Staphylococcus aureus (S. aureus) plays a predominant role in both hospital- and community-acquired infections [1]. Epidemiological studies have reported strong association of S. aureus strains causing necrotizing pneumonia and the presence of the bicomponent pore-forming toxin, Panton-Valentine leucocidin (PVL) which targets and kills innate immune cells [2, 3]. Recent studies, however, challenged the notion that the PVL toxin kills by punching holes into the plasma membrane and there are increasing evidences showing that S. aureus use PVL to hijack host molecular pathway. In order to identify the host factors that contribute to PVL toxicity, we performed a genome-wide CRISPR screen with the aim to isolate resistant innate immune cells, and among the top 10 candidate genes were C5aR1 and FBXO11.
C5aR1 is a member of G-protein coupled receptor that is highly expressed on myeloid cells. The use of live cell imaging showed that deletion of C5aR1 using CRISPR/Cas9 technology resulted in decreased susceptibility to PVL, even at a concentration of 1mg/mL, which confirmed findings from previous studies that have shown surface expression of C5aR1 is required for PVL-mediated toxicity [4]. Similarly, ablation of FBXO11 which forms part of E3 ubiquitin ligase complex, resulted in decreased susceptibility to PVL. The use of western blot, flow cytometry and indirect immunofluorescence microscopy showed that this was due to decreased expression of C5aR1 on the cell surface, thereby decreasing toxin binding. The mechanism by which C5aR1 expression and/or localization is regulated is largely unknown. However, we present evidence that FBXO11 regulates C5aR1 protein level and its potential as new therapeutic strategies against bacterial infections.