Background. Hepatocellular carcinoma (HCC) is one of the top five causes of cancer-related deaths worldwide. Recent developments in the treatment of HCC still have failed to prevent HCC. Genome-wide gene-expression profile analyses can now detect many candidate genes that are modified by HCC. We have developed a new technique to identify suppressor genes of HCC: triple-combination array analysis, which combines gene expression profile, single nucleotide polymorphism array and methylation array.

Methods. Triple-combination array analysis was performed on one HCC sample from a 68-year-old female patient, and one candidate of tumor suppressor gene was selected. Subsequently, we analyzed the identified gene by quantitative real-time reverse-transcriptase polymerase chain reaction (PCR) and methylation-specific PCR in samples from 48 HCC patients and in nine cell lines.

Results. Using this method, protein tyrosine kinase 7 (PTK7) was detected as a candidate of tumor suppressor gene. PTK7 gene is located on 6q21.2, and expression was reduced in HCC tissues at the high level of -2.5 compared with normal tissues. PTK7 locus did not show any deletion or amplification in the SNP array. The methylation value (0-1.0) in the tumor sample was 0.825 compared to 0.047 in normal tissues, indicating high methylation in tumor tissues in the methylation array. Of the 48 clinical samples, 30 (62.5%) showed PTK7 promoter hypermethylation. The PTK7 promoter hypermethylated cases were significantly low expressions status (P=0.035), and bad prognosis in both overall survival (P<0.01) and recurrence-free survival (P=0.018) compared to hypomethylated cases. On the other hand, the cases, of which the PTK7 expressions in tumor tissues decreased by more than 20% degrees compared to those in normal tissues, were significantly worse prognosis in overall survival (P=0.0136) than the other cases, but not in recurrence-free survival (P=0.3102).

Conclusions. We suggest that the PTK7 gene acts as a tumor suppressor gene in HCC. This present study indicates that triple-combination array is an available and convenient technique for detecting the genes with altered expression in disease.

Citation Format: Mitsuhiro Hishida, Shuji Nomoto, Yoshikuni Inokawa, Masamichi Hayashi, Suguru Yamada, Tsutomu Fujii, Hiroyuki Sugimoto, Shin Takeda, Yasuhiro Kodera. Identification of protein tyrosine kinase 7 gene in hepatocellular carcinoma using a novel triple-combination array analysis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1152. doi:10.1158/1538-7445.AM2013-1152