CKMT1 regulates the mitochondrial permeability transition pore in a process that provides evidence for alternative forms of the complex

Abstract

The permeability transition pore (PT-pore) mediates cell death through the dissipation of the mitochondrial membrane potential (DY m ). Because the exact composition of the PT-pore is controversial, it is crucial to investigate the actual molecular constituents and regulators of this complex. We found that mitochondrial creatine kinase-1 (CKMT1) is a universal and functionally necessary gatekeeper of the PT-pore, as its depletion induces mitochondrial depolarization and apoptotic cell death. This can be inhibited efficiently by bongkrekic acid, a compound that is widely used to inhibit the PT-pore. However, when the 'classical' PTpore subunits cyclophilin D and VDAC1 are pharmacologically inhibited or their expression levels reduced, mitochondrial depolarization by CKMT1 depletion remains unaffected. At later stages of drug-induced apoptosis, CKMT1 levels are reduced, suggesting that CKMT1 downregulation acts to reinforce the commitment of cells to apoptosis. A novel high-molecular-mass CKMT1 complex that is distinct from the known CKMT1 octamer disintegrates upon treatment with cytotoxic drugs, concomitant with mitochondrial depolarization. Our study provides evidence that CKMT1 is a key regulator of the PT-pore through a complex that is distinct from the classical PT-pore.

Decreased sarcomeric mitochondrial creatine kinase 2 impairs skeletal muscle mitochondrial function independently of insulin action in type 2 diabetes

“…Of note, the ex vivo respirometry assays were conducted in the absence of creatine and phosphocreatine – potent modulators of mitochondrial respiration 32 –, indicating that the observed increase in mitochondrial respiration was independent of concomitant changes in CKMT2 kinase activity and creatine-ADP stoichiometry. This result is compatible with CKMT1 isoform depletion-induced mitochondrial depolarization, independently of phosphocreatine availability, in HeLa cells 33 . Moreover, both CKMT1 and CKMT2 induce and stabilize contact sites between the inner and outer mitochondrial membrane by colocalizing with ANT and VDAC 34–36 .…”

Mitochondrial control of microglial phagocytosis by the translocator protein and hexokinase 2 in Alzheimer’s disease

“…Our findings indicate these adaptor proteins may also be key components of the functional TSPO complex in the brain; future studies are needed to determine if these interactions are regulated by endogenous and synthetic ligands. Other previously reported interactors of the TSPO–VDAC complex identified here in the brain TSPO interactome included ATP synthase (Atp5a1) ( 57 ), mitochondrial solute carrier family 25 ( 58 ), and mitochondrial creatine kinase ( 59 , 60 ). Interestingly, ATP synthase has also been previously shown to be regulated by the 14-3-3 adaptor proteins.…”

Cyclophilin D and myocardial ischemia–reperfusion injury: A fresh perspective

“…Correspondingly, creatine kinase mitochondrial 1 (CKMT1) and hexokinase 1 (HK1), as part of supramolecular complexes containing VDAC1 and ANT, were also documented to bear mPTP-like electrophysiological properties [22]. Since both CKMT1 and HK1 are involved in important metabolic reactions, they are proposed to have a more regulatory role in mPTP formation [22,27,30]. Largely based on pharmacological studies, the translocator protein (TSPO), a component of peripheral benzodiazepine receptor, has also been listed as a regulator of the mPTP [31,32].…”