Symposia

We have previously demonstrated a primarily mitochondrial localisation of the TASK-3 potassium channels in cultured melanoma cells. We hypothesised that mitochondrial TASK-3 channels may exert antiapoptotic effects via contributing to mitochondrial function, most likely by maintaining mitochondrial membrane potential. To confirm this hypothesis and to study possible other functions of TASK-3 channels, we employed RNA interference. Our present experiments were conducted on WM35 cells in which TASK-3 biosynthesis was stably knocked-down. WM35 cells that were stably transfected with a scrambled RNA sequence served as control. To monitor mitochondrial function, Jc-1 fluorescent dye was applied at a concentration of 5 μg/ml. Mitochondrial depolarisation was evoked by carbonyl cyanide mchlorophenylhydrazone (50μmol/l CCCP). TASK-3 knockdown cells had depolarised mitochondrial membrane potential. In addition, their mitochondrial membrane could be more easily depolarised, suggesting that melanoma cells having reduced TASK-3 expression are less capable of increasing their mitochondrial activity in response to metabolic challenges. An MTT assay, that measures mitochondrial reducing capacity, also indicated reduced mitochondrial function in the knock-down cell cultures. In addition, TASK-3 gene-silenced cells showed slower proliferation rate (confirmed by Cyquant assay) and increased Annexin V binding. The latter observation indicates that knock-down melanoma cells are more prone to apoptotic cell death. Knockdown cells also had decreased cell volume which may be the result of apoptotic volume decrease. During the apoptotic events the translocation of AIF from mitochondria to cytosol and cell nuclei occurs. Our data indicate that reduced TASK-3 expression of the melanoma cells results in mitochondrial depolarisation, reduced mitochondrial function, decreased rate of proliferation, and a markedly increased rate of intrinsic apoptosis.1 page(s