Distinct high-profile methylated genes in colorectal cancer.
BACKGROUND
Mutations and promoters' methylation of a set of candidate cancer genes (CAN genes) are associated with progression of colorectal cancer (CRC). We hypothesized that these genes' promoters are inactivated through epigenetic silencing and may show a different profile in high-risk populations. We investigated the status of CAN gene methylation and CHD5 protein expression in African American CRC tissue microarrays (TMA) using immunohistochemical staining.


RESULTS
The promoter methylation status of the CAN genes was studied by methylation-specific PCR (MSP) in 51 Iranians (a white population) and 51 African Americans (AA). Microsatellite instability (MSI) was analyzed as well. The differential frequency of methylation for each gene was tested by chi-square analysis between the two groups based on matched age and sex. CHD5 protein expression was evaluated in moderate to well differentiated and poorly differentiated carcinomas compared to matched normal tissue using TMA. In addition, the correlation between these epigenetic biomarkers and various clinicopathological factors, including, age, location, and stage of the disease were analyzed. Seventy-seven and 34% of tumors were distal in Iranian and African American patients, respectively. In both populations, the percentage of methylation was >65% for SYNE1, MMP2, APC2, GPNMB, EVL, PTPRD, and STARD8, whereas methylation was <50% for LGR6, RET, CD109, and RNF. The difference in methylation between the two populations was statistically significant for CHD5, ICAM5 and GPNMB. Thirty-one percent AA tumors showed MSI-H, compared to 28% in Iranians.


CONCLUSIONS
A significantly higher methylation rate was found for GPNMB, ICAM5, and CHD5 genes in AA patients compared to Iranians. These genes might play a role in the high incidence and aggressiveness of CRC in the AA population. The hypermethylation of the CAN genes can be considered as a marker of colon carcinogenesis.
Mokarram
Pooneh
P
Department of Internal Medicine and Gastroenterology Research Center, Shiraz, Iran University of Medical Sciences, Tehran, Iran.
Kumar
Krishan
K
Brim
Hassan
H
Naghibalhossaini
Fakhraddin
F
Saberi-firoozi
Mehdi
M
Nouraie
Mehdi
M
Green
Robert
R
Lee
Ed
E
Smoot
Duane T
DT
Ashktorab
Hassan
H
D001741:Black or African American; D000368:Aged; D015179:Colorectal Neoplasms / Q000208:ethnology / Q000235:genetics* / Q000378:metabolism*; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007492:Iran; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D012737:Sex Factors; D014481:United States