Inhibition of the ULK1 protein complex suppresses Staphylococcus-induced autophagy and cell death

Abstract

Autophagy plays multiple roles in host cells challenged with extracellular pathogens. Here, we aimed to explore whether autophagy inhibition could prevent bacterial infections. We first confirmed widely distinct patterns of autophagy responses in host cells infected with <i>Staphylococcus aureus</i>, as compared with <i>Salmonella</i> Only infection with <i>Staphylococcus</i> produced strong accumulation of lipidated autophagy-related protein LC3B (LC3B-II). Infection with virulent <i>Staphylococcus</i> strains induced formation of p62-positive aggregates, suggestive of accumulated ubiquitinated targets. During <i>Salmonella</i> infection, bacteria remain enclosed by lysosomal-associated membrane protein 2 (LAMP2)-positive lysosomes, whereas virulent <i>Staphylococcus</i> apparently exited from enlarged lysosomes and invaded the cytoplasm. Surprisingly, <i>Staphylococcus</i> appeared to escape from the lysosome without generation of membrane-damage signals as detected by galectin-3 recruitment. In contrast, <i>Salmonella</i> infection produced high levels of lysosomal damage, consistent with a downstream antibacterial xenophagy response. Finally, we studied the Unc-51-like autophagy-activating kinase 1 (ULK1) regulatory complex, including the essential subunit autophagy-related protein 13 (ATG13). Infection of cells with either <i>Staphylococcus</i> or <i>Salmonella</i> led to recruitment of ATG13 to sites of cytosolic bacterial cells to promote autophagosome formation. Of note, genetic targeting of ATG13 suppressed autophagy and the ability of <i>Staphylococcus</i> to infect and kill host cells. Two different ULK1 inhibitors also prevented <i>Staphylococcus</i> intracellular replication and host cell death. Interestingly, inhibition of the ULK1 pathway had the opposite effect on <i>Salmonella</i>, sensitizing cells to the infection. Our results suggest that ULK1 inhibitors may offer a potential strategy to impede cellular infection by <i>S. aureus</i>.