1. ¹Department of Food Science Research for Health, National Institute of Health and Nutrition, 1-23-1 Toyama, Shinjuku, 162-8636 Tokyo, Japan
2. ²Faculty of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo, 260-8675 Chiba, Japan
3. ³Department of Pathology, Yokohama City University Medical School, 3-8 Fukuura, Kanazawa, 236-0004 Kanagawa, Japan
4. ⁴Japan Human Sciences Foundation, 13-4 Nihonbashi-Kodenmacho, Chuo, 103-0001 Tokyo, Japan
5. ⁵Department of Pathology, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan
6. ⁶Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, 669-1337 Hyogo, Japan

Correspondence: T Yano, E-mail: yano@nih.go.jp

Received 21 April 2004; Revised 3 December 2004; Accepted 6 December 2004; Published online 14 March 2005.

Abstract

Connexin genes expressing gap junction proteins have tumor-suppressive effects on primary cancers with certain cell specificity, but the suppressive effects on metastatic cancers are still conflicting. In this study, we show that connexin32 (Cx32) has a strong tumor-suppressive effect on a human metastatic renal cell carcinoma cell line (Caki-1 cell). Cx32 expression in Caki-1 cells reduced in vitro malignant phenotypes of the cells such as anchorage independency and invasion capacity. Furthermore, the Cx32 expression drastically reduced the development of Caki-1 cells in nude mice. We also determined that Cx32 reduced the malignant phenotypes in Caki-1 cells mainly through the inactivation of Src signaling. Especially, Cx32-dependent inactivation of Src decreased the production of vascular epithelial growth factor (VEGF) via the suppression of signal transducers and activators of transcription 3 (Stat3) activation, and we confirmed this result using short interfering RNA. In nude mice, Cx32-transfected Caki-1 cells showed lower serum level of VEGF comparing mock transfectant, and the development of the cells in nude mice positively related to the VEGF level. These data suggest that Cx32 acts as a tumor suppressor gene in Caki-1 cells and that the tumor-suppressive effect partly depends on the inhibition of Src-Stat3-VEGF signal pathway.