COX4I1 and glioblastoma: To decipher the functional properties of COX4 isoforms in GBM proliferation, U251 cells depleted of endogenous COX4-2 were stably transfected with expression vectors encoding either FLAG-epitope-tagged COX4-1 (U251-TgCOX4-1) or FLAG-epitope-tagged COX4-2 (U251-TgCOX4-2).