Serine/threonine kinase 33 mediates thrombin-induced interleukin-8 release from human lung epithelial cells in severe asthma

Interleukin (IL)-8, also known as chemokine (CXC motif) ligand 8, contributes to the pathogenesis of neutrophilic asthma. Thrombin exacerbates IL-8/CXCL8-mediated inflammatory responses. However, the underlying mechanisms remain unclear. Phosphorylation of serine/threonine kinase 33 (STK33) by extracellular signal-regulated kinase (ERK) has been implicated in lung cancer metastasis, but its role in thrombin-induced airway inflammation remains to be determined. In this study, we investigated whether STK33 mediates thrombin-induced IL-8/CXCL8 release from airway epithelial cells in severe asthma. Single-cell RNA sequencing revealed upregulated STK33 expression in bronchial epithelial cells from patients with severe asthma. Immunofluorescence staining indicated increased coexpression of STK33 and macrophage inflammatory protein 2 (murine homolog of IL-8/CXCL8) in the airway epithelial cells of mice with ovalbumin- and house dust mite–induced asthma. Thrombin induced STK33 phosphorylation at serine residues. Notably, STK33 knockdown markedly inhibited thrombin-induced IL-8/CXCL8 release from A549 and BEAS-2B cells. Thrombin also induced the formation of an ERK–STK33 complex, and STK33 knockdown reduced thrombin-induced ERK phosphorylation. Colocalization of STK33, p-c-Myc, and thrombin was increased in asthmatic mice. Moreover, thrombin increased the phosphorylation of c-Myc in A549 cells; this increase in c-Myc phosphorylation was significantly attenuated by ERK inhibition (U0126 treatment) and STK33 knockdown. Furthermore, thrombin promoted the binding of c-Myc to the IL-8/CXCL8 promoter, and c-Myc knockdown suppressed thrombin-induced IL-8/CXCL8 release from A549 and BEAS-2B cells. Collectively, these findings indicate that thrombin induces IL-8/CXCL8 release through the ERK/STK33/c-Myc pathway, highlighting STK33 as a potential therapeutic target in severe asthma.