Biology subjects

Georgiou, I. C.

Publications and source records attributed to Georgiou, I. C..

2 recordsLinked to original sources

bioRxiv2026

Arrested PPTC7 import couples mitochondrial depolarisation to NIX and BNIP3 degradation

Mitophagy is initiated by two distinct pathways that are both coupled to mitochondrial protein import. Import stress stabilises PINK1 at the outer mitochondrial membrane, activating the Parkin and ubiquitin-dependent pathway. Receptor-mediated pathways are governed by the expression of outer mitochondrial membrane proteins NIX and BNIP3. Mitophagy is limited by their degradation, via SCFFBXL4. This requires the PP2C-family phosphatase PPTC7 as an obligate substrate recognition factor, captured at the outer membrane en route to the matrix. We show that mitochondrial depolarisation exerts opposing effects on these two pathways. In RPE1 cells, depolarisation drives rapid, ubiquitin and proteasome-dependent loss of NIX and BNIP3 that requires ongoing protein synthesis of PPTC7. Using a doxycycline-mediated pulse-chase assay, we demonstrate directly that depolarisation inhibits import of newly synthesised PPTC7, and that this arrested PPTC7 is itself degraded in an FBXL4-dependent manner alongside its substrates. Thus, import arrest both stabilises PINK1 and eliminates NIX and BNIP3, coordinating a switch between mitophagy pathways, while concurrent degradation of PPTC7 couples mitophagy receptor turnover to PPTC7 synthesis rates.

cell biology↗

bioRxiv2024

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

The Parkinsons 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.

cell biology↗