Real-time methylomic aberrations during initiation and progression of induced human mammary epithelial cell tumorigenesis.

Epigenomics

PubMedID: 23566093

Mitchell NE, Wilson ML, Bray MS, Crossman DK, Tollefsbol TO. Real-time methylomic aberrations during initiation and progression of induced human mammary epithelial cell tumorigenesis. Epigenomics. 2013;5(2):155-65.
AIM
Neoplastic transformation provides one of the few existing opportunities to analyze molecular changes in real time during the initiation and progression of breast cancer.

MATERIALS & METHODS
Human mammary epithelial cells underwent neoplastic reprogramming, generating one line of semitransformed, premalignant cells and two separate, temporal lines of fully transformed human mammary epithelial cells (THMECs). An Illumina Infinium HumanMethylation27 BeadChip was used to analyze DNA methylation alterations in 27,578 CpG loci at three consecutive time points over an 80-day (d) transformation period.

RESULTS
The mean ß value for semitransformed human mammary epithelial cells CpG loci (0.245) was much greater than for either THMEC-40d (0.055) or THMEC-80d (0.066), indicating a large loss of methylation after neoplastic induction. In addition, 54% of CpG loci were hypermethylated during the THMEC-40d to THMEC-80d transition. We observed that the CpG loci exhibiting DNA methylation changes during early oncogenesis were enriched for biological functions like cellular movement; this was distinctly different than in the later, more progressive stages of the transformation process enriched for processes involving differentiation.

CONCLUSION
The timing of major methylomic changes may be important in directing the cell toward a more cancerous phenotype. In addition, gene-specific hypermethylation appears to silence developmentally related genes, leading to dedifferentiation.