Essential Roles of the Kar2/BiP Molecular Chaperone Downstream of the UPR Pathway in Cryptococcus neoformans
Essential Roles of the Kar2/BiP Molecular Chaperone Downstream of the UPR Pathway in Cryptococcus neoformans
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DOI：
10.1371/journal.pone.0058956
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发表时间：
2013-03-06
期刊：
影响因子：
3.7
通讯作者：
Bahn, Yong-Sun
中科院分区：
文献类型：
--
作者：
Jung, Kwang-Woo;Kang, Hyun Ah;Bahn, Yong-Sun
内质网（ER）是真核生物中分泌或膜结合蛋白质成熟和正确折叠的中心枢纽。ER稳态的维持对于人类真菌病原体特别重要，例如新型隐球菌，其在感染期间遇到过多的宿主介导的应激。我们的前期研究表明，由进化上保守的Ire 1激酶和独特的Hxl 1转录因子组成的未折叠蛋白反应（unfolded protein response，UPR）通路在毛癣菌的内质网应激反应、耐热性、抗真菌药物抗性和毒力等方面具有多效性。新人类在这里，我们对C中的ER驻留分子伴侣Kar 2/BiP进行了功能表征。新人类通过铜调控启动子的条件性表达KAR 2揭示了Kar 2对C.新人类由强组蛋白H3启动子组成型表达的KAR 2部分恢复了ire 1 Delta和hxl 1 Delta突变体对ER应激、细胞壁应激、耐热性和遗传毒性应激的抗性，这表明Kar 2主要在UPR途径的下游起作用。此外，Kar 2似乎控制C. UPR通路下游的新生儿，不受ERG 11或ERG 3的调节。有趣的是，我们发现唑类药物治疗被认为是ER应激，随后激活Ire 1依赖性Hxl 1剪接事件，并通过UPR途径诱导KAR 2。相反，Kar 2的组成型表达不足以恢复Ire 1介导的C. UPR突变体。总之，本研究表明Kar 2不仅是营养生长所必需的，而且是响应和适应环境压力和UPR途径下游的抗真菌药物所必需的。新人类
The endoplasmic reticulum (ER) is a central hub where secreted or membrane-bound proteins are maturated and folded properly in eukaryotes. Maintenance of ER homeostasis is particularly important for human fungal pathogens, such as Cryptococcus neoformans, which encounter a plethora of host-mediated stresses during infection. Our previous study demonstrated that the unfolded protein response (UPR) pathway, composed of the evolutionarily conserved Ire1 kinase and the unique Hxl1 transcription factor, has pleiotropic roles in ER stress response, thermotolerance, antifungal drug resistance, and virulence in C. neoformans. Here, we functionally characterized an ER-resident molecular chaperone, Kar2/BiP, in C. neoformans. Conditional expression of KAR2 by the copper-regulated promoter revealed that Kar2 is essential for the viability of C. neoformans. Constitutive expression of KAR2 by the strong histone H3 promoter partially restores resistance to ER stress, cell wall stress, thermotolerance, and genotoxic stress in ire1 Delta and hxl1 Delta mutants, suggesting that Kar2 mainly functions downstream of the UPR pathway. Furthermore, Kar2 appears to control azole resistance in C. neoformans downstream of the UPR pathway without regulation of ERG11 or ERG3. Interestingly, we discovered that azole treatment is sensed as ER-stress and subsequently activates the Ire1-dependent Hxl1 splicing event and induction of KAR2 by the UPR pathway. In contrast, the constitutive expression of Kar2 is not sufficient to restore the Ire1-mediated regulation of capsule production in C. neoformans UPR mutants. In conclusion, this study demonstrates that Kar2 is not only essential for vegetative growth but also required for response and adaptation to the environmental stresses and antifungal drugs downstream of the UPR pathway in C. neoformans.