mtCLIC is up‐regulated and maintains a mitochondrial membrane potential in mtDNA‐depleted L929 cells

To explain why mitochondrial DNA (mtDNA)‐depleted or rho0 cells still keep a mitochondrial membrane potential (Δψm) in the absence of respiration, several hypotheses have been proposed. The principal and well accepted one involves a reverse of action for ANT combined to F1‐ATPase activity. However, the existence of other putative electrogenic channels has been speculated. Here, using mRNA differential display reverse transcriptase‐polymerase chain reaction on L929 mtDNA‐depleted cells, we identified mtCLIC as a differentially expressed gene in cells deprived from mitochondrial ATP production. Mitochondrial chloride intracellular channel (mtCLIC), a member of a recently discovered and expanding family of chloride intracellular channels, is up‐regulated in mtDNA‐depleted and rho0 cells. We showed that its expression is dependent on CREB and p53 and is sensitive to calcium and tumor necrosis factor α. Interestingly, up‐ or down‐regulation of mtCLIC protein expression changes Δψm whereas the chloride channel inhibitor NPPB reduces the Δψm in mtDNA‐depleted L929 cells, measured with the fluorescent probe rhodamine 123. Finally, we demonstrated that purified mitochondria from mtDNA‐depleted cells incorporate, in a NPPB‐sensitive manner, more 36chloride than parental mitochondria. These findings suggest that mtCLIC could be involved in mitochondrial membrane potential generation in mtDNA‐depleted cells, a feature required to prevent apoptosis and to drive continous protein import into mitochondria.