In mammalian skeletal muscle, phosphorylation of TOMM22 by protein kinase CSNK2/CK2 controls mitophagy
In mammalian skeletal muscle, phosphorylation of TOMM22 by protein kinase CSNK2/CK2 controls mitophagy
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DOI：
10.1080/15548627.2017.1403716
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发表时间：
2018-01-01
期刊：
影响因子：
13.3
通讯作者：
Hashemolhosseini, Said
中科院分区：
文献类型：
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作者：
Kravic, Bojana;Harbauer, Angelika B.;Hashemolhosseini, Said
在酵母中，Tom 22是TOMM（线粒体外膜转位酶）受体复合物的中心组分，负责合成的线粒体前体蛋白的识别和转位，其蛋白激酶CK 2依赖性磷酸化是TOMM复合物生物合成和适当线粒体蛋白输入的必需条件。在哺乳动物中，蛋白激酶CSNK 2/CK 2的生物学功能仍然非常难以捉摸，并且尚不清楚TOMM蛋白亚基的CSNK 2依赖性磷酸化是否具有与酵母中类似的作用。为了解决这个问题，我们使用骨骼肌特异性Csnk 2b/Ck 2条件性敲除（cKO）小鼠模型。从表型上看，这些骨骼肌Csnk 2b cKO小鼠显示出肌力降低和主要是氧化性肌纤维的异常代谢活性，这表明线粒体功能障碍。在酶促作用下，来自骨骼肌Csnk 2b cKO小鼠的活性肌肉裂解物磷酸化小鼠TOMM 22（酵母Tom 22的哺乳动物直系同源物）的程度低于从对照制备的裂解物。从机制上讲，CSNK 2介导的TOMM 22磷酸化改变了其对线粒体前体蛋白的结合亲和力。然而，与酵母相反，线粒体蛋白的输入似乎不受影响，在体外使用从骨骼肌Csnk 2b cKO小鼠的肌肉中分离的线粒体。PINK 1是一种线粒体健康传感器，在生理条件下经历组成性输入，在骨骼肌Csnk 2b cKO纤维内积累，并标记异常线粒体以通过线粒体自噬去除，如通过电子显微镜观察的含线粒体的自噬体的外观所证明的。线粒体自噬可以通过在培养的肌管中引入拟磷酸化TOMM 22突变体或通过将拟磷酸化TOMM 22体内电穿孔到小鼠肌肉中来正常化。重要的是，在具有消融的Csnk 2b的肌细胞中转染磷酸化模拟Tomm 22突变体恢复了与野生型水平相当的耗氧速率。总之，我们的数据表明，哺乳动物CSNK 2依赖的TOMM 22磷酸化是线粒体自噬的关键开关，并揭示了CSNK 2依赖的代谢，肌肉完整性和行为的生理意义。
In yeast, Tom22, the central component of the TOMM (translocase of outer mitochondrial membrane) receptor complex, is responsible for the recognition and translocation of synthesized mitochondrial precursor proteins, and its protein kinase CK2-dependent phosphorylation is mandatory for TOMM complex biogenesis and proper mitochondrial protein import. In mammals, the biological function of protein kinase CSNK2/CK2 remains vastly elusive and it is unknown whether CSNK2-dependent phosphorylation of TOMM protein subunits has a similar role as that in yeast. To address this issue, we used a skeletal muscle-specific Csnk2b/Ck2-conditional knockout (cKO) mouse model. Phenotypically, these skeletal muscle Csnk2b cKO mice showed reduced muscle strength and abnormal metabolic activity of mainly oxidative muscle fibers, which point towards mitochondrial dysfunction. Enzymatically, active muscle lysates from skeletal muscle Csnk2b cKO mice phosphorylate murine TOMM22, the mammalian ortholog of yeast Tom22, to a lower extent than lysates prepared from controls. Mechanistically, CSNK2-mediated phosphorylation of TOMM22 changes its binding affinity for mitochondrial precursor proteins. However, in contrast to yeast, mitochondrial protein import seems not to be affected in vitro using mitochondria isolated from muscles of skeletal muscle Csnk2b cKO mice. PINK1, a mitochondrial health sensor that undergoes constitutive import under physiological conditions, accumulates within skeletal muscle Csnk2b cKO fibers and labels abnormal mitochondria for removal by mitophagy as demonstrated by the appearance of mitochondria-containing autophagosomes through electron microscopy. Mitophagy can be normalized by either introduction of a phosphomimetic TOMM22 mutant in cultured myotubes, or by in vivo electroporation of phosphomimetic Tomm22 into muscles of mice. Importantly, transfection of the phosphomimetic Tomm22 mutant in muscle cells with ablated Csnk2b restored their oxygen consumption rate comparable to wild-type levels. In sum, our data show that mammalian CSNK2-dependent phosphorylation of TOMM22 is a critical switch for mitophagy and reveal CSNK2-dependent physiological implications on metabolism, muscle integrity and behavior.