title: Phosphorylation of cyclin-dependent kinase 5 (Cdk5) at Tyr-15 is inhibited by Cdk5 activators and does not contribute to the activation of Cdk5.
abstract: Cdk5 is a member of the cyclin-dependent kinase (Cdk) family. In contrast to other Cdks that promote cell proliferation, Cdk5 plays a role in regulating various neuronal functions, including neuronal migration, synaptic activity, and neuron death. Cdks responsible for cell proliferation need phosphorylation in the activation loop for activation in addition to binding a regulatory subunit cyclin. Cdk5, however, is activated only by binding to its activator, p35 or p39. Furthermore, in contrast to Cdk1 and Cdk2, which are inhibited by phosphorylation at Tyr-15, the kinase activity of Cdk5 is reported to be stimulated when phosphorylated at Tyr-15 by Src family kinases or receptor-type tyrosine kinases. We investigated the activation mechanism of Cdk5 by phosphorylation at Tyr-15. Unexpectedly, however, it was found that Tyr-15 phosphorylation occurred only on monomeric Cdk5, and the coexpression of activators, p35/p25, p39, or Cyclin I, inhibited the phosphorylation. In neuron cultures, too, the activation of Fyn tyrosine kinase did not increase Tyr-15 phosphorylation of Cdk5. Further, phospho-Cdk5 at Tyr-15 was not detected in the p35-bound Cdk5. In contrast, expression of active Fyn increased p35 in neurons. These results indicate that phosphorylation at Tyr-15 is not an activation mechanism of Cdk5 but, rather, indicate that tyrosine kinases could activate Cdk5 by increasing the protein amount of p35. These results call for reinvestigation of how Cdk5 is regulated downstream of Src family kinases or receptor tyrosine kinases in neurons, which is an important signaling cascade in a variety of neuronal activities.
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kobayashi
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Saito
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Ko
authors.initials: K
authors.lastname: Sato
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Furusawa
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Hosokawa
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Tsutsumi
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Asada
authors.affiliation: the Biosignal Research Center, Kobe University, 1-1 Rokkodaicho, Nada, Kobe, 657-8501, and.
authors.forename: Shinji
authors.initials: S
authors.lastname: Kamada
authors.affiliation: the Department of Life Science and Medical Bio-Science, Waseda University, 2-2 Wakamatsu, Shinjuku, Tokyo 162-8480, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Ohshima
authors.affiliation: From the Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan, hisanaga-shinichi@tmu.ac.jp.
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Hisanaga
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D051360:Cyclin-Dependent Kinase 5; D003598:Cytoskeletal Proteins; D004789:Enzyme Activation / Q000502:physiology; D020536:Enzyme Activators / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D058635:Lipid-Linked Proteins; D051379:Mice; D008813:Mice, Inbred ICR; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; C492236:Cdk5r1 protein, mouse; C578513:Cdk5r2 protein, mouse; D003598:Cytoskeletal Proteins; D020536:Enzyme Activators; D058635:Lipid-Linked Proteins; D009419:Nerve Tissue Proteins; D014443:Tyrosine; D010770:Phosphotransferases; D019061:src-Family Kinases; D051360:Cyclin-Dependent Kinase 5; C495906:Cdk5 protein, mouse
keywords: Activation Mechanism; Cdk5; Cyclin; Cyclin-dependent Kinase (Cdk); Fyn; Protein Phosphorylation; Protein-tyrosine Kinase (Tyrosine Kinase); neuron; p35