Edward E. Penhoet Distinguished Chair in Global Public Health and Infectious Diseases and Professor of Biochemistry, Biophysics and Structural Biology*
*And Affiliate, Division of Immunology & Pathogenesis
Intracellular pathogens are responsible for an enormous amount of worldwide morbidity and mortality and the development of vaccines and therapeutics to treat diseases caused by these pathogens continues to represent one of the biggest challenges facing the international biomedical community. By virtue of their intracellular niche, these pathogens avoid extracellular immune defense mechanisms, and consequently, vaccine strategies that target the production of antibodies have been largely ineffective. The Portnoy lab tackles a wide range of problems related to the pathogenesis and host response to intracellular pathogens with the goal of developing vaccines and therapeutics. Specifically, the lab works on Listeria monocytogenes, a facultative intracellular food-borne bacterial pathogen that is an outstanding model system with which to dissect basic aspects of host-pathogen interactions.
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, circumvent autophagy, avoid cell death pathways, 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. Current research covers many topics including basic microbiology, the cell biology of infection, innate immune responses, acquired immunity, and vaccine development to both infectious diseases and cancer.
Characterization of the essential virulence factor LLO. The L. monocytogenes pore-forming cytolysin, Listeriolysin O (LLO) is an essential determinant of pathogenesis that mediates escape of the bacteria from host phagosomes allowing the bacteria to grow in the cytosol.Although LLO is related to dozens of other members of this family of cytolysins, LLO is the only one that is required by an intracellular pathogen. Accordingly, LLO has evolved numerous properties that allow it to specifically act within the host cell without causing cell death. We are currently studying the regulation of LLO synthesis and the cell biology of its trafficking in cells. Most recently, we discovered that LLO synthesized by cytosolic bacteria forms pores in the cytoplasmic membrane but prevents killing the host cell by mediating endocytosis and targeting LLO for degradation. Mutants lacking this activity are 10,000-fold less virulent.
Regulation of virulence gene expression. L. monocytogenes lives a biphasic lifestyle that includes growth in the environment, including food, and infection of warm-blooded animals, including humans. Most determinants of pathogenesis are controlled by the master virulence transcriptional regulator. We recently found that intracellular bacteria detect the host environment by responding to the redox state of the host cell. We are currently using bacterial genetics to study how the bacteria sense and respond to alterations in redox. Most recently, we identified an 8-gene locus that encodes a flavin-based extracellular electron transport system that makes L. monocytogenes electrogenic. Importantly, we have also found these genes in 100s of other bacterial species including members of the intestinal microbiota. We are now studying how this system contributes to growth in the intestine and during infection.
Interaction of L. monocytogenes with the innate immune system. We have three new projects that relate bacterial metabolism to host innate immunity.
(1) We discovered that the bacteria secrete c-di-AMP, a conserved signaling molecule that binds to and activates STING, a critical hub for the detection of microorganisms and tumors. We are currently studying the basic microbiology of c-di-AMP and its role during pathogenesis. Most recently, we have begun to explore how activation of STING can lead to placental infection.
(2) Humans possess a particular type of T-cell (gamma delta T- cell) that is activated by an intermediate of bacterial isoprenoid biosynthesis. Some bacteria synthesize this intermediate while others use the same pathway as humans. L. monocytogenes is one of the very few bacteria that use both pathways. We are currently seeking to understand why the bacteria have both pathways and determine the role of each during infection.
(3) Humans and mice have T-cells called MAIT cells that are stimulated by bacterial metabolic intermediates of riboflavin biosynthesis. L. monocytogenes is a riboflavin auxotroph and is not predicted to stimulate MAIT cells. We are current examining if MAIT cells respond to L. monocytogenes infection and if these T cells play a role during L. monocytogenes infection and immunity.
Light SH, Su L, Rivera-Lugo R, Cornejo JA, Louie A, Iavarone AT, Ajo-Franklin CM, Portnoy DA. A flavin-based extracellular electron transfer mechanism in diverse gram-positive bacteria. Light SH, Su L, Rivera-Lugo R, Cornejo JA, Louie A, Iavarone AT, Ajo-Franklin CM, Portnoy DA. Nature. In press. (2018)
Deng W, Lira V, Hudson T, Lemmens EE, Hanson WG, Flores R, Barajas G, Katibah GE, Desbien AL, Lauer P, Leong ML, Portnoy DA, Dubensky Jr. TW. Recombinant Listeria promotes tumor rejecton by remodeling tumor microenvironment dependent upon induction of functional CD8+ T cells. Proc Natl Acad Sci USA. In press. (2018)
Cheng MI, Chen C, Engström P, Portnoy DA, Mitchell G. Actin-based motility allows Listeria monocytogenes to avoid autophagy in the macrophage cytosol. Cellular Microbiol. 2018 May 3:e12854. (2018)
Chen C, Nguyen BN, Mitchell G, Margolis SR, Ma D, Portnoy DA. The Listeriolysin O PEST-like sequence co-opts AP-2-mediated endocytosis to prevent plasma membrane damage during Listeria infection. Cell Host Microbe. 23(6):786-795. (2018)
Mitchell G, Cheng MI, Chen C, Nguyen BN, Whiteley AT, Kianian S, Cox JS, Green DR, McDonald KL, Portnoy DA. Listeria monocytogenes triggers non-canonical autophagy upon phagocytosis, but avoids subsequent growth-restricting xenophagy. Proc Natl Acad Sci USA. 115(2):E210-E217. (2018)
Portman JL, Dubensky SB, Peterson BN, Whiteley AT, Portnoy DA. Activation of the Listeria monocytogenes virulence program by a reducing environment. MBio. 8(5):E1595-17. (2017)
Portman JL, Huang Q, Reniere ML, Iavarone AT, Portnoy DA. Activity of the pore-forming virulence factor Listeriolysin O is reversibly inhibited by naturally occuring S-glutathionylation. Infect Immun. 85(4):E959-16. (2017)
Whiteley AT, Garelis NE, Peterson BN, Choi PH, Tong L, Woodward JJ, Portnoy DA. c-di-AMP modulates Listeria monocytogenes central metabolism to regulate growth, antibiotic resistance, and osmoregulation. Mol Microbiol. 104(2):212-233. (2017)
Whiteley AT, Portnoy DA. An in vivo selection to identify how Listeria monocytogenes recognizes the intracellular environment. PLoS Pathog. 12(7):E1005741. (2016)
Burke TP, Portnoy DA. SpoVG is a conserved RNA-binding protein that regulates Listeria monocytogenes lysozyme resistance, virulence, and swarming motility. MBio. 7(2):E00240. (2016)
Whiteley AT, Pollock AJ, Portnoy DA. The PAMP c-di-AMP is essential for Listeria monocytogenes growth in rich but not minimal media, due to a toxic increase in (p)ppGpp. Cell Host Microbe. 17(6):788-98. (2015)
Reniere ML, Whiteley AT, Hamilton KL, John SM, Lauer P, Brennan RG, Portnoy DA. Glutathione activates virulence gene expression of an intracellular pathogen. Article. Nature. 517(7533):170-3. (2015)
Photo credit: Mark Hanson at Mark Joseph Studios.
Last Updated 2018-07-18