Localization of GRP78 to mitochondria under the unfolded protein response
Localization of GRP78 to mitochondria under the unfolded protein response
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DOI：
10.1042/bj20051916
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发表时间：
2006-05-15
影响因子：
4.1
通讯作者：
Lai, Yiu-Kay
中科院分区：
文献类型：
--
作者：
Sun, Fang-Chun;Wei, Shou;Lai, Yiu-Kay
普遍表达的分子伴侣GRP 78（78 k-Da葡萄糖调节蛋白）通常定位于ER（内质网）。GRP 78在UPR（未折叠蛋白反应）下在细胞中被特异性诱导，这可以通过用钙离子载体A23187和肌质/内质网Ca 2 +-ATP酶抑制剂TG（毒胡萝卜素）处理来引发。通过使用共聚焦显微镜，我们已经证明，GRP 78集中在核周区域和共定位与ER标记蛋白，钙连接蛋白和PDI（蛋白质二硫化物异构酶），在正常生长条件下的细胞。然而，用A23187和TG处理导致减少其ER靶向，导致重定向为细胞质囊泡模式，并与线粒体标记物MitoTracker重叠。细胞分级分离和蛋白酶消化分离的线粒体ER应激细胞表明，一个显着的部分GRP 78是本地化的线粒体和蛋白酶抗性。GRP 78在内质网和线粒体中的定位通过使用免疫电镜证实。内质网应激细胞中，GRP 78主要定位于线粒体内，并装饰线粒体膜室。亚线粒体分离研究进一步表明，GRP 78主要分布在膜间隙、内膜和基质中，而与外膜无关。此外，放射性标记，然后亚细胞分级显示，新合成的GRP 78的显着部分是本地化的线粒体在UPR下的细胞。两者合计，我们的研究结果表明，至少在某些情况下，ER驻留的伴侣GRP 78可以重新定位到线粒体，从而可能参与这两个细胞器之间的相关UPR信号。
The ubiquitously expressed molecular chaperone GRP78 (78 k-Da glucose-regulated protein) generally localizes to the ER (endoplasmic reticulum). GRP78 is specifically induced in cells under the UPR (unfolded protein response), which can be elicited by treatments with calcium ionophore A23187 and sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor TG (thapsigargin). By using confocal microscopy, we have demonstrated that GRP78 was concentrated in the perinuclear region and co-localized with the ER marker proteins, calnexin and PDI (protein disulphide-isomerase), in cells under normal growth conditions. However, treatments with A23187 and TG led to diminish its ER targeting, resulting in redirection into a cytoplasmic vesicular pattern, and overlapping with the mitochondrial marker MitoTracker. Cellular fractionation and protease digestion of isolated mitochondria from ER-stressed cells suggested that a significant portion of GRP78 is localized to the mitochondria and is protease-resistant. Localizations of GRP78 in ER and mitochondria were confirmed by using immunoelectron microscopy. In ER-stressed cells, GRP78 mainly localized within the mitochondria and decorated the mitochondrial membrane compartment. Submitochondrial fractionation studies indicated further that the mitochondria-resided GRP78 is mainly located in the intermembrane space, inner membrane and matrix, but is not associated with the outer membrane. Furthermore, radioactive labelling followed by subcellular fractionation showed that a significant portion of the newly synthesized GRP78 is localized to the mitochondria in cells under UPR. Taken together, our results indicate that, at least under certain circumstances, the ER-resided chaperone GRP78 can be retargeted to mitochondria and thereby may be involved in correlating UPR signalling between these two organelles.