磷脂酰肌醇磷酸酯是具有一系列调节作用的关键磷脂,包括膜运输和细胞极性。高尔基体上的磷脂酰肌醇-4-磷酸[PI(4)P]是人类致病真菌白色念珠菌中出芽到丝状生长过渡所必需的;但是,质膜PI(4)P的作用尚不清楚。我们已经研究了这种磷脂在白色念珠菌生长中的重要性,应激反应,通过产生质膜PI(4)P水平降低的突变株和毒力,通过缺失PI-4激酶复合物的成分,即,Efr3、Ypp1和Stt4。efr3Δ/Δ和ypp1Δ/Δ突变体中质膜PI(4)P的含量分别为〜60%和〜40%,分别,在野生型菌株中,而在stt4Δ/Δ突变体中几乎检测不到。所有三种突变体均具有降低的血浆膜磷脂酰丝氨酸(PS)。尽管这些突变体具有正常的酵母期生长,它们在丝状生长方面有缺陷,表现出细胞壁完整性的缺陷,并且增加了细胞壁β(1,3)-葡聚糖的暴露,然而他们诱导了一系列菌丝特异性基因。在血液播散性念珠菌病的小鼠模型中,真菌质膜PI(4)P水平与毒力直接相关;efr3Δ/Δ突变体具有野生型毒力,ypp1Δ/Δ突变体具有减弱的毒力,而stt4Δ/Δ突变体没有引起致死性。在口咽念珠菌病小鼠模型中,只有ypp1Δ/Δ突变体的毒力降低,表明质膜PI(4)P对口咽的增殖不太重要。总的来说,这些结果表明,质膜PI(4)P水平在成丝中起核心作用,细胞壁完整性,以及白色念珠菌的毒力.重要性虽然PI-4激酶Pik1和Stt4都产生PI(4)P,前者在高尔基体产生PI(4)P,后者在质膜产生PI(4)P,这两个池在功能上是不同的。为了解决白色念珠菌质膜PI(4)P的重要性,我们产生了三种推定的质膜PI-4激酶复合物组分的缺失突变体,并定量了这些菌株中每个菌株的质膜PI(4)P水平.我们的工作表明,这种磷脂酰肌醇磷酸酯对于酵母到菌丝的转变是特别关键的,细胞壁完整性,和小鼠全身感染模型中的毒力。这项工作的意义在于确定具有感染特异性作用的质膜磷脂,这归因于质膜PI(4)P的损失,导致β(1,3)-葡聚糖的掩蔽。
Phosphatidylinositol phosphates are key phospholipids with a range of regulatory roles, including membrane trafficking and cell polarity. Phosphatidylinositol-4-phosphate [PI(4)P] at the Golgi apparatus is required for the budding-to-filamentous-growth transition in the human-pathogenic fungus Candida albicans; however, the role of plasma membrane PI(4)P is unclear. We have investigated the importance of this phospholipid in C. albicans growth, stress response, and virulence by generating mutant strains with decreased levels of plasma membrane PI(4)P, via deletion of components of the PI-4-kinase complex, i.e., Efr3, Ypp1, and Stt4. The amounts of plasma membrane PI(4)P in the efr3Δ/Δ and ypp1Δ/Δ mutants were ∼60% and ∼40%, respectively, of that in the wild-type strain, whereas it was nearly undetectable in the stt4Δ/Δ mutant. All three mutants had reduced plas7ma membrane phosphatidylserine (PS). Although these mutants had normal yeast-phase growth, they were defective in filamentous growth, exhibited defects in cell wall integrity, and had an increased exposure of cell wall β(1,3)-glucan, yet they induced a range of hyphal-specific genes. In a mouse model of hematogenously disseminated candidiasis, fungal plasma membrane PI(4)P levels directly correlated with virulence; the efr3Δ/Δ mutant had wild-type virulence, the ypp1Δ/Δ mutant had attenuated virulence, and the stt4Δ/Δ mutant caused no lethality. In the mouse model of oropharyngeal candidiasis, only the ypp1Δ/Δ mutant had reduced virulence, indicating that plasma membrane PI(4)P is less important for proliferation in the oropharynx. Collectively, these results demonstrate that plasma membrane PI(4)P levels play a central role in filamentation, cell wall integrity, and virulence in C. albicans. IMPORTANCE While the PI-4-kinases Pik1 and Stt4 both produce PI(4)P, the former generates PI(4)P at the Golgi apparatus and the latter at the plasma membrane, and these two pools are functionally distinct. To address the importance of plasma membrane PI(4)P in Candida albicans, we generated deletion mutants of the three putative plasma membrane PI-4-kinase complex components and quantified the levels of plasma membrane PI(4)P in each of these strains. Our work reveals that this phosphatidylinositol phosphate is specifically critical for the yeast-to-hyphal transition, cell wall integrity, and virulence in a mouse systemic infection model. The significance of this work is in identifying a plasma membrane phospholipid that has an infection-specific role, which is attributed to the loss of plasma membrane PI(4)P resulting in β(1,3)-glucan unmasking.