Bacterial Pathogen-Host Cell Interactions
 My
laboratory is interested understanding the complex interplay between
microbial pathogens and their host eukaryotic cells, a field that
has only recently come into its own recognition and is referred
to as cellular microbiology. To that end, we have combined the techniques
of eukaryotic cell biology with microbial genetics to investigate
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. Initially we carried
out a novel genetic screen to identify mutants that are deficient
in injuring epithelial 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
involved in virulence. 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. Our genetic screen for non-cytotoxic
mutants revealed several new genes involved in pilin assembly and
function.
Currently, our work focuses on several
aspects of P. aeruginosa-host cell interactions. First, we
are further characterizing the pathway by which P. aeruginosa
enters into polarized and non-polarized epithelial cells. We have
found that P. aeruginosa activates Rho upon entry. This pathway
is downregulated as epithelial cells polarize, and is upregulated
during wound healing. These observations help to explain the relative
resistance of intact epithelium to injury by P. aeruginosa and
the susceptibility of injured epithelium to colonization and injury.
Second, we are dissecting the function of the type III secreted
effector ExoT. Third, we are further investigating the role of pili
in virulence, especially as it pertains to type III-mediated secretion.
Fourth, we are continuing our studies
of the functions and roles of the novel protein FimL and the products
of the Chp regulon, likely involved in a complex signal transduction
pathway that responds to environmental signals, in pilin biogenesis.
Together, these studies will expand our knowledge of bacterial pathogenesis,
host cell injury, and pilin function and may 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 recent studies have been aimed
at studying the interactions between C. trachomatis and the
host epithelial cell. Currently we are studying the mechanism of
entry, including the roles of lipid rafts and 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 employing novel genetic approaches to define host
genes required for the intracellular developmental life cycle.
Back to top
|
