Hypomethylation of long interspersed nuclear element-1 (LINE-1) leads to activation of proto-oncogenes in human colorectal cancer metastasis. Issue 4 (23rd May 2013)

• Record Type: Journal Article
• Authors: Hur, Keun; Cejas, Paloma; Feliu, Jaime; Moreno-Rubio, Juan; Burgos, Emilio; Boland, C Richard; Goel, Ajay
• Is Part Of: Gut. Volume 63:Issue 4(2014)
• Page Start: 635
• Page End: 646
• Publication Date: 2013-05-23
• Subjects: Colorectal Neoplasia -- Methylation -- Oncogenes; Gastroenterology -- Periodicals; 616.33
• DOI: 10.1136/gutjnl-2012-304219
• Languages: English
• ISSNs: 0017-5749

Abstract

Abstract : Objective: Hypomethylation of LINE-1 elements has emerged as a distinguishing feature in human cancers. Limited evidence indicates that some LINE-1 elements encode an additional internal antisense promoter, and increased hypomethylation of this region may lead to inadvertent activation of evolutionarily methylation-silenced downstream genes. However, the significance of this fundamental epigenetic mechanism in colorectal cancer (CRC) has not been investigated previously. Design: We analysed tissue specimens from 77 CRC patients with matched sets of normal colonic mucosa, primary CRC tissues (PC), and liver metastasis tissues (LM). LINE-1 methylation levels were determined by quantitative bisulfite pyrosequencing. MET, RAB3IP and CHRM3 protein expression was determined by western blotting and IHC. MET proto-oncogene transcription and 5-hydroxymethylcytosine (5-hmc) were evaluated by quantitative real-time-PCR. Results: Global LINE-1 methylation levels in LM were significantly lower compared with the matched PC (PC=66.2% vs LM=63.8%; p<0.001). More importantly, we observed that specific LINE-1 sequences residing within the intronic regions of multiple proto-oncogenes, MET (p<0.001), RAB3IP (p=0.05) and CHRM3 (p=0.01), were significantly hypomethylated in LM tissues compared with corresponding matched PC. Furthermore, reduced methylation of specific LINE-1 elements within the MET gene inversely correlated with induction of MET expression in CRC metastases (R=−0.44; p<0.0001). Finally, increased 5-hmc content was associated with LINE-1 hypomethylation. Conclusions: Our results provide novel evidence that hypomethylation of specific LINE-1 elements permits inadvertent activation of methylation-silenced MET, RAB3IP and CHRM3 proto-oncogenes in CRC metastasis. Moreover, since 5-hmc content inversely correlated with LINE-1 hypomethylation in neoplastic tissues, our results provide important mechanistic insights into the fundamental processes underlying global DNA hypomethylation in human CRC.