Identification and Characterization ofCPS1as a Hyaluronic Acid Synthase Contributing to the Pathogenesis ofCryptococcus neoformansInfection

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Abstract
Cryptococcus neoformansis a pathogenic yeast that often causes devastating meningoencephalitis in immunocompromised individuals. We have previously identified theC. neoformans CPS1gene, which is required for a capsular layer on the outer cell wall. In this report, we investigate the function of theCPS1gene and its pathogenesis. We demonstrated that treatment of yeast with either 4-methylumbelliferone or hyaluronidase resulted in a reduction of the level ofC. neoformansbinding to human brain microvascular endothelial cells (HBMEC). Yeast extracellular structures were also altered accordingly in hyaluronidase-treated cells. Furthermore, observation of yeast strains with different hyaluronic acid contents showed that the ability to bind to HBMEC is proportional to the hyaluronic acid content. A killing assay withCaenorhabditis elegansdemonstrated that theCPS1wild-type strain is more virulent than thecps1Δ strain. WhenCPS1is expressed inSaccharomyces cerevisiaeandEscherichia coli, hyaluronic acid can be detected in the cells. Additionally, we determined by fluorophore-assisted carbohydrate electrophoretic analysis that hyaluronic acid is a component of theC. neoformanscapsule. The size of hyaluronic acid molecules is evaluated by gel filtration and transmission electron microscopy studies. Together, our results support thatC. neoformans CPS1encodes hyaluronic acid synthase and that its product, hyaluronic acid, plays a role as an adhesion molecule during the association of endothelial cells with yeast.