1. ¹Department of Human Pathology, Kanazawa University Graduate School of Medicine, Kanazawa, Japan
2. ²Department of Diagnostic Pathology, Kanazawa University Hospital, Kanazawa, Japan
3. ³Department of Surgical Oncology, Nagoya University Graduate School of Medicine, Nagoya, Japan
4. ⁴Department of Pediatric Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan
5. ⁵Department of Gastroenterologic Surgery, Kanazawa University Graduate School of Medicine, Kanazawa, Japan
6. ⁶Department of Pediatric Surgery, Osaka Medical Center and Research Institute for Maternal and Child Health, Osaka, Japan
7. ⁷Department of Surgery, Toyama Prefectural Central Hospital, Toyama, Japan
8. ⁸Department of Gastroenterological Surgery, Aichi Cancer Center Hospital, Aichi, Japan

Correspondence: Dr Y Nakanuma, MD, Department of Human Pathology, Kanazawa University Graduate School of Medicine, Kanazawa 920-8640, Japan. E-mail: pbcpsc@kenroku.kanazawa-u.ac.jp

Received 18 February 2009; Revised 11 May 2009; Accepted 18 May 2009; Published online 29 June 2009.

Abstract

Cellular senescence, an irreversible growth arrest, is considered to play as safeguard against malignant progression, though such a mechanism is speculative in human carcinogenesis. In gallbladder carcinoma, cholecystolithiasis and pancreaticobiliary maljunction (PBM) are major risk factors. Here, by using 113 surgically resected gallbladders and cultures of human gallbladder epithelial cells (HGECs) and gallbladder carcinoma cell line (TGBC2TKB), we examined carcinogenesis with respect to cellular senescence. Among 15 cases of PBM in which carcinoma was found in 4 cases, nonneoplastic gallbladder mucosa showed diffuse papillary hyperplasia (PHP). PHP was not found in gallbladders with cholecystolithiasis. Interestingly, PHP exhibited senescent features such as expression of p16^INK4A and low cell proliferative activity. In contrast, EZH2, a polycomb group protein, was overexpressed in intraepithelial neoplasm and carcinoma in gallbladders with cholecystolithiasis. In PBM, EZH2 was expressed only in carcinoma foci but not in PHP. Cultured HGECs treated with lysolecithin, the level of which is elevated in gallbladder bile of PBM, showed increased expression of p16^INK4A and senescence-associated -galactosidase. Conversely, enforced overexpression of EZH2 in senescent HGECs reduced p16^INK4A expression. A knockdown of EZH2 in cultured TGBC2TKB cells increased p16^INK4a expression. In conclusion, PHP in PBM may act as a barrier to malignant transformation for decades. EZH2 may be responsible for the escape from cellular senescence followed by malignant transformation in the gallbladder of PBM.