Pharmacological inhibition of polycomb repressive complex-2 activity induces apoptosis in human colon cancer stem cells

• PRC2 inactivation results in apoptosis in human colon cancer stem cells (CCSC).
• PRC2 inactivation increases PTEN expression in human CCSCs.
• DZNep treatment decreases H3K27me3 levels at the PTEN promoter in human CCSCs.
• PTEN increased expression in CCSC is associated with reduced Akt phosphorylation.

Colorectal cancer is among the leading causes of cancer death in the USA. The polycomb repressive complex 2 (PRC2), including core components SUZ12 and EZH2, represents a key epigenetic regulator of digestive epithelial cell physiology and was previously shown to promote deleterious effects in a number of human cancers, including colon. Using colon cancer stem cells (CCSC) isolated from human primary colorectal tumors, we demonstrate that SUZ12 knockdown and treatment with DZNep, one of the most potent EZH2 inhibitors, increase apoptosis levels, marked by decreased Akt phosphorylation, in CCSCs, while embryonic stem (ES) cell survival is not affected. Moreover, DZNep treatments lead to increased PTEN expression in these highly tumorigenic cells. Taken together, our findings suggest that pharmacological inhibition of PRC2 histone methyltransferase activity may constitute a new, epigenetic therapeutic strategy to target highly tumorigenic and metastatic colon cancer stem cells.