The Rewiring of Ubiquitination Targets in a Pathogenic Yeast Promotes Metabolic Flexibility, Host Colonization and Virulence.
The Rewiring of Ubiquitination Targets in a Pathogenic Yeast Promotes Metabolic Flexibility, Host Colonization and Virulence.
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DOI：
10.1371/journal.ppat.1005566
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发表时间：
2016-04
期刊：
影响因子：
6.7
通讯作者：
Brown AJ
中科院分区：
文献类型：
--
作者：
Childers DS;Raziunaite I;Mol Avelar G;Mackie J;Budge S;Stead D;Gow NA;Lenardon MD;Ballou ER;MacCallum DM;Brown AJ
高效的碳同化对微生物的生长和致病至关重要。环境酵母菌酿酒酵母呈克拉布特里阳性，表现出从同化替代碳源到糖类的快速代谢转换。在接触糖之后，这种转换是通过基因转录抑制(碳分解代谢抑制)和参与替代碳源同化的酶的周转(分解代谢失活)来调节的。致病酵母菌白色念珠菌为克拉布特里阴性。它保留了碳分解代谢抑制机制，但经历了转录后重连，使得糖异生和乙醛循环酶不受泛素介导的分解代谢失活的影响。因此，当葡萄糖可用时，白色念珠菌可以继续与葡萄糖一起吸收替代碳源。我们表明，这种代谢的灵活性促进了宿主的定植和毒力。在白色念珠菌中，乙醛循环酶异柠檬酸裂解酶(CaICl1)对泛素介导的分解代谢物失活变得敏感。这种突变会在葡萄糖存在的情况下抑制乳酸的同化，降低白色念珠菌细胞抵抗巨噬细胞杀伤、在胃肠道定植和引起小鼠全身感染的能力。有趣的是，我们检查的大多数酿酒酵母临床分离株(67%)在葡萄糖存在的情况下获得了同化乳酸的能力(即它们变成了Crabtree阴性)。与CRABTREE阳性临床分离株相比，这些酿酒酵母菌株对巨噬细胞杀伤的抵抗力更强。此外，缺乏葡萄糖诱导降解复合体的关键成分Gid8的Crabtree阴性酿酒酵母突变株对巨噬细胞杀伤更具抵抗力，并在免疫受损的小鼠中表现出更高的毒力。因此，虽然Crabtree阳性可能赋予酵母菌在环境生态位中的适应性优势，但Crabtree负性提供的更灵活的碳同化策略增强了酵母菌定植和感染哺乳动物宿主的能力。大多数酵母物种占据了环境中的生态位，但也有一些会感染人类。所有物种都必须吸收碳才能生长和定居它们的生态位，但不同的生态位碳来源的可获得性差异很大。环境酵母酿酒酵母被认为是在糖宴和饥荒条件下进化的，因为它进化出了首先利用能量有利的糖，然后转向使用替代碳源的机制。这些机制依赖于分解代谢失活--当葡萄糖存在时，参与替代碳源同化的酶的降解。在致病酵母白色念珠菌中，这些酶不会受到分解代谢失活的影响，它是在缺乏糖的宿主利基环境中进化而来的。因此，白念珠菌可以同时利用糖和替代碳源。我们证明，这种代谢的灵活性提高了对巨噬细胞杀伤、肠道定植和引起全身感染的能力。我们还发现，许多酿酒酵母临床分离株已经失去了分解代谢失活，因此可以同时吸收糖和替代碳源。酿酒酵母分解代谢失活的破坏使其对吞噬细胞的杀伤更具抵抗力，毒力也更强。我们的结论是，新陈代谢的灵活性增强了毒力。
Efficient carbon assimilation is critical for microbial growth and pathogenesis. The environmental yeast Saccharomyces cerevisiae is “Crabtree positive”, displaying a rapid metabolic switch from the assimilation of alternative carbon sources to sugars. Following exposure to sugars, this switch is mediated by the transcriptional repression of genes (carbon catabolite repression) and the turnover (catabolite inactivation) of enzymes involved in the assimilation of alternative carbon sources. The pathogenic yeast Candida albicans is Crabtree negative. It has retained carbon catabolite repression mechanisms, but has undergone posttranscriptional rewiring such that gluconeogenic and glyoxylate cycle enzymes are not subject to ubiquitin-mediated catabolite inactivation. Consequently, when glucose becomes available, C. albicans can continue to assimilate alternative carbon sources alongside the glucose. We show that this metabolic flexibility promotes host colonization and virulence. The glyoxylate cycle enzyme isocitrate lyase (CaIcl1) was rendered sensitive to ubiquitin-mediated catabolite inactivation in C. albicans by addition of a ubiquitination site. This mutation, which inhibits lactate assimilation in the presence of glucose, reduces the ability of C. albicans cells to withstand macrophage killing, colonize the gastrointestinal tract and cause systemic infections in mice. Interestingly, most S. cerevisiae clinical isolates we examined (67%) have acquired the ability to assimilate lactate in the presence of glucose (i.e. they have become Crabtree negative). These S. cerevisiae strains are more resistant to macrophage killing than Crabtree positive clinical isolates. Moreover, Crabtree negative S. cerevisiae mutants that lack Gid8, a key component of the Glucose-Induced Degradation complex, are more resistant to macrophage killing and display increased virulence in immunocompromised mice. Thus, while Crabtree positivity might impart a fitness advantage for yeasts in environmental niches, the more flexible carbon assimilation strategies offered by Crabtree negativity enhance the ability of yeasts to colonize and infect the mammalian host. Most yeast species occupy environmental niches, but some infect humans. All species must assimilate carbon to grow and colonize their niche, but carbon source availability differs significantly between niches. The environmental yeast Saccharomyces cerevisiae is thought to have evolved under conditions of sugar feast and famine because it has evolved mechanisms to exploit energetically favourable sugars first, and then switch to using alternative carbon sources. These mechanisms depend on catabolite inactivation—the degradation of enzymes involved in the assimilation of alternative carbon sources when glucose is present. In the pathogenic yeast Candida albicans, which has evolved in sugar-poor host niches, these enzymes are not subject to catabolite inactivation. Consequently, C. albicans can simultaneously exploit sugars and alternative carbon sources. We demonstrate that this metabolic flexibility promotes resistance to macrophage killing, gut colonization, and the ability to cause systemic infection. We also show that many S. cerevisiae clinical isolates have lost catabolite inactivation, and hence can simultaneously assimilate sugars and alternative carbon sources. The disruption of catabolite inactivation in S. cerevisiae renders it more resistant to phagocytic killing, and more virulent. We conclude that virulence is enhanced by metabolic flexibility.