IGF-1通过SRF结合位点调节SMYD1在C2C12细胞中的表达

SMYD1是组蛋白甲基转移酶,在骨骼肌和心肌中特异表达,是调节心肌和骨骼肌发育的关键因子.虽然SMYD1的生物学功能比较清楚,但细胞外因子调节SMYD1基因表达的机制还没有报导.IGF-1能促进心肌和骨骼肌的发育、加速肌肉的损伤修复过程.通过Western印迹发现,在用IGF-1处理的C2C12细胞中,SMYD1的表达水平随处理时间逐步升高,SRF蛋白和Myogenin的表达也呈现类似的趋势.通过构建不同长度的SMYD1基因启动子荧光素酶报告基因载体,发现SMYD1基因启动子上IGF-1的应答区域位于-620～-110 bp;EMSA实验表明,SRF结合在SMYD1启动子的CArG位点,而IGF-1则能促进SRF与SMYD1启动子的结合;若将启动子上的CArG元件突变,IGF-1对SMYD1启动子的激活效应被削弱.可见IGF-1能够上调SMYD1在C2C12细胞中的表达,并且这种调控作用是部分通过调节SRF与SMYD1启动子上CArG位点的结合而实现的.此外,通过荧光素酶报告基因分析,发现SMYD1能够激活肌肉标志因子肌肉肌酸激酶(MCK)基因活性,而且与MyoD基因存在协同激活效应.因此,SMYD1可能是IGF-1的下游靶基因,SMYD1可能通过与MyoD协同作用,促进肌肉的分化。

IGF-1 Regulates SMYD1 Expression through SRF Response Element in C2C12 Cells

nsulin-like growth factor 1 (IGF-1) plays an essential role in cardiac and skeletal muscle development. SMYD1(SET and MYND domain containing protein 1), a heart and muscle-specific histone methyltransferase, has been demonstrated to be an essential regulator during cardiomyocyte differentiation. However, it is not clear whether IGF-1 regulates SMYD1 expression during myogenesis. The expression of SMYD1 was up-regulated in C2C12 cells during myogenic differentiation. Upon IGF-1 stimulation, the protein level of SMYD1 was significantly increased. By luciferase reporter assay, we narrowed the core IGF-1 response region in SMYD1 gene promoter to -620~-110 bp relative to start codon. Using gel shift assay, we found that SRF bound to CArG site in SMYD1 promoter and the affinity was increasing during C2C12 cell differentiation. When the serum response factor (SRF) binding element was mutated, IGF-1 did not be fully activated SMYD1 promoter activity. It suggests that the SRF binding element in SMYD1 promoter is partially response to IGF-1 induction. Taken together, we report here that the expression of SMYD1 is up-regulated during myogenic differentiation and IGF-1 stimulates SMYD1 expression partially through SRF binding site in the promoter.