SM22 is needed for actin‐rich structures formed by enteropathogenic Escherichia coli and Listeria monocytogenes

Abstract

Food‐borne bacterial pathogens colonize the intestinal epithelia and cause various diseases. Enteropathogenic Escherichia coli (EPEC) remains extracellular and uses disease‐causing bacterial proteins to generate membrane‐bound actin protrusions on the host cell surface. These protrusions, called pedestals are crucial for disease and allow the bacteria to surf atop the intestinal epithelia ultimately leading to progressive changes to the tissue that cause diarrhea in the host. On the other hand, Listeria monocytogenes enters intestinal cells. Once within the cells these microbes initially form of branched networks of actin filaments around the bacterium called an actin cloud. These actin filaments then concentrate to one end of the microbe forming a comet tail that allows the bacterium to move within the host cell. L. monocytogenes can then use its comet tail to spread from cell‐to‐cell and infect various organs in the host. Through a previous mass spectrometry analysis of EPEC pedestals, we found that the actin bundling protein SM22 was concentrated through the full length of the pedestal. Because SM22 was enriched in EPEC pedestals, we then hypothesized that SM22 plays a crucial role in actin‐rich structures formed by both EPEC and other bacteria that hijack the actin filaments of the host during their disease processes. To test this, we initially used immunolocalization with L. monocytogenes infected cultured cells and found SM22 concentrated at L. monocytogenes actin clouds and comet tails. Using small interfering RNA, we depleted SM22 expression levels in host cells and found that fewer EPEC pedestals were able to form and less L. monocytogenes bacteria formed comet tails. The average comet tail length was also significantly shorter. As the reduction of SM22 diminished the abundance of actin‐rich structures generated by both EPEC and L. monocytogenes, we then determined if expressing EGFP‐tagged SM22 would increase the amount of EPEC pedestals and L. monocytogenes comet tails. Although EPEC pedestal formation was unchanged in cells overexpressing SM22, more comet tails were formed in L. monocytogenes‐infected cells and those comet tails were longer. Taken together, EPEC pedestals and L. monocytogenes comet tails rely on SM22 for their formation and the disease process and identify SM22 as a target for regulating these infections.Support or Funding InformationThis study was funded through NSERC.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.