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The Cell-Cycle Regulatory Protein p21CIP1/WAF1 Is Required for Cytolethal Distending Toxin (Cdt)-Induced Apoptosis
Open AccessArticle

Aggregatibacter actinomycetemcomitans LtxA Hijacks Endocytic Trafficking Pathways in Human Lymphocytes

1
Department of Basic and Translational Sciences, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
2
Department of Life Science and Chemistry, Jacobs University Bremen, 28759 Bremen, Germany
*
Author to whom correspondence should be addressed.
Pathogens 2020, 9(2), 74; https://doi.org/10.3390/pathogens9020074
Received: 17 December 2019 / Revised: 15 January 2020 / Accepted: 16 January 2020 / Published: 21 January 2020
Leukotoxin (LtxA), from oral pathogen Aggregatibacter actinomycetemcomitans, is a secreted membrane-damaging protein. LtxA is internalized by β2 integrin LFA-1 (CD11a/CD18)-expressing leukocytes and ultimately causes cell death; however, toxin localization in the host cell is poorly understood and these studies fill this void. We investigated LtxA trafficking using multi-fluor confocal imaging, flow cytometry and Rab5a knockdown in human T lymphocyte Jurkat cells. Planar lipid bilayers were used to characterize LtxA pore-forming activity at different pHs. Our results demonstrate that the LtxA/LFA-1 complex gains access to the cytosol of Jurkat cells without evidence of plasma membrane damage, utilizing dynamin-dependent and presumably clathrin-independent mechanisms. Upon internalization, LtxA follows the LFA-1 endocytic trafficking pathways, as identified by co-localization experiments with endosomal and lysosomal markers (Rab5, Rab11A, Rab7, and Lamp1) and CD11a. Knockdown of Rab5a resulted in the loss of susceptibility of Jurkat cells to LtxA cytotoxicity, suggesting that late events of LtxA endocytic trafficking are required for toxicity. Toxin trafficking via the degradative endocytic pathway may culminate in the delivery of the protein to lysosomes or its accumulation in Rab11A-dependent recycling endosomes. The ability of LtxA to form pores at acidic pH may result in permeabilization of the endosomal and lysosomal membranes. View Full-Text
Keywords: Aggregatibacter actinomycetemcomitans; RTX toxin; localized aggressive periodontitis; LFA-1; leukotoxin (LtxA); endocytosis Aggregatibacter actinomycetemcomitans; RTX toxin; localized aggressive periodontitis; LFA-1; leukotoxin (LtxA); endocytosis
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Lally, E.T.; Boesze-Battaglia, K.; Dhingra, A.; Gomez, N.M.; Lora, J.; Mitchell, C.H.; Giannakakis, A.; Fahim, S.A.; Benz, R.; Balashova, N. Aggregatibacter actinomycetemcomitans LtxA Hijacks Endocytic Trafficking Pathways in Human Lymphocytes. Pathogens 2020, 9, 74.

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