title: Neurotoxic calcium transfer from endoplasmic reticulum to mitochondria is regulated by cyclin-dependent kinase 5-dependent phosphorylation of tau.
abstract: Increased levels of mitochondrial-free calcium have been associated with several cell-death paradigms, such as excitotoxicity and ceramide-mediated neuronal death. In the latter, calcium is transferred from the endoplasmic reticulum to mitochondria by a mechanism that is only partly understood. We show here that CDK5 (cyclin-dependent kinase 5) plays a role. Free calcium levels in the endoplasmic reticulum and mitochondria were measured with fluorescent markers in C2-ceramide-treated primary cultures of mesencephalic neurons and differentiated pheochromocytoma PC12 cells. Calcium levels decreased in the endoplasmic reticulum as they increased in mitochondria. Both changes were blocked by the pharmacological and molecular CDK5 inhibitors roscovitine and a dominant-negative form of CDK5. Although the kinase did not mediate the transfer of calcium per se, which required the proapoptotic Bcl-2 family protein t-Bid (the truncated form of Bid), it facilitated the transfer by inducing the clustering of endoplasmic reticulum and mitochondria around the centrosome where they formed close contacts, as shown by immunocytochemistry and electron microscopy. Organelle clustering resulted from CDK5-dependent phosphorylation of the microtubule-associated protein tau on threonine 231. This caused its release from microtubules into the soluble fraction of cellular proteins, which appears to favor retrograde transport of the organelles. Mutation of threonine 231 to alanine, so that tau could not be phosphorylated at this site, prevented the ceramide-induced release of tau from microtubules, organelle clustering, the increase in mitochondrial-free calcium levels, and neuronal death, demonstrating the importance of the CDK5-dependent signaling cascade in this calcium-dependent cell-death mechanism.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U679, Neurologie et Thérapeutique Expérimentale, Hôpital de la Salpêtrière, 75013 Paris, France. darios@mrc-lmb.cam.ac.uk <darios@mrc-lmb.cam.ac.uk>
authors.forename: Frédéric
authors.initials: F
authors.lastname: Darios
authors.forename: Marie-Paule
authors.initials: MP
authors.lastname: Muriel
authors.forename: Myriam Escobar
authors.initials: ME
authors.lastname: Khondiker
authors.forename: Alexis
authors.initials: A
authors.lastname: Brice
authors.forename: Merle
authors.initials: M
authors.lastname: Ruberg
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002118:Calcium / Q000378:metabolism*; D002452:Cell Count / Q000379:methods; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D002518:Ceramides / Q000494:pharmacology; D003001:Cloning, Molecular / Q000379:methods; D051360:Cyclin-Dependent Kinase 5 / Q000502:physiology*; D015638:Cytochalasin D / Q000494:pharmacology; D004347:Drug Interactions; D004622:Embryo, Mammalian; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D006575:Heterocyclic Compounds, 3-Ring; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D008636:Mesencephalon / Q000166:cytology; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D009474:Neurons / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D015739:Nocodazole / Q000494:pharmacology; D010766:Phosphorylation; D011247:Pregnancy; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D000077546:Roscovitine; D013997:Time Factors; D014162:Transfection / Q000379:methods; D014404:Tubulin / Q000378:metabolism; D016875:tau Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002518:Ceramides; D004791:Enzyme Inhibitors; D006575:Heterocyclic Compounds, 3-Ring; D011687:Purines; D014404:Tubulin; D016875:tau Proteins; D000077546:Roscovitine; C068483:rhod-2; D015638:Cytochalasin D; D051360:Cyclin-Dependent Kinase 5; D015739:Nocodazole; D002118:Calcium