Day Alison M, Cao Min, Dantas Alessandra da Silva, Ianieva Olga, Herrero-de-Dios Carmen, Brown Alistair J P, Quinn Janet
Newcastle University Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
School of Dental Sciences, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
PLoS Pathog. 2024 Dec 23;20(12):e1012314. doi: 10.1371/journal.ppat.1012314. eCollection 2024 Dec.
The Hog1 stress-activated protein kinase (SAPK) is a key mediator of stress resistance and virulence in Candida albicans. Hog1 activation via phosphorylation of the canonical TGY motif is mediated by the Pbs2 MAPKK, which itself is activated by the Ssk2 MAPKKK. Although this three-tiered SAPK signalling module is well characterised, it is unclear how Hog1 activation is regulated in response to different stresses. Functioning upstream of the Ssk2 MAPKKK is a two-component related signal transduction system comprising three sensor histidine kinases, a phosphotransfer protein Ypd1, and a response regulator Ssk1. Here, we report that Ssk1 is a master regulator of the Hog1 SAPK that promotes stress resistance and Hog1 phosphorylation in response to diverse stresses, except high osmotic stress. Notably, we find Ssk1 regulates Hog1 in a two-component independent manner by functioning to promote interactions between the Ssk2 and Pbs2 kinases. We propose this function of Ssk1 is important to maintain a basal level of Hog1 phosphorylation which is necessary for oxidative stress, but not osmotic stress, mediated Hog1 activation. We find that osmotic stress triggers robust Pbs2 phosphorylation which drives its dissociation from Ssk2. In contrast, Pbs2 is not robustly phosphorylated following oxidative stress and the Ssk1-mediated Ssk2-Pbs2 interaction remains intact. Instead, oxidative stress-stimulated increases in phosphorylated Hog1 is dependent on the inhibition of protein tyrosine phosphatases that negatively regulate Hog1 coupled with the Ssk1-mediated promotion of basal Hog1 activity. Furthermore, we find that inhibition of protein tyrosine phosphatases is linked to the hydrogen peroxide induced oxidation of these negative regulators in a mechanism that is partly dependent on thioredoxin. Taken together these data reveal stress contingent changes in Hog1 pathway architecture and regulation and uncover a novel mode of action of the Ssk1 response regulator in SAPK regulation.
Hog1应激激活蛋白激酶（SAPK）是白色念珠菌应激抗性和毒力的关键介质。通过经典TGY基序的磷酸化激活Hog1由Pbs2 MAPKK介导，而Pbs2本身由Ssk2 MAPKKK激活。尽管这个三层的SAPK信号模块已得到充分表征，但尚不清楚Hog1激活如何响应不同应激而受到调节。在Ssk2 MAPKKK上游起作用的是一个双组分相关信号转导系统，包括三个传感器组氨酸激酶、一个磷酸转移蛋白Ypd1和一个响应调节因子Ssk1。在此，我们报告Ssk1是Hog1 SAPK的主要调节因子，可促进对多种应激（高渗应激除外）的应激抗性和Hog1磷酸化。值得注意的是，我们发现Ssk1以双组分独立的方式调节Hog1，其作用是促进Ssk2和Pbs2激酶之间的相互作用。我们提出Ssk1的这一功能对于维持Hog1磷酸化的基础水平很重要，这对于氧化应激介导的Hog1激活是必需的，但对于渗透应激则不是。我们发现渗透应激会触发强烈的Pbs2磷酸化，从而导致其与Ssk2解离。相反，氧化应激后Pbs2不会被强烈磷酸化，并且Ssk1介导的Ssk2-Pbs2相互作用保持完整。取而代之的是，氧化应激刺激的磷酸化Hog1增加依赖于对负调节Hog1的蛋白酪氨酸磷酸酶（PTP）的抑制，以及Ssk1介导的基础Hog1活性的促进。此外，我们发现抑制蛋白酪氨酸磷酸酶与过氧化氢诱导的这些负调节因子的氧化有关，其机制部分依赖于硫氧还蛋白。这些数据共同揭示了Hog1途径结构和调节中的应激依赖性变化，并揭示了Ssk1响应调节因子在SAPK调节中的一种新作用模式。
