Background

Promoter hypermethylation and global hypomethylation in the human genome are hallmarks of most cancers. Detection of aberrant methylation in white blood cells (WBC) has been suggested as a marker for cancer development, but has not been extensively investigated. This study was carried out to determine whether aberrant methylation in WBC DNA can be used as a surrogate biomarker for breast cancer risk.

Patients and Methods

Promoter hypermethylation of 8 tumor suppressor genes (RASSF1A, APC, HIN1, BRCA1, cyclinD1, RARβ, CDH1 and TWIST1) and DNA methylation for three repetitive elements (LINE1, Sat2M1 and AluM2) were analyzed in invasive ductal carcinoma of the breast, paired adjacent normal tissue and WBC from 40 breast cancer patients by the MethyLight assay. Methylation in WBC from 40 controls was also analyzed.

Results

Tumor and adjacent tissues showed frequent hypermethylation for all genes tested, while WBC DNA was rarely hypermethylated. For HIN1, RASSF1A, APC and TWIST1 there was agreement between hypermethylation in tumor and adjacent tissues (P=0.04, P=0.02, P=0.005 and P<0.0001, respectively). DNA methylation for the three repetitive elements was lower in tumor compared to adjacent tissue and WBC DNA. Significant correlations in the methylation of Sat2M1 between tumor and adjacent tissues and WBC DNA were found (P<0.0001 and P=0.046, respectively). There was also a significant difference in methylation of Sat2M1 between cases and controls (P=0.01).

Conclusion

These results suggest that further studies of WBC methylation, including prospective studies, may provide biomarkers of breast cancer risk.

AIM: To determine global DNA methylation in paired hepatocellular carcinoma (HCC) samples using several different assays and explore the correlations between hypomethylation and clinical parameters and biomarkers, including that of aflatoxin B1 exposure.

METHODS: Using the radio labeled methyl acceptance assay as a measure of global hypomethylation, as well as two repetitive elements, including satellite 2 (Sat2) by MethyLight and long interspersed nucleotide elements (LINE1), by pyrosequencing.

RESULTS: By all three assays, mean methylation levels in tumor tissues were significantly lower than that in adjacent tissues. Methyl acceptance assay log (mean ± SD) disintegrations/min/ng DNA are 70.0 ± 54.8 and 32.4 ± 15.6, respectively, P = 0.040; percent methylation of Sat2 42.2 ± 55.1 and 117.9 ± 88.8, respectively, P < 0.0001 and percent methylation LINE1 48.6 ± 14.8 and 71.7 ± 1.4, respectively, P < 0.0001. Aflatoxin B1-albumin (AFB1-Alb) adducts, a measure of exposure to this dietary carcinogen, were inversely correlated with LINE1 methylation (r = -0.36, P = 0.034).

CONCLUSION: Consistent hypomethylation in tumor compared to adjacent tissue was found by the three different methods. AFB1 exposure is associated with DNA global hypomethylation, suggesting that chemical carcinogens may influence epigenetic changes in humans.

Background. MicroRNAs are a type of small noncoding RNA molecules that have been shown to control gene expression in eukaryotes. Aberrant expression and alteration of miRNAs may be responsible for human diseases including cancer. An miR16-1 (C > T) + 7 gene mutation has been previously found in familial chronic lymphocytic leukemia patients, one of which reported a family history of breast cancer. miR16-1 regulates the expression of bcl-2, which is important in retinoblastoma, and is located in a genomic region that is frequently lost in nasopharyngeal and hepatocellular carcinomas (HCCs). Therefore, miR16-1 may be potentially important in the etiology of several solid tumors. To understand the power of the miR16-1 (C > T) + 7 mutation as a prognostic and diagnostic risk factor, we investigated the mutation in patients with seven different types of cancer including 188 with breast, 102 with ovarian, and 22 nasopharyngeal carcinomas, 96 HCC, 872 chronic myeloid leukemia (CML), 39 chronic lymphocytic leukemia (CLL), and 46 retinoblastoma cases from three different ethnic groups and of hereditary and sporadic etiology. Methods. 5′Nuclease TaqMan SNP genotyping assay was used to detect the miR16-1 gene C > T substitution. Results. The miR16-1 (C > T) + 7 substitution was not detected in any of the groups studied. Conclusions. Considering the large scale of our study, the representation of different ethnicities and levels of hereditary risk, we conclude that the miR-16-1 (C > T) + 7 mutation is not a good diagnostic or prognostic indicator of risk for the cancers tested.