Loss of function mutations in the PTEN‐induced putative kinase 1 (Pink1) gene have been linked with an autosomal recessive familial form of early onset Parkinson's disease (PD). However, the underlying mechanism(s) responsible for degeneration remains elusive. Presently, using co‐immunoprecipitation in HEK (Human embryonic kidney) 293 cells, we show that Pink1 endogenously interacts with FK506‐binding protein 51 (FKBP51 or FKBP5), FKBP5 and directly phosphorylates FKBP5 at Serine in an in vitro kinase assay. Both FKBP5 and Pink1 have been previously associated with protein kinase B (AKT) regulation. We provide evidence using primary cortical cultured neurons from Pink1‐deficient mice that Pink1 increases AKT phosphorylation at Serine 473 (Ser473) challenged by 1‐methyl‐4‐phenylpyridinium (MPP+) and that over‐expression of FKBP5 using an adeno‐associated virus delivery system negatively regulates AKT phosphorylation at Ser473 in murine‐cultured cortical neurons. Interestingly, FKBP5 over‐expression promotes death in response to MPP+ in the absence of Pink1. Conversely, shRNA‐mediated knockdown of FKBP5 in cultured cortical neurons is protective and this effect is reversed with inhibition of AKT signaling. In addition, shRNA down‐regulation of PH domain leucine‐rich repeat protein phosphatase (PHLPP) in Pink1 WT neurons increases neuronal survival, while down‐regulation of PHLPP in Pink1 KO rescues neuronal death in response to MPP+. Finally, using co‐immunoprecipitation, we show that FKBP5 interacts with the kinase AKT and phosphatase PHLPP. This interaction is increased in the absence of Pink1, both in Mouse Embryonic Fibroblasts (MEF) and in mouse brain tissue. Expression of kinase dead Pink1 (K219M) enhances FKBP5 interaction with both AKT and PHLPP. Overall, our results suggest a testable model by which Pink1 could regulate AKT through phosphorylation of FKBP5 and interaction of AKT with PHLPP. Our results suggest a potential mechanism by which PINK1‐FKBP5 pathway contributes to neuronal death in PD. Open Science Badges This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

DNA damage is an important initiator of neuronal apoptosis and activates signaling events not yet fully defined. Using the camptothecininduced DNA damage model in neurons, we previously showed that cyclin D1-associated cell cycle cyclin-dependent kinases (Cdks) (Cdk4/6) and p53 activation are two major events leading to activation of the mitochondrial apoptotic pathway. With gene array analyses, we detected upregulation of Cited2, a CBP (cAMP response element-binding protein-binding protein)/p300 interacting transactivator, in response to DNA damage. This upregulation was confirmed by reverse transcription-PCR and Western blot. CITED2 was functionally important because CITED2 overexpression promotes death, whereas CITED2 deficiency protects. Cited2 upregulation is upstream of the mitochondrial death pathway (BAX, Apaf1, or cytochrome c release) and appears to be independent of p53. However, inhibition of the Cdk4 blocked Cited2 induction. The Cited2 prodeath mechanism does not involve Bmi-1 or p53. Instead, Cited2 activates peroxisome proliferator-activated receptor-␥ (PPAR␥), an activity that we demonstrate is critical for DNA damage-induced death. These results define a novel neuronal prodeath pathway in which Cdk4-mediated regulation of Cited2 activates PPAR␥ and consequently caspase.

Developmental and pathological death of neurons requires activation of a defined pathway of cell cycle proteins. However, it is unclear how this pathway is regulated and whether it is relevant in vivo. A screen for transcripts robustly induced in cultured neurons by DNA damage identified Sertad1, a Cdk4 (cyclin-dependent kinase 4) activator. Sertad1 is also induced in neurons by nerve growth factor (NGF) deprivation and A␤ (␤-amyloid). RNA interference-mediated downregulation of Sertad1 protects neurons in all three death models. Studies of NGF withdrawal indicate that Sertad1 is required to initiate the apoptotic cell cycle pathway since its knockdown blocks subsequent pathway events. Finally, we find that Sertad1 expression is required for developmental neuronal death in the cerebral cortex. Sertad1 thus appears to be essential for neuron death in trophic support deprivation in vitro and in vivo and in models of DNA damage and Alzheimer's disease. It may therefore be a suitable target for therapeutic intervention.

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DNA damage is a critical component of neuronal death underlying neurodegenerative diseases and injury. Neuronal death evoked by DNA damage is characterized by inappropriate activation of multiple cell cycle components. However, the mechanism regulating this activation is not fully understood. We demonstrated previously that the cell division cycle (Cdc) 25A phosphatase mediates the activation of cyclin‐dependent kinases and neuronal death evoked by the DNA damaging agent camptothecin. We also showed that Cdc25A activation is blocked by constitutive checkpoint kinase 1 activity under basal conditions in neurons. Presently, we report that an additional factor is central to regulation of Cdc25A phosphatase in neuronal death. In a gene array screen, we first identified Pim‐1 as a potential factor up‐regulated following DNA damage. We confirmed the up‐regulation of Pim‐1 transcript, protein and kinase activity following DNA damage. This induction of Pim‐1 is regulated by the nuclear factor kappa beta (NF‐κB) pathway as Pim‐1 expression and activity are significantly blocked by siRNA‐mediated knockdown of NF‐κB or NF‐κB pharmacological inhibitors. Importantly, Pim‐1 activity is critical for neuronal death in this paradigm and its deficiency blocks camptothecin‐mediated neuronal death. It does so by activating Cdc25A with consequent activation of cyclin D1‐associated kinases. Taken together, our results demonstrate that Pim‐1 kinase plays a central role in DNA damage‐evoked neuronal death by regulating aberrant neuronal cell cycle activation.