Department of Molecular Biology and Biochemistry, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita 565-0871, Japan.
Department of Biomolecular Science and Engineering, The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Ibaraki, 8-1 Mihogaoka, Osaka 567-0047, Japan.
J Cell Sci. 2020 Nov 10;133(21):jcs249045. doi: 10.1242/jcs.249045.
Cytoskeleton-associated protein 4 (CKAP4) is a palmitoylated type II transmembrane protein localized to the endoplasmic reticulum (ER). Here, we found that knockout (KO) of CKAP4 in HeLaS3 cells induces the alteration of mitochondrial structures and increases the number of ER-mitochondria contact sites. To understand the involvement of CKAP4 in mitochondrial functions, the binding proteins of CKAP4 were explored, enabling identification of the mitochondrial porin voltage-dependent anion-selective channel protein 2 (VDAC2), which is localized to the outer mitochondrial membrane. Palmitoylation at Cys of CKAP4 was required for the binding between CKAP4 and VDAC2. In CKAP4 KO cells, the binding of inositol trisphosphate receptor (IP3R) and VDAC2 was enhanced, the intramitochondrial Ca concentration increased and the mitochondrial membrane potential decreased. In addition, CKAP4 KO decreased the oxidative consumption rate, cancer cell proliferation under low-glucose conditions and xenograft tumor formation. The phenotypes were not rescued by expression of a palmitoylation-deficient CKAP4 mutant. These results suggest that CKAP4 plays a role in maintaining mitochondrial functions through the binding to VDAC2 at ER-mitochondria contact sites and that palmitoylation is required for this novel function of CKAP4.This article has an associated First Person interview with the first author of the paper.
细胞骨架相关蛋白 4（CKAP4）是一种棕榈酰化的 II 型跨膜蛋白，定位于内质网（ER）。在这里，我们发现 HeLaS3 细胞中 CKAP4 的敲除（KO）会诱导线粒体结构的改变，并增加 ER-线粒体接触位点的数量。为了了解 CKAP4 参与线粒体功能的情况，我们探索了 CKAP4 的结合蛋白，从而鉴定出线粒体孔蛋白电压依赖性阴离子选择性通道蛋白 2（VDAC2），其定位于外线粒体膜。CKAP4 的半胱氨酸棕榈酰化对于 CKAP4 和 VDAC2 之间的结合是必需的。在 CKAP4 KO 细胞中，三磷酸肌醇受体（IP3R）和 VDAC2 的结合增强，线粒体内部 Ca 浓度增加，线粒体膜电位降低。此外，CKAP4 KO 降低了氧化消耗率、低糖条件下癌细胞的增殖和异种移植肿瘤的形成。表达棕榈酰化缺陷型 CKAP4 突变体不能挽救这些表型。这些结果表明，CKAP4 通过与 ER-线粒体接触位点处的 VDAC2 结合，在维持线粒体功能方面发挥作用，而棕榈酰化是 CKAP4 这一新型功能所必需的。本文有一篇与该论文第一作者的相关第一人称采访。
