gene copy number is not altered in colorectal carcinoma.

AIM

To investigate if the down-regulation of () expression in colorectal carcinoma (CRC) is due to loss of the allele(s).

METHODS

The following were investigated in the human colorectal cancer cell lines DLD-1, LoVo and SW-480: NDRG2 mRNA expression levels using quantitative reverse transcription-polymerase chain reaction (qRT-PCR); interaction of the MYC gene-regulatory protein with the promoter using chromatin immunoprecipitation; and promoter methylation using bisulfite sequencing. Furthermore, we performed qPCR to analyse the copy numbers of and genes in the above three cell lines, 8 normal colorectal tissue samples and 40 CRC tissue samples.

RESULTS

As expected, NDRG2 mRNA levels were low in the three colorectal cancer cell lines, compared to normal colon. Endogenous MYC protein interacted with the core promoter in all three cell lines. In addition, the promoter was heavily methylated in these cell lines, suggesting an epigenetic regulatory mechanism. Unaltered gene copy numbers of were observed in the three cell lines. In the colorectal tissues, one normal and three CRC samples showed partial or complete loss of one allele. In contrast, the gene was amplified in one cell line and in more than 40% of the CRC cases.

CONCLUSION

Our study suggests that the reduction in expression observed in CRC is due to transcriptional repression by MYC and promoter methylation, and is not due to allelic loss.