How CBX proteins regulate normal and leukemic blood cells

Hematopoietic stem cell (HSC) fate decisions are dictated by epigenetic landscapes. The Polycomb Repressive Complex 1 (PRC1) represses genes that induce differentiation, thereby maintaining HSC self‐renewal. Depending on which chromobox (CBX) protein (CBX2, CBX4, CBX6, CBX7, or CBX8) is part of the PRC1 complex, HSC fate decisions differ. Here, we review how this occurs. We describe how CBX proteins dictate age‐related changes in HSCs and stimulate oncogenic HSC fate decisions, either as canonical PRC1 members or by alternative interactions, including non‐epigenetic regulation. CBX2, CBX7, and CBX8 enhance leukemia progression. To target, reprogram, and kill leukemic cells, we suggest and describe multiple therapeutic strategies to interfere with the epigenetic functions of oncogenic CBX proteins. Future studies should clarify to what extent the non‐epigenetic function of cytoplasmic CBX proteins is important for normal, aged, and leukemic blood cells. CBX proteins are epigenetic reader proteins that can recognize histone modifications and thereby dictate cell fate. In this review, we describe how CBX proteins dictate cell fate in normal hematopoiesis and leukemia. In addition, we discuss which CBX proteins can promote leukemic cell growth and whether pharmacological inhibition of CBX proteins can reverse leukemic cell fate.