蛋白激酶A調控熱帶念珠菌之生長及致病力

Abstract

熱帶念珠菌(Candida tropicalis)是一伺機性人體病原真菌，會感染皮膚、口腔黏膜、生殖道，甚至造成高致死率的全身性感染。研究指出，念珠菌的生物膜形成及附著於寄主之能力與致病性有高度相關。在啤酒酵母菌(Saccharomyces cerevisiae)與白色念珠菌(Candida albicans)中，與蛋白激酶A 途徑相關的基因和型態發育及附著能力有顯著相關。白色念珠菌的蛋白激酶A 是由Tpk1 及Tpk2 共同組成，調控菌絲生長、附著、生物膜等；而在壓力反應及致病力中也扮演較關鍵的角色。然而蛋白激酶A 在熱帶念珠菌所扮演的角色尚未被釐清，因此本研究欲探討其調控機制。我們的實驗證明TPK1 與真菌遭遇壓力反應時細胞壁完整性及藥物耐受性相關；而TPK2 基因缺失後造成蛋白激酶A 活性喪失，且造成菌絲生長及附著力之缺陷等影響；當兩基因共同敲除後突變株生長速率明顯減緩、菌絲生長能力受損。透過小鼠系統性感染實驗，證實TPK1 及TPK2 共同調控熱帶念珠菌的致病力。我們進一步進行反轉錄即時聚合酶鏈式反應實驗，結果顯示EFG1 及HWP1 受到蛋白激酶A 的調控，而BCR1、FLO8、GAL4、RIM101 可能與tpk1/tpk1 tpk2/tpk2 突變株細胞聚集相關，說明Tpk1 和Tpk2 與調控轉錄因子有密切關連性。本研究發現熱帶念珠菌的Tpk1 參與壓力反應，Tpk2 在菌絲生成和附著力上扮演關鍵調控因子，而Tpk1 和Tpk2 兩者在真菌生長與致病力中是不可或缺的。

Candida tropicalis is one of the most important human fungal pathogens causing superficial infections in locations such as the oral mucosa and genital tract, as well as systemic infections with high mortality. In Candida albicans, the cyclic AMP/protein kinase A (cAMP/PKA) pathway regulates fungal adhesion and dimorphism, both of which correlate closely with virulence. CaTpk1 and CaTpk2, the catalytic subunits of PKA, not only share redundant functions in hyphal growth, adhesion, and biofilm formation, but also have distinct roles in stress responses and pathogenesis, respectively. However, studies on PKA of the emerging fungal pathogen C. tropicalis are limited. Our results suggest that Tpk1 is involved in cell wall integrity and drug tolerance. The tpk2/tpk2 mutants, which have no protein kinase A activity, have reduced hyphal growth and adhesion. In addition, the tpk1/tpk1 tpk2/tpk2 double deletion mutant demonstrated delayed growth and impaired hyphal formation. In a murine model of systemic infection, both TPK1 and TPK2 are required for full virulence. We further found that EFG1 and HWP1 expression is regulated by PKA, while BCR1, FLO8, GAL4, and RIM101 might be associated with cell aggregation in the tpk1/tpk1 tpk2/tpk2 mutant. This study demonstrates that Tpk1 is involved in stress responses, while Tpk2 serves as a key regulator in dimorphism and adhesion. Both Tpk1 and Tpk2 are required for growth and full virulence in C. tropicalis.