Welcome to the Dziejman Laboratory!
What We Study
The Dziejman Lab is interested in the evolution of bacterial pathogens and the molecular interactions at the host-microbe interface that promote colonization and infectious disease. We are particularly interested in novel mechanisms used by enteric organisms to disrupt intestinal homeostasis. Our focus is on Vibrio cholerae, which can cause the life-threatening diarrheal disease known as cholera. Cholera is historically defined by the activity of cholera toxin, a well known and long studied virulence factor. However, there are pathogenic V. cholerae strains that cause clinically similar disease, yet do not carry the genes encoding cholera toxin.
We recently discovered a Type Three Secretion System (T3SS) in V. cholerae, encoded on a horizontally acquired, ~47kb pathogenicity island. We found that the V. cholerae T3SS is essential for causing disease in infection models, and is conserved in a subset of non-O1/non-O139 serogroup strains that lack cholera toxin and the primary colonization factor known as the toxin co-regulated pilus (TCP). We are therefore working to identify and characterize the virulence factors and molecular mechanisms used by T3SS-positive V. cholerae to colonize host tissues and cause disease. Our goal is to answer the outstanding question of how T3SS-positive V. cholerae strains cause clinically similar disease using molecular mechanisms that are fundamentally different from TCP and CT, and are as of yet, undefined.
Many Gram-negative bacteria use T3SSs to translocate virulence factors, referred to as effector proteins, directly into the cytosol of eukaryotic cells. Although the proteins encoding components of the secretion apparatus are highly conserved, the effector proteins are not. Most often, effector proteins are unique amino acid sequences with novel functions. Consequently, although our early studies showed that the V. cholerae T3SS is required to cause disease, the effector proteins and molecular mechanisms leading to colonization and secretory diarrhea were unknown.
We subsequently identified 13 effector proteins encoded within the T3SS island and named them Vops, with specific letter designations (e.g. VopF, VopM, VopX). We determined which Vops were necessary for colonizing host tissues, and began Vop characterization. The challenge: How do you discover the eukaryotic targets and activities of novel proteins that don’t look like any proteins of known function?
How We Study It
We’ve chosen to take complementary approaches to identify effector protein functions: deconstructionist methods that target individual effectors for expression in heterologous systems, and holistic approaches that take advantage of Vibrio genetics and use the "whole bug" to probe questions at the host-pathogen interface. In house collaborations with Profs. J. Scott Butler, Brian Ward, and John G. Frelinger facilitate our use of multiple model systems. For example, we’ve taken advantage of Saccharomyces cerevisiae genetics to identify host proteins targeted for interaction by effectors, and overexpression in cultured mammalian cells to identify effector-specific phenotypes. Our work also combines infection models, genomic technologies, and immunofluorescence microscopy, to tell us about the host response to Vop activities. Using the combined results from multi-disciplinary approaches, we are working to reveal the story about how effector proteins cooperate to cause cholera using previously undefined mechanisms.
And…Let’s Not Forget
Another important aspect of T3SS mediated pathogenesis is virulence gene regulation. We identified two open reading frames within the T3SS island encoding ToxR-like transmembrane transcriptional regulatory proteins that are essential for virulence: VttRA and VttRB. Using genomic, genetic and molecular biology approaches, we are investigating how VttRA, VttRB, and ToxR co-ordinate and regulate T3SS gene expression in response to environmental signals.
Remember that the T3SS is a horizontally acquired virulence factor. Acquisition can convert a non-pathogenic strain into one that causes disease. However, the conversion takes place within the context of regulatory circuits governing existing bacterial processes and phenotypes. We are therefore interested in understanding how virulence gene regulation is integrated with regulatory networks that coordinate other important aspects of the Vibrio lifestyle.