Candida albicans IRS4 contributes to hyphal formation and virulence after the initial stages of disseminated candidiasis

1 Department of Medicine, University of Florida College of Medicine, Box 100277 JHMHC, 1600 SW Archer Rd, Gainesville, FL 32610, USA 2 Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, Box 100277 JHMHC, 1600 SW Archer Rd, Gainesville, FL 32610, USA 3 the North Florida/South Georgia VA Medical Center, University of Florida College of Medicine, Box 100277 JHMHC, 1600 SW Archer Rd, Gainesville, FL 32610, USA Correspondence Cornelius J. Clancy clancyn{at}medicine.ufl.edu Candida albicans is a common cause of mucosal and bloodstream infections. As a screening strategy to identify novel candidal virulence factors, sera recovered from HIV-infected patients with active oropharyngeal candidiasis (OPC) were previously used to probe a C. albicans genomic expression library. IRS4 was identified as a gene that encodes an immunogenic protein. In the present study, the presence of IRS4 transcripts was verified within OPC pseudomembranes recovered from patients. Having confirmed that the gene is expressed during human candidiasis, gene disruption strains were created and this implicated IRS4 in diverse processes, including hyphal formation on solid media and under embedded conditions, cell wall integrity and structure, and adherence to human epithelial cells in vitro . IRS4 disruption, however, did not influence hyphal formation or virulence in a murine model of OPC. Rather, the gene was found to be necessary for normal morphogenesis and full virulence during murine intravenously disseminated candidiasis (DC). IRS4 's effects on hyphal formation and virulence during DC were not evident on the first day after intravenous inoculation, even though transcripts were detected within murine kidneys. After 4 days, however, an irs4 null mutant strain was associated with attenuated mortality, diminished tissue burdens, less extensive infections, impaired C. albicans hyphal formation and decreased kidney damage. Taken together, these findings suggest that IRS4 makes distinct temporal-spatial contributions to the pathogenesis of candidiasis, which appear to vary between different tissue sites as well as within a given tissue over time. Abbreviations: DC, disseminated candidiasis; FCS, fetal calf serum; FOA, fluoroorotic acid; GMS, gomori methenamine silver; HIV, human immunodeficiency virus; MAP, mitogen-activated protein; OMP, orotidine 5'-monophosphate; OPC, oropharyngeal candidiasis; PI(4,5)P 2 , phosphatidylinositol (4,5) bisphosphate;