Graduate Programs in the Life Sciences

"The study of intracellular microbial pathogens allows a multidisciplinary approach to fundamental questions related to host cell/microbe interactions. My laboratory is studying the facultative intracellular Gram-positive bacterium Listeria monocytogenes. L. monocytogenes multiplies in the cytosol of eukaryotic cells and subverts the host humoral immune system by spreading from cell to cell without leaving the intracellular milieu. The long-term goal of our research is to define the mechanisms leading to the formation of the spreading vacuole and to bacterial escape from this vacuole. A number of bacterial factors involved in cell-to-cell spread have been identified. Among these factors are a broad-range phospholipase C (PC-PLC), a zinc-dependent metalloprotease (Mpl), and a phosphatidylinositol-specific PLC (PI-PLC). The following projects are presently being pursued in the lab.

• Regulation of PC-PLC activity: PC-PLC is made as a proenzyme whose activation requires proteolytic cleavage of a N-terminal prodomain. We have shown that bacteria multiplying in the cytosol of macrophages carry a pool of PC-PLC and that active PC-PLC is specifically released in the spreading vacuole in a pH-dependent manner. Further analyses have indicated that activation of PC-PLC and bacterial release of active PC-PLC are two independent steps, and that a drop in pH is essential but not sufficient. We are interested in defining the mechanism(s) regulating storage, activation, and release of PC-PLC during infection.
• Regulation of the metalloprotease activity: Mpl is associated with PC-PLC activation. Like PC-PLC, Mpl is made as a proenzyme whose activation requires proteolytic cleavage of a N-terminal prodomain. We have shown that activation of bacteria-associated PC-PLC is Mpl-dependent. We propose that Mpl activation itself is the pH-regulated step in PC-PLC activation. Whether Mpl is directly responsible for activating PC-PLC remains to be determined. We are interested in defining the mechanism(s) regulating Mpl activity and the specific role(s) of Mpl in pathogenesis.
• Biogenesis of the spreading vacuole: Recently, we have observed that PI-PLC influences the biogenesis of the spreading vacuole, and that the phenotype of a PI-PLC mutant is reproducible by blocking the activities of specific host signaling molecules in wild-type infected cells. We are interested in defining signaling molecules and pathways regulating L. monocytogenes cell-to-cell spread.