Department of Biotechnology, Center for Fungal Pathogenesis, College of Life Science and Biotechnology, Yonsei University, Seoul, Republic of Korea.
Fungal Genet Biol. 2012 Apr;49(4):332-45. doi: 10.1016/j.fgb.2012.02.001. Epub 2012 Feb 11.
Maintenance of cation homeostasis is essential for survival of all living organisms in their biological niches. It is also important for the survival of human pathogenic fungi in the host, where cation concentrations and pH will vary depending on different anatomical sites. However, the exact role of diverse cation transporters and ion channels in virulence of fungal pathogens remains elusive. In this study we functionally characterized ENA1 and NHA1, encoding a putative Na(+)/ATPase and Na(+)/H(+) antiporter, respectively, in Cryptococcus neoformans, a basidiomycete fungal pathogen which causes fatal meningoencephalitis. Expression of NHA1 and ENA1 is induced in response to salt and osmotic shock mainly in a Hog1-dependent manner. Phenotypic analysis of the ena1Δ, nha1Δ, and ena1Δnha1Δ mutants revealed that Ena1 controls cellular levels of toxic cations, such as Na(+) and Li(+) whereas both Ena1 and Nha1 are important for controlling less toxic K(+) ions. Under alkaline conditions, Ena1 was highly induced and required for growth in the presence of low levels of Na(+) or K(+) salt and Nha1 played a role in survival under K(+) stress. In contrast, Nha1, but not Ena1, was essential for survival at acidic conditions (pH 4.5) under high K(+) stress. In addition, Ena1 and Nha1 were required for maintenance of plasma membrane potential and stability, which appeared to modulate antifungal drug susceptibility. Perturbation of ENA1 and NHA1 enhanced capsule production and melanin synthesis. However, Nha1 was dispensable for virulence of C. neoformans although Ena1 was essential. In conclusion, Ena1 and Nha1 play redundant and discrete roles in cation homeostasis, pH regulation, membrane potential, and virulence in C. neoformans, suggesting that these transporters could be novel antifungal drug targets for treatment of cryptococcosis.
维持阳离子内环境稳态对于所有生物在其生态位中的生存都是至关重要的。这对于人类病原真菌在宿主中的生存也是很重要的，因为阳离子浓度和 pH 值会根据不同的解剖部位而变化。然而，不同阳离子转运体和离子通道在真菌病原体毒力中的确切作用仍然难以捉摸。在这项研究中，我们对荚膜组织胞浆菌（一种担子菌真菌病原体，可引起致命性脑膜脑炎）中的 ENA1 和 NHA1 进行了功能表征，分别编码一种假定的 Na(+)/ATP 酶和 Na(+)/H(+)反向转运蛋白。NHA1 和 ENA1 的表达在盐和渗透压冲击下被诱导，主要以 Hog1 依赖的方式诱导。ena1Δ、nha1Δ 和 ena1Δnha1Δ 突变体的表型分析表明，Ena1 控制细胞内有毒阳离子（如 Na(+)和 Li(+)）的水平，而 Ena1 和 Nha1 对于控制毒性较小的 K(+)离子都很重要。在碱性条件下，Ena1 高度诱导，在低浓度 Na(+)或 K(+)盐存在的情况下生长需要 Ena1，而 Nha1 在 K(+)应激下的存活中起作用。相比之下，Nha1 但不是 Ena1，对于高 K(+)应激下的酸性条件（pH 4.5）的生存是必需的。此外，Ena1 和 Nha1 对于维持质膜电位和稳定性是必需的，这似乎调节了抗真菌药物的敏感性。ENA1 和 NHA1 的扰动增强了荚膜的产生和黑色素的合成。然而，尽管 Ena1 是必需的，但 Nha1 对于荚膜组织胞浆菌的毒力是可有可无的。总之，Ena1 和 Nha1 在阳离子内环境稳态、pH 调节、膜电位和荚膜组织胞浆菌的毒力中发挥冗余和离散的作用，这表明这些转运蛋白可能是新型抗真菌药物治疗隐球菌病的靶点。
