Institute of Molecular and Cellular Biology, National Tsing Hua University, Hsinchu 30013, Taiwan.
Department of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan.
FEMS Yeast Res. 2019 Mar 1;19(2). doi: 10.1093/femsyr/foz005.
Candida albicans is an important fungal pathogen in humans. Rhb1 is a small GTPase of the Ras superfamily and is conserved from yeasts to humans. In C. albicans, Rhb1 regulates the expression of secreted protease 2, low nitrogen-mediated morphogenesis, and biofilm formation. Moreover, our previous studies have indicated that Rhb1 is associated with the target of rapamycin (TOR) signaling pathway. In this study, we further explored the relationship between Rhb1 and drug susceptibility. The RHB1 deletion mutant exhibited reduced fluconazole susceptibility, and this phenotype occurred mainly through the increased gene expression and activity of efflux pumps. In addition, Mrr1 and Tac1 are transcription factors that can activate efflux pump gene expression. However, the RHB1 deletion, RHB1/MRR1 and RHB1/TAC1 double deletion mutants had no significant differences in efflux pump gene expression and fluconazole susceptibility, suggesting that Rhb1-regulated efflux pump genes do not act through Mrr1 and Tac1. We also showed that membrane localization is crucial for Rhb1 activity in response to fluconazole. Finally, Rhb1 was linked not only to the TOR but also to the Mkc1 mitogen-activated protein kinase signaling pathway in response to fluconazole. In sum, this study unveiled a new role of Rhb1 in the regulation of C. albicans drug susceptibility.
白色念珠菌是一种重要的人类真菌病原体。Rhb1 是 Ras 超家族的一种小 GTPase，从酵母到人类都保守存在。在白色念珠菌中，Rhb1 调节分泌蛋白酶 2、低氮介导的形态发生和生物膜形成的表达。此外，我们之前的研究表明 Rhb1 与雷帕霉素（TOR）信号通路的靶标有关。在这项研究中，我们进一步探讨了 Rhb1 与药物敏感性之间的关系。RHB1 缺失突变体表现出对氟康唑敏感性降低，这种表型主要是通过增加外排泵的基因表达和活性来实现的。此外，Mrr1 和 Tac1 是可以激活外排泵基因表达的转录因子。然而，RHB1 缺失、RHB1/MRR1 和 RHB1/TAC1 双缺失突变体在外排泵基因表达和氟康唑敏感性方面没有显著差异，这表明 Rhb1 调节的外排泵基因不通过 Mrr1 和 Tac1 起作用。我们还表明，膜定位对于 Rhb1 对氟康唑的反应活性至关重要。最后，Rhb1 不仅与 TOR 有关，而且与 Mkc1 有丝分裂原激活蛋白激酶信号通路有关，以响应氟康唑。总之，这项研究揭示了 Rhb1 在调节白色念珠菌药物敏感性方面的新作用。
