Abstract 362: Repression of Smad3 by Stat3 and c-Ski/SnoN induces gefitinib resistance in lung adenocarcinoma

<jats:title>Abstract</jats:title> <jats:p>Cancer-associated inflammation develops resistance to the epidermal growth-factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in non-small cell lung cancers (NSCLCs) harboring oncogenic EGFR mutations. Stat3-mediated Interleukin (IL)-6 signaling and Smad-mediated transforming growth factor-β (TGF-β) signaling play crucial regulatory roles in cancer-associated inflammation. Here we show that Stat3 represses Smad3 in cooperation with c-Ski and SnoN, whereby renders gefitinib-sensitive HCC827 cells resistant. IL-6 signaling via phosphorylated Stat3 induced gefitinib resistance. By contrast, TGF-β upregulated gefitinib sensitivity. We found that IL-6 signaling via phosphorylated Stat3 repressed, whereas TGF-β upregulated the expression of Smad3 in HCC827 cells. Promoter analyses showed that Stat3 synergized with c-Ski/SnoN to repress Smad-induced transcription of the Smad3 gene. Smad3 induced apoptosis by upregulating pro-apoptotic genes such as Caspase 3 and downregulating anti-apoptotic genes such as Bcl2. Our results suggest that preventing IL-6/Stat3-induced loss of Smad3 can be a therapeutic strategy to prevent gefitinib resistance in NSCLCs with gefitinib-sensitive EGFR mutation.</jats:p> <jats:p>Citation Format: Yojiro Makino, Jeong-Hwan Yoon, Eunjin Bae, Mitsuyasu Kato, Keiji Miyazawa, Tatsuo Ohira, Norihiko Ikeda, Masahiko Kuroda, Mizuko Mamura. Repression of Smad3 by Stat3 and c-Ski/SnoN induces gefitinib resistance in lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 362. doi:10.1158/1538-7445.AM2017-362</jats:p>