A long-lived pool of PINK1 imparts a molecular memory of depolarisation-induced activity

The Parkinson’s disease linked kinase, PINK1, is a short lived protein that undergoes cleavage upon mitochondrial import leading to its release to the cytosol and proteasomal degradation. Under mitochondria depolarising conditions, it accumulates on mitochondria where it becomes activated, phosphorylating both ubiquitin and the ubiquitin E3 ligase Parkin, at Ser65. Here we have used a ubiquitylation inhibitor TAK-243 to accumulate cleaved PINK1 (cPINK1) in a cell line that lacks Parkin. We show that cPINK1 phosphorylates free ubiquitin and can be released to the cytosol in an active form. We show that in RPE1 cells under mitochondria depolarising conditions (i) the majority of PINK1 cleavage proceeds unimpeded and (ii) accrued PINK1 cannot be accounted for by protein stabilisation alone. Accordingly, we suggest that translation of PINK1 mRNA must be mobilised under mitochondrial depolarisation. We have further discovered a pre-conditioning phenomenon, whereby an initial depolarising treatment leaves a residual pool of active PINK1, which remains competent for seeding the activation of nascent cPINK1, despite a 16 hour recuperation period.