Quantitative proteomics and phosphoproteomics reveal glucocorticoid stimulation of TLR and Rho GTPase signaling in neutrophil-like cells

BACKGROUND: Glucocorticoids are corticosteroid hormones that are commonly used for treating systemic inflammatory diseases and acute infections. Immunosuppressive effects of glucocorticoids have been studied in many cell types, particularly macrophages and T cells. Despite the importance and abundance of neutrophils in the human immune system, glucocorticoid responses remain understudied in neutrophils. RESULTS: Here, we perform quantitative mass spectrometry-based proteomics of primary neutrophils and neutrophil-like cells differentiated from human HL-60 promyelocyte cells. Primary neutrophils exhibited CK2 kinase activation and increase phosphorylation of HSP90 following 2-h incubation, highlighting potential effects of short-term ex vivo handling. Proteome and flow cytometry analysis show that neutrophil-like cells share features of neutrophils. Quantitative proteomics and phosphoproteomics of neutrophil-like cells treated with two synthetic glucocorticoid compounds, the clinical drugs dexamethasone and prednisolone, identify higher numbers of significantly regulated proteins and phosphosites compared to parental HL-60 cells. Glucocorticoid treatments modulated toll-like receptor signaling and CXCR4 serine phosphorylation. In addition, we identify RIPOR2 as a glucocorticoid-regulated protein associated with Rho GTPase signaling networks and actin cytoskeletal remodeling in neutrophils and neutrophil-like cells, though its exact functional role requires further investigation. CONCLUSIONS: Our results not only reveal unconventional regulatory mechanisms of glucocorticoids in the human immune system but also provide valuable resources for discovering novel glucocorticoid-responsive protein targets in neutrophils.