ATF3 and cancer: We selected a panel of 14 genes for which polycomb-mediated silencing is supported by genetic and pharmacologic disruption studies5,12–21 and protein mapping studies22–25 in human cancers and stem cells: ATF3, CADM1, CASZ1, CDH1, CDKN2A, CLU, HK2, HOXA6, HOXB4, IRF8, LAMB3, RUNX3, TRIM22, and WT1. We transfected U-2 OS, SK-N-SH, and K562 cells with a PcTF-expressing plasmid (Fig. 1) via Lipofectamine LTX and allowed transfected cells to grow for 24, 48, and 72 h prior to further analysis.