Sec6-dependent sorting of fungal extracellular exosomes and laccase of Cryptococcus neoformans
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Abstract
12 p. : il.The 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