Ra. Garduno et al., SURFACE-ASSOCIATED HSP60 CHAPERONIN OF LEGIONELLA-PNEUMOPHILA MEDIATES INVASION IN A HELA-CELL MODEL, Infection and immunity, 66(10), 1998, pp. 4602-4610
HeLa cells have been previously used to demonstrate that virulent stra
ins of Legionella pneumophila (but not salt-tolerant avirulent strains
) efficiently invade nonphagocytic cells. Hsp60, a member of the GroEL
family of chaperonins, is displayed on the surface of virulent L. pne
umophila (R. A. Garduno et al., J. Bacteriol. 180: 505-513, 1988), Bec
ause Hsp60 is largely involved in protein-protein interactions, we inv
estigated its role in adherence-invasion in the HeLa cell model. Hsp60
-specific antibodies inhibited the adherence and invasiveness of two v
irulent L. pneumophila strains in a dose-dependent manner but had no e
ffect on the association of their salt-tolerant avirulent derivatives
with HeLa cells, A monospecific anti-OmpS (major outer membrane protei
n) serum inhibited the association of both virulent and avirulent stra
ins of L. pneumophila to Beta cells, suggesting that while both Hsp60
and OmpS may mediate bacterial association to HeLa cells, only virulen
t strains selectively displayed Hsp60 on their surfaces. Furthermore,
the surface-associated Hsp60 of virulent bacterial cells was susceptib
le to the action of trypsin, which rendered the bacteria noninvasive,
Additionally, pretreatment of HeLa cells with purified Hsp60 or precoa
ting of the plastic surface where HeLa cells attached with Hsp60 reduc
ed the adherence and invasiveness of the two virulent strains. Finally
, recombinant Hsp60 covalently bound to latex beads promoted the early
association of beads with HeLa cells by a factor of 20 over bovine se
rum albumin (BSA)-coated beads and competed with virulent strains for
association with HeLa cells, Hsp60-coated heads mere internalized in l
arge numbers by Beta cells and remained in tight endosomes that did no
t fuse with other vesicles, whereas internalized BSA-coated beads, for
which endocytic trafficking is well established, resided in more loos
e or elongated endosomes, Mature intracellular forms of L, pneumophila
, which were up to 100-fold more efficient than agar-grown bacteria at
associating with HeLa cells, were enriched for Hsp60 on the bacterial
surface, as determined by immunolocalization techniques. Collectively
, these results establish a role for surface-exposed Hsp60 in invasion
of HeLa cells by L. pneumophila.