Candida albicans causes invasive infections like candidemia and intra-abdominal canididiasis (IAC) that are common among hospitalized patients. The C. albicans cell wall is central to the pathogenesis of candidiasis, but mechanisms that link cell wall regulation and virulence are only beginning to be understood. Cell wall-active echinocandin antifungals are front-line agents against invasive candidiasis. However, mortality rates among patients with candidemia or IAC who are treated with echinocandins are 40% or higher. We have shown that C. albicans rapidly delocalizes phosphatidylinositol-(4,5)-bisphosphate (PI(4,5)P2) and septins as part of the natural response to echinocandins. Targeted disruption of C. albicans INP51, which encodes a PI(4,5)P2-specific 5'- phosphatase, results in PI(4,5)P2 and septin dysregulation, echinocandin hypersusceptibility, over-activation of the PKC-Mkc1 cell wall integrity pathway in response to stress, cell wall damage gene expression profiles in absence of stress, and attenuated virulence during hematogenously disseminated candidiasis (DC) and IAC in mice. Our data demonstrate that balanced PI(4,5)P2 regulation promotes protective cell wall responses and virulence through activation of the PKC-Mkc1 pathway, while PI(4,5)P2 dysregulation is associated with deleterious septin, plasma membrane and cell wall responses. More recently, we established that C. albicans CAS5, which encodes a major transcription factor downstream of Inp51 and Mkc1, and RIM101, which encodes a transcription factor induced at pH>5.5, during IAC and in the inp51 mutant, are important determinants of echinocandin responses and virulence. The objectives of this project are to determine mechanisms by which C. albicans CAS5 and RIM101 regulate cell wall stress responses and contribute to echinocandin resistance and the pathogenesis of invasive candidiasis.
In aim 1, we will validate genes regulated by C. albicans CAS5 during IAC as virulence determinants, and identify their biologic functions. Toward these ends, we will use RNA-Seq to perform transcriptional profiling of cas5 null mutant and CAS5 reconstitution strains in vitro and temporal- spatially during IAC of mice. Then, we will validate certain Cas5-regulated genes as virulence determinants by testing mutant strains in the mouse models of IAC and DC, and characterize their functions.
In aim 2, we will use similar approaches to validate genes regulated by RIM101 during IAC as virulence determinants, and identify their functions.
In aim 3, we will identify genes regulated by C. albicans CAS5 and RIM101 in response to micafungin during IAC, and validate their roles in echinocandin resistance or susceptibility. We will perform RNA-Seq transcriptional profiling of C. albicans wild-type SC5314, cas5, rim101 and the respective reconstitution strains in response to micafungin in vitro and during IAC, and validate certain genes as contributing to micafungin responses in vivo . This project will provide new insights into echinocandin and cell wall stress responses by C. albicans that are relevant to the treatment and pathogenesis of invasive candidiasis, and which have the potential to identify new therapeutic and diagnostic targets.
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