The HIV positive population is at increased risk for mucosal candidiasis and, in late stage AIDS, for disseminated candidiasis. In the HIV positive population, Candida albicans and Candida glabrata are the first and second most frequent causative agents of vaginal and esophageal candidiasis. Mirroring what is seen in the HIV positive population, C. glabrata is the second most frequently isolated fungal species (after C. albicans) in ICUs in the United States. Little is understood about the interaction of C. glabrata with the human host. The objective of this continuation is to build on our recent discoveries in C. glabrata of a large family of putative adhesins, that have a demonstrated role in virulence. C. glabrata encodes at least 20 cell wall proteins with homology to EPA1, a lectin mediating in vitro adherence to epithelial cells. Most of these genes are telomeric and transcriptionally silent. We have found that this repression is brought about by epigenetic chromatin based silencing and have identified mutants in some of the trans acting factors that mediate this repression. Mutants in these epigenetic regulators show increased EPA gene expression and significant effects on virulence. This finding is significant in as much as it links epigenetic gene regulation with virulence for the first time in a fungal species. This grant proposes to examine how epigenetic control of gene expression impacts virulence in C. glabrata. Mutants in components of the silencing machinery that have been demonstrated to alter virulence will be tested in relevant animal models. Since little is known, even in S. cerevisiae about the cis-acting sequences that serve to initiate silencing at telomeres, the silencer elements required for EPA silencing will be mapped for four EPA clusters. Additional epigenetic regulators of EPA gene expression will be identified using genetic and bioinformatic approaches. IVET approaches will be used to monitor in vivo changes in silencing to determine where and when EPA genes normally repressed by sub telomeric silencing are expressed. This analysis will lead to a much increased understanding of how epigenetic regulation can alter expression of C. glabrata genes, in particular adhesin genes, and how that regulation impacts on colonization and infection of the host.
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