CDKN2A and breast cancer: To investigate the epigenetic effects of GE, we evaluated the patterns of histone modifications in the promoter regions of p16 (Fig. 4A) and p21 (Fig. 4B) in precancerous SH cells (left panel) and breast cancer SHR cells (right panel) by detecting several chromatin markers such as transcriptional active markers, acetyl-H3, acetyl-H4 and trimethyl-H3K4 as well as transcriptional repressor markers, trimethy-H3K9 and trimethyl-H3K27.