Sit4p/PP6 regulates ER-to-Golgi traffic by controlling the dephosphorylation of COPII coat subunits.
Sit4p/PP6 regulates ER-to-Golgi traffic by controlling the dephosphorylation of COPII coat subunits.
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DOI：
10.1091/mbc.e13-02-0114
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发表时间：
2013-09
影响因子：
3.3
通讯作者：
Ferro-Novick S
中科院分区：
文献类型：
--
作者：
Bhandari D;Zhang J;Menon S;Lord C;Chen S;Helm JR;Thorsen K;Corbett KD;Hay JC;Ferro-Novick S
先前的研究表明，COPII外壳是磷酸化的。然而，磷酸化的外壳不能重新结合到ER以启动新一轮的囊泡出芽。目前的研究表明，Sit 4p/PP 6，一个丝氨酸/苏氨酸磷酸酶，去磷酸化COPII外壳。与外套回收的作用一致，Sit 4p/PP 6调节ER到高尔基体的交通。从内质网（ER）到高尔基复合体的交通开始时，激活形式的GTP酶Sar 1 p招募Sec 23 p-Sec 24 p复合物ER膜。Sec 23 p-Sec 24 p复合物形成COPII外壳的内壳，将货物分类到ER衍生的囊泡中。被膜内壳募集Sec 13 p-Sec 31 p复合物，导致被膜聚合和囊泡出芽。最近的研究表明，Sec 23 p亚基顺序与三种不同的结合伙伴相互作用，直接COPII囊泡的高尔基体。这些结合配偶体之一是丝氨酸/苏氨酸激酶Hrr 25 p。hrr 25 p磷酸化COPII涂层，驱动膜结合池进入胞质溶胶。磷酸化的外壳不能重新结合到ER启动新一轮的囊泡出芽，除非它是去磷酸化。在这里，我们在酵母中筛选所有已知的蛋白磷酸酶，以确定其功能丧失改变COPII外壳亚基的细胞分布。该筛选鉴定了PP 2A样磷酸酶Sit 4p作为COPII外壳去磷酸化的调节剂。过度磷酸化的外壳亚基在体内积累在sit 4 Δ突变体中。在体外，Sit 4p使COPII外壳亚基去磷酸化。与外套回收中的作用一致，Sit 4p及其哺乳动物直向同源物PP 6调节从ER到高尔基复合体的交通。
Previous studies show that the COPII coat is phosphorylated. The phosphorylated coat, however, cannot rebind to the ER to initiate a new round of vesicle budding. The present study shows that Sit4p/PP6, a Ser/Thr phosphatase, dephosphorylates the COPII coat. Consistent with a role in coat recycling, Sit4p/PP6 regulates ER-to-Golgi traffic. Traffic from the endoplasmic reticulum (ER) to the Golgi complex is initiated when the activated form of the GTPase Sar1p recruits the Sec23p-Sec24p complex to ER membranes. The Sec23p-Sec24p complex, which forms the inner shell of the COPII coat, sorts cargo into ER-derived vesicles. The coat inner shell recruits the Sec13p-Sec31p complex, leading to coat polymerization and vesicle budding. Recent studies revealed that the Sec23p subunit sequentially interacts with three different binding partners to direct a COPII vesicle to the Golgi. One of these binding partners is the serine/threonine kinase Hrr25p. Hrr25p phosphorylates the COPII coat, driving the membrane-bound pool into the cytosol. The phosphorylated coat cannot rebind to the ER to initiate a new round of vesicle budding unless it is dephosphorylated. Here we screen all known protein phosphatases in yeast to identify one whose loss of function alters the cellular distribution of COPII coat subunits. This screen identifies the PP2A-like phosphatase Sit4p as a regulator of COPII coat dephosphorylation. Hyperphosphorylated coat subunits accumulate in the sit4Δ mutant in vivo. In vitro, Sit4p dephosphorylates COPII coat subunits. Consistent with a role in coat recycling, Sit4p and its mammalian orthologue, PP6, regulate traffic from the ER to the Golgi complex.