1. ¹Department of Human Pathology, Kanazawa University Graduate School of Medicine, Kanazawa, Japan
2. ²Department of Diagnostic Pathology, Kanazawa University Graduate School of Medicine, Kanazawa, Japan
3. ³Department of Surgery (II), Kanazawa University Graduate School of Medicine, Kanazawa, 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 24 January 2008; Revised 23 March 2008; Accepted 24 March 2008; Published online 30 June 2008.

Abstract

Polycomb-group proteins Bmi1 and EZH2 are involved in the malignant transformation and biological aggressiveness of several human carcinomas. We herein examined the significance of the Bmi1 and EZH2 expression in hepatocellular carcinoma (HCC) and its preneoplastic lesions, dysplastic nodules. The expression of Bmi1 and EZH2 were examined immunohistochemically in HCC (n=27) and dysplastic nodules (n=14), and combined hepatocellular and cholangiocarcinoma (HC-CC) (n=14). The effect of Bmi1 and EZH2 knockdown was examined in cultured HCC cells (HuH7 and HepG2) using siRNA. It was determined that Bmi1 was constantly expressed in cholangiocytes, but not in hepatocytes, and EZH2 was detected in neither cholangiocytes nor hepatocytes. Bmi1 and EZH2 were overexpressed in HCC and more extensively in HC–CC (P<0.01). Interestingly, Bmi1 and EZH2 were not overexpressed in the dysplastic nodules. The expression of Bmi1 and EZH2 was heterogeneous and associated with vascular infiltration, the histological grades, and the cell proliferation activity in HCC and HC–CC. In cultured carcinoma cells overexpressing Bmi1 and EZH2, knockdown of Bmi1 and EZH2 resulted in decreased cell proliferation activities. Therefore, the overexpression of polycomb-group proteins Bmi1 and EZH2 is associated with the malignant progression of HCC, thereby reflecting the aggressive biological behavior in HCC and HC–CC.