Interplay between the heat shock response and histidine kinase pathways in the thermally dimorphic fungal pathogen Histoplasma capsulatum

项目摘要 摘要荚膜组织胞浆菌是一种能改变其生长的系统性二型性真菌病原体。 从土壤中的感染性霉菌到哺乳动物宿主中的致病酵母菌。荚膜隐球藻 仅在美国每年就造成多达25,000起危及生命的感染，死亡率高达50%，而且 健康宿主中真菌呼吸道感染的最常见原因。感染发生在土壤 被破坏，便于人类吸入的菌丝碎片或孢子的扩散。孢子和菌丝 片段是主要的感染源；然而，一旦进入宿主，病原体就会转化为 萌芽酵母形式，在宿主巨噬细胞内存活和复制。在实验室里，在 通过改变生长温度来模拟感染和寄生状态：细胞在丝状结构中生长 在室温下形成(菌丝)，而在37℃下生长足以引发酵母形式的生长和 毒力因子的表达。 尽管它对人类健康很重要，但人们对它的感觉和反应知之甚少 对人体温度的影响。我们之前的研究结果极大地有助于理解 包膜螺旋体调节细胞形态和毒力基因表达的分子机制：我们发现 四个转录调控因子，Ryp1，2，3，4，是温度敏感交叉点的核心成分 监管网络。在未发表的研究中，我们全面鉴定了与RYP相互作用的潜在蛋白质 监管角色。在不同的Ryp2相互作用蛋白中，我们鉴定了一种热休克蛋白， HSP90，以及Ssk1和SKn7两个蛋白，具有预测的反应调节结构域。我们发现Hsp90， Ssk1和Skn7调控囊状隐翅虫的酵母相生长。热休克蛋白90在热休克中起关键作用 响应；而响应调节器与传感器组氨酸激酶一起工作，并经常参与感知 环境信号。在这个项目中，我们建议在我们之前的发现的基础上，充分描述 热休克反应和组氨酸激酶通路参与调节Ryp蛋白、细胞 荚膜隐翅虫的形态和毒力特性对寄主温度的响应。这些研究将提供 关于细胞如何感知温度和启动宿主中适当的毒力途径的基本信息。 最终，从这个项目中获得的信息可以用来开发治疗包虫病的药物。 感染，并帮助防止其他二相性真菌感染。

Project Summary Histoplasma capsulatum is one of several systemic dimorphic fungal pathogens that switch their growth program from an infectious mold form in the soil to a pathogenic yeast form in mammalian hosts. H. capsulatum causes up to 25,000 life-threatening infections per year in the U.S. alone with up to 50% mortality rate, and is the most common cause of fungal respiratory infections in healthy hosts. Infection occurs when the soil is disrupted, facilitating dispersion of hyphal fragments or spores that are inhaled by humans. Spores and hyphal fragments are the primary infectious agents; however, once introduced into the host, the pathogen converts to a budding-yeast form, which survives and replicates within host macrophages. In the laboratory, the switch between the infectious and parasitic states is modeled by changing the growth temperature: cells grow in the filamentous form (hyphal) at room temperature, whereas growth at 37ºC is sufficient to trigger growth in the yeast form and expression of virulence factors. Despite its importance to human health, very little is known about how H. capsulatum senses and responds to human body temperature. Our prior research findings significantly contributed to the understanding of the molecular mechanism used by H. capsulatum to regulate cell morphology and virulence gene expression: we found that four transcriptional regulators, Ryp1,2,3,4, are the core components of a temperature-responsive intersecting regulatory network. In unpublished studies, we comprehensively identified Ryp-interacting proteins with potential regulatory roles. Among the diverse set of Ryp2-interacting proteins, we characterized a heat shock protein, Hsp90, and two proteins, Ssk1 and Skn7, with predicted response regulator domains. We found that Hsp90, Ssk1 and Skn7 regulate yeast phase growth in H. capsulatum. Hsp90 plays a key role in the heat shock response; and response regulators work with sensor histidine kinases and are often involved in sensing environmental signals. In this project, we propose to build upon our previous findings and fully characterize the involvement of the heat shock response and histidine kinase pathways in regulating Ryp proteins, cell morphology and virulence traits in H. capsulatum in response to host temperature. These studies will provide fundamental information on how cells sense temperature and turn on the appropriate virulence pathways in the host. Ultimately, the information obtained from this project can be used to develop therapeutics for H. capsulatum infections and help prevent other dimorphic fungal infections.