Epigenetic reprogramming stability of tumour suppressor genes in AOE. Reprogramming of the tumour suppressor gene RARB persists 6 days after treatment of MCF-7 and HC1954 cells with AOE. (A) Promoter activity in HMEC, MCF-7 and HCC1954 cells with or without RA treatment measured by luciferase assay (* indicates P < 0.05 for RA treated cells different from the untreated group). (B) RARB promoter in retinoic acid resistant HCC1954 cells can respond to RA after reprogramming (P < 0.05; a = AOE and AOE+RA vs UN; b = AOE + RA vs AOE). (C) RARB expression by Q-PCR. * indicates P < 0.05 of treated cells compared to UN. (D) DNA demethylation is maintained in HCC1954 cells after 6 days of treatment as shown by bisulfite sequencing (similar results were obtained with MCF-7 cells).