RESUMO
The mechanisms underlying inflammation induced insulin resistance are poorly understood. Here, we report that the expression of PIMT, a transcriptional co-activator binding protein, was up-regulated in the soleus muscle of high sucrose diet (HSD) induced insulin resistant rats and TNF-α exposed cultured myoblasts. Moreover, TNF-α induced phosphorylation of PIMT at the ERK1/2 target site Ser(298). Wild type (WT) PIMT or phospho-mimic Ser298Asp mutant but not phospho-deficient Ser298Ala PIMT mutant abrogated insulin stimulated glucose uptake by L6 myotubes and neonatal rat skeletal myoblasts. Whereas, PIMT knock down relieved TNF-α inhibited insulin signaling. Mechanistic analysis revealed that PIMT differentially regulated the expression of GLUT4, MEF2A, PGC-1α and HDAC5 in cultured cells and skeletal muscle of Wistar rats. Further characterization showed that PIMT was recruited to GLUT4, MEF2A and HDAC5 promoters and overexpression of PIMT abolished the activity of WT but not MEF2A binding defective mutant GLUT4 promoter. Collectively, we conclude that PIMT mediates TNF-α induced insulin resistance at the skeletal muscle via the transcriptional modulation of GLUT4, MEF2A, PGC-1α and HDAC5 genes.
Assuntos
Transportador de Glucose Tipo 4/metabolismo , Proteína D-Aspartato-L-Isoaspartato Metiltransferase/metabolismo , Transcrição Gênica/efeitos dos fármacos , Fator de Necrose Tumoral alfa/farmacologia , Animais , Glicemia/análise , Células Cultivadas , Regulação para Baixo/efeitos dos fármacos , Transportador de Glucose Tipo 4/genética , Células HEK293 , Histona Desacetilases/genética , Histona Desacetilases/metabolismo , Humanos , Resistência à Insulina , Fatores de Transcrição MEF2/genética , Fatores de Transcrição MEF2/metabolismo , Masculino , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Mioblastos Esqueléticos/citologia , Mioblastos Esqueléticos/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Fosforilação/efeitos dos fármacos , Proteína D-Aspartato-L-Isoaspartato Metiltransferase/genética , Ratos , Ratos Wistar , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Fator de Necrose Tumoral alfa/sangueRESUMO
The ß-catenin/Wnt signaling pathway is activated in many cancers and its constitutive activation has a central role in colorectal cancer pathogenesis. Recent studies have highlighted the role of microRNAs as novel regulators of gene expression including that of signaling intermediates from the Wnt signaling pathway. The purpose of our study was to determine the role of miR-29b in the regulation of Wnt signaling in human colorectal cancer cells. TOPFlash/FOPFlash reporter assays, gene expression studies by quantitative RT-PCR and western blot analysis were used to study the effect of ectopic expression of miR-29b on canonical Wnt signaling. miR-29b antagonized transactivation of ß-catenin target genes by downregulating coactivators of ß-catenin (TCF7L2, Snail, and BCL9L) in SW480 cells. miR-29b targeted the 3'UTR of BCL9L and decreased its expression with a consequent decrease in nuclear translocation of ß-catenin. Ectopic expression of miR-29b inhibited anchorage independent cell growth, promoted reversal of epithelial to mesenchymal transition and reduced the ability of conditioned medium from SW480 cells to induce in vitro tube formation in endothelial cells. These results have unraveled a novel role of miR-29b in Wnt signaling in human colorectal cancer cells with implications in the treatment of colorectal cancer.
