Abstract 3133: Apoptosis signal-regulating kinase 1 and cyclin D1 compose a positive feedback loop contributing to tumor growth in gastric cancer
Authors: Hayakawa Yoku , Hirata Yoshihiro , Nakagawa Hayato , Sakamoto Kei , Nakata Wachiko , Kinoshita Hiroto , Takahashi Ryota , Sakitani Kohsuke , Hikiba Yohko , Yanai Ayako , Akanuma Masao , Takeda Kohsuke , Ichijo Hidenori , Omata Masao , Maeda Shin , Koike Kazuhiko 
Published: June 2012

Abstract
Gastric cancer is a common cancer worldwide, associated with a high mortality despite its declining incidence in recent decades. Although the role of H. pylori in causing mucosal effects has been investigated, which molecular signal(s) initiate the program of irreversible transformation remain unclear, and thus molecular targeting therapies for GC have not been well established. Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and have been demonstrated to be highly active in many types of human cancers, and we have previously reported that c-Jun-N-terminal kinase 1 (JNK1) is important for gastric tumorigenesis. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK known to be involved in apoptosis, inflammation, and carcinogenesis. In the current study, we investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression compared to non-tumor epithelium, while we found no difference between colon cancer and non-tumor colon epithelium. Using the chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice displayed both a lower number and smaller tumor size compared to wild-type mice. In gastric cancer cell lines, immunoprecipitation analysis revealed constitutive ASK1 activation in several cell lines. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, while these effects were uncommon in other cancer cells, suggesting that the ASK1-dependent regulation of the cyclin D1 level and cellular proliferation is specific to gastric cancer. Overexpression of ASK1 induced the transcription of cyclin D1 through AP-1 activation in a kinase-dependent manner. In addition, we found that the expression of ASK1 was elevated following epidermal growth factor (EGF) or Helicobacter pylori (H.pylori) treatment in control cells but not in cyclin D1 silencing cells. Overexpression of cyclin D1 enhanced phosphorylation of Rb, followed by the increase in ASK1 expression. Chromatin immunoprecipitation (ChIP) assay showed that cyclin D1 expression increase E2F1 binding to ASK1 promoter, suggesting that the levels of ASK1 were regulated by cyclin D1 through the Rb-E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by an elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Through targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3133. doi:10.1158/1538-7445.AM2011-3133