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ABSTRACTThe ability of Candida albicansto invade mucosal tissues is a major virulence determinant of this organism; however, the mechanism of invasion is not understood in detail. Proteolytic breakdown of E-cadherin, the major protein in epithelial cell junctions, has been proposed as a mechanism of invasion of certain bacteria in the oral mucosa. The objectives of this study were (i) to assess whether C. albicansdegrades E-cadherin expressed by oral epithelial cells in vitro; (ii) to compare the abilities of strains with different invasive potentials to degrade this protein; and (iii) to investigate fungal virulence factors responsible for E-cadherin degradation. We found that while E-cadherin gene expression was not altered, E-cadherin was proteolytically degraded during the interaction of oral epithelial cells with C. albicans. Moreover, C. albicans-mediated degradation of E-cadherin was completely inhibited in the presence of protease inhibitors. Using a three-dimensional model of the human oral mucosa, we found that E-cadherin was degraded in localized areas of tissue invasion by C. albicans. An invasion-deficient rim101−/rim101−strain was deficient in degradation of E-cadherin, and this finding suggested that proteases may depend on Rim101p for expression. Indeed, reverse transcription-PCR data indicated that expression of the SAP4, SAP5, and SAP6genes is severely reduced in the rim101−/rim101−mutant. These SAPgenes are functional Rim101p targets, because engineered expression of SAP5in the rim101−/rim101−strain restored E-cadherin degradation and invasion in the mucosal model. Our data support the hypothesis that there is a mechanism by which C. albicansinvades mucosal tissues by promoting the proteolytic degradation of E-cadherin in epithelial adherens junctions.

ABSTRACTCandida albicansis a major opportunistic pathogen in immunocompromised patients. Production of proinflammatory cytokines by host cells in response to C. albicansplays a critical role in the activation of immune cells and final clearance of the organism. Invasion of host cells and tissues is considered one of the virulence attributes of this organism. The purpose of this study was to investigate whether the ability of C. albicansto invade host cells and tissues affects the proinflammatory cytokine responses by epithelial and endothelial cells. In this study we used the invasion-deficient RIM101gene knockout strain DAY25, the highly invasive strain SC5314, and highly invasive RIM101-complemented strain DAY44 to compare the proinflammatory cytokine responses by oral epithelial or endothelial cells. Using a high-throughput approach, we found both qualitative and quantitative differences in the overall inflammatory responses to C. albicansstrains with different invasive potentials. Overall, the highly invasive strains triggered higher levels of proinflammatory cytokines in host cells than the invasion-deficient mutant triggered. Significant differences compared to the attenuated mutant were noted in interleukin-1α (IL-1α), IL-6, IL-8, and tumor necrosis factor alpha in epithelial cells and in IL-6, growth-related oncogene, IL-8, monocyte chemoattractant protein 1 (MCP-1), MCP-2, and granulocyte colony-stimulating factor in endothelial cells. Our results indicate that invasion of host cells and tissues by C. albicansenhances the host proinflammatory response to infection.