Nuclear envelope dispersion triggered by deregulated Cdk5 precedes neuronal death

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Deregulated Cdk5 causes neurotoxic amyloid beta peptide (Aβ) processing and cell death, two hallmarks of Alzheimer's disease, through the Foxo3 transcriptional factor in hippocampal cells, primary neurons and an Alzheimer's disease mouse model. Using an innovative chemical genetic screen, we identified Foxo3 as a direct substrate of Cdk5 in brain lysates. Cdk5 directly phosphorylates Foxo3, which increased its levels and nuclear translocation. Nuclear Foxo3 initially rescued cells from ensuing oxidative stress by upregulating MnSOD (also known as SOD2). However, following prolonged exposure, Foxo3 upregulated Bim (also known as BCL2L11) and FasL (also known as FASLG) causing cell death. Active Foxo3 also increased Aβ(1-42) levels in a phosphorylationdependent manner. These events were completely inhibited either by expressing phosphorylation-resistant Foxo3 or by depleting Cdk5 or Foxo3, highlighting a key role for Cdk5 in regulating Foxo3. These results were confirmed in an Alzheimer's disease mouse model, which exhibited increased levels and nuclear localization of Foxo3 in hippocampal neurons, which preceded neurodegeneration and Aβ plaque formation, indicating this phenomenon is an early event in Alzheimer's disease pathogenesis. Collectively, these results show that Cdk5-mediated phospho-regulation of Foxo3 can activate several genes that promote neuronal death and aberrant Aβ processing, thereby contributing to the progression of neurodegenerative pathologies.

Section: Methodsmentioning

confidence: 99%

Section: Foxo3a Is a Direct Substrate Of Cdk5mentioning

confidence: 99%

Cdk5–Foxo3 axis: initially neuroprotective, eventually neurodegenerative in Alzheimer's disease models

Shi

Viccaro

Lee

et al. 2016

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“…A complementary substituent on ATP is created by attaching a bulky substituent at the N6 position of ATP. Because the ATP analog is not accepted by wild-type kinases, this strategy allows for unbiased identification of direct substrates of any kinase in a global environment (Shah et al, 1997;Shah and Shokat, 2002;Shah and Shokat, 2003;Shah and Vincent, 2005;Kim and Shah, 2007;Sun et al, 2008a;Sun et al, 2008b;Sun et al, 2009;Chang et al, 2011).…”

Section: Limk2 Is An Aurora a Substrate In Breast Cancer Cellsmentioning

confidence: 99%

LIMK2 is a crucial regulator and effector of Aurora-A-kinase-mediated malignancy

Johnson

Chang

Ghosh

et al. 2012

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SummaryAurora A is overexpressed in majority of breast carcinomas. With the exception of BRCA1 and PHLDA1, no oncogenic Aurora A substrates are known in breast cancer. In this study, a chemical genetic approach was used to identify malignant targets of Aurora A, which revealed LIMK2 as a novel Aurora A substrate. Aurora A regulates LIMK2 kinase activity, subcellular localization and protein levels by direct phosphorylation at S283, T494 and T505. In response, LIMK2 also positively regulates the level of Aurora A, thereby engaging in a positive-feedback loop, promoting Aurora-A-mediated oncogenic pathways. Most importantly, LIMK2 ablation fully abrogates Aurora-A-mediated tumorigenesis in nude mice, suggesting that LIMK2 is a key oncogenic effector of Aurora A. Furthermore, LIMK2 ablation acts synergistically with inhibition of Aurora A in promoting cell death. Finally, Aurora-A-mediated upregulation of LIMK2 appears to be a common mechanism in many cancers. LIMK2 inhibition or ablation is therefore an alternative approach for modulating Aurora A deregulation in cancer.

“…Nuclear Cdk5 or nuclear free p35 is suggested to prevent re-entry of postmitotic neurons into cell cycle (Zhang et al, 2008;Zhang et al, 2010). On the other hand, it is well documented that dysregulation of Cdk5 activity by cleavage of p35 to p25 by calpain induces neuronal death (Patrick et al, 1999;Gong et al, 2003;Smith et al, 2006;Saito et al, 2007;Kim et al, 2008;Wen et al, 2008;Chang et al, 2011). p25-Cdk5, which has lost p35 membrane binding sites, is shown to translocate into the nucleus to exert its cell death activity.…”

Section: Discussionmentioning

confidence: 99%

“…p35-Cdk5 and p39-Cdk5 are predominantly cytoplasmic and membrane-associated due to myristoylation of p35 and p39 (Patrick et al, 1999;Asada et al, 2008). However, when Cdk5 is dysregulated by calpain-mediated cleavage of p35 to p25, the C-terminal fragment of p35, hyperactive p25-Cdk5 translocates to the nucleus, leading to cell death in neurodegenerative diseases (Patrick et al, 1999;Gong et al, 2003;Smith et al, 2006;Saito et al, 2007;Kim et al, 2008;Wen et al, 2008;Chang et al, 2011). In contrast, several reports also implicate p35 in nuclear Cdk5 activity, indicated by the presence of nuclear p35-Cdk5 complexes (Qu et al, 2002;Fu et al, 2004;Zhang et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Cdk5 phosphorylation of its activators p35 and p39 determines subcellular location of the holokinase in a phosphorylation site-specific manner

Asada¹,

Saito²,

Hisanaga³

2012

SummaryCdk5 is a member of the cyclin-dependent kinase (Cdk) family, which is activated by neuronal activators p35 or p39. Cdk5 regulates a variety of neuronal activities including migration, synaptic activity and neuronal death. p35 and p39 impart cytoplasmic membrane association of p35-Cdk5 and p39-Cdk5, respectively, through their myristoylation, but it is not clearly understood how the cellular localization is related to different functions. We investigated the role of Cdk5 activity in the subcellular localization of p35-Cdk5 and p39-Cdk5. Cdk5 activity affected the localization of p35-Cdk5 and p39-Cdk5 through phosphorylation of p35 or p39. Using unphosphorylated or phosphomimetic mutants of p35 and p39, we found that phosphorylation at Ser8, common to p35 and p39, by Cdk5 regulated the cytoplasmic localization and perinuclear accumulation of unphosphorylated S8A mutants, and whole cytoplasmic distribution of phosphomimetic S8E mutants. Cdk5 activity was necessary to retain Cdk5-activator complexes in the cytoplasm. Nevertheless, small but distinct amounts of p35 and p39 were detected in the nucleus. In particular, nuclear p35 and p39 were increased when the Cdk5 activity was inhibited. p39 had a greater propensity to accumulate in the nucleus than p35, and phosphorylation at Thr84, specific to p39, regulated the potential nuclear localization activity of the Lys cluster in p39. These results suggest that the subcellular localization of the Cdk5-activator complexes is determined by its kinase activity, and also implicate a role for p39-Cdk5 in the nucleus.