Dissection of Ire1 functions reveals stress response mechanisms uniquely evolved in Candida glabrata.
Dissection of Ire1 functions reveals stress response mechanisms uniquely evolved in Candida glabrata.
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DOI：
10.1371/journal.ppat.1003160
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发表时间：
2013-01
期刊：
影响因子：
6.7
通讯作者：
Kohno S
中科院分区：
文献类型：
--
作者：
Miyazaki T;Nakayama H;Nagayoshi Y;Kakeya H;Kohno S
在所有真核生物中，内质网中适当的蛋白质折叠是至关重要的。当错误折叠的蛋白质在内质网腔内积累时，跨膜激酶/核糖核酸内切酶Ire1启动HAC1 mRNA剪接，生成bZIP转录因子HAC1， HAC1随后激活其靶基因，增加内质网的蛋白质折叠能力。这种细胞机制被称为未折叠蛋白反应（UPR），被认为是真核生物的一种进化保守机制。在这项研究中，我们全面表征了人类真菌病原体念珠菌（Candida glabrata）中IRE1及其他相关基因的突变表型。出乎意料的是，在这种真菌中，Ire1是独立于Hac1的内质网应激反应所必需的。C. glabrata Ire1不切割编码Hac1和其他在C. glabrata基因组中发现的bZIP转录因子的mrna。微阵列分析显示，内质网应激的转录反应不是由Ire1介导的，而是主要依赖钙调磷酸酶信号传导和部分依赖Slt2 MAPK通路。Ire1基因的缺失并不会增加光毛霉的抗真菌敏感性，这与其他真菌中upr缺陷突变体相反。综上所述，我们的研究结果表明，典型的Ire1-Hac1 UPR在C. glabrata中并不保守。众所周知，在后生动物中，活性Ire1非特异性地切割和降解内质网定位mrna的子集以减少内质网负荷。有趣的是，这种细胞反应可能以Ire1核酸酶依赖的方式发生在C. glabrata。我们还发现了C. glabrata Δire1突变体在播散性念珠菌病小鼠模型中的毒性减弱。本研究揭示了光棘内质网应激反应机制的独特演化。大多数分泌蛋白和跨膜蛋白在内质网（ER）中结构成熟。错误折叠蛋白在内质网中的积累（内质网应激）激活内质网应激传感器Ire1，该传感器有两种不同的输出：未折叠蛋白反应（UPR）和调节Ire1依赖性衰变（RIDD）。UPR是一种增加内质网蛋白质折叠能力的转录反应。RIDD诱导内质网定位mrna的降解以减少内质网负荷。迄今为止，UPR被认为是几乎所有真核生物物种的进化保守途径，而RIDD仅在后生动物中被发现。最近对几种病原真菌的研究表明，UPR与抗真菌耐药性和毒力有关，因此它作为一种治疗靶点引起了人们的关注。在这里，我们证明了重要的真菌病原体念珠菌（Candida glabrata）已经失去了典型的UPR，而是拥有RIDD途径，并且对内质网胁迫相对耐受。对内质网胁迫的转录应答主要依赖于钙信号转导，由钙调磷酸酶钙调磷酸酶介导。我们的研究结果为内质网质量控制机制提供了新的见解，并有助于理解进化生物学和开发针对UPR的抗真菌药物。
Proper protein folding in the endoplasmic reticulum (ER) is vital in all eukaryotes. When misfolded proteins accumulate in the ER lumen, the transmembrane kinase/endoribonuclease Ire1 initiates splicing of HAC1 mRNA to generate the bZIP transcription factor Hac1, which subsequently activates its target genes to increase the protein-folding capacity of the ER. This cellular machinery, called the unfolded protein response (UPR), is believed to be an evolutionarily conserved mechanism in eukaryotes. In this study, we comprehensively characterized mutant phenotypes of IRE1 and other related genes in the human fungal pathogen Candida glabrata. Unexpectedly, Ire1 was required for the ER stress response independently of Hac1 in this fungus. C. glabrata Ire1 did not cleave mRNAs encoding Hac1 and other bZIP transcription factors identified in the C. glabrata genome. Microarray analysis revealed that the transcriptional response to ER stress is not mediated by Ire1, but instead is dependent largely on calcineurin signaling and partially on the Slt2 MAPK pathway. The loss of Ire1 alone did not confer increased antifungal susceptibility in C. glabrata contrary to UPR-defective mutants in other fungi. Taken together, our results suggest that the canonical Ire1-Hac1 UPR is not conserved in C. glabrata. It is known in metazoans that active Ire1 nonspecifically cleaves and degrades a subset of ER-localized mRNAs to reduce the ER load. Intriguingly, this cellular response could occur in an Ire1 nuclease-dependent fashion in C. glabrata. We also uncovered the attenuated virulence of the C. glabrata Δire1 mutant in a mouse model of disseminated candidiasis. This study has unveiled the unique evolution of ER stress response mechanisms in C. glabrata. The majority of secretory and transmembrane proteins are structurally matured in the endoplasmic reticulum (ER). The accumulation of misfolded proteins in the ER (ER stress) activates the ER-resident stress transducer Ire1, which has two distinct outputs: the unfolded protein response (UPR) and regulated Ire1-dependent decay (RIDD). The UPR is a transcriptional response to increase the protein folding capacity of the ER. RIDD induces degradation of ER-localized mRNAs to reduce the ER load. To date, the UPR has been believed to be an evolutionarily conserved pathway in almost all eukaryotic species, while RIDD has been found only in metazoans. Recent studies in several pathogenic fungi revealed that the UPR is implicated in antifungal resistance and virulence, and thus it has attracted attention as a therapeutic target. Here, we demonstrate that the important fungal pathogen Candida glabrata has lost the canonical UPR, but instead possesses the RIDD pathway and is relatively tolerant to ER stress. The transcriptional response to ER stress was dependent mainly on calcium signaling mediated by the protein phosphatase calcineurin in C. glabrata. Our results provide novel insights into ER quality control mechanisms and are useful for understanding evolutionary biology and the development of antifungal agents targeting the UPR.
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影响因子：
3.5
作者：
El Barkani, A;Haynes, K;Mühlschlegel, FA
通讯作者：
Mühlschlegel, FA
影响因子：
6.7
作者：
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64.5
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Weissman JS
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64.8
作者：
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通讯作者：
Souciet, JL
影响因子：
64.8
作者：
Calfon, M;Zeng, HQ;Ron, D
通讯作者：
Ron, D