Sec6‐dependent sorting of fungal extracellular exosomes and laccase of Cryptococcus neoformans

Abstract

SummaryThe cell wall of pathogenic fungi such as Cryptococcus neoformans, provides a formidable barrier to secrete virulence factors that produce host cell damage. To study secretion of virulence factors to the cell periphery, sec6 RNAi mutant strains of C. neoformans were tested for virulence factor expression. The studies reported here show that SEC6 RNAi mutant strains were defective in a number of virulence factors including laccase, urease as well as soluble polysaccharide and demonstrated attenuated virulence in mice. Further analysis by transmission electron microscopy detected the production of abundant extracellular exosomes in wild-type strains containing empty plasmid, but a complete absence in the iSEC6 strain. In addition, a green fluorescent protein-laccase fusion protein demonstrated aberrant localization within cytoplasmic vesicles in iSEC6 strains. In contrast, iSEC6 strains retained normal growth at 37°C, as well as substantially normal capsule formation, phospholipase activity and total secreted protein. These results provide the first molecular evidence for the existence of fungal exosomes and associate these vesicles with the virulence of C. neoformans.

Cryptococcus neoformans Requires the ESCRT Protein Vps23 for Iron Acquisition from Heme, for Capsule Formation, and for Virulence

“…Capsule polysaccharide is transported to the cell surface in vesicles via exocytosis, and it is clear that trafficking of polysaccharide and other virulence-related factors such as laccase is important for the virulence of C. neoformans (60,66,67). Our observations that deletion of VPS23 caused increased sensitivity to BFA and monensin, two intracellular trafficking inhibitors, and that these inhibitors reduce capsule size, are consistent with a contribution to proper trafficking (13).…”

Extracellular Vesicles from Cryptococcus neoformans Modulate Macrophage Functions

“…These results strongly suggest the potential of these vesicular structures to modify the course of cryptococcal infections through their effects on host phagocytic cells. Fungal vesicles are apparently related to mammalian exosomes (58,64). In this regard, it is noteworthy that exosome preparations from dendritic cells are being investigated as potential anticancer vaccines (26).…”

Vesicle-associated melanization in Cryptococcus neoformans

“…Cryptococcosis is currently the fourth leading cause of death in Africa and it is estimated to affect one million individuals worldwide each year (Park et al, 2009). C. neoformans is found in the environment, and serological studies have shown that infection is common even though disease is rare (Goldman et al, 2001).…”

“…Thus, these vesicles may be involved in transport of virulence factors out of the cell. Indeed, extracellular vesicle secretion has been associated with cryptococcal virulence in an animal model of infection (Panepinto et al, 2009). …”