Regulation of Bcl-xL–ATP Synthase Interaction by Mitochondrial Cyclin B1–Cyclin-Dependent Kinase-1 Determines Neuronal Survival

The survival of postmitotic neurons needs continuous degradation of cyclin B1, a mitotic protein accumulated aberrantly in the damaged brain areas of Alzheimer9s disease and stroked patients. Degradation of cyclin B1 takes place in the proteasome after ubiquitylation by the anaphase-promoting complex/cyclosome (APC/C)–cadherin 1 (Cdh1), an E3 ubiquitin ligase that is highly active in neurons. However, during excitotoxic damage—a hallmark of neurological disorders—APC/C–Cdh1 is inactivated, causing cyclin B1 stabilization and neuronal death through an unknown mechanism. Here, we show that an excitotoxic stimulus in rat cortical neurons in primary culture promotes cyclin B1 accumulation in the mitochondria, in which it binds to, and activates, cyclin-dependent kinase-1 (Cdk1). The cyclin B1–Cdk1 complex in the mitochondria phosphorylates the anti-apoptotic protein B-cell lymphoma extra-large (Bcl-xL), leading to its dissociation from the β subunit of F 1 F o –ATP synthase. The subsequent inhibition of ATP synthase activity causes complex I oxidative damage, mitochondrial inner membrane depolarization, and apoptotic neuronal death. These results unveil a previously unrecognized role for mitochondrial cyclin B1 in the oxidative damage associated with neurological disorders.