Work in the Ellermeier Lab focuses on how Gram-positive bacteria sense and respond to extracellular signals. Our work is focused on the opportunistic human pathogen Clostridium difficile and the model organism Bacillus subtilis. We are interested in understanding how cells respond to changes in their environment by altering gene expression. To alter gene expression bacteria must detect changes in their environment and then transduce that signal from outside the cell to a transcriptional response inside the cell. We are interested in understanding the basic molecular mechanisms involved in how cells sense and respond to extracellular signals. We utilize genetic, molecular, biochemical and structural approaches to dissect these signal transduction systems.
We are particularly interested in understanding the response of C. difficile to factors produced by the innate immune system. Our work has revealed the presence of an Extra Cytoplasmic Function (ECF) σ factor, σV, present in C. difficile and B. subtilis as well as other Gram-positive bacteria that is activated specifically by lysozyme, an essential component of the innate immune system. We have found that σV is required for lysozyme resistance in both B. subtilis and C. difficile. The activity of σV is inhibited by the anti-sigma factor RsiV. Activation of σV occurs via proteolytic destruction of an anti-sigma factor RsiV. This degradation occurs only in the presence of lysozyme and requires multiple proteases to destroy RsiV in a process of regulated intramembrane proteolysis (RIP). We are interested in identifying the proteases required for σV activation and understanding the mechanism by which site-1 cleavage of RsiV, and thus σV activation, is controlled. We are also studying the role of additional ECF sigma factors encoded by C. difficile to determine their role in response to cell envelope stress. In addition, we are interested in understanding the role of these ECF sigma factors play in survival of the bacterium during an infection.
The protozoan parasite, Leishmania chagasi, causes the fatal human disease visceral leishmaniasis. L. chagasi express an abundant surface protease GP63, which is important for parasite survival. GP63 is encoded by >18 tandem MSP genes, falling into 3 homologous classes whose expression varies throughout the parasite life cycle. MSPL genes are expressed in logarithmic, whereas MSPS genes are expressed in stationary phase when parasites achieve maximal virulence and express high levels of GP63 protein. Our studies focus on the post-transcriptional mechanisms regulating expression of different MSP gene classes. These include mRNA T½, the efficiency of trans-splicing, and protein T½. Using reporter gene constructs and transfection techniques we are localizing unique sequences in MSP 3'UTRs that interact with regulatory proteins. Additionally, using MALDI-TOF mass spec we are examining products of specific MSP class genes that are expressed in different parasite stages. An ongoing epidemic of visceral leishmaniasis in northeast Brazil has led to our studies genetic loci associated with different outcomes of human L. chagasi infection (asymptomatic versus fatal). Using molecular genotyping methods (microsatellites, SSCP, RFLP, sequencing) we are examining polymorphic alleles of candidate genes for their contributions to disease susceptibility, in collaboration with Dr. Selma Jeronimo of Natal, Brazil. These studies will extend to a genome-wide scan and fine mapping of loci linked to different disease outcomes.
Our research has diversified into two main areas: 1) How viruses infect and disseminate in skin; 2) How microbial and environmental factors play a role in the development of metabolic syndrome. Our prior research addressed how human cells senesce, leading to aging, and how they become immortal, leading to cancer, with a particular interest in on how human papillomaviruses transform cells. Our expertise in cell immortalization and cell culture techniques has allowed us develop 3D cell culture models that recapitulate human tissue for our research.
1) How viruses infect and disseminate in skin. Collaborative studies were recently initiated with Wendy Maury’s lab to examine how Ebola virus (EBOV) infects and transmits through human skin. We found that EBOV can infect and replicate in different skin cell populations. We are currently working to understand the course of infection in skin, what specific receptors are being utilized by EBOV in skin cells, and what role skin infection plays in transmission and pathogenesis.
2) How microbial and environmental factors play a role in the development of metabolic syndrome. Our success with immortalizing human preadipocytes (pre-fat) cells has led to studies on how environmental and bacterial toxins cause or exacerbate type II diabetes through effects on fat tissue. We found that dioxin-like polychlorinated biphenyls (PCBs), which are persistent organic pollutants, can disrupt adipogenesis (i.e. the development of functional fat cells) through activation of the aryl hydrocarbon receptor (AhR). This causes a proinflammatory response and inhibits master regulatory genes involved in adipogenesis. Endogenous microbial-derived tryptophan metabolites are also able to activate AhR. Studies are underway to determine the mechanism by which AhR activation disrupts adipogenesis and to develop 3D cultures and in vivo genetic models to assess the role of AhR in the development of metabolic syndrome.
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