C ryptococcus neoformans phospholipase B 1 activates host cell Rac 1 for traversal across the blood–brain barrier

Summary C ryptococcus neoformans penetration into the central nervous system ( CNS ) requires traversal of the blood–brain barrier that is composed of a single layer of human brain microvascular endothelial cells ( HBMEC ), but the underlying mechanisms of C . neoformans traversal remain incompletely understood. C . neoformans transcytosis of HBMEC monolayer involves rearrangements of the host cell actin cytoskeleton and small GTP ‐binding Rho family proteins such as Rac 1 are shown to regulate host cell actin cytoskeleton. We, therefore, examined whether C . neoformans traversal of the blood–brain barrier involves host Rac 1. While the levels of activated Rac 1 ( GTP ‐ Rac 1) in HBMEC increased significantly upon incubation with C . neoformans strains, pharmacological inhibition and down‐modulation of Rac 1 significantly decreased C . neoformans transcytosis of HBMEC monolayer. Also, Rac 1 inhibition was efficient in preventing C . neoformans penetration into the brain. I n addition, C . neoformans phospholipase B 1 ( Plb 1) was shown to contribute to activating host cell Rac 1, and STAT 3 was observed to associate with GTP ‐ Rac 1 in HBMEC that were incubated with C . neoformans strain but not with its Δ plb1 mutant. These findings demonstrate for the first time that C . neoformans Plb 1 aids fungal traversal across the blood–brain barrier by activating host cell Rac 1 and its association with STAT 3, and suggest that pharmacological intervention of host–microbial interaction contributing to traversal of the blood–brain barrier may prevent C . neoformans penetration into the brain.