BMI1 and glioblastoma: Because BMI1 is a component of both cPRC1 and ncPRC1 complexes (20,21), we selected RYBP, a well-characterized member of ncPRC1 (65), as a pull-down target for our IP-MS studies on the same GBM cell lines to characterize the RYBP interactome and the composition of the ncPRC1.