Abstract 95: Increased hypomethylation of LINE-1 and Alu in human colorectal cancer metastasis

Abstract

Abstract Background: Global hypomethylation of cytosines within CpG dinucleotides is one of the distinguishing features of the neoplastic cells in human cancers. More specifically, hypomethylation of evolutionarily conserved repetitive elements (Alu and LINE-1) is associated with increased chromosomal instability in colorectal cancer (CRC). Recent data indicates that transcription start sites of certain proto-oncogenes are located within these repeat elements, and increased hypomethylation of these regions may induce the expression of illegitimate oncogenic transcripts. Primary CRCs demonstrate frequent global Alu and LINE-1 hypomethylation; however, it is unclear whether hypomethylation of these repeat sequences may be associated with a metastatic phenotype Aim: This study was aimed to determine the role of increased hypomethylation of Alu and LINE-1 sequences in CRC metastasis development. Materials and Methods: We analyzed a panel of CRC cells with different metastatic potential, as well as tissues from 50 CRC patients with matched primary colon cancer and corresponding liver metastasis tissues. Alu and LINE-1 methylation levels were determined by quantitative bisulfite pyrosequencing. Results: Lower levels of Alu and LINE-1 methylation were observed in CRC cell lines that came from metastatic foci. When we analyzed Alu and LINE-1 methylation levels in clinical specimens, the levels of Alu methylation in liver metastatis were significantly lower compared to the matched primary CRC tissues (77.2%±8.3 and 80.9%±10.7, respectively; P<0.01). Similarly, the levels of LINE-1 methylation in metastasized liver foci was significantly lower compared to the corresponding matched primary CRC (61.2%±9.7 vs 65.8%±7.0 (P<0.01). The relative demethylation level was higher in LINE-1 (4.6%) than Alu (3.7%) sequences. In further support of our results, methylation analysis of surrounding normal liver tissue showed higher methylation levels for Alu (82.2%±4.7) and LINE1 (71.3%±8.3) compared with both primary CRC and liver metastasis. Conclusion: Our results provide evidence that increased Alu and LINE-1 hypomethylation is a novel feature of liver metastasis from CRC. We speculate that hypomethylation of these repeat elements may inadvertently permit activation of previously silenced proto-oncogenes, which may facilitate a more aggressive malignant phenotype in these advanced stage cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 95. doi:10.1158/1538-7445.AM2011-95