Neisseria meningitidis adhesin A (NadA) is a meningococcus surface protein 
thought to assist in the adhesion of the bacterium to host cells. We have 
previously shown that NadA also promotes bacterial internalization in a 
heterologous expression system. Here we have used the soluble recombinant NadA 
(rNadA) lacking the membrane anchor region to characterize its internalization 
route in Chang epithelial cells. Added to the culture medium, rNadA internalizes 
through a PI3K-dependent endocytosis process not mediated by the canonical 
clathrin or caveolin scaffolds, but instead follows an ARF6-regulated recycling 
pathway previously described for MHC-I. The intracellular pool of rNadA reaches 
a steady state level within one hour of incubation and colocalizes in endocytic 
vesicles with MHC-I and with the extracellularly labeled chaperone Hsp90. 
Treatment with membrane permeated and impermeable Hsp90 inhibitors 17-AAG and 
FITC-GA respectively, lead to intracellular accumulation of rNadA, strongly 
suggesting that the extracellular secreted pool of the chaperone is involved in 
rNadA intracellular trafficking. A significant number of intracellular vesicles 
containing rNadA recruit Rab11, a small GTPase associated to recycling 
endosomes, but do not contain transferrin receptor (TfR). Interestingly, cell 
treatment with Hsp90 inhibitors, including the membrane-impermeable FITC-GA, 
abolished Rab11-rNadA colocalization but do not interfere with Rab11-TfR 
colocalization. Collectively, these results are consistent with a model whereby 
rNadA internalizes into human epithelial cells hijacking the recycling endosome 
pathway and recycle back to the surface of the cell via an ARF6-dependent, Rab11 
associated and Hsp90-regulated mechanism. The present study addresses for the 
first time a meningoccoccal adhesin mechanism of endocytosis and suggests a 
possible entry pathway engaged by N. meningitidis in primary infection of human 
epithelial cells.