Mitochondrial import of PKCε is mediated by HSP90: a role in cardioprotection from ischaemia and reperfusion injury

Protein kinase C epsilon (PKC epsilon) is critical for cardiac protection from ischaemia and reperfusion (IR) injury. PKC epsilon substrates that mediate cytoprotection reside in the mitochondria. However, the mechanism enabling mitochondrial translocation and import of PKC epsilon to enable phosphorylation of these substrates is not known. Heat shock protein 90 (HSP90) is a cytoprotective protein chaperone that participates in mitochondrial import of a number of proteins. Here, we investigated the role of HSP90 in mitochondrial import of PKC epsilon. Using an ex vivo perfused rat heart model of IR, we found that PKC epsilon translocates from the cytosol to the mitochondrial fraction following IR. Immunogold electron microscopy and mitochondrial fractionation demonstrated that following IR, mitochondrial PKC epsilon is localized within the mitochondria, on the inner mitochondrial membrane. Pharmacological inhibition of HSP90 prevented IR-induced interaction between PKC epsilon and the translocase of the outer membrane (Tom20), reduced mitochondrial import of PKC epsilon, and increased necrotic cell death by similar to 70%. Using a rational approach, we designed a 7-amino acid peptide activator of PKC epsilon, derived from an HSP90 homologous sequence located in the C2 domain of PKC epsilon (termed Sigma epsilon HSP90). Treatment with this peptide (conjugated to the cell permeating TAT protein-derived peptide, TAT(47-57)) increased PKC epsilon-HSP90 protein-protein interaction, enhanced mitochondrial translocation of PKC epsilon, increased phosphorylation and activity of an intra-mitochondrial PKC epsilon substrate, aldehyde dehydrogenase 2, and reduced cardiac injury in ex vivo and in vivo models of myocardial infarction. Our results suggest that HSP90-mediated mitochondrial import of PKC epsilon plays an important role in the protection of the myocardium from IR injury.