In the repair process after lung injury, the regeneration of alveolar epithelial cells plays an important role by covering the damaged alveolar wall and preventing the activated fibroblasts from invading the intra- alveolar spaces. Hepatocyte growth factor (HGF) is a potent mitogen for alveolar epithelial cells and has been reported to be capable of repressing the fibrosing process by connecting to the c-Met/HGF receptor on alveolar epithelial cells. However, it has been reported that the c-Met expression was downregulated in an acute phase of lung injury, which may limit the effect of HGF for therapeutic use. In the present study we observed that interferon (IFN)-γ upregulates the c-Met messenger RNA (mRNA) and protein expression in A549 alveolar epithelial cells. We analyzed the mechanism of this upregulation and found that IFN-γ enhances the transcription of the c-met proto-oncogene, and that it does not prolong the stability of the c-Met mRNA. HGF is known to act as a motogen as well as a mitogen for epithelial cells. We also found that the migratory activity of A549 cells induced by HGF is strongly enhanced by preincubation with IFN-γ. Finally, we administered recombinant IFN-γ to C57BL/6 mice and confirmed that this upregulation is also observed in vivo. These results suggest that the combination of HGF and IFN-γ co
Neutrophil-mediated injury to gut epithelium may lead to disruption of the epithelial barrier function with consequent organ dysfunction, but the mechanisms of this are incompletely characterized. Because the epithelial apical junctional complex, comprised of tight and adherens junctions, is responsible in part for this barrier function, we investigated the effects of neutrophil transmigration on these structures. Using a colonic epithelial cell line, we observed that neutrophils migrating across cell monolayers formed clusters that were associated with focal epithelial cell loss and the creation of circular defects within the monolayer. The loss of epithelial cells was partly attributable to neutrophil-derived proteases, likely elastase, because it was prevented by elastase inhibitors. Spatially delimited disruption of epithelial junctional complexes with focal loss of E-cadherin, β-catenin, and zonula occludens 1 was observed adjacent to clusters of transmigrating neutrophils. During neutrophil transmigration, fragments of E-cadherin were released into the apical supernatant, and inhibitors of neutrophil elastase prevented this proteolytic degradation. Addition of purified leukocyte elastase also resulted in release of E-cadherin fragments, but only after opening of tight junctions. Taken together, these data demonstrate that neutrophil-derived proteases can mediate spatially delimited disruption of epithelial apical junctions during transmigration. These processes may contribute to epithelial loss and disruption of epithelial barrier function in inflammatory diseases.
Human airway epithelial cells (HAEC) constitutively express the CXC chemokine receptor CXCR3, which regulates epithelial cell movement. In diseases such as chronic obstructive pulmonary disease and asthma, characterized by denudation of the epithelial lining, epithelial cell migration may contribute to airway repair and reconstitution. This study compared the potency and efficacy of three CXCR3 ligands, I-TAC/CXCL11, IP-10/CXCL10, and Mig/CXCL9, as inducers of chemotaxis in HAEC and examined the underlying signaling pathways involved. Studies were performed in cultured HAEC from normal subjects and the 16-HBE cell line. In normal HAEC, the efficacy of I-TAC-induced chemotaxis was 349 ± 88% (mean ± SE) of the medium control and approximately one-half the response to epidermal growth factor, a highly potent chemoattractant. In normal HAEC, Mig, IP-10, and I-TAC induced chemotaxis with similar potency and a rank order of efficacy of I-TAC = IP-10 > Mig. Preincubation with pertussis toxin completely blocked CXCR3-induced migration. Of interest, intracellular [Ca2+] did not rise in response to I-TAC, IP-10, or Mig. I-TAC induced a rapid phosphorylation (5–10 min) of two of the three MAPKs, i.e., p38 and ERK1/2. Pretreatment of HAEC with the p38 inhibitor SB 20358 or the PI3K inhibitor wortmannin dose-dependently inhibited the chemotactic response to I-TAC. In contrast, the ERK1/2 inhibitor U0126 had no effect on chemotaxis. These data indicate that in HAEC, CXCR3-mediated chemotaxis involves a G protein, which activates both the p38 MAPK and PI3K pathways in a calcium-independent fashion.