Aim
To investigate if the down-regulation of N-myc Downstream Regulated Gene 2 (NDRG2) expression in colorectal carcinoma (CRC) is due to loss of the NDRG2 allele(s).
Conclusion
Our study suggests that the reduction in NDRG2 expression observed in CRC is due to transcriptional repression by MYC and promoter methylation, and is not due to allelic loss.
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 NDRG2 promoter using chromatin immunoprecipitation; and NDRG2 promoter methylation using bisulfite sequencing. Furthermore, we performed qPCR to analyse the copy numbers of NDRG2 and MYC 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 NDRG2 core promoter in all three cell lines. In addition, the NDRG2 promoter was heavily methylated in these cell lines, suggesting an epigenetic regulatory mechanism. Unaltered gene copy numbers of NDRG2 were observed in the three cell lines. In the colorectal tissues, one normal and three CRC samples showed partial or complete loss of one NDRG2 allele. In contrast, the MYC gene was amplified in one cell line and in more than 40% of the CRC cases.