Studies on signal transduction pathway, which affect virulence of Candida albicans

在各种细胞外信号的作用下，人类真菌病原体白色念珠菌的形态从酵母菌转变为菌丝体。在这里，我们报告了编码G蛋白偶联受体的GPR1和编码Gα亚单位的GPA2是白念珠菌菌丝形成和形态发生所必需的。缺乏Gpr1(gpr1/gpr1)或Gpa2(gpa2/gpa2)的突变体在固体菌丝诱导培养基上菌丝形成和形态发生均有缺陷。固体培养中的这些表型缺陷被外源添加的二丁酰cAMP抑制。生化研究还表明，GPR1和GPA2是葡萄糖依赖的细胞内cAMP增加所必需的。上位性分析表明，Gpr1在Gpa2上游以相同的信号通路发挥作用，双杂交分析表明Gpr1的羧基末端尾巴与Gpa2相互作用。此外，HWP1和ECE1是cAMP依赖的菌丝特异性基因，在两个突变株中的表达水平都降低了。这些发现支持Gpr1和Gpa2以cAMP依赖的方式调节菌丝形成和形态发生的模型。相反，GPR1和GPA2在液体FBS培养基中不是菌丝形成所必需的。此外，gpr11和gpa2突变株在小鼠感染中是完全毒力的。这些发现表明，Gpr1和Gpa2参与了葡萄糖传感机制，该机制通过cAMP依赖的机制调节固体培养中的形态发生和菌丝形成，但在液体培养中或侵袭性念珠菌病期间，它们不是菌丝形成所必需的。

In response to various extracellular signals, the morphology of the human fungal pathogen Candida albicans switches from yeast to hyphal form. Here, we report that GPR1 encoding a putative G-protein coupled receptor and GPA2 encoding a Gα subunit are required for hyphal formation and morphogenesis in C.albicans. Mutants lacking Gpr1(gpr1/gpr1) or Gpa2(gpa2/gpa2) are defective in hyphal formation and morphogenesis on solid hyphal-inducing media. These phenotypic defects in solid cultures are suppressed by exogenously added dibutyryl-cAMP. Biochemical studies also reveal that GPR1 and GPA2 are required for a glucose-dependent increase in cellular cAMP. An epistasis analysis indicates that Gpr1 functions upstream of Gpa2 in the same signaling pathway, and a two-hybrid assay reveals that the carboxyl terminal tail of Gpr1 interacts with Gpa2. Moreover, expression levels of HWP1 and ECE1, which are cAMP-dependent hyphal-specific genes, are reduced in both mutant strains. These findings support a model that Gpr1 as well as Gpa2 regulates hyphal formation and morphogenesis in a cAMP-dependent manner. In contrast, GPR1 and GPA2 are not required for hyphal formation in liquid FBS medium. Furthermore, the gpr1l and the gpa2 mutant strains are fully virulent in a mouse infection. These findings suggest that Gpr1 and Gpa2 are involved in the glucose sensing machinery that regulates morphogenesis and hyphal formation in solid media via a cAMP-dependent mechanism, but they are not required for hyphal formation in liquid medium or during invasive candidiasis.