Background: Gene silencing via promoter hypermethylation plays a crucial role in the pathogenesis of cancers. Neuronal pentraxin II (NPTX2) has been observed to be hypermethylated in pancreatic cancers. Methylation of NPTX2 might provide a novel diagnostic marker for pancreatic cancers.
Aim: The objective of this study is to investigate the abnormal patterns of DNA methylation of NPTX2 in pancreatic cancers, and its role in the transcriptional silencing of NPTX2.
Methods: NPTX2 expression was detected by reverse-transcription polymerase chain reaction (RT-PCR), and the methylation status of NPTX2 was assessed by methylation-specific polymerase chain reaction (MSP). Immunohistochemistry was used to examine the NPTX2 protein expression. The pancreatic cancer cell lines were treated with the DNA methyltransferase inhibitor, histone deacetylase inhibitors, either alone or in combination.
Results: The MSP analysis revealed that the promoter region of NPTX2 gene was largely unmethylated in normal pancreatic tissues, while NPTX2 was frequently hypermethylated in pancreatic cancer cells and in primary pancreatic carcinomas. Quantitative RT-PCR revealed that the mean mRNA expression level of NPTX2 in the pancreatic cancer tissues was significantly lower than that in the paired adjacent normal tissues (0.96 ± 0.91 vs. 2.78 ± 1.42, P < 0.001). Consistent with RT-PCR detection, treatment with 5Aza-dC resulted in different degrees of induction of NPTX2 protein in the various cancer cell lines.
Conclusion: We demonstrate that the NPTX2 protein is down-regulated in human primary pancreatic cancers and in pancreatic cancer cell lines. This study provides the first evidence that the down-regulation of NPTX2 tightly correlates with its promoter hypermethylation.