Home Faculty and Research Faculty by Name Daniel Portnoy

Daniel Portnoy

Professor of Biochemistry and Molecular Biology*
*And Affiliate, Division of Immunology & Pathogenesis

Lab Homepage: http://mcb.berkeley.edu/labs/portnoy/

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Research Interests

The overall goal of our research is to understand the molecular and cellular basis of microbial pathogenesis and the mechanisms used by the host to defend against infection. Specifically, the lab is focused on the interaction of the facultative intracellular bacterial pathogen Listeria monocytogenes and its mammalian host. This fascinating microorganism is able to enter cells, escape from a phagosome and grow rapidly in the cytosol. By exploiting a host system of actin-based motility, the bacteria move through the cytosol to the cell membrane and into pseudopod-like projections (listeriopods) that are ingested by neighboring cells. This mechanism allows pathogens to spread from one cell to another without ever leaving the host cytoplasm thereby avoiding the immune response.

 

 

Escape from a vacuole and cell to cell spread of L. monocytogenes. The stippled material depicts F-actin.

Current Projects

Cell biology of infection. The primary L.monocytogenes determinant responsible for lysis of host cell vacuoles is the pore-forming cytolysin, listeriolysin O (LLO). We will continue to focus on the control of LLO synthesis and secretion, and its mechanism of action. The ultimate goal is to relate structural and biochemical information to its precise mechanism of action in both tissue culture and in mice. We are also characterizing a number of fail-safe mechanisms that prevent LLO toxicity in the host cytosol and thereby compartmentalize its activity to acidic vacuoles. Interestingly, mutants that fail to properly compartmentalize LLO activity are cytotoxic to infected host cells and attenuated for virulence in mice. We have recently developed a model to examine the interaction of L. monocytogenes with cultured Drosophila cells and are using RNA interference to identify and characterize the role of host proteins that control the infectious process.

Innate immunity to infection. Murine listeriosis is an outstanding model to study basic aspects of innate and acquired cell-mediated immunity. Using bacterial mutants blocked at various stages in the infection process, we are elucidating pathways of host cell gene expression in response to microbial infection. Our studies clearly document the presence of a vacuolar and cytosolic pathway of innate immune recognition. Microarrary analysis has revealed dozens of genes expressed in response to the cytosolic pathway including beta-interferon. Currently, we are using both bacterial and host mutants to identify how the pathogen manipulates host innate immunity to promote infection.

Acquired immunity to infection. Mice that survive a challenge with sublethal doses of L. monocytogenes acquire antigen-specific cell-mediated immunity that renders the mice resistant to subsequent challenge. Although a number of bacterial antigens are recognized, the primary target of T-cell-mediated immunity is directed to peptides generated from the pore-forming cytolysin, listeriolysin O (LLO). We hypothesize that the features of LLO necessary for pathogenesis, such as its short cytosolic half-life, render LLO a target of host immunity. These studies impact upon the rational design of vaccines to other intracellular pathogens. Also, we are collaborating on studies to develop L. monocytogenes as a live, attenuated vector for vaccines to cancer and other intracellular pathogens.

Trafficking of bacteria during infection. L. monocytogenes normally infects via the oral route leading to invasion of the gastrointestinal tract and transplacental infection in pregnant women and animals causing miscarriage. We have developed a pregnant Guinea Pig model of listeriosis that recapitulates human disease and allows us to study trafficking from maternal organs to the placenta and back.

Selected Publications

O'Riordan, M., M. A. Moors, and D. A. Portnoy. Listeria intracellular growth and virulence require host-derived lipoic acid. Science. 302:462-464. (2003)

Lenz, L. L., S. Mohammadi, A. Geissler, and D. A. Portnoy. SecA2-dependent secretion of autolytic enzymes promotes Listeria monocytogenespathogenesis. Proc. Natl. Acad. Sci. 100:12432-12437. (2003)

McCaffrey, R., P. Fawcett, M. O'Riordan, K.D. Lee, E. A. Havell, P. O. Brown, and D. A. Portnoy. A specific gene expression program triggered by Gram-positive bacteria in the cytosol. Proc. Natl. Acad. Sci. 101:11386-91. (2004)

Auerbuch, V., D. G. Brockstedt, N. Meyer-Morse, M. O'Riordan, and D. A. Portnoy. Mice lacking the type I interferon receptor are resistant to Listeria monocytogenes. J. Exp. Med. 200:527-533. (2004)

Brockstedt, D. G, M. A. Giedlin, M. L. Leong, K. S. Bahjat, Y. Gao, W. Luckett, W. Liu, D. N. Cook, D. A. Portnoy, and T. W. Dubensky Jr. Cancer Immunotherapy using severly attenuated Listeria monocytogenes-based Vaccine Strains with enhanced immunogenicity and negligible toxicity. Proc. Natl. Acad. Sci. 101:13832-13837. (2004)

Cheng, L. W., J. P. M. Viala, N. Stuurman, U. Wiedemann, R. D. Vale and D. A. Portnoy. Use of RNA interference in Drosophila S2 cells to identify host pathways controlling compartmentalization of an intracellular pathogen. Proc. Natl. Acad. Sci. 102:13646-13651 (2005).

Schnupf, P., D. A. Portnoy and A. L. Decatur. Phosphorylation, ubiquitination, and degradation of Listeriolysin O in mammalian cells: Role of the PEST-like sequence.  Cell. Microbiol. 8:353-364. (2006).

Bakardjiev, A.I., J.A. Theriot, and D. A. Portnoy. Listeria monocytogenes traffics from the maternal organs to the placenta and back. PloS Pathogens 2:623-631. (2006).

Last Updated 2006-08-09