The Candida albicans fimbrin Sac6 regulates oxidative stress response (OSR) and morphogenesis at the transcriptional level

• SAC6 encodes the actin bundling protein fimbrin in C. albicans.
• Sac6 highly affects oxidative stress tolerance.
• Sac6 regulates OSR by affecting cytoplasm-to-nucleus transport of Cap1.
• Sac6 regulates transcription of morphogenesis-related genes.
• Sac6 is involved regulation of secretion and pathogenicity of C. albicans.

The actin cytoskeleton coordinates numerous fundamental cellular processes. Fimbrins are a class of evolutionally conserved ABPs that mediate actin bundling and regulate actin dynamics and functions. In this study, we identified the fimbrin Sac6 from the important fungal pathogen, Candida albicans. Interestingly, deletion of SAC6 led to increased tolerance to oxidative stress, while its overexpression caused hyper-susceptibility to this stress. Further investigations revealed that Sac6, by interaction with actin, negatively regulated the cytosol-to-nucleus transport of the key OSR (oxidative stress response) transcription factor Cap1 and consequent expression of OSR genes. Moreover, loss of Sac6 enhanced hyphal maintenance, and its overexpression caused a defect in hyphal development, which was attributed to abnormal expression of morphogenesis-related genes. In addition, Sac6 was involved in regulation of secretion of lytic enzymes and virulence of C. albicans. This study reveals a novel mechanism by which fimbrin transcriptionally regulates OSR and morphogenesis, and sheds a novel light on the functions of actin cytoskeleton.

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