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

Abstract

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-κB 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-κB 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-κB was inhibited by siRNA and NF-κB activation was inhibited by overexpression of IκBα. 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-κB prevented LPS-induced CRAMP mRNA. An important role for NF-κB in CRAMP gene expression was confirmed by overexpression of IκBα, which reduced both basal and induced levels of CRAMP mRNA. Conclusions: NF-κB, but not MAPKs, plays an important role in LPS-mediated induction of CRAMP gene in mast cells. Defects which inhibit NF-κB activity may increase susceptibility to bacterial and viral pathogens which are sensitive to cathelicidins.

Mouse Bone Marrow Sca-1 + CD44 + Mesenchymal Stem Cells Kill Avirulent Mycobacteria but Not Mycobacterium tuberculosis through Modulation of Cathelicidin Expression via the p38 Mitogen-Activated Protein Kinase-Dependent Pathway

“…Therefore, the observed activation of the MyD88 -IRAK-4 signaling pathway and NF-B could be attributed to the absence of ESAT-6 in M. bovis BCG. Moreover, activated NF-B was also shown to activate Camp expression (62). In agreement with those results, we also observed decreased Camp expression levels after the inhibition of nuclear translocation of NF-B in M. bovis BCG-infected cells.…”

Regulation of Cathelicidin Antimicrobial Peptide Expression by an Endoplasmic Reticulum (ER) Stress Signaling, Vitamin D Receptor-independent Pathway

“…A resent study also shows the requirement of NF-B for lipopolysaccharide (LPS)-induced stimulation of CRAMP in murine mast cells (47). Although we demonstrated that ER stress increases CRAMP expression in murine epidermis ex vivo, it remains to be resolved whether the C/EBP␣ signal is also required for the regulation of CRAMP under non-stressed conditions.…”

Stk38 protein kinase preferentially inhibits TLR9-activated inflammatory responses by promoting MEKK2 ubiquitination in macrophages

“…However, overexpression of MEKK2 did not affect LPS-induced cathelicidin-related antimicrobial peptide gene expression in mast cells 9 . In our experiments, MEKK2 knockdown only slightly inhibited LPS-induced ERK1/2 activation, suggesting that endogenous MEKK2 might be dispensable or redundant for ERK1/2 activation in TLR4 signalling.…”

“…It was reported that MEKK2 was associated with TRAF6 and phosphorylated following LPS stimulation in RAW264.7 cells, and overexpression of MEKK2(S519A) mutant inhibited LPS-induced Elk1 luciferase reporter gene expression in the cells, suggesting that MEKK2 might be involved in TLR4 signal transduction 8 . However, overexpression of MEKK2 did not affect LPS-induced cathelicidin-related antimicrobial peptide gene expression in mast cells 9 . The exact role of endogenous MEKK2 in TLR-mediated immune responses requires further investigation.…”