DNMT3B and neoplasm: DNA methylation, mediated by the combined action of three DNMTs (DNMT1, DNMT3a and DNMT3b), is associated with tumour initiation and progression.12 Western blot analysis showed that overexpression of OCT4 up‐regulated DNMT1 expression in MDA‐MB‐231 cells (Figure 4A), whereas OCT4 overexpression in MCF‐7 cells dramatically down‐regulated DNMT1 expression (Figure 4B).