Differential regulation of epidermal growth factor receptor by hydrogen peroxide and flagellin in cultured lung alveolar epithelial cells

Epidermal growth factor receptor in asthma: A promising therapeutic target?

Activation of the epidermal growth factor receptor (EGFR) pathway is involved in the pathogenesis of asthma. Although decades of intensive research have focused on the role of EGFR in asthma, the specific mechanisms and pathways of EGFR signaling remain unclear. Various reports have indicated that inhibition of EGFR improves the pathological features in asthma models. However, extending these experimental findings to clinical applications is difficult. Several measures can be adopted to promote clinical application of EGFR inhibitors. This review focuses on the role of EGFR in the pathogenesis of asthma and the development of a potentially novel therapeutic target for asthma.

Regulation of epidermal growth factor receptor expression and morphology of lung epithelial cells by interleukin-1β

Accumulating evidences suggested that the overactivation of epidermal growth factor receptor (EGFR) was involved in the development of adult respiratory distress syndrome and pulmonary fibrosis. Elucidation of the mechanisms that regulate EGFR residence on the plasma membrane during inflammatory lung conditions is important for identifying potential therapies. We have demonstrated that flagellin phosphorylated EGFR at Ser1047 and induced transient EGFR internalization. In this study, we examined the molecular pathway and effect of interleukin 1 beta (IL-1β) on EGFR in alveolar epithelial cells. Treatment of A549 cells with IL-1β induced the activation of p38 mitogen-activated protein kinase (MAP kinase) and MAP kinase-activated protein kinase-2 (MAPKAPK-2), as well as EGFR phosphorylation at serine 1047. Both MAPKAPK-2 activation and EGFR phosphorylation were inhibited by SB203580, a p38 MAP kinase inhibitor. In addition, MK2a inhibitor (a MAPKAPK-2 inhibitor) suppressed EGFR phosphorylation. Assessment of the biotinylation of cell surface proteins indicated that IL-1β induced EGFR internalization. Furthermore, long-term treatment of A549 cells with IL-1β caused morphological changes and loss of cell-cell contact. Moreover, IL-1β augmented the effect of transforming growth factor beta 1 on the epithelial-mesenchymal transition. These results suggested that IL-1β regulates EGFR functions and induces morphological changes of alveolar epithelial cells.

Increased expression of EGR1 and KLF4 by polysulfide via activation of the ERK1/2 and ERK5 pathways in cultured intestinal epithelial cells

Sodium trisulfide (Na₂S₃) releases hydrogen polysulfide (H₂S_n) and is useful for the investigation of the effects of H₂S_n on the cell functions. In the present study, we first examined the effects of Na₂S₃ on the gene expression of IEC-6 cells, a rat intestinal epithelial cell line. Microarray analysis and reverse transcription-polymerase chain reaction analysis revealed that Na₂S₃ increased the gene expression of early growth response 1 (EGR1) and Kruppel-like transcription factor 4 (KLF4). It was interesting that U0126, an inhibitor of the activation of extracellular signal-regulated kinase 1 (ERK1), ERK2, and ERK5, inhibited the Na₂S₃-induced gene expression of EGR1 and KLF4. Na₂S₃ activated ERK1 and ERK2 (ERK1/2) within 15 min. In addition to ERK1/2, Na₂S₃ activated ERK5. We noticed that the electrophoretic mobility of ERK5 was decreased after Na₂S₃ treatment. Phos-tag analysis and in vitro dephosphorylation of the cell extracts indicated that the gel-shift of ERK5 was due to its phosphorylation. The gel-shift of ERK5 was inhibited completely by both U0126 and ERK5-IN-1, a specific inhibitor of ERK5. From these results, we concluded that the gel-shift of ERK5 was induced through autophosphorylation by activated ERK5 after Na₂S₃ treatment. The present study suggested that H₂S_n affected various functions of intestinal epithelial cells through the activation of the ERK1/2 and ERK5 pathways.

Potential implications of hydrogen peroxide in the pathogenesis and therapeutic strategies of gliomas

Glioma is the most common type of primary brain tumor, and it has a high mortality rate. Currently, there are only a few therapeutic approaches for gliomas, and their effects are unsatisfactory. Therefore, uncovering the pathogenesis and exploring more therapeutic strategies for the treatment of gliomas are urgently needed to overcome the ongoing challenges. Cellular redox imbalance has been shown to be associated with the initiation and progression of gliomas. Among reactive oxygen species (ROS), hydrogen peroxide (H₂O₂) is considered the most suitable for redox signaling and is a potential candidate as a key molecule that determines the fate of cancer cells. In this review, we discuss the potential cellular and molecular roles of H₂O₂ in gliomagenesis and explore the potential implications of H₂O₂ in radiotherapy and chemotherapy and in the ongoing challenges of current glioma treatment. Moreover, we evaluate H₂O₂ as a potential redox sensor and potential driver molecule of nanocatalytic therapeutic strategies for glioma treatment.

Epidermal growth factor receptor transactivation is involved in the induction of human hepatoma SMMC7721 cell proliferation by insufficient radiofrequency ablation

Our previous study revealed that insufficient radiofrequency ablation (RFA) promotes the malignancy of human hepatocellular carcinoma (HCC) SMMC7721 cells via the Ca²⁺/calmodulin-dependent protein kinase II (CaMKII)/extracellular signal-regulated kinase (ERK)-induced overexpression of vascular endothelial growth factor (VEGF). The aims of the present study were to address the involvement of epidermal growth factor receptor (EGFR) transactivation in the enhanced SMMC7721 cell proliferation induced by insufficient RFA, in addition to its association with the CaMKII/ERK/VEGF signaling cascade. SMMC7721 cells were subjected to a 47°C treatment regimen to simulate insufficient RFA. Cell proliferation was determined using MTT and colony formation assays. The expression levels of VEGF, CaMKII, phosphorylated (phospho)-CaMKII, ERK, phospho-ERK, EGFR and phospho-EGFR were analyzed using western blotting. The results demonstrated that the enhancement of SMMC7721 cell proliferation by the 47°C treatment regimen was significantly inhibited by exposure of the cells to AG178 (a specific inhibitor of EGFR). Furthermore, AG1478 exposure prevented the overexpression of VEGF and phosphorylation of ERK, but had no significant effects on CaMKII phosphorylation. By contrast, 47°C treatment-induced EGFR phosphorylation was inhibited by treatment with KN93 (a specific inhibitor of CaMKII). Overall, the results of the present study have suggested a role for EGFR transactivation in the RFA-promoted growth of residual HCC. Thus, targeting EGFR may represent a useful preventive and therapeutic strategy for RFA-induced HCC progression and recurrence.

Pirfenidone inhibits p38-mediated generation of procoagulant microparticles by human alveolar epithelial cells

Pirfenidone is a drug recently approved for idiopathic pulmonary fibrosis but its mechanisms of action are partially unknown. We have previously demonstrated that the airways of patients with idiopathic pulmonary fibrosis contain procoagulant microparticles that activate coagulation factor X to its active form, Xa, a proteinase that signals fibroblast growth and differentiation, thus potentially contributing to the pathogenesis of the disease. We also reported that in vitro exposure of human alveolar cells to H2O2 causes microparticle generation. Since p38 activation is involved in microparticle generation in some cell models and p38 inhibition is one of the mechanisms of action of pirfenidone, we investigated the hypothesis that H2O2-induced generation of microparticles by alveolar cells is dependent on p38 phosphorylation and is inhibited by pirfenidone. H2O2 stimulation of alveolar cells caused p38 phosphorylation that was inhibited by pirfenidone. The drug also inhibited H2O2 induced microparticle generation as assessed by two independent methods (solid phase thrombin generation and flow cytometry). The shedding of microparticle-bound tissue factor activity was also inhibited by pirfenidone. Inhibition of p38-mediated generation of procoagulant microparticle is a previously unrecognized mechanism of action of the antifibrotic drug, pirfenidone.

Antiseptic solutions modulate the paracrine-like activity of bone chips: differential impact of chlorhexidine and sodium hypochlorite

AIM

Chemical decontamination increases the availability of bone grafts; however, it remains unclear whether antiseptic processing changes the biological activity of bone.

MATERIALS AND METHODS

Bone chips were incubated with four different antiseptic solutions including (1) povidone-iodine (0.5%), (2) chlorhexidine diguluconate (0.2%), (3) hydrogen peroxide (1%) and (4) sodium hypochlorite (0.25%). After 10 min. of incubation, changes in the capacity of the bone-conditioned medium (BCM) to modulate gene expression of gingival fibroblasts was investigated.

RESULTS

Conditioned medium obtained from freshly prepared bone chips increased the expression of TGF-β target genes interleukin 11 (IL11), proteoglycan4 (PRG4), NADPH oxidase 4 (NOX4), and decreased the expression of adrenomedullin (ADM), and pentraxin 3 (PTX3) in gingival fibroblasts. Incubation of bone chips with 0.2% chlorhexidine, followed by vigorously washing resulted in a BCM with even higher expression of IL11, PRG4 and NOX4. These findings were also detected with a decrease in cell viability and an activation of apoptosis signalling. Chlorhexidine alone, at low concentrations, increased IL11, PRG4 and NOX4 expression, independent of the TGF-β receptor I kinase activity. In contrast, 0.25% sodium hypochlorite almost entirely abolished the activity of BCM, whereas the other two antiseptic solutions, 1% hydrogen peroxide and 0.5% povidone-iodine, had relatively no impact respectively.

CONCLUSION

These in vitro findings demonstrate that incubation of bone chips with chlorhexidine differentially affects the activity of the respective BCM compared to the other antiseptic solutions. The data further suggest that the main effects are caused by chlorhexidine remaining in the BCM after repeated washing of the bone chips.