Determination of morphology and virulence in Candida albicans

描述(申请人提供)：白色念珠菌，人类的主要真菌病原体，负责各种系统和粘膜感染。艾滋病患者、器官移植受者、接受化疗的癌症患者、人工关节和假体设备的接受者以及其他免疫功能低下的人特别容易受到白色念珠菌的感染。众所周知，白念珠菌经历了从酵母(单个圆形萌发细胞)到假菌丝和菌丝(细长细胞端到端连接)的形态转变，这是毒力所必需的。我们的长期目标是确定白色念珠菌如何控制形态并提高毒力，以响应宿主环境线索。尽管假菌丝和菌丝形态之间的表型差异已经被很好地描述，但人们对决定每种形态生长的调控机制或每种形态在毒力中所起的具体作用知之甚少。为了解决这些问题，我们最近培育了一株白色念珠菌，可以通过遗传操作在体外非丝状诱导条件下完全生长在菌丝形态中。我们还发现，这种菌株能够促进系统性念珠菌病小鼠模型中菌丝形成的增加和毒力的提高。我们的菌株是通过将白念珠菌菌丝延伸和毒力的一种新的细丝特异转录调节因子UME6的一个等位基因置于可调节启动子的控制下而产生的。有趣的是，虽然高水平的UME6表达驱动着完整的菌丝生长，但中间水平的UME6指定了一个主要的假菌丝种群，这表明UME6表达水平足以以一种剂量依赖的方式决定白色念珠菌的形态。初步研究表明，随着UME6水平的升高，诱导的细丝特异转录本的数量及其诱导水平都会增加。我们的假设是，受宿主环境线索影响的UME6水平通过控制重叠的细丝特异转录组的表达水平来决定白色念珠菌的形态和毒力。为了解决这一假设，我们计划实现以下三个特定目标：1)确定上游宿主环境信号和已知的白念珠菌丝状生长调控电路如何控制UME6的表达；2)确定UME6剂量表达的白念珠菌基因的转录图谱；3)确定UME6水平对确定白念珠菌形态和促进毒力的能力至关重要的特定下游机制。最终，这些研究将显著提高我们对真菌病原体如何在宿主环境中指定形态和促进毒力的理解，并将提供可能导致开发新的和更有效的抗真菌策略的信息。 与公共卫生相关：白色念珠菌是导致酵母感染的主要酵母，也会导致免疫系统薄弱的人死亡。这项研究建议旨在更好地了解白色念珠菌是如何作为一种有效的病原体发挥作用的。最终，这些研究应该提供信息，从而开发出更有效的酵母感染治疗方法。

DESCRIPTION (provided by applicant): Candida albicans, the major human fungal pathogen, is responsible for a wide variety of systemic and mucosal infections. AIDS patients, organ transplant recipients, cancer patients undergoing chemotherapy, recipients of artificial joints and prosthetic devices and other immunocompromised individuals are particularly susceptible to C. albicans infections. C. albicans is known to undergo a morphological transition from yeast (single, round budding cells) to pseudohyphal and hyphal filaments (elongated cells attached end-to-end) which is required for virulence. Our long-term goal is to determine how C. albicans controls morphology and promotes virulence in response to host environmental cues. Although phenotypic differences between pseudohyphal and hyphal forms have been well-characterized, very little is known about the regulatory mechanisms that determine growth in each morphology or the specific role that each morphology plays in virulence. In order to address these questions, we have recently generated a C. albicans strain that can be genetically manipulated to grow completely in the hyphal morphology under non-filament-inducing conditions in vitro. We have also found that this strain is capable of driving increased hyphal formation and promoting virulence in a mouse model of systemic candidiasis. Our strain was generated by placing one allele of a novel filament-specific transcriptional regulator of C. albicans hyphal extension and virulence, UME6, under the control of a regulatable promoter. Interestingly, while high-level UME6 expression drives complete hyphal growth, intermediate UME6 levels specify a largely pseudohyphal population, indicating that UME6 expression levels are sufficient to determine C. albicans morphology in a dosage-dependent manner. Preliminary studies show an increase in both the number of filament-specific transcripts induced as well as their level of induction as UME6 levels rise. Our hypothesis is that UME6 levels, which are affected by host environmental cues, determine C. albicans morphology and virulence by controlling the expression level of overlapping sets of filament-specific transcripts. In order to address this hypothesis we plan to carry out the following three specific aims: 1) determine how upstream host environmental signals and known C. albicans filamentous growth regulatory circuits control the expression of UME6, 2) determine the transcriptional profile of C. albicans genes expressed as UME6 dosage specifies pseudohyphal and hyphal morphologies and promotes virulence during infection, 3) identify specific downstream mechanisms that are important for the ability of UME6 levels to determine C. albicans morphology and promote virulence. Ultimately, these studies will significantly improve our understanding of how fungal pathogens specify morphology and promote virulence in the host environment and will provide information that could lead to the development of novel and more effective antifungal strategies. PUBLIC HEALTH RELEVANCE: Candida albicans is the major yeast that causes yeast infections and also kills people with weakened immune systems. This research proposal aims to gain a better understanding of how Candida albicans is able to function as such an effective pathogen. Ultimately, these studies should provide information leading to the development of more effective treatments for yeast infections.