E3 ubiquitin ligase SKP2 limits autophagy during S. aureus infection

Abstract

Ubiquitination is a posttranslational modification that affects protein function, stability, and localization and is thereby balancing protein homeostasis. During infection, ubiquitination is crucial in regulating host cell signaling pathways in pathogen recognition, clearance and mounting an efficient immune response. S. aureus is an opportunistic pathogen that is able to invade and multiply within both phagocytic and non-phagocytic mammalian cells depending on virulence factor expression of the respective S. aureus strain. Selective autophagy serves as a host defense mechanism to combat intracellular bacterial persistence by targeting and degrading intracellular pathogens. However, S. aureus can subvert autophagosomal degradation and exploit these organelles for intracellular replication. We examined the role of the E3 ligase S-phase kinase-associated protein 2 (SKP2), a component of the SKP1-Cullin1-F-box (SCF) - complex, during S. aureus infection in alveolar epithelial and in macrophage-like cells. Upon S. aureus infection, we demonstrate increased SKP2 abundance through acetylation-induced stabilization and translocation into the cytoplasm. Cytoplasmic SKP2 modulated autophagy induction. By downregulation of SKP2, the level of the autophagy marker LC3-II was elevated which was accompanied by increased survival of intracellular S. aureus. Conversely, SKP2 overexpression in host cells reduced LC3-II levels followed by reduced intracellular bacteria. These findings underscore that SKP2 is an important regulator of autophagy, preventing excessive autophagy from being exploited by S. aureus. In conclusion, our findings reveal novel molecular mechanisms involved in the interaction between host cells and S. aureus providing potential approaches for targeted therapeutic intervention. ImportanceStaphylococcus aureus is a major pathogen responsible for a wide range of human and animal infections and toxin-mediated syndromes. For many years, S. aureus was mainly recognized as an extracellular pathogen. However, it has been shown that S. aureus can survive in epithelial cells and phagocytes. Intracellular persistence complicates the treatment by protecting the bacteria from antibiotics and immune detection. Elimination of pathogens from intracellular compartments relies on cellular mechanisms such as recognition and ubiquitination by host E3 ligases followed by selective autophagy. S. aureus has developed strategies to manipulate this process by evading degradation by interfering with autophagosome formation or even exploiting the formation of autophagosomes as replication niches. The present study reveals an intricate cellular response pathway that is involved in the intracellular recognition and elimination of the pathogen. This knowledge opens new avenues towards targeted treatment.