Mechanisms of Host Adaptation for Candida albicans

描述(申请人提供)：专性共生生物白色念珠菌定植于其人类宿主的肠道，通常不会引起疾病。然而，免疫受损的个体有可能从这种共生的微生物群中获得机会性感染。因此，清楚地了解从共生到病原体的转变是公共卫生的当务之急。在新生隐球菌和烟曲霉等真菌病原体中，膜结合的固醇调节元件结合蛋白(SREBP)是宿主适应和毒力所必需的关键低氧转录因子。在哺乳动物细胞中，SREBPs调节脂质动态平衡。白念珠菌有一个称为Cph2的SREBP同源物，但已知的SREBP功能，如毒力、低氧反应和调节固醇稳态不需要CPH2。然而，白色念珠菌的肠道定植需要Cph2，这表明Cph2控制着一个对共生至关重要的未定义的转录程序。在哺乳动物细胞和新生担子菌中，SREBP蛋白降解需要高尔基位点-1和高尔基位点-2蛋白水解酶。然而，像白色念珠菌这样的子囊菌缺乏Site-2蛋白水解酶。我们最近在裂殖酵母中发现了SREBP激活所需的高尔基体E3连接酶复合体。白念珠菌含有SREBP裂解(DSC)E3连接酶复合体中所有亚基的同源物。在这里，我们将我们对SREBP和DSC E3连接酶复合体的研究带到白色念珠菌。由于为这种专性共生创造生态位的宿主环境的质量尚不清楚，我们将重点关注白色念珠菌的宿主肠道定植。了解定居的具体要求将允许比较共生环境和致病环境，阐明治疗和治疗白色念珠菌感染的潜在靶点。我们假设白色念珠菌SREBP Cph2是宿主肠道定植过程中基因表达所需的主要转录因子，保守的DSC E3连接酶复合体通过介导Cph2激活而在肠道定植中发挥作用。我们的具体目标是：1.确定Cph2在肠道定植过程中的转录靶点。目的2.检测Cph2在肠道定植中的作用是否需要切割和DNA结合。识别宿主肠道中的Cph2转录靶标是了解白色念珠菌所处宿主环境的第一步。我们的研究将产生鉴定小鼠肠道真菌基因表达程序的方案，为其他转录网络的研究提供蓝图。

DESCRIPTION (provided by applicant): The obligate commensal organism Candida albicans colonizes the intestinal tract of its human host, and normally causes no disease. However, immunocompromised individuals risk acquiring opportunistic infections originating from this commensal population of microflora. Thus, a clear understanding of the transition from commensal to pathogen is a public health imperative. In fungal pathogens such as Cryptococcus neoformans and Aspergillus fumigatus, the membrane-bound sterol regulatory element binding protein (SREBP) is a key hypoxic transcription factor required for host adaptation and virulence. In mammalian cells, SREBPs regulate lipid homeostasis. C. albicans has an SREBP homolog called Cph2, but known SREBP functions such as virulence, the hypoxic response, and regulation of sterol homeostasis do not require CPH2. However, C. albicans host intestinal colonization requires Cph2, suggesting that Cph2 controls an undefined transcriptional program essential for commensalism. In mammalian cells and the basidiomycete C. neoformans, SREBP proteolysis requires the Golgi Site-1 and Site-2 proteases. However, ascomycetous fungi like C. albicans lack the Site-2 protease. Our recent work in Schizosaccharomyces pombe identified a Golgi E3 ligase complex required for SREBP activation. C. albicans contains homologs of all subunits in this Defective for SREBP Cleavage (Dsc) E3 ligase complex. Here, we bring our studies of SREBP and the Dsc E3 ligase complex to C. albicans. Because the qualities of the host environment that generate a niche for this obligate commensal are unknown, we will focus on C. albicans host intestinal colonization. Knowing specific requirements for colonization will allow comparison between the commensal and the pathogenic environments, elucidating potential targets for therapeutics and treatment of C. albicans infections. We hypothesize that the C. albicans SREBP Cph2 is a principal transcription factor required for gene expression during host intestinal colonization and that the conserved Dsc E3 ligase complex functions in intestinal colonization by mediating Cph2 activation. Our specific aims are: AIM 1. To determine the transcriptional targets of Cph2 during intestinal colonization. AIM 2. To test whether Cph2 function in intestinal colonization requires cleavage and DNA binding. Identification of Cph2 transcriptional targets in the host intestine represents the first step toward understanding the host environment that Candida albicans inhabits. Our studies will yield protocols for the identification of fungal gene expression programs in the mouse intestine, providing a blueprint for studies of other transcriptional networks.