From the School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India.
J Biol Chem. 2014 Feb 7;289(6):3365-82. doi: 10.1074/jbc.M113.528802. Epub 2013 Dec 19.
Candida albicans is a leading cause of fungal infections worldwide. It has several glycosylphosphatidylinositol (GPI)-anchored virulence factors. Inhibiting GPI biosynthesis attenuates its virulence. Building on our previous work, we explore the interaction of GPI biosynthesis in C. albicans with ergosterol biosynthesis and hyphal morphogenesis. This study is also the first report of transcriptional co-regulation existing between two subunits of the multisubunit enzyme complex, GPI-N-acetylglucosaminyltransferase (GPI-GnT), involved in the first step of GPI anchor biosynthesis in eukaryotes. Using mutational analysis, we show that the accessory subunits, GPI2 and GPI19, of GPI-GnT exhibit opposite effects on ergosterol biosynthesis and Ras signaling (which determines hyphal morphogenesis). This is because the two subunits negatively regulate one another; GPI19 mutants show up-regulation of GPI2, whereas GPI2 mutants show up-regulation of GPI19. Two different models were examined as follows. First, the two GPI-GnT subunits independently interact with ergosterol biosynthesis and Ras signaling. Second, the two subunits mutually regulate one another and thereby regulate sterol levels and Ras signaling. Analysis of double mutants of these subunits indicates that GPI19 controls ergosterol biosynthesis through ERG11 levels, whereas GPI2 determines the filamentation by cross-talk with Ras1 signaling. Taken together, this suggests that the first step of GPI biosynthesis talks to and regulates two very important pathways in C. albicans. This could have implications for designing new antifungal strategies.
白色念珠菌是全球真菌感染的主要原因。它有几种糖基磷脂酰肌醇（GPI）锚定的毒力因子。在我们之前的工作基础上，我们探索了白色念珠菌 GPI 生物合成与麦角固醇生物合成和菌丝形态发生的相互作用。这项研究也是第一个报道真核生物 GPI 锚生物合成第一步中涉及的多亚基酶复合物的两个亚基之间存在转录共调节的报告。通过突变分析，我们表明 GPI-N-乙酰葡萄糖胺基转移酶（GPI-GnT）的辅助亚基 GPI2 和 GPI19 对麦角固醇生物合成和 Ras 信号（决定菌丝形态发生）表现出相反的影响。这是因为这两个亚基相互负调控；GPI19 突变体显示 GPI2 的上调，而 GPI2 突变体显示 GPI19 的上调。检查了以下两种不同的模型。首先，两个 GPI-GnT 亚基独立地与麦角固醇生物合成和 Ras 信号相互作用。其次，两个亚基相互调节彼此，从而调节固醇水平和 Ras 信号。这些亚基的双突变体分析表明，GPI19 通过 ERG11 水平控制麦角固醇生物合成，而 GPI2 通过与 Ras1 信号的交叉对话决定丝状生长。总的来说，这表明 GPI 生物合成的第一步与白色念珠菌中的两个非常重要的途径进行了对话并进行了调节。这可能对设计新的抗真菌策略具有重要意义。
