It has been firmly established in recent years that PINK1, a protein kinase found on the surface of mitochondria, will recruit an E3 ligase, parkin, from the cytosol to remove damaged mitochondria by autophagy. As both of these proteins are mutated in recessive parkinsonism, it therefore seems likely that mitochondrial turnover is a critical process in disease. One well established way to trigger PINK1-dependent parkin recruitment and subsequent mitophagy is to depolarize mitochondria. However, the details of the signaling mechanism(s) by which PINK1 and parkin are activated in this process are not well understood. In order to identify novel components of PINK1/parkin activation, we undertook a genome-wide screen using shRNA against a substantial proportion of the human genome, using recruitment of parkin under depolarizing conditions as a measure of activity of the signaling pathway. We recovered PINK1 as expected but also a novel modifier, hexokinase 2. This enzyme phosphorylates glucose to produce glucose-6-phosphate and therefore influences the relative utilization of glycolysis and oxidative phosphorylation for energy production in cells. In our hands, both hexokinase 2 (expressed in many tumor cell types) and hexokinase 1 (expressed in the brain) can support parkin relocalization. We also demonstrated that the AKt pathway is upstream of hexokinase activity. We plan to follow this work by examining the role of hexokinase in other contexts relevant to Parkinsons disease.
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