title: The Phosphatase-Resistant Isoform of CaMKI, Ca²⁺/Calmodulin-Dependent Protein Kinase Iδ (CaMKIδ), Remains in Its "Primed" Form without Ca²⁺ Stimulation.
abstract: Ca²⁺/calmodulin-dependent protein kinase I (CaMKI) is known to play pivotal roles in Ca²⁺ signaling pathways. Four isoforms of CaMKI (α, β, γ, and δ) have been reported so far. CaMKI is activated through phosphorylation by the upstream kinase, CaMK kinase (CaMKK), and phosphorylates downstream targets. When CaMKI was transiently expressed in 293T cells, CaMKIα was not phosphorylated at all under low-Ca²⁺ conditions in the cells. In contrast, we found that CaMKIδ was significantly phosphorylated and activated to phosphorylate cAMP response element-binding protein (CREB) under the same conditions. Herein, we report that the sustained activation of CaMKIδ is ascribed to its phosphatase resistance resulting from the structure of its N-terminal region. First, we examined whether CaMKIδ is more readily phosphorylated by CaMKK than CaMKIα, but no significant difference was observed. Next, to compare the phosphatase resistance between CaMKIα and CaMKIδ, we assessed the dephosphorylation of the phosphorylated CaMKIs by CaMK phosphatase (CaMKP/PPM1F). Surprisingly, CaMKIδ was hardly dephosphorylated by CaMKP, whereas CaMKIα was significantly dephosphorylated under the same conditions. To date, there have been no detailed reports concerning dephosphorylation of CaMKI. Through extensive analysis of CaMKP-catalyzed dephosphorylation of various chimeric and point mutants of CaMKIδ and CaMKIα, we identified the amino acid residues responsible for the phosphatase resistance of CaMKIδ (Pro-57, Lys-62, Ser-66, Ile-68, and Arg-76). These results also indicate that the phosphatase resistance of CaMKI is largely affected by only several amino acids in its N-terminal region. The phosphatase-resistant CaMKI isoform may play a physiological role under low-Ca²⁺ conditions in the cells.
authors.affiliation: †Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan.|‡National Institute of Advanced Industrial Science and Technology, Amagasaki, Hyogo 661-0974, Japan.
authors.forename: Yukako
authors.initials: Y
authors.lastname: Senga
authors.affiliation: §Laboratory of Molecular Brain Science, Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan.
authors.forename: Atsuhiko
authors.initials: A
authors.lastname: Ishida
authors.affiliation: ∥National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Shigeri
authors.affiliation: †Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan.
authors.forename: Isamu
authors.initials: I
authors.lastname: Kameshita
authors.affiliation: †Department of Life Sciences, Faculty of Agriculture, Kagawa University, Miki-cho, Kagawa 761-0795, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Sueyoshi
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054730:Protein Interaction Domains and Motifs; D011499:Protein Processing, Post-Translational; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D029961:Zebrafish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D050505:Mutant Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D029961:Zebrafish Proteins; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; C517598:Camk1 protein, mouse; C517602:Camk1d protein, mouse; D010749:Phosphoprotein Phosphatases