Willger Sven D, Cornish E Jean, Chung Dawoon, Fleming Brittany A, Lehmann Margaret M, Puttikamonkul Srisombat, Cramer Robert A
Department of Immunology and Infectious Disease, Montana State University, Bozeman, Montana, USA.
Eukaryot Cell. 2012 Dec;11(12):1557-67. doi: 10.1128/EC.00252-12. Epub 2012 Oct 26.
Hypoxia is an environmental stress encountered by Aspergillus fumigatus during invasive pulmonary aspergillosis (IPA). The ability of this mold to adapt to hypoxia is important for fungal virulence and genetically regulated in part by the sterol regulatory element binding protein (SREBP) SrbA. SrbA is required for fungal growth in the murine lung and to ultimately cause lethal disease in murine models of IPA. Here we identified and partially characterized four genes (dscA, dscB, dscC, and dscD, here referred to as dscA-D) with previously unknown functions in A. fumigatus that are orthologs of the Schizosaccharomyces pombe genes dsc1, dsc2, dsc3, and dsc4 (dsc1-4), which encode a Golgi E3 ligase complex critical for SREBP activation by proteolytic cleavage. A. fumigatus null dscA-D mutants displayed remarkable defects in hypoxic growth and increased susceptibility to triazole antifungal drugs. Consistent with the confirmed role of these genes in S. pombe, both ΔdscA and ΔdscC resulted in reduced cleavage of the SrbA precursor protein in A. fumigatus. Inoculation of corticosteroid immunosuppressed mice with ΔdscA and ΔdscC strains revealed that these genes are critical for A. fumigatus virulence. Reintroduction of SrbA amino acids 1 to 425, encompassing the N terminus DNA binding domain, into the ΔdscA strain was able to partially restore virulence, further supporting a mechanistic link between DscA and SrbA function. Thus, we have shown for the first time the importance of a previously uncharacterized group of genes in A. fumigatus that mediate hypoxia adaptation, fungal virulence, and triazole drug susceptibility and that are likely linked to regulation of SrbA function.
缺氧是烟曲霉在侵袭性肺曲霉病（IPA）过程中遇到的一种环境应激。这种霉菌适应缺氧的能力对真菌毒力很重要，并且部分受固醇调节元件结合蛋白（SREBP）SrbA的基因调控。SrbA是烟曲霉在小鼠肺部生长以及在IPA小鼠模型中最终导致致命疾病所必需的。在这里，我们鉴定并部分表征了烟曲霉中四个功能未知的基因（dscA、dscB、dscC和dscD，以下简称dscA - D），它们是粟酒裂殖酵母基因dsc1、dsc2、dsc3和dsc4（dsc1 - 4）的直系同源基因，后者编码一种高尔基体E3连接酶复合物，该复合物对通过蛋白水解切割激活SREBP至关重要。烟曲霉dscA - D基因缺失突变体在缺氧生长方面表现出显著缺陷，并且对三唑类抗真菌药物的敏感性增加。与这些基因在粟酒裂殖酵母中已证实的作用一致，ΔdscA和ΔdscC都导致烟曲霉中SrbA前体蛋白的切割减少。用ΔdscA和ΔdscC菌株接种皮质类固醇免疫抑制小鼠表明，这些基因对烟曲霉毒力至关重要。将包含N端DNA结合结构域的SrbA氨基酸1至425重新导入ΔdscA菌株能够部分恢复毒力，进一步支持了DscA和SrbA功能之间的机制联系。因此，我们首次证明了烟曲霉中一组先前未表征的基因的重要性，这些基因介导缺氧适应、真菌毒力和三唑类药物敏感性，并且可能与SrbA功能的调节有关。
