Two Major Inositol Transporters and Their Role in Cryptococcal Virulence

ABSTRACTCryptococcus neoformansis an AIDS-associated human fungal pathogen and the most common cause of fungal meningitis, with a mortality rate over 40% in AIDS patients. Significant advances have been achieved in understanding its disease mechanisms. Yet the underlying mechanism of a high frequency of cryptococcal meningitis remains unclear. The existence of high inositol concentrations in brain and our earlier discovery of a large inositol transporter (ITR) gene family in C. neoformansled us to investigate the potential role of inositol in Cryptococcus-host interactions. In this study, we focus on functional analyses of two major ITRgenes to understand their role in virulence of C. neoformans. Our results show that ITR1Aand ITR3Care the only two ITRgenes among 10 candidates that can complement the growth defect of a Saccharomyces cerevisiaestrain lacking inositol transporters. Both S. cerevisiaestrains heterologously expressing ITR1Aor ITR3Cshowed high inositol uptake activity, an indication that they are major inositol transporters. Significantly, itr1a itr3cdouble mutants showed significant virulence attenuation in murine infection models. Mutating both ITR1Aand ITR3Cin an ino1mutant background activates the expression of several remaining ITRcandidates and does not show more severe virulence attenuation, suggesting that both inositol uptake and biosynthetic pathways are important for inositol acquisition. Overall, our study provides evidence that host inositol and fungal inositol transporters are important for Cryptococcuspathogenicity.