USE OF DISTINCT IRON UPTAKE SYSTEMS BY CANDIDA ALBICANS

描述(申请人提供)：白色念珠菌(Ca)是一种常见的机会性真菌病原体，可导致免疫功能低下的患者发生严重感染。耐药性正在增加，需要确定新的药物靶点。铁的获取已被证明是细菌毒力的一个重要因素，对钙也是如此。缺乏CaFTR1铁渗透酶的基因敲除突变在小鼠模型中是无毒的。我们发现，事实上，钙使用三种遗传和生物化学上不同的铁摄取系统。需要CaFTR1的还原系统能够还原和释放铁的螯合物，包括转铁蛋白螯合物。铁载体系统介导铁载体络合物的吸收，需要铁载体转运蛋白CaSIT1。最后，一个血红素铁利用系统需要由CaHMX1编码的血红素加氧酶。 在AIM1中，将通过测量不同底物的铁摄取以及通过测量CaSIT1、CaFTR1和CaHMX1的表达来测试不同系统在不同类型的压力下的使用情况。缺乏其中一个铁吸收系统的缺失菌株将被测试生长特性、表型和敏感性。在目标2中，将在包括口咽(上)念珠菌病、内皮细胞侵袭、中性粒细胞相互作用和小鼠静脉感染的模型系统中评估不同摄取系统的使用。缺乏个体摄取系统的敲除基因将在这些模型系统中对其行为进行评估，并注意可能改变毒力的缺陷。最后，在目标3中，将使用微阵列来检测来自不同铁源的铁吸收(通过不同的吸收系统)对毒力基因表达的影响。 这项工作的假设是，不同的铁获取途径在不同的宿主环境中活跃，并可能在这些环境中介导毒力感染。

DESCRIPTION (provided by applicant): Candida albicans (Ca) is a common opportunistic fungal pathogen that causes serious infections in immunocompromised patients. Drug resistance is increasing, and there is a need to identify new drug targets. Iron acquisition has been shown to be an important factor for virulence of bacteria, as well as for Ca. Knockout mutants lacking the CaFTR1 iron permease are avirulent in mouse models. We have found that Ca, in fact, uses three genetically and biochemically distinct iron uptake systems. A reductive system, requiring CaFTR1, is able to reduce and release ferric iron chelates, including transferrin chelates. A siderophore system mediates uptake of ferrisiderophore chelates of the ferrichrome type and requires the siderophore transporter CaSIT1. Finally, a heme iron utilization system requires heme oxygenase encoded by CaHMXl. In Aim1 usage of the different systems will be tested under varied types of stress by measuring iron uptake from different substrates and by measuring expression of CaSIT1, CaFTR1 and CaHMX1. Deletion strains lacking in one of the iron uptake systems will be tested for growth properties, phenotypes and sensitivities. In Aim 2, usage of the different uptake systems will be evaluated in model systems that include a model of oropharyngeal (epithelial) candidiasis, endothelial cell invasion, neutrophil interaction and intravenous infection of mice. Knockouts lacking individual uptake systems will be evaluated for their behavior in these model systems, with attention to deficits that may alter virulence. Finally in Aim 3, microarrays will be used to examine the effects of iron uptake from different iron sources (via different uptake systems) on expression of virulence genes. The hypothesis of this work is that different iron acquisition pathways are active in different host environments and may mediate virulent infections in those settings.