Protein tyrosine kinase 7: A hepatocellular carcinoma-related gene detected by triple-combination array

Background Hepatocellular carcinoma (HCC) is one of the top five causes of cancer-related deaths worldwide. We developed a novel technique to identify cancer-related genes of HCC as follows: triple-combination array analysis, which combines gene expression profiles, single nucleotide polymorphism arrays, and methylation arrays. Materials and methods Triple-combination array analysis was performed on one HCC sample from a 68-y-old female patient, and one candidate cancer-related gene was selected. Subsequently, we analyzed the identified gene by quantitative real-time reverse-transcriptase polymerase chain reaction (PCR) and methylation-specific PCR in nine HCC cell lines and in samples from 48 HCC patients. Additionally, we evaluated gene expression by immunohistochemistry and Western blotting. Results Using this method, protein tyrosine kinase 7 (PTK7) was detected as a candidate cancer-related gene. PTK7 was revealed to be hypermethylated (methylation value 0.826, range 0-1.0) in cancer tissue, compared with that of adjacent noncancerous tissues (0.047) by methylation array. Of the 48 clinical samples, 30 HCC samples (62.5%) showed PTK7 promoter hypermethylation. Downregulation of PTK7 (expressions in tumor tissues decreased by ≥50% compared with the noncancerous tissues) was significantly associated with age >60 y (P = 0.030) and elevation in serum protein induced by vitamin K absence or antagonists-II (P = 0.033). Moreover, patients with downregulation were significantly inferior in overall survival (P < 0.001) than the others. Conclusions Our data imply that PTK7 acts as a cancer-related gene and may be a potent prognostic marker for HCC. Triple-combination array analysis was once again found to be useful in identifying cancer-related genes.