Background: Phosphoinositide 3-kinase is a potent target for cancer therapy due to its significant role in the regulation of cellular growth and proliferation. Dysregulation of the PI3k signaling cascade can constitutively activate growth pathways to trigger the progression of cancer, resulting in the development of multiple inhibitors as cancer therapeutics. Objectives: The wide array of cells expressing PI3k also include immune cells, and the inhibition of these receptors has shown promise in combating inflammation and infectious disease, a relationship we sought to examine further. Methods: We infected wild-type and PI3kγ knockout murine macrophages as well as PI3kγ inhibitor-treated THP-1 human macrophage-like cells with Staphylococcus aureus and quantified inflammation through gene expression analysis, protein secretion assays, and immunofluorescence imaging. Results: We observed that knockout of PI3kγ in murine macrophages alongside pharmacological inhibition through IPI549 treatment in THP-1 cells led to an NF-κB-driven suppression in transcription and release of inflammatory cytokines upon infection with methicillin-resistant Staphylococcus aureus. We were also able to confirm that this suppression of NF-κB translocation and subsequent decrease in inflammatory cytokine release did not compromise and even slightly boosted the bacterial killing ability. Conclusion: PI3k is primarily targeted for cancer therapies, but further exploration can also be carried out on its potential roles in treating bacterial infection.

Staphylococcus aureus (SA) causes a broad range of invasive human diseases, increasingly complicated by antibiotic resistance. Macrophages (MΦ) play a central role in innate immunity, yet key aspects of their interaction with SA remain incompletely understood because of the pathogen’s diverse immune evasion strategies. Using multi-omics and systems-level analytics, we identified the E3 ubiquitin ligase cullin 4B (CUL4B) as a host factor that modulates MΦ responses to SA infection. CRISPR-mediated deletion of CUL4B in human THP-1 MΦ enhanced intracellular bacterial killing, reduced cell death, decreased caspase-1 activation, and lowered interleukin-1β production, consistent with altered inflammasome signaling. In a murine methicillin-resistant SA (MRSA) pneumonia model, CUL4B deficiency improved pulmonary bacterial clearance, reduced bacteremia, and decreased inflammatory tissue injury. Whole-lung and serum proteomics further revealed increased antimicrobial protein abundance and reduced markers of inflammatory damage. Together, these findings identify CUL4B as a regulator of MΦ inflammatory responses during MRSA infection and suggest a potential host-directed pathway that could be leveraged to improve outcomes against this major pathogen.