Biology subjects

Engstrom, P.

Publications and source records attributed to Engstrom, P..

3 recordsLinked to original sources

bioRxiv2020

Lysine methylation shields an intracellular pathogen from ubiquitylation

Many intracellular pathogens avoid detection by their host cells. However, it remains unknown how they avoid being tagged by ubiquitin, an initial step leading to anti-microbial autophagy. Here, we show that the intracellular bacterial pathogen Rickettsia parkeri uses two protein-lysine methyltransferases (PKMTs) to modify outer membrane proteins (OMPs) and prevent their ubiquitylation. Mutants deficient in the PKMTs were avirulent in mice and failed to grow in macrophages due to ubiquitylation and autophagy. Analysis of the lysine-methylome revealed that PKMTs modify a subset of OMPs by methylation at the same sites that are recognized by host ubiquitin. These findings show that lysine methylation is an essential determinant of rickettsial pathogenesis that shields bacterial proteins from ubiquitylation to evade autophagic targeting.

microbiology↗

bioRxiv2020

Rickettsia parkeri Sca2 promotes dissemination in an intradermal infection mouse model

Rickettsia are arthropod-borne pathogens that cause severe human disease worldwide. The spotted fever group (SFG) pathogen Rickettsia parkeri elicits skin lesion (eschar) formation in humans after tick bite. However, intradermal inoculation of inbred mice with millions of bacteria fails to elicit eschar formation or disseminated disease, hindering investigations into understanding eschar-associated rickettsiosis. Here, we report that intradermal infection of mice deficient for both interferon receptors (Ifnar-/-Ifngr-/-) with R. parkeri causes eschar formation, recapitulating the hallmark clinical feature of human disease. Intradermal infection with doses that recapitulate tick infestation caused eschar formation and lethality, including with as few as 10 bacteria. Using this model, we found that the actin-based motility protein Sca2 is required for R. parkeri dissemination from the skin to internal organs and for causing lethal disease, and that the abundant R. parkeri outer membrane protein OmpB contributes to eschar formation. We also found that immunizing mice with sca2 and ompB mutant R. parkeri protects against subsequent rechallenge with wild-type bacteria, revealing live-attenuated vaccine candidates. Thus, interferon receptor-deficient mice are a tractable model to investigate rickettsiosis, bacterial virulence factors, and immunity. Our results suggest that differences in interferon signaling in the skin between mice and humans may explain the discrepancy in susceptibility to SFG Rickettsia.

microbiology↗

bioRxiv2020

Mechanical competition triggered by innate immune signaling drives the collective extrusion of bacterially-infected epithelial cells

Multiple distinct types of intracellular bacterial pathogens have been shown to alter the mechanics of their mammalian host cells to promote cell-to-cell spread. Conversely, host cells may respond by altering their own mechanical behavior to limit infection. We monitored epithelial cell monolayers sparsely infected with the intracellular bacterial pathogens Listeria monocytogenes or Rickettsia parkeri over the course of several days. Under conditions where these pathogens were able to trigger innate immune signaling through the NF-{kappa}B pathway and to use actin-based motility to spread non-lytically from cell to cell, domains of infected cells formed enormous three-dimensional mounds, where uninfected cells surrounding the infected cells became stiffer and actively moved toward the site of infection, collectively squeezing the softer and weaker infected cells up and ejecting them from the epithelial monolayer. Bacteria in mounds were less able to spread laterally in the monolayer, limiting the growth of the focus, while mounded cells eventually underwent cell death. Cells in infected monolayers exhibited behavioral and molecular signatures of the epithelial to mesenchymal transition (EMT), such that coordinated forceful action by uninfected bystander cells actively eliminated large domains of infected cells, consistent with the hypothesis that this collective cell response represents an innate immune response.

microbiology↗