Genetic evidence for a role of BiP/Kar2 that regulates Ire1 in response to accumulation of unfolded proteins
Genetic evidence for a role of BiP/Kar2 that regulates Ire1 in response to accumulation of unfolded proteins
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DOI：
10.1091/mbc.e02-11-0708
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发表时间：
2003-06-01
影响因子：
3.3
通讯作者：
Kohno, K
中科院分区：
文献类型：
--
作者：
Kimata, Y;Kimata, YL;Kohno, K
在未折叠蛋白反应（UPR）信号通路中，未折叠蛋白在内质网（ER）中的积累激活跨膜激酶/核糖核酸酶Ire 1，其引起ER驻留分子伴侣（包括BiP/Kar 2）的转录诱导。以前假设BiP/Kar 2在信号传导机制中起直接作用。在该模型中，BiP/Kar 2与Ire 1的结合抑制UPR途径，而在ER应激条件下，BiP/Kar 2解离导致激活。为了测试这个模型，我们分析了酵母KAR 2基因的五个温度敏感等位基因。当在Kar 2底物结合结构域中携带突变的细胞在限制性温度下孵育时，Kar 2与Ire 1的结合被破坏，并且即使在没有外源性ER应激的情况下，UPR途径也被激活。相反，在Kar 2 ATP酶结构域中携带突变的细胞，即使在衣霉素（一种有效的ER应激诱导剂）的存在下，Kar 2与Ire 1的解离也很差，无法激活该途径。我们的研究结果提供了强有力的证据，支持BiP/Kar 2依赖的Ire 1调节模型，并建议Ire 1与Kar 2作为伴侣底物。我们推测未折叠蛋白的识别是基于它们与Ire 1竞争与BiP/Kar 2结合。
In the unfolded protein response (UPR) signaling pathway, accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates a transmembrane kinase/ribonuclease Ire1, which causes the transcriptional induction of ER-resident chaperones, including BiP/Kar2. It was previously hypothesized that BiP/Kar2 plays a direct role in the signaling mechanism. In this model, association of BiP/Kar2 with Ire1 represses the UPR pathway while under conditions of ER stress, BiP/Kar2 dissociation leads to activation. To test this model, we analyzed five temperature-sensitive alleles of the yeast KAR2 gene. When cells carrying a mutation in the Kar2 substrate-binding domain were incubated at the restrictive temperature, association of Kar2 to Ire1 was disrupted, and the UPR pathway was activated even in the absence of extrinsic ER stress. Conversely, cells carrying a mutation in the Kar2 ATPase domain, in which Kar2 poorly dissociated from Ire1 even in the presence of tunicamycin, a potent inducer of ER stress, were unable to activate the pathway. Our findings provide strong evidence in support of BiP/Kar2-dependent Ire1 regulation model and suggest that Ire1 associates with Kar2 as a chaperone substrate. We speculate that recognition of unfolded proteins is based on their competition with Ire1 for binding with BiP/Kar2.