Luna-Tapia Arturo, Kerns Morgan E, Eberle Karen E, Jursic Branko S, Palmer Glen E
Department of Microbiology, Immunology and Parasitology, Louisiana State University Health Sciences Center, School of Medicine, New Orleans, Louisiana, USA.
Department of Chemistry, University of New Orleans, New Orleans, Louisiana, USA.
Antimicrob Agents Chemother. 2015 Apr;59(4):2410-20. doi: 10.1128/AAC.04239-14. Epub 2015 Feb 9.
The azole antifungals block ergosterol biosynthesis by inhibiting lanosterol demethylase (Erg11p). The resulting depletion of cellular ergosterol and the accumulation of "toxic" sterol intermediates are both thought to compromise plasma membrane function. However, the effects of ergosterol depletion upon the function of intracellular membranes and organelles are not well described. The purpose of this study was to characterize the effects of azole treatment upon the integrity of the Candida albicans vacuole and to determine whether, in turn, vacuolar trafficking influences azole susceptibility. Profound fragmentation of the C. albicans vacuole can be observed as an early consequence of azole treatment, and it precedes significant growth inhibition. In addition, a C. albicans vps21Δ/Δ mutant, blocked in membrane trafficking through the late endosomal prevacuolar compartment (PVC), is able to grow significantly more than the wild type in the presence of several azole antifungals under standard susceptibility testing conditions. Furthermore, the vps21Δ/Δ mutant is able to grow despite the depletion of cellular ergosterol. This phenotype resembles an exaggerated form of "trailing growth" that has been described for some clinical isolates. In contrast, the vps21Δ/Δ mutant is hypersensitive to drugs that block alternate steps in ergosterol biosynthesis. On the basis of these results, we propose that endosomal trafficking defects may lead to the cellular "redistribution" of the sterol intermediates that accumulate following inhibition of ergosterol biosynthesis. Furthermore, the destination of these intermediates, or the precise cellular compartments in which they accumulate, may be an important determinant of their toxicity and thus ultimately antifungal efficacy.
唑类抗真菌药通过抑制羊毛甾醇脱甲基酶（Erg11p）来阻断麦角固醇的生物合成。由此导致的细胞麦角固醇耗竭以及“有毒”甾醇中间体的积累，都被认为会损害质膜功能。然而，麦角固醇耗竭对细胞内膜和细胞器功能的影响尚无详尽描述。本研究的目的是描述唑类处理对白色念珠菌液泡完整性的影响，并确定液泡运输是否反过来影响唑类敏感性。作为唑类处理的早期结果，可以观察到白色念珠菌液泡的严重碎片化，且发生在显著的生长抑制之前。此外，在标准药敏试验条件下，一个在通过晚期内体前液泡区室（PVC）的膜运输中受阻的白色念珠菌vps21Δ/Δ突变体，在存在几种唑类抗真菌药的情况下，其生长能力明显强于野生型。此外，尽管细胞麦角固醇耗竭，vps21Δ/Δ突变体仍能生长。这种表型类似于已在一些临床分离株中描述的“拖尾生长”的夸张形式。相比之下，vps21Δ/Δ突变体对阻断麦角固醇生物合成中其他步骤的药物高度敏感。基于这些结果，我们提出内体运输缺陷可能导致麦角固醇生物合成受抑制后积累的甾醇中间体在细胞内“重新分布”。此外，这些中间体的去向，或者它们积累的确切细胞区室，可能是其毒性以及最终抗真菌疗效的重要决定因素。
