Hernández-Hernández J Manuel, Delgado-Olguín Paul, Aguillón-Huerta Verónica, Furlan-Magaril Mayra, Recillas-Targa Félix, Coral-Vázquez Ramón M
Unidad de Investigación Médica en Genética Humana, Hospital de Pediatría, Centro Médico Nacional Siglo XXI-IMSS, México, D.F., México.
J Mol Biol. 2009 Nov 20;394(1):1-14. doi: 10.1016/j.jmb.2009.08.057. Epub 2009 Aug 31.
Alpha sarcoglycan (alpha-SG) is highly expressed in differentiated striated muscle, and its disruption causes limb-girdle muscular dystrophy. Accordingly, the myogenic master regulator MyoD finely modulates its expression. However, the mechanisms preventing alpha-SG gene expression at early stages of myogenic differentiation remain unknown. In this study, we uncovered Sox9, which was not previously known to directly bind muscle gene promoters, as a negative regulator of alpha-SG gene expression. Reporter gene and chromatin immunoprecipitation assays revealed three functional Sox-binding sites that mediate alpha-SG promoter activity repression during early myogenic differentiation. In addition, we show that Sox9-mediated inhibition of alpha-SG gene expression is independent of MyoD. Moreover, we provide evidence suggesting that Smad3 enhances the repressive activity of Sox9 over alpha-SG gene expression in a transforming growth factor-beta-dependent manner. On the basis of these results, we propose that Sox9 and Smad3 are responsible for preventing precocious activation of alpha-SG gene expression during myogenic differentiation.
α-肌聚糖（α-SG）在分化的横纹肌中高表达，其破坏会导致肢带型肌营养不良症。因此，成肌主调节因子MyoD可精细调节其表达。然而，在成肌分化早期阻止α-SG基因表达的机制仍不清楚。在本研究中，我们发现了Sox9，它以前并不被认为能直接结合肌肉基因启动子，是α-SG基因表达的负调节因子。报告基因和染色质免疫沉淀试验揭示了三个功能性Sox结合位点，它们在早期成肌分化过程中介导α-SG启动子活性的抑制。此外，我们表明Sox9介导的α-SG基因表达抑制与MyoD无关。而且，我们提供的证据表明，Smad3以转化生长因子-β依赖的方式增强Sox9对α-SG基因表达的抑制活性。基于这些结果，我们提出Sox9和Smad3负责在成肌分化过程中防止α-SG基因表达的过早激活。
