Clinical Research
Copyright ©2007 Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Dec 21, 2007; 13(47): 6396-6403
Published online Dec 21, 2007. doi: 10.3748/wjg.v13.i47.6396
Two distinct pathways of p16 gene inactivation in gallbladder cancer
Hiroyuki Tadokoro, Takako Shigihara, Tomomi Ikeda, Masaru Takase, Masafumi Suyama
Hiroyuki Tadokoro, Masafumi Suyama, Department of Gastroenterology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 136-0075, Japan
Takako Shigihara, Tomomi Ikeda, Biochemical Research Center, Division of Molecular and Biochemical Research, Juntendo University School of Medicine, Tokyo 136-0075, Japan
Masaru Takase, Department of Human Pathology, Juntendo University School of Medicine, Tokyo 136-0075, Japan
Author contributions: All authors contributed equally to the work.
Correspondence to: Hiroyuki Tadokoro, MD, Department of Gastroenterology, Juntendo Tokyo Koto Geriatric Medical Center, 3-3-20 Shinsuna, Koto-ku, Tokyo 136-0075, Japan. heroyou27@yahoo.co.jp
Telephone: +81-356-323111 Fax: +81-356-323728
Received: July 19, 2007
Revised: September 12, 2007
Accepted: November 14, 2007
Published online: December 21, 2007
Abstract

AIM: To examine the mechanism of inactivation of the p16 gene in gallbladder cancer, and to investigate p16 alterations and their correlation with clinicopathological features.

METHODS: Specimens were collected surgically from 51 patients with gallbladder cancer. We evaluated the status of protein expression, loss of heterozygosity (LOH), homozygous deletion and promoter hypermethylation using immunohistochemistry, microsatellite analysis, quantitative real-time polymerase chain reaction (PCR) and methylation-specific PCR, respectively. In addition, mutations were examined by direct DNA sequencing.

RESULTS: Homozygous deletions of the p16 gene exon2, LOH at 9p21-22, p16 promoter hypermethylation, and loss of p16 protein expression were detected in 26.0% (13/50), 56.9% (29/51), 72.5% (37/51) and 62.7% (32/51), respectively. No mutations were found. LOH at 9p21 correlated with the loss of p16 protein expression (P < 0.05). Homozygous deletion of the p16 gene, a combination LOH and promoter hypermethylation, and multiple LOH at 9p21 were significantly correlated with the loss of p16 protein expression (P < 0.05). LOH at 9p21 and promoter hypermethylation of the p16 gene were detected in 15.4% (2/13) and 92.3% (12/13) of the tumors with homozygous deletion of the p16 gene, respectively. P16 alterations were not associated with clinicopathological features.

CONCLUSION: Our results suggest that LOH and homozygous deletion may be two distinct pathways in the inactivation of the p16 gene. Homozygous deletion, a combination of LOH and promoter hypermethylation, and multiple LOH are major mechanisms of p16 inactivation in gallbladder cancer.

Keywords: Gallbladder cancer; Homozygous deletion; Loss of heterozygosity; p16; Quantitative real time PCR