Involvement of a Novel Q-SNARE, D12, in Quality Control of the Endomembrane System*
Involvement of a Novel Q-SNARE, D12, in Quality Control of the Endomembrane System*
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DOI：
10.1074/jbc.m509715200
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发表时间：
2006-02
影响因子：
4.8
通讯作者：
A. Okumura;K. Hatsuzawa;Taku Tamura;Hisao Nagaya;Kazuko Saeki;Fumihiko Okumura;K. Nagao;M. Nishikawa;A. Yoshimura;I. Wada
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文献类型：
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作者：
A. Okumura;K. Hatsuzawa;Taku Tamura;Hisao Nagaya;Kazuko Saeki;Fumihiko Okumura;K. Nagao;M. Nishikawa;A. Yoshimura;I. Wada
细胞内膜系统需要其单个组分的合成和降解的适当动力学平衡，这部分地由特定的膜融合装置维持。在这项研究中，我们描述了D12的分子特性，它是从小鼠表达文库中鉴定出来的。这种C-末端锚定的膜蛋白与酵母可溶性N-乙基马来酰亚胺敏感因子附着蛋白（SNAP）受体（SNARE），p1 p/Slt 1 p和最近鉴定的人类突触融合蛋白18结合蛋白p31具有序列相似性。D12与syntaxin 18和Sec 22 b形成紧密复合物，并与α-SNAP结合，表明D12是SNARE蛋白。虽然大多数的D12位于内质网和内质网-高尔基体的中间隔室在稳态，过表达或敲低D12没有明显的影响膜运输的早期分泌途径。然而，抑制D12的表达引起的脂褐质颗粒的快速出现，伴随着细胞凋亡的细胞死亡，而没有明显激活的未折叠的蛋白质反应。脂褐素形成的典型原因是受损的溶酶体降解酶的线粒体的降解，并且，与此一致，我们发现，适当的组织蛋白酶D的高尔基体后成熟受损的D12缺陷细胞。这一意想不到的观察结果得到了D12与VAMP 7（内体-溶酶体途径中的SNARE）相关的证据的支持。因此，我们认为D12参与了溶酶体的降解功能。
The cellular endomembrane system requires the proper kinetic balance of synthesis and degradation of its individual components, which is maintained in part by a specific membrane fusion apparatus. In this study, we describe the molecular properties of D12, which was identified from a mouse expression library. This C-terminal anchored membrane protein has sequence similarity to both a yeast soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE), Use1p/Slt1p, and a recently identified human syntaxin 18-binding protein, p31. D12 formed a tight complex with syntaxin 18 as well as Sec22b and bound to α-SNAP, indicating that D12 is a SNARE protein. Although the majority of D12 is located in the endoplasmic reticulum and endoplasmic reticulum-Golgi intermediate compartments at steady state, overexpression or knockdown of D12 had no obvious effects on membrane trafficking in the early secretory pathway. However, suppression of D12 expression caused rapid appearance of lipofuscin granules, accompanied by apoptotic cell death without the apparent activation of the unfolded protein response. The typical cause of lipofuscin formation is the impaired degradation of mitochondria by lysosomal degradative enzymes, and, consistent with this, we found that proper post-Golgi maturation of cathepsin D was impaired in D12-deficient cells. This unexpected observation was supported by evidence that D12 associates with VAMP7, a SNARE in the endosomal-lysosomal pathway. Hence, we suggest that D12 participates in the degradative function of lysosomes.