Serratia marcescens serralysin induces inflammatory responses through protease-activated receptor 2

The Serratia marcescens-derived protease serralysin is considered to play an important role in the pathogenesis of infection. Protease-activated receptor 2 (PAR-2) is activated by trypsin and also several other trypsin-like serine proteases, leading to the modulation of inflammatory and immune responses. However, little is known about the activation of PAR-2 by bacterial proteases and its roles in bacterial infection. In this study, we investigated whether S. marcescens serralysin activates host inflammatory responses through PAR-2. Our results demonstrated that serralysin induces interleukin-6 (IL-6) and IL-8 mRNA expression in a human lung squamous cell carcinoma, EBC-1 cells. In addition, serralysin activated activator protein 1 (AP-1)-, CCAAT/enhancer-binding protein (C/EBP)-, and nuclear factor-kappa B (NF-kappa B)-driven promoters in EBC-1 cells. An electrophoretic mobility shift assay showed that serralysin activates the binding of AP-1, C/EBP beta, and NF-kappa B in the cells. Inactivation of serralysin resulted in the failure of transactivation of AP-1-, C/EBP-, and NF-kappa B-driven promoters in the cells. Furthermore, serralysin activated AP-1-, C/EBP-, and NF-kappa B-driven promoters via PAR-2 in HeLa cells. PAR-2 antagonist peptides decreased serralysin-induced transactivation of AP-1-, C/EBP-, and NF-kappa B-driven promoters in EBC-1 cells. Considered together, these results suggest that serralysin requires PAR-2 to activate the critical transcription factors AP-1, C/EBP beta, and NF-kappa B for host inflammatory responses.