Because CPZ blocks CcO activity and cell proliferation when COX4-1 is expressed, we next compared the effect of CPZ on cell cycle progression in glioma cells transfected with COX4-1 (U251-TgCOX4-1) or with COX4-2 (U251-TgCOX4-2). The gene discussed is COX4I2; the disease is glioma.