The ubiquitin C-terminal hydrolase UCH-L1 promotes bacterial invasion by altering the dynamics of the actin cytoskeleton

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Abstract
Invasion of eukaryotic target cells by pathogenic bacteria requires extensive remodelling of the membrane and actin cytoskeleton. Here we show that the remodelling process is regulated by the ubiquitin C-terminal hydrolase UCH-L1 that promotes the invasion of epithelial cells by Listeria monocytogenes and Salmonella enterica. Knockdown of UCH-L1 reduced the uptake of both bacteria, while expression of the catalytically active enzyme promoted efficient internalization in the UCH-L1-negative HeLa cell line. The entry of L. monocytogenes involves binding to the receptor tyrosine kinase Met, which leads to receptor phosphorylation and ubiquitination. UCH-L1 controls the early membrane-associated events of this triggering cascade since knockdown was associated with altered phosphorylation of the c-cbl docking site on Tyr1003, reduced ubiquitination of the receptor and altered activation of downstream ERK1/2- and AKT-dependent signalling in response to the natural ligand Hepatocyte Growth Factor (HGF). The regulation of cytoskeleton dynamics was further confirmed by the induction of actin stress fibres in HeLa expressing the active enzyme but not the catalytic mutant UCH-L1C90S. These findings highlight a previously unrecognized involvement of the ubiquitin cycle in bacterial entry. UCH-L1 is highly expressed in malignant cells that may therefore be particularly susceptible to invasion by bacteria-based drug delivery systems.

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