Aggravation of necrotic death of glucose-deprived cells by the MEK1 inhibitors U0126 and PD184161 through depletion of ATP

The extracellular-regulated kinases (ERK) modulate cell proliferation and survival in response to several different stimuli and are therefore important drug targets. ERKs are activated by the dual phosphorylation kinase MEK1 and MEK1 inhibitors PD98059, U0126 and CI-1040 are now widely used to inhibit ERKs in cell and animal studies. In an analysis of ERK functions in astrocytes we found that PD98059 (100microM) failed to inhibit ERK phosphorylation but U0126 (50microM) inhibited ERK phosphorylation to approximately 80%. Surprisingly, U0126 also caused profound depletion of ATP in glucose-deprived cells, leading to death by necrosis. Since glucose-deprived cells depend mainly on mitochondrial ATP-synthase for ATP production, we tested whether U0126 or PD184161, a derivative of CI-1040, might inhibit ATP synthase activity, using 143B(Rho0) cells (which lack a functional F0 subunit) to further parse this effect. We found that the F1F0ATPase activity extracted from U0126- or PD184161-treated parental 143B cells or astrocytes was indeed inhibited by >or=80% suggesting a covalent change in the enzyme. However, F1F0ATPase activity extracted from similarly treated 143B(Rho0) cells was spared. Because F1F0ATPase activity in isolated mitochondria was not inhibited directly, we propose that U0126 and PD184161 inhibit ATP-synthase via an indirect action on F0. The MEK1 inhibitors also induced necrosis of other glucose-deprived cell types including primary neurons at the same concentrations required for inhibition of ERK phosphorylation. Thus, the MEK1/ERK signalling pathway may modulate ATP synthase function, and its inhibition may cause cells unable to perform glycolysis to die by necrosis.