Iyer Dinakar, Belaguli Narasimhaswamy, Flück Martin, Rowan Brian G, Wei Lei, Weigel Nancy L, Booth Frank W, Epstein Henry F, Schwartz Robert J, Balasubramanyam Ashok
Department of Medicine, Division of Endocrinology, Baylor College of Medicine, Houston, Texas 77030, USA.
Biochemistry. 2003 Jun 24;42(24):7477-86. doi: 10.1021/bi030045n.
Serum response factor (SRF) is a phosphoprotein that regulates skeletal and cardiac alpha-actin gene transcription. Myotonic dystrophy protein kinase (DMPK), a muscle- and neuron-restricted kinase, enhanced SRF-mediated promoter activity of the skeletal and cardiac alpha-actin genes in C2C12 myoblasts as well as in nonmyogenic cells. DMPK phosphorylated SRF in vitro in the alphaI coil of the DNA-binding domain in the MADS box, a highly conserved region required for DNA binding, dimerization, and co-activator interaction in COS and CV1 cells. Threonine 159 in the MADS box alphaI coil was a specific phosphorylation target in vitro as well as in vivo of both DMPK and protein kinase C-alpha. Substitution of threonine 159 with the nonphosphorylatable residue alanine markedly diminished activation of the cardiac alpha-actin promoter in the presence of kinase, while its substitution with aspartic acid, to introduce a negative charge and mimic phosphorylation, restored activation completely. Phosphorylation of the MADS box may constitute a novel mechanism for regulation of SRF-dependent actin gene transcription.
血清反应因子（SRF）是一种磷蛋白，可调节骨骼肌和心肌α-肌动蛋白基因的转录。强直性肌营养不良蛋白激酶（DMPK）是一种在肌肉和神经元中特异性表达的激酶，它在C2C12成肌细胞以及非肌源性细胞中增强了SRF介导的骨骼肌和心肌α-肌动蛋白基因的启动子活性。在COS和CV1细胞中，DMPK能在体外将SRF的MADS盒中DNA结合结构域的αI螺旋区域磷酸化，该区域是DNA结合、二聚化以及与共激活因子相互作用所必需的高度保守区域。MADS盒αI螺旋中的苏氨酸159是DMPK和蛋白激酶C-α在体外和体内的特异性磷酸化靶点。将苏氨酸159替换为不可磷酸化的丙氨酸，在激酶存在的情况下显著降低了心肌α-肌动蛋白启动子的活性，而将其替换为天冬氨酸以引入负电荷并模拟磷酸化，则完全恢复了启动子活性。MADS盒的磷酸化可能构成了一种调节SRF依赖的肌动蛋白基因转录的新机制。
