DNA methylation is related to the occurrence of breast cancer and is not affected by culture conditions

Abstract

The present study aimed to explore the relationship between DNA methylation and breast cancer under different cell culture conditions. MCF-7 breast cancer cells were cultured in two-dimensional (2D), three-dimensional (3D) and orthotopic transplantation (Ti) adhesion substrates. Principal component analysis (PCA) was used for global visualization of these three samples. The methylation status of CpG sites was examined by unsupervised clustering analysis. Scatter plots and histograms were constructed from the mean β-values from 3D vs. 2D, 3D vs. Ti and Ti vs. 2D analysis. In addition, analyses of Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were conducted to explore the putative biological functions in which mutL homolog (MLH), phosphatase and tensin homolog (PTEN), runt-related transcription factor (RUNX), Ras association domain family (RASSF), cadherin 1 (CDH1), O-6-methylguanine-DNA methyltransferase (MGMT) and P16 may serve a role. Quantitative methylation-specific polymerase chain reaction (QMSP) was performed to determine the influence of culturing conditions on important gene expression. Results from PCA analysis indicated that the three samples were closely connected with each other. Venn diagrams revealed that certain differential methylation positions were common among the three sample groups, and 116 CpG positions were identified that appeared to be hypermethylated. The methylation patterns were more similar between 3D vs. 2D cultures compared with those between 3D vs. Ti or between Ti vs. 2D. Results of GO term and KEGG pathway analyses indicated that genes were enriched in four pathways, including transporter activity and G-protein coupled receptor activity. In addition, QMSP analysis identified no notable differences in the methylation status of MLH, PTEN, RUNX, RASSF, CDH1, MGMT and P16 under 2D, 3D and Ti culture conditions. In conclusion, abnormal DNA methylation is related with breast cancer, and the methylation status did not change in breast cancer cells cultured in different conditions.