EP300 and breast cancer: ATF5 is acetylated at lysine-29 (K29) by interacting with the transcriptional coactivator e1A-binding protein p300 (P300) (Figure 1), which in turn enhances the interaction between ATF5 and P300 and activates the early growth response 1 (EGR1) gene, thereby regulating tumorigenesis and tumor progression in glioblastoma and breast cancer [18,19].