F-027. Role of Candida albicans SSK1 Response Regulator in Interaction with Endothelial Cells

X. Li, V. Menon, R. Calderone, N. Cauhan;
Georgetown Univ., Washington, DC.

Two-component signal transduction proteins have been reported in bacteria and lower eukaryotes. To date they have not yet been identified in animals and are absent in the human genome. These features make two-component proteins very attractive targets for antifungal drug discovery. The genome of Candida albicans encodes three histidine kinases and two response regulators. During haematogenously disseminated candidiasis, endothelial cell lining of the vasculature is one of the first host cells the organism encounters during tissue invasion. We therefore, hypothesize that information relevant to the in vitro interaction of C. albicans and endothelial cells will serve as a model for studying host-Candida interactions and provide information on adherence, invasion and damage to the vascular endothelium. Our hypothesis is that each of these events is crucial to disease development in the vasculature. In the present study, we have investigated the role of the Ssk1 response regulator protein in the interaction of C. albicans with endothelial cells. We used an in vitro assay to measure the adherence of wild type (CAF2-1), ssk1 mutant (SSK21) and the gene reconstituted (SSK23) stains to C166 endothelial cells. The C166 cell line has been shown to exhibit normal endothelial characteristics, proliferate rapidly with a cell doubling time of <24 h, and remain stable for more than 24 passages (>100 doublings). We observed significantly less adherence of SSK21 to C166 endothelial cells. For wild type cells (CAF2-1), the % of adhering cells was 65% compared to only 36% for SSK21, while the strain SSK23 adherence was intermediate, with 57% of cells adhering. From microarray data, we have identified that ALS1, encoding a major adhesion protein of C. albicans, is down regulated in the ssk1 mutant, an observation that may partially explain the reduced adherence of the ssk1 mutant to C166 endothelial cells. Current experiments are focused on analysis of genes, identified by microarray, regulated by SSK1 upon interaction with endothelial cells. Our data will provide information for the development of novel therapeutic approaches to block candidal adherence and enhance host defense.