Regulation of Human β-Defensin-2 in Gingival Epithelial Cells: The Involvement of Mitogen-Activated Protein Kinase Pathways, But Not the NF-κB Transcription Factor Family

摘要

Stratified epithelia of the oral cavity are continually exposed to bacterial challenge that is initially resisted by neutrophils and epithelial factors, including antimicrobial peptides of the β-defensin family. Previous work has shown that multiple signaling pathways are involved in human β-defensin (hBD)-2 mRNA regulation in human gingival epithelial cells stimulated with a periodontal bacterium, Fusobacterium nucleatum , and other stimulants. The goal of this study was to further characterize these pathways. The role of NF-κB in hBD-2 regulation was investigated initially due to its importance in inflammation and infection. Nuclear translocation of p65 and NF-κB activation was seen in human gingival epithelial cells stimulated with F. nucleatum cell wall extract, indicating possible involvement of NF-κB in hBD-2 regulation. However, hBD-2 induction by F. nucleatum was not blocked by pretreatment with two NF-κB inhibitors, pyrrolidine dithiocarbamate and the proteasome inhibitor, MG132. To investigate alternative modes of hBD-2 regulation, we explored involvement of mitogen-activated protein kinase pathways. F. nucleatum activated p38 and c-Jun NH2-terminal kinase (JNK) pathways, whereas it had little effect on p44/42. Furthermore, inhibition of p38 and JNK partially blocked hBD-2 mRNA induction by F. nucleatum , and the combination of two inhibitors completely blocked expression. Our results suggest that NF-κB is neither essential nor sufficient for hBD-2 induction, and that hBD-2 regulation by F. nucleatum is via p38 and JNK, while phorbol ester induces hBD-2 via the p44/42 extracellular signal-regulated kinase pathway. Studies of hBD-2 regulation provide insight into how its expression may be enhanced to control infection locally within the mucosa and thereby reduce microbial invasion into the underlying tissue.