RESUMO
Peroxisomal proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), a transcriptional coactivator, is selectively expressed in slow-twitch fibers in skeletal muscle. Ectopic expression of the PGC-1alpha gene in either a cell or an animal has been shown to promote fast to slow fiber-type switch. The expression of PGC-1alpha in muscle is regulated by myocyte enhancer factor 2 and Forkhead in rhabdomyosarcoma, two transcription factors implicated in terminal muscle differentiation. In this study we found that PGC-1alpha expression was activated during terminal muscle differentiation in both C2C12 and Sol8 myoblasts. Using retrovirus-mediated MyoD overexpression in C3H10T1/2 cells, we also demonstrated that MyoD, the master regulator of terminal differentiation, could activate PGC-1alpha expression in vivo. Our transient transfection results also show that myogenic basic helix-loop-helix (bHLH) proteins, especially MyoD, can activate PGC-1alpha expression by targeting its promoter. Myogenic bHLH protein target sites on PGC-1alpha promoter were localized to a short region (-49 to approximately +2) adjacent to the transcription start site, which contains two putative E boxes. Mutation of either site significantly reduced MyoD-mediated transactivation in the cells, suggesting that both sites are required for myogenic bHLH protein-mediated activation. However, only one site, the E2 box, was directly bound by glutathione-S-transferase-MyoD protein in EMSAs. Our results indicate that myogenic bHLH proteins not only are involved in lineage determination and terminal differentiation, but also are directly implicated in activation of the key fiber-type and metabolic switch gene, PGC-1alpha.
Assuntos
Fatores de Transcrição Hélice-Alça-Hélice Básicos/fisiologia , Diferenciação Celular , Regulação da Expressão Gênica , Proteínas de Choque Térmico/genética , Mioblastos Esqueléticos/citologia , Fatores de Transcrição/genética , Animais , Sequência de Bases , Linhagem da Célula , Células Cultivadas , Proteínas de Choque Térmico/fisiologia , Humanos , Camundongos , Dados de Sequência Molecular , Proteína MyoD/fisiologia , Fatores de Regulação Miogênica/metabolismo , Miogenina/fisiologia , Proteínas Nucleares/metabolismo , Coativador 1-alfa do Receptor gama Ativado por Proliferador de Peroxissomo , Regiões Promotoras Genéticas , Fatores de Transcrição/fisiologiaRESUMO
The online game market has been growing rapidly and has received an increasing amount of attention in recent years. The results of a survey conducted in China to explore online game players' attitude formation reveal that (a) the online game player's level of materialism positively influences the motivation for playing, (b) motivation positively influences attitude toward online games, and (c) motivation fully mediates the effects of materialism on attitude.