COX4I1 and central nervous system cancer: Because we previously demonstrated that the expression of COX4-1, rather than COX4-2, is in part responsible for the expansion of GSCs [11], the cells implicated in tumor recurrence and resistance to therapy in patients with glioblastoma, we tested the effect of CPZ in U251 glioma cells transfected with FLAG-epitope-tagged COX4-1 (U251-TgCOX4-1) or FLAG-epitope-tagged COX4-2 (U251-TgCOX4-2).