Background: TNF is a cytokine with many biological properties including both anti- and pro-apoptotic signaling pathways. However, the molecular switch, which determines TNF regulation of these two different functions, is not well characterized. EGFR and other ErbB family members could be activated by direct interaction with EGF-like ligands initiating formation of homo- and/or hetero-dimers and increased kinase activity. In addition to direct EGFR ligands, EGFR can be transactivated by various extracellular stimuli, such as agonists for GPCR and cytokine receptors. Previously, we have reported that EGFR and ErbB2 were transactivated via Src kinase family activation with TNF exposure and blockade of EGFR enhanced intestinal epithelial cells apoptosis. Furthermore, TNF administration enhanced apoptotic cells in colonic grand of EGFRwa2 mice. Hypothesis: The induction of pulmonary epithelial cell apoptosis is a persistent finding in lung tissue from patients with emphysema and pulmonary fibrosis. We hypothesized that EGFR tyrosine kinase activity is required for protection from pulmonary cell apoptosis in TNF-rich condition. Methods: We employed C57BL/6 mice as a control and surfactant protein-C (SP-C)/TNF transgenic (TG) mice (6-8 weeks old), which showed over-expression of TNF in lung tissue by induction of SP-C production. The lung tissue sections were stained by H&E and trichrome stain. Apoptosis and signal transduction was determined by TUNEL assay and Western-blot analysis, respectively. The accumulation of collagen was measured by Sircol assay. Results: Control mice and TG mice was administrated gefitinib 100mg/kg for 14days. Gefitinib increased lymphocyte infiltration into interstitial spaces of the TG mice lung, significantly. Although TG mice lung was severely injured by gefitinib, fibroblast proliferation was not observed and the accumulation of collagen was not detected. In TG mice, gefitinib increased apoptotic response 10-fold compared to 1% tween80 treated TG mice in interstitial spaces. To test the role of EGFR in apoptosis induction in TG mice, the protein was isolated from whole lung tissue. The tyrosine kinase activity of EGFR was increased and the downstream of AKT and ERK were activated in TG mice. Conversely, treating with gefitinib on TG mice, EGFR phosphorylation was inhibited and, AKT and ERK were inactivated. One of the pro-apoptotic signals, p38 MAPK was activated via MKK3/6 by gefitinib treatment in TG mice, suggesting activation of ASK1/p38 MAPK signals leading to pulmonary epithelial cell apoptosis. Conclusions: The dysregulated production of TNF is a mediator of inflammation and tumor growth. Therefore, the mechanisms of TNF-regulated anti-/pro- apoptotic responses are important in understanding the role of TNF in the pathogenesis of pulmonary disorders, such as inflammation and cancer.
Citation Format: Toshimitsu Yamaoka, Yasunari Oki, Yasunori Murata, Sojiro Kusumoto, Hiroo Ishida, Takao Shirai, Etsuko Toya, Motoi Ohba, Ken-ichi Fujita, Satoru Arata, Tohru Ohmori, Tsukasa Ohnishi, Hironori Sagara, Yasutsuna Sasaki. TNF transactivation of EGFR protects EGFR-TKI, gefitinib induced pulmonary epithelial cell apoptosis and injury in TNF transgenic mice. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2277. doi:10.1158/1538-7445.AM2014-2277