecting transcription activators and RNA polymerase II. Recent work has shown that the nuclear receptor-interacting MED1/TRAP220 subunit of Mediator is required for peroxisome proliferator-activated receptor γ (PPARγ)-stimulated adipogenesis of mouse embryonic fibroblasts (MEFs). However, the molecular mechanisms remain undefined. Here, we show an intracellular PPARγ-Mediator interaction that requires the two LXXLL nuclear receptor recognition motifs on MED1/TRAP220 and, furthermore, we show that the intact LXXLL motifs are essential for optimal PPARγ function in a reconstituted cell-free transcription system. Surprisingly, a conserved N-terminal region of MED1/TRAP220 that lacks the LXXLL motifs but gets incorporated into Mediator fully supports PPARγ-stimulated adipogenesis. Moreover, in undifferentiated MEFs, MED1/TRAP220 is dispensable both for PPARγ-mediated target gene activation and for recruitment of Mediator to a PPAR response element on the aP2 target gene promoter. However, PPARγ shows significantly reduced transcriptional activity in cells deficient for a subunit (MED24/TRAP100) important for the integrity of the Mediator complex, indicating a general Mediator requirement for PPARγ function. These results indicate that there is a conditional requirement for MED1/TRAP220 and that a direct interaction between PPARγ and Mediator through MED1/TRAP220 is not essential either for PPARγ-stimulated adipogenesis or for PPARγ target gene expression in cultured fibroblasts. As Mediator is apparently essential for PPARγ transcriptional activity, our data indicate the presence of alternative mechanisms for Mediator recruitment, possibly through intermediate cofactors or other cofactors that are functionally redundant with MED1/TRAP220.

scholarly journals MED14 Tethers Mediator to the N-Terminal Domain of Peroxisome Proliferator-Activated Receptor γ and Is Required for Full Transcriptional Activity and Adipogenesis

2010 ◽  
Vol 30 (9) ◽  
pp. 2155-2169 ◽  
Author(s):  
Lars Grøntved ◽  
Maria S. Madsen ◽  
Michael Boergesen ◽  
Robert G. Roeder ◽  
Susanne Mandrup
Keyword(s):  
Rna Polymerase Ii ◽  
Transcriptional Activity ◽  
Target Gene ◽  
Target Genes ◽  
Gene Activation ◽  
Proximal Promoter ◽  
Peroxisome Proliferator ◽  
Independent Manner ◽  
Peroxisome Proliferator Activated Receptor ◽  
Terminal Domain

ABSTRACT The Mediator subunit MED1/TRAP220/DRIP205/PBP interacts directly with many nuclear receptors and was long thought to be responsible for tethering Mediator to peroxisome proliferator-activated receptor (PPAR)-responsive promoters. However, it was demonstrated recently that PPARγ can recruit Mediator by MED1-independent mechanisms. Here, we show that target gene activation by ectopically expressed PPARγ and PPARα is independent of MED1. Consistent with this finding, recruitment of PPARγ, MED6, MED8, TATA box-binding protein (TBP), and RNA polymerase II (RNAPII) to the enhancer and proximal promoter of the PPARγ target gene Fabp4 is also independent of MED1. Using a small interfering RNA (siRNA)-based approach, we identify MED14 as a novel critical Mediator component for PPARγ-dependent transactivation, and we demonstrate that MED14 interacts directly with the N terminus of PPARγ in a ligand-independent manner. Interestingly, MED14 knockdown does not affect the recruitment of PPARγ, MED6, and MED8 to the Fabp4 enhancer but does reduce their occupancy of the Fabp4 proximal promoter. In agreement with the necessity of MED14 for PPARγ transcriptional activity, we show that knockdown of MED14 impairs adipogenesis of 3T3-L1 cells. Thus, MED14 constitutes a novel anchoring point between Mediator and the N-terminal domain of PPARγ that is necessary for functional PPARγ-mediated recruitment of Mediator and transactivation of PPARγ subtype-specific target genes.

Interleukin enhancer-binding factor 3 functions as a liver receptor homologue-1 co-activator in synergy with the nuclear receptor co-activators PRMT1 and PGC-1α

2011 ◽  
Vol 437 (3) ◽  
pp. 531-540 ◽  
Author(s):  
Masae Ohno ◽  
Jun Komakine ◽  
Eiko Suzuki ◽  
Makoto Nishizuka ◽  
Shigehiro Osada ◽  
...  
Keyword(s):  
Gene Expression ◽  
Nuclear Receptor ◽  
Transcriptional Control ◽  
Molecular Mechanisms ◽  
Target Genes ◽  
Peroxisome Proliferator ◽  
Gene Encoding ◽  
Peroxisome Proliferator Activated Receptor ◽  
Binding Factor ◽  
Protein Arginine Methyltransferase 1

LRH-1 (liver receptor homologue-1), a transcription factor and member of the nuclear receptor superfamily, regulates the expression of its target genes, which are involved in bile acid and cholesterol homoeostasis. However, the molecular mechanisms of transcriptional control by LRH-1 are not completely understood. Previously, we identified Ku80 and Ku70 as LRH-1-binding proteins and reported that they function as co-repressors. In the present study, we identified an additional LRH-1-binding protein, ILF3 (interleukin enhancer-binding factor 3). ILF3 formed a complex with LRH-1 and the other two nuclear receptor co-activators PRMT1 (protein arginine methyltransferase 1) and PGC-1α (peroxisome proliferator-activated receptor γ co-activator-1α). We demonstrated that ILF3, PRMT1 and PGC-1α were recruited to the promoter region of the LRH-1-regulated SHP (small heterodimer partner) gene, encoding one of the nuclear receptors. ILF3 enhanced SHP gene expression in co-operation with PRMT1 and PGC-1α through the C-terminal region of ILF3. In addition, we found that the small interfering RNA-mediated down-regulation of ILF3 expression led to a reduction in the occupancy of PGC-1α at the SHP promoter and SHP expression. Taken together, our results suggest that ILF3 functions as a novel LRH-1 co-activator by acting synergistically with PRMT1 and PGC-1α, thereby promoting LRH-1-dependent gene expression.

Disruption of transforming growth factor-β signaling by curcumin induces gene expression of peroxisome proliferator-activated receptor-γ in rat hepatic stellate cells

2007 ◽  
Vol 292 (1) ◽  
pp. G113-G123 ◽  
Author(s):  
Shizhong Zheng ◽  
Anping Chen
Keyword(s):  
Gene Expression ◽  
Hepatic Stellate Cells ◽  
Molecular Mechanisms ◽  
Transforming Growth Factor ◽  
Gene Promoter ◽  
Stellate Cells ◽  
Transforming Growth Factor Β ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Ppar Γ

Activation of hepatic stellate cells (HSC), the major effectors of hepatic fibrogenesis, is coupled with sequential alterations in gene expression, including an increase in receptors for transforming growth factor-β (TGF-β) and a dramatic reduction in the peroxisome proliferator-activated receptor-γ (PPAR-γ). The relationship between them remains obscure. We previously demonstrated that curcumin induced gene expression of PPAR-γ in activated HSC, leading to reducing cell proliferation, inducing apoptosis and suppressing expression of extracellular matrix genes. The underlying molecular mechanisms are largely unknown. We recently observed that stimulation of PPAR-γ activation suppressed gene expression of TGF-β receptors in activated HSC, leading to the interruption of TGF-β signaling. This observation supported our assumption of an antagonistic relationship between PPAR-γ activation and TGF-β signaling in HSC. In this study, we further hypothesize that TGF-β signaling might negatively regulate gene expression of PPAR-γ in activated HSC. The present report demonstrates that exogenous TGF-β1 inhibits gene expression of PPAR-γ in activated HSC, which is eliminated by the pretreatment with curcumin likely by interrupting TGF-β signaling. Transfection assays further indicate that blocking TGF-β signaling by dominant negative type II TGF-β receptor increases the promoter activity of PPAR-γ gene. Promoter deletion assays, site-directed mutageneses, and gel shift assays localize two Smad binding elements (SBEs) in the PPAR-γ gene promoter, acting as curcumin response elements and negatively regulating the promoter activity in passaged HSC. The Smad3/4 protein complex specifically binds to the SBEs. Overexpression of Smad4 dose dependently eliminates the inhibitory effects of curcumin on the PPAR-γ gene promoter and TGF-β signaling. Taken together, these results demonstrate that the interruption of TGF-β signaling by curcumin induces gene expression of PPAR-γ in activated HSC in vitro. Our studies provide novel insights into the molecular mechanisms of curcumin in the induction of PPAR-γ gene expression and in the inhibition of HSC activation.

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