Staphylococcus aureus reprograms CASP8 (caspase 8) signaling to evade cell death and Xenophagy.

Abstract

Regulated cell death and xenophagy constitute fundamental cellular mechanisms against invading microorganisms. Staphylococcus aureus, a notorious pathogen, can invade and persist within host cells for extended periods. Here, we describe a novel mechanism by which S. aureus subverts these host defenses through the manipulation of the CASP8 (caspase 8) signaling pathway. Upon invasion, S. aureus triggers the assembly of a RIPK3 (receptor interacting serine/threonine kinase 3) complex to induce CASP8 autoprocessing. However, the bacterium inhibits CUL3 (cullin 3)-dependent K63-linked ubiquitination, leading to an atypical activation of CASP8. This non-canonical activation does not initiate the CASP8-CASP3 cascade but instead suppresses RIPK3-dependent necroptosis, a regulated cell death pathway typically activated when apoptosis fails. The resulting non-apoptotic, cleaved CASP8 redirects its enzymatic activity toward cleaving SQSTM1/p62, a selective macroautophagy/autophagy receptor, thus enabling S. aureus to evade antimicrobial xenophagy. The results of this study suggest that S. aureus reprograms the CASP8 signaling pathway from inducing cell death to preserving cell survival and inhibiting xenophagy, a critical strategy that supports its stealthy replication and persistence within host cells.Abbreviations: CASP3: caspase 3; CASP8: caspase 8; CFU: colony-forming units; CUL3: cullin 3; DUB: deubiquitinating enzyme; MAP1LC3B-II/LC3B-II: microtubule associated protein 1 light chain 3 beta-II; MOI: multiplicity of infection; RIPK1: receptor interacting protein kinase 1; RIPK3: receptor interacting protein kinase 3; S. aureus: Staphylococcus aureus.