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 Cys¹⁰⁰ 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 Ca²⁺ concentration increased and the mitochondrial membrane potential decreased. In addition, CKAP4 KO decreased the oxidative consumption rate, in vitro cancer cell proliferation under low-glucose conditions and in vivo 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 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内质网-线粒体接触位点的数量。为了了解 CKAP4 在线粒体功能中的参与，我们探索了 CKAP4 的结合蛋白，从而能够鉴定位于线粒体外膜的线粒体孔蛋白电压依赖性阴离子选择性通道蛋白 2 (VDAC2)。CKAP4 和 VDAC2 之间的结合需要 CKAP4 的Cys ^{100处的棕榈酰化。}在CKAP4 KO细胞中，肌醇三磷酸受体（IP3R）与VDAC2的结合增强，线粒体内Ca ²⁺浓度升高，线粒体膜电位降低。此外，CKAP4 KO还降低了氧化消耗率、低血糖条件下的体外癌细胞增殖和体内异种移植肿瘤的形成。棕榈酰化缺陷的 CKAP4 突变体的表达并不能挽救表型。这些结果表明，CKAP4 通过在 ER-线粒体接触位点与 VDAC2 结合而在维持线粒体功能中发挥作用，并且棕榈酰化是 CKAP4 的这一新功能所必需的。

本文有对该论文第一作者的相关第一人称采访。