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Bacterial
Pathogen-Host Cell Interactions
My laboratory is interested understanding and exploiting the complex interplay
of microbial pathogens with eukaryotic cells. To that end, we have investigated
the key processes of microbial attachment and entry, intracellular survival,
and host cell injury in the context of two important human pathogens,
Pseudomonas aeruginosa and Chlamydia trachomatis . Each of these microorganisms
has developed a unique strategy for successful survival that involves
subverting and exploiting host cell pathways. Dissecting these processes
will allow the development of new diagnostics, therapeutics, and vaccines
and will provide a unique window into eukaryotic cell biology. Part of
the lab focuses on how P. aeruginosa, an opportunistic pathogen of man,
injures epithelial cells. The common element underlying these opportunistic
infections is the ability of P. aeruginosa to colonize and further damage
injured epithelium surfaces, leading to local tissue damage and dissemination
to distant organs. We carried out a novel genetic screen to identify mutants
that are deficient in injuring cells in vitro. This analysis has revealed
that pili and products of a novel secretion system (type III secretion),
are required for host cell injury by P. aeruginosa. In particular, we
have identified three new type III-secreted virulence factors. These include
a novel cytotoxin, ExoU, a bacterially-encoded apoptosis inducing factor,
and a bacterially-encoded anti-internalization factor, ExoT, that acts
as a GTPase activating protein (GAP) for Rho family GTPases. Current and
future directions include further characterizing and determining the mechanism
of action of these new virulence factors. For example, we have found that
P. aeruginosa activates Rho upon entry and that the GAP activity of ExoT
prevents bacterial internalization. Moreover, this entry pathway is downregulated
as epithelial cells polarize and is upregulated during wound healing.
These observations explain the relative resistance of intact epithelium
to injury by P. aeruginosa and the susceptibility of injured epithelium
to colonization and injury. These studies will expand our knowledge of
bacterial pathogenesis, apoptosis, and will identify new targets for drug
and vaccine development. C. trachomatis is the leading cause of venereal
disease and preventable sterility in the United States and the most common
cause of non-congenital blindness in third world countries. It replicates
via a unique developmental cycle involving the serial alternation of two
distinct forms sequestered within a membrane bound compartment (the "vacuole")
in the cytoplasm of the infected epithelial cell. While this organism
presents major experimental challenges, its importance as a human pathogen
merits overcoming the difficulty in manipulating and growing the bacteria
in the laboratory. Our work has encompassed several aspects of chlamydial
pathogenesis that are unique to this obligate intracellular bacterium.
Currently we are studying the mechanism of entry. and the role of the
actin cytoskeleton in this process. As well, we have characterized the
chlamydial vacuole in order to learn how it avoids fusion with the host
cell lysosomes, a key feature of the ability of C. trachomatis to survive
intracellularly. We have shown that sphingolipid precursors that are trafficked
from the Trans Golgi Network to the C. trachomatis vacuole are required
for intracellular growth. We are currently identifying the cellular pathways
that Chlamydia subverts in order to acquire host cell sphingolipids. The
latter is a prime example of how the study of microbial pathogens provides
new tools and approaches to the study of eukaryotic cell biology.
Selected Publications:
Kang, P. J., Hauser, A., Apodaca, G., Wiener-Kronish, J., Mostov, K.,
Fleizig, S., and Engel, J. (1997) Identification of Pseudomonas aeruginosa
Genes Required for Epithelial Cell Injury, Molecular Microbiology, 24:1249-1262.
Hauser, A., Kang, P., and Engel, J. PepA (1998) a novel secreted protein
of Pseudomonas aeruginosa, is necessary for cytotoxicity and virulence,
Molecular Microbiology, 27:807-818,1998.
Van Ooij, C., Apodoca, G., and Engel, J. N. (1997) Characterization of
the Chlamydia trachomatis vacuole and its interaction with the host endocytic
pathway in HeLa cells, Infection and Immunity, 65:758-766.
Hauser, A., Fleizsig, S., Kang, P. J., Mostov, K., and Engel, J. (1998)
Defects in type III secretion correlate with internalization of Pseudomonas
aeruginosa by epithelial cells, Infection and Immunity, 66:1413-1420.
Comolli, J., Hauser, A., Waite, L., Whitchurch, C., Mattick, J., and Engel,
J. (1999) Pseudomonas aeruginosa gene products PilT and PilU are required
for cytotoxicity in vitro and virulence in a mouse model of acute pneumonia,
Infection and Immunity, 67:3625-3630.
Hauser, A., and Engel, J., Pseudomonas aeruginosa induces Type III secretion-mediated
apoptosis (1999) Infection and Immunity, 67: 5530-5537.
Van Ooij, C., Kalman, L., van IJzendoorn, S., Nishijima, M., Hantada,
K., Mostov, K., and Engel, J. (2000) Host-cell derived sphingolipids are
required for the intracellular growth of Chlamydia trachomatis, Cellular
Microbiology, 2:627-638.
Garrity-Ryan, L, Kazmierczak, B., Kowal, R., Comolli, J., Hauser, A. and
Engel, J. (2000) The arginine finger domain of ExoT contributes to actin
cytoskeleton disruption and inhibition of internalization of Pseudomonas
aeruginosa into epithelial cells and macrophages, Infection and Immunity,
68: 7100-7113.
Kazmierczak, B., Jou, T.-S., Mostov, K., and Engel, J. (2001) Rho-family
GTPases Modulate Pseudomonas aeruginosa Internalization by Epithelial
Cells, Cellular Microbiology, in press.
Geiser, T., Kazmierczak, B., Garrity-Ryan, L, Matthay, M., and Engel,
J. (2001) Pseudomonas aeruginosa ExoT inhibits in vitro lung epithelial
wound repair, Cellular Microbiology, in press.
Contact Information:
Email: jengel@medicine.ucsf.edu
Phone: 415/ 476-7355
Address: Box 0654, Room C443
The University of California, San Francisco, CA 94143, (415) 476-9000
Copyright 2003, The Regents of the University of California.
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