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最近研究证实,转基因表达Ca2+/calmodulin依赖的蛋白激酶IV(CaMKIV)或CaMKIIδB这两种定位于细胞核内的蛋白激酶可以导致心脏肥厚。然而,CaMKIV不在心脏中表达,心肌细胞在表达核蛋白CaMKIIδB同时也表达其胞浆同功酶CaMKIIδC。在最近的研究中,我们证实在压力负荷出现后的第二天以及其后的连续七天里,CaMKII的δC同功酶的表达选择性增强,磷酸化活性升高。为了确定胞浆δC同功酶活性的增加是否会使Ca2+调节蛋白磷酸化并且导致心肌肥厚,我们培育了表达CaMKI鄄IδC同功酶的转基因小鼠。从这些小鼠中分离出心肌细胞做免疫细胞化学染色表明,转入基因的表达仅限于细胞浆。这些小鼠表现出扩张型心肌病,心肌短缩分率的降低超过65%,并在幼年死亡。分离出的心肌细胞体积变大,收缩能力降低,Ca2+摄入能力也发生改变。Ryanodine受体(RyR)CaMKII位点的磷酸化在心衰发生前就有增加,免疫共沉淀表明CaMKII可以与转基因鼠中的RyR发生作用。PLB的磷酸化同样在CaMKII位点被特异性增强,但其PKA磷酸化位点未发生改变。这些发现首次阐明CaMKIIδC能够在体内介导Ca2+调节蛋白的磷酸化,并为CaMKIIδC的活化参与了扩张型心肌病和心衰的病程提供了证据。
Recent studies confirm that PKK / calmodulin-dependent protein kinase IV (CaMKIV) or CaMKIIδB, a genetically-engineered protein that localizes in the nucleus, can lead to cardiac hypertrophy. However, CaMKIV is not expressed in the heart, and cardiomyocytes express their cytoplasmic isozyme CaMKIIδC while expressing the nuclear protein CaMKIIδB. In a recent study, we demonstrated that expression of Ca2 + isoenzyme of CaMKII is selectively increased and phosphorylation activity increases on the second day after stress loading and for seven consecutive days. To determine if an increase in cytosolic δC isoenzyme activity would phosphorylate Ca2 + regulatory protein and lead to cardiac hypertrophy, we cultured transgenic mice expressing the CaMKI-IδC isozyme. Cardiomyocytes isolated from these mice were immunocytochemically stained to show that transgene expression was restricted to cytoplasm. These mice showed dilated cardiomyopathy with a reduction in myocardial shortening fraction of more than 65% and died at an early age. Isolated myocardial cells become larger, reduced ability to shrink, Ca2 + intake capacity also changed. Phosphorylation of the Ryanodine receptor (RyR) at the CaMKII site increased before heart failure, and coimmunoprecipitation suggested that CaMKII could interact with RyR in transgenic mice. Phosphorylation of PLB was also specifically enhanced at the CaMKII site but its PKA phosphorylation site was unchanged. These findings for the first time demonstrate that CaMKIIδC mediates phosphorylation of Ca2 + regulatory proteins in vivo and provide evidence that activation of CaMKIIδC is involved in the pathogenesis of dilated cardiomyopathy and heart failure.