Hsu Jia-Wei, Tang Pei-Hua, Wang I-Hao, Liu Chia-Lun, Chen Wen-Hui, Tsai Pei-Chin, Chen Kuan-Yu, Chen Kuan-Jung, Yu Chia-Jung, Lee Fang-Jen S
Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 100, Taiwan; Department of Medical Research, National Taiwan University Hospital, Taipei 100, Taiwan;
Department of Cell and Molecular Biology, College of Medicine, Chang Gung University, Tao-Yuan 333, Taiwan.
Proc Natl Acad Sci U S A. 2016 Mar 22;113(12):E1683-90. doi: 10.1073/pnas.1518260113. Epub 2016 Mar 10.
ADP ribosylation factor (Arf) GTPases are key regulators of membrane traffic at the Golgi complex. In yeast, Arf guanine nucleotide-exchange factor (GEF) Syt1p activates Arf-like protein Arl1p, which was accompanied by accumulation of golgin Imh1p at late Golgi, but whether and how this function of Syt1p is regulated remains unclear. Here, we report that the inositol-requiring kinase 1 (Ire1p)-mediated unfolded protein response (UPR) modulated Arl1p activation at late Golgi. Arl1p activation was dependent on both kinase and endo-RNase activities of Ire1p. Moreover, constitutively active transcription factor Hac1p restored the Golgi localization of Arl1p and Imh1p inIRE1-deleted cells. Elucidating the mechanism of Ire1p-Hac1p axis actions, we found that it regulated phosphorylation of Syt1p, which enhances Arl1p activation, recruitment of Imh1p to the Golgi, and Syt1p interaction with Arl1p. Consistent with these findings, the induction of UPR by tunicamycin treatment increases phosphorylation of Syt1p, resulting in Arl1p activation. Thus, these findings clarify how the UPR influences the roles of Syt1p, Arl1p, and Imh1p in Golgi transport.
ADP核糖基化因子（Arf）GTP酶是高尔基体复合体膜转运的关键调节因子。在酵母中，Arf鸟嘌呤核苷酸交换因子（GEF）Syt1p激活类Arf蛋白Arl1p，这伴随着高尔基体蛋白Imh1p在晚期高尔基体的积累，但Syt1p的这种功能是否以及如何受到调节仍不清楚。在这里，我们报告肌醇需要激酶1（Ire1p）介导的未折叠蛋白反应（UPR）调节晚期高尔基体中Arl1p的激活。Arl1p的激活依赖于Ire1p的激酶和内切核糖核酸酶活性。此外，组成型活性转录因子Hac1p恢复了缺失IRE1的细胞中Arl1p和Imh1p的高尔基体定位。在阐明Ire1p-Hac1p轴作用机制时，我们发现它调节Syt1p的磷酸化，这增强了Arl1p的激活、Imh1p向高尔基体的募集以及Syt1p与Arl1p的相互作用。与这些发现一致，衣霉素处理诱导的UPR增加了Syt1p的磷酸化，导致Arl1p激活。因此，这些发现阐明了UPR如何影响Syt1p、Arl1p和Imh1p在高尔基体转运中的作用。
