AUTHOR=Sui Zhi-hai , Xu Haijiao , Wang Hongda , Jiang Shuai , Chi Heng , Sun Li 

TITLE=Intracellular Trafficking Pathways of Edwardsiella tarda: From Clathrin- and Caveolin-Mediated Endocytosis to Endosome and Lysosome

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=7

YEAR=2017

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2017.00400

DOI=10.3389/fcimb.2017.00400

ISSN=2235-2988

ABSTRACT=<p><italic>Edwardsiella tarda</italic> is a Gram-negative bacterium that can infect a broad range of hosts including humans and fish. Accumulating evidences have indicated that <italic>E. tarda</italic> is able to survive and replicate in host phagocytes. However, the pathways involved in the intracellular infection of <italic>E. tarda</italic> are unclear. In this study, we examined the entry and endocytic trafficking of <italic>E. tarda</italic> in the mouse macrophage cell line RAW264.7. We found that <italic>E. tarda</italic> entered RAW264.7 and multiplied intracellularly in a robust manner. Cellular invasion of <italic>E. tarda</italic> was significantly impaired by inhibition of clathrin- and caveolin-mediated endocytic pathways and by inhibition of endosome acidification, but not by inhibition of macropinocytosis. Consistently, RAW264.7-infecting <italic>E. tarda</italic> was co-localized with clathrin, caveolin, and hallmarks of early and late endosomes, and intracellular <italic>E. tarda</italic> was found to exist in acid organelles. In addition, <italic>E. tarda</italic> in RAW264.7 was associated with actin and microtubule, and blocking of the functions of these cytoskeletons by inhibitors significantly decreased <italic>E. tarda</italic> infection. Furthermore, formaldehyde-killed <italic>E. tarda</italic> exhibited routes of cellular uptake and intracellular trafficking similar to that of live <italic>E. tarda</italic>. Together these results provide the first evidence that entry of live <italic>E. tarda</italic> into macrophages is probably a passive, virulence-independent process of phagocytosis effected by clathrin- and caveolin-mediated endocytosis and cytoskeletons, and that the intracellular traffic of <italic>E. tarda</italic> involves endosomes and endolysosomes.</p>