1. ¹Department of Surgery and Regenerative Medicine, Division of Surgery and Physiology of the Digestive System, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kawaramachi, Kamigyo-ku, Kyoto, Japan
2. ²Division of Gastroenterology and Hepatology, Graduate School of Internal Medicine, Kyoto University, Kawahara-cho, Sakyo-ku, Kyoto, Japan
3. ³Department of Surgery and Regenerative Medicine, Division of Surgery and Oncology of Digestive System, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kawaramachi-dori, Kyoto, Japan
4. ⁴Division of Gastroenterology, Graduate School of Internal Medicine, Kyoto Prefectural University of Medicine, Kawaramachi, Kamigyo-ku, Kyoto, Japan
5. ⁵Institute of Molecular and Cell Biology, Proteos, Singapore, Singapore

Correspondence: Dr C Sakakura, Department of Surgery and Regenerative Medicine, Division of Surgery and Oncology of Digestive System, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kawaramachi-dori, Kyoto 602-8566, Japan. E-mail: sakakura@koto.kpu-m.ac.jp

Received 29 December 2006; Revised 6 February 2007; Accepted 8 February 2007; Published online 26 March 2007.

Abstract

Radiotherapy is an effective treatment for some esophageal cancers, but the molecular mechanisms of radiosensitivity remain unknown. RUNX3, a novel tumor suppressor of gastric cancer, functions in transforming growth factor (TGF)--dependent apoptosis. We obtained paired samples from 62 patients with advanced esophageal cancers diagnosed initially as T3 or T4 with image diagnosis; one sample was obtained from a biopsy before presurgical radiotherapy, and the other was resected in surgical specimens after radiotherapy. RUNX3 was repressed in 67.7% cases of the pretreatment biopsy samples and 96.7% cases of the irradiated, resected samples. The nuclear expression of RUNX3 was associated with radiosensitivity and a better prognosis than cytoplasmic or no RUNX3 expression (P<0.003); cytoplasmic RUNX3 expression was strictly associated with radioresistance. RUNX3 was downregulated and its promoter was hypermethylated in all radioresistant esophageal cancer cell lines examined. Stable transfection of esophageal cancer cells with RUNX3 slightly inhibited cell proliferation in vitro, enhanced the antiproliferative and apoptotic effects of TGF- and increased radiosensitivity in conjunction with Bim induction. In contrast, transfection of RUNX3-expressing cells with a RUNX3 antisense construct or a Bim-specific small interfering RNA induced radioresistance. Treatment with 5-aza-2'-deoxycytidine restored RUNX3 expression, increased radiosensitivity and induced Bim in both control and radioresistant cells. These results suggest that RUNX3 silencing promotes radioresistance in esophageal cancers. Examination of RUNX3 expression in pretreatment specimens may predict radiosensitivity, and induction of RUNX3 expression may increase tumor radiosensitivity.