NF-kappa B-Dependent Induction of Cathelicidin-Related Antimicrobial Peptide in Murine Mast Cells by Lipopolysaccharide

Background: An important aspect of the innate immune response to pathogens is the production of anti-microbial peptides such as cathelicidin-related antimicrobial peptide (CRAMP), the murine homologue of human cathelicidin LL-37. In this study, mechanisms regulating LPS-induction of CRAMP gene expression in mast cells were investigated. NF-kappa B and MAPK pathways were the focus of investigation. Methods: Mouse bone marrow-derived mast cells were grown in culture and stimulated with LPS. MAPKs and NF-kappa B were monitored by immunoblot analysis. ERK, JNK and p38 MAPK were inhibited using siRNAs or a pharmacological inhibitor. Accumulation of the p65 component of NF-kappa B was inhibited by siRNA and NF-kappa B activation was inhibited by overexpression of I kappa B alpha. MEKK2 or MEKK3 were overexpressed by transfection. The effects of all of these treatments on CRAMP gene expression were monitored by RT-PCR. Results: Inhibition of ERK, JNK or p38 MAPK had little discernible effect on LPS-inducible CRAMP gene expression. Overexpression of MEKK2 or MEKK3 likewise had little impact. However, inhibition of the accumulation of p65 NF-kappa B prevented LPS-induced CRAMP mRNA. An important role for NF-kappa B in CRAMP gene expression was confirmed by overexpression of I kappa B alpha, which reduced both basal and induced levels of CRAMP mRNA. Conclusions: NF-kappa B, but not MAPKs, plays an important role in LPS-mediated induction of CRAMP gene in mast cells. Defects which inhibit NF-kappa B activity may increase susceptibility to bacterial and viral pathogens which are sensitive to cathelicidins. Copyright (C) 2009 S. Karger AG, Basel