Activation of a Src-dependent Raf–MEK1/2–ERK signaling pathway is required for IL-1α-induced upregulation of β-defensin 2 in human middle ear epithelial cells

Abstract

beta-defensin 2 is produced by a variety of epithelial cell types in the body and exhibits potent antimicrobial activity against a variety of pathogens, including the bacteria that are most commonly associated with otitis media (OM). The human beta-defensin 2 (hBD-2) gene is an NF-kappa B regulated gene and a variety of proinflammatory stimuli can induce its expression. Although the presence of molecules of innate immunity such as lysozyme and lactoferrin has been demonstrated in the middle ear, to date there have been no reports on the expression of beta-defensin 2. In the present study, we demonstrate that beta-defensin 2 is expressed in the middle ear mucosa of humans and rats. We also show that it is expressed in a human middle ear epithelial cell line and that its expression is induced by proinflammatory stimuli such as interleukin 1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF-alpha), and lipopolysaccharide (LPS). Moreover, we demonstrate that the transcriptional activation of hBD-2 gene by IL-1 alpha is mediated through an Src-dependent Raf-MEK1/2-ERK signaling pathway.

Isoleucine, an Essential Amino Acid, Induces the Expression of Human <i>β</i> Defensin 2 through the Activation of the G-Protein Coupled Receptor-ERK Pathway in the Intestinal Epithelia

“…IL-1α activates the ERK signaling pathway, which is known to be important for HBD2 expression [17]. The present study confirmed the effect of IL-1α on the activation of the ERK signaling pathway, and in addition, we found that Ile treatment extended the interval of the activation of the ERK signaling pathway.…”

“…GPCRs comprise a large protein family of transmembrane receptors that sense molecules outside the cell [31]. Once a ligand binds to a GPCR, the structure of the GPCR is changed, and a trimer-forming G protein is activated, leading to changes in the concentration of second messengers such as calcium ions and cAMP, and the subsequent activation of internal signal transduction pathways.…”

“…ERK signaling pathway mediated the increase in the expression of HBD2 [17], the phosphorylation of p44/42 ERK by IL-1α or Ile was examined by a Western blot analysis. IL-1α phosphorylated p44/42 beginning from 10 to 15 minutes after the start of treatment, and the effect was reversed within 30 minutes.…”

Identification and Characterization of a Mucosal Antimicrobial Peptide Expressed by the Chinchilla (Chinchilla lanigera) Airway

“…hBD-1 is constitutively expressed in normal and inflamed nasal and middle ear mucosae, whereas hBD-2 is expressed only in inflamed tissues (8,9). Additionally, inducible hBD-2 expression was demonstrated in both a human middle ear epithelial cell line and in primary nasal epithelial cells in response to proinflammatory cytokines or bacterial components, a common feature of hBD-2 expression in multiple in vitro systems (10). The detection of these defensins in nasal and middle ear mucosae suggests a role for these peptides in maintaining the health of the uppermost airway and thus perhaps preventing OM.…”

Establishment of Cell Lines from the Human Middle and Inner Ear Epithelial Cells

“…Beta defensin 2, which is released from the epithelial cells in response to microorganisms or cytokines, exhibits potent antimicrobial activity against gramnegative bacteria and candida. HMEEC-1 cells were found to up-regulate beta defensin 2 in response to interleukin 1 alpha (IL-1a) via a Srcdependent Raf-MEK1/2-ERK signaling pathway [34]. We also found that nontypeable H. influenzae-induced up-regulation of beta defensin 2 requires a TLR2/MyD88-dependent p38 MAP kinase pathway [35].…”