3 research outputs found
Binding of Serum Mannan Binding Lectin to a Cell Integrity-Defective Cryptococcus neoformans ccr4Δ Mutant▿
Mannan binding lectin (MBL) is an innate immune mediator belonging to the collectin family known to bind to the surfaces of many viruses, bacteria, and fungi. However, pathogenic strains of the fungus Cryptococcus neoformans are resistant to MBL binding. To dissect the mechanism of cryptococcal resistance to MBL, we compared MBL binding to an encapsulated wild-type strain, an encapsulated ccr4Δ mutant defective in cell integrity, and an acapsular cap60Δ strain. No MBL binding was detected on wild-type C. neoformans. In contrast, the ccr4Δ mutant bound MBL to the cell wall, predominantly at the ends of enlarged buds, whereas the acapsular strain bound MBL only at the bud neck and bud scars. In addition, the ccr4Δ mutant was sensitive to the cell wall-active antifungal caspofungin and other cell wall stress inducers, and its virulence was reduced in a mouse model of cryptococcosis. Interestingly, treatment of wild-type cells with caspofungin also increased MBL binding to C. neoformans. These results suggest that both the presence of capsule and wild-type cell wall architecture preclude MBL binding to C. neoformans
Sec6-dependent sorting of fungal extracellular exosomes and laccase of Cryptococcus neoformans
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