Regulation of intracellular proliferation of Salmonella typhimurium by CD63.

Background: Autophagy is an intracellular degradation process involving the lysosomal breakdown of unnecessary or abnormal cellular components. Targets of autophagy include pathogens, altered organelles, and protein aggregates, which are sequestered within double-membrane-limited vesicles known as autophagosomes. A variety of lysosomal membrane proteins play essential roles in numerous cellular processes, including lysosomal acidification, metabolite transport, and interaction with other membrane systems. Cluster of differentiation 63 (CD63), a member of the transmembrane 4 superfamily, is present on the cell surface and in intracellular membrane compartments, such as endosomal and lysosomal membranes. This protein is also associated with several diseases, including Hermansky-Pudlak syndrome and immunoglobulin E-mediated allergies. However, its role in the autophagy pathway and intracellular bacterial proliferation remains poorly understood.

Objective: This study aimed to investigate changes in CD63 expression in response to Salmonella infection and to analyze the effects of these changes on Salmonella proliferation.

Methods: Changes in CD63 expression were examined following Salmonella infection using cellular models. Expression regulation was assessed for dependence on nuclear factor kappa B signaling. Colocalization of CD63 was evaluated with green fluorescent protein-tagged Salmonella and the lysosomal marker LysoTracker. Intracellular Salmonella titers were measured and correlated with CD63 expression levels to determine impacts on bacterial survival.

Results: CD63 expression increased in response to Salmonella infection in a nuclear factor kappa B-dependent manner. CD63 colocalized with green fluorescent protein-tagged Salmonella and the lysosomal marker LysoTracker. The titer of intracellular Salmonella was inversely correlated with CD63 expression, suggesting that higher CD63 levels reduce bacterial survival.

Conclusion: CD63 contributes to the regulation of intracellular Salmonella survival through the autophagy pathway, specifically xenophagy (autophagy targeting pathogens). This is the first report documenting the inhibition of Salmonella proliferation via induction of CD63 expression and Xenophagy.