Elsevier BV Acta Medica Okayama 0143-4160 137 2026 Activation phosphorylation and dephosphorylation dynamics of Ca2+/Calmodulin-dependent protein kinase Iα in HeLa cells 103183 EN Yerun Chen Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masao Miki Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masumi Eto Graduate School of Veterinary Science, Okayama University of Science Atsuhiko Ishida Laboratory of Molecular Brain Science, Graduate School of Integrated Sciences for Life, Hiroshima University Futoshi Suizu Clinical Examination Department, Kagawa Prefectural University of Health Sciences Akihiro Mizutani Department of Pharmacotherapeutics, Showa Pharmaceutical University Hideaki Ando Laboratory for Developmental Neurobiology, RIKEN Center for Brain Science Katsuhiko Mikoshiba Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ca²⁺/calmodulin-dependent protein kinase I (CaMKI), a multifunctional CaM-activated protein kinase, is involved in various Ca²⁺ signaling pathways including neuronal development. Here, we characterize the phosphorylation at Thr177 (an activation Thr residue) and subsequent dephosphorylation dynamics of CaMKIα in HeLa cells upon physiological stimulation that elevates intracellular Ca²⁺. ATP induced CaMKIα phosphorylation within 5–10 min; phosphorylation was then blocked by CaMKK inhibitor TIM-063, or by the depletion of extracellular Ca²⁺. This was followed by gradual dephosphorylation to basal levels within 30–60 min. Histamine induced CaMKIα phosphorylation, peaking within 3–4 min; this process was abolished by treatment with either TIM-063 or intracellular Ca²⁺ chelation using BAPTA-AM and thapsigargin; however, not by extracellular Ca²⁺ depletion. CaMKIα was then rapidly dephosphorylated to basal levels within 10 min. Consistently, histamine-induced (but not ATP-induced) CaMKIα phosphorylation was absent in triple IP₃ receptor-knockout HeLa cells. Dephosphorylation of CaMKIα after ATP-induced phosphorylation was unaffected by okadaic acid or CaMK phosphatase (CaMKP, known as PPM1F) inhibitors (ANS and ANDS). We found that HeLa cell extracts contained Mg2+/Mn2+-dependent CaMKIα dephosphorylation activity that was insensitive to ANS and ANDS. Furthermore, co-expression of PP2Cα fully abolished ATP-, histamine-, or ionomycin-stimulated CaMKIα phosphorylation, which is consistent with in vitro dephosphorylation of CaMKIα at Thr177 by recombinant PP2Cα. Taken together, these results reveal that agonist-induced Ca²⁺ influx from the extracellular space or release from intracellular stores transiently activates CaMKK-CaMKIα signaling in HeLa cells, which is shut off by dephosphorylation catalyzed by PP2Cα as a promising candidate for CaMKIα phosphatase. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0143-4160 135 2026 Regulation of brain-specific kinases 1 and 2 (BRSK1/2) by Ca2+/calmodulin 103134 EN Naoyuki Washida Moe Kataoka Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Okayama University Anna R. Brun Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Uryu Takezaki Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ko Hijikawa Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Okayama University Haruki Yamauchi Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ryo Morishita CellFree Sciences Co., Ltd. Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University We conducted a genome-wide calmodulin (CaM) interaction screening of 462 GST-fused human protein kinases to identify novel CaM-dependent protein kinases (CaMKs). In addition to known CaMKs, including myosin light chain kinases, CaMK2γ, and death-associated kinase 2, we identified the brain-specific protein kinase 2 (BRSK2, also known as SAD-A) as a novel CaM interactant. Proximity biotinylation and CaM–sepharose chromatography assays revealed that rat BRSK isoforms (BRSK1/2) interact with CaM in a Ca2+-dependent manner in vitro. We found that CaM suppresses the activation-loop phosphorylation of BRSK1 (at Thr189) and BRSK2 (at Thr175) by liver kinase B1 (LKB1), an activating kinase, in a Ca2+-dependent manner (IC50 of ∼7 µM), thereby inhibiting BRSK activation. LKB1-catalyzed phosphorylation of the catalytic domain mutant of BRSK1 (residues 1–294) at Thr189 was suppressed by the addition of Ca2+/CaM, consistent with direct CaM binding of the kinase domain, as well as wild-type BRSK1. We confirmed that the LKB1 activity was not directly suppressed by Ca2+/CaM, supporting the hypothesis that the direct interaction of Ca2+/CaM with the kinase domain blocks the phosphorylation/activation of BRSK1/2 by LKB1. The kinase activity and PP2Cα-catalyzed dephosphorylation of LKB1-phosphorylated BRSK1 were not altered by Ca2+/CaM, although it was demonstrated to bind to Ca2+/CaM like that of unphosphorylated BRSK1. This unrecognized mechanism of BRSK1/2 regulation, involving the direct role of Ca2+/CaM binding, which inhibits phosphorylation/activation by LKB1, may open a new Ca2+ signal transduction pathway in neurons. No potential conflict of interest relevant to this article was reported.

American Chemical Society (ACS) Acta Medica Okayama 0006-2960 64 20 2025 Characterization of Autonomous and Ca2+/Calmodulin-Dependent Activities of CaMKK Isoforms In Vitro and in Mouse Tissues 4309 4317 EN Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yerun Chen Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Teruhiko Ishikawa Department of Science Education, Graduate School of Education, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Futoshi Suizu Clinical Examination Department, Kagawa Prefectural University of Health Sciences Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ca2+/CaM-dependent protein kinase kinase (CaMKK) phosphorylates and activates downstream kinases, including CaMKI, CaMKIV, PKB, and AMPK, regulating various cellular functions such as neuronal morphogenesis, metabolic control, and pathophysiological pathways, such as cancer progression. CaMKKα/1 is tightly regulated by an autoinhibitory mechanism. CaMKKβ/2 activity is highly Ca2+/CaM-independent (autonomous activity) in vitro and Ca2+/CaM-dependent in cultured cells. Whether these two activity states of CaMKKβ/2 exist in vivo and the detailed regulatory mechanisms for the transition of both activity states remain unclear due to the difficulty in distinguishing the two activity states. In this study, we detected Ca2+-dependent and autonomous CaMKK activity in HeLa cells and successfully separated both activity states of CaMKKβ/2 in mouse brain and testis extracts using a recently developed CaMKK inhibitor (TIM-063)-coupled sepharose, which binds to the catalytic domain in the active state but not in the autoinhibited state. Furthermore, lambda protein phosphatase treatment converted the Ca2+/CaM-dependent form to the autonomous form of CaMKKβ/2, which was not affected by Ala mutation of Ser128, Ser132, and Ser136. The two activity forms of CaMKKβ/2 had equivalent Ca2+/CaM-binding ability. The findings demonstrate the presence of autonomous and Ca2+/CaM-dependent forms of CaMKKβ/2 independently in mouse tissues and cultured cells. The transition of these states of CaMKKβ/2 may be dynamically regulated by the phosphorylation/dephosphorylation of serine residues in the N-terminal regulatory domain. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 0014-5793 599 13 2025 Characterization of molecular mechanisms of CaMKKα/1 oligomerization 1914 1924 EN Shun Uenoyama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hayato Nitta Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Futoshi Suizu Department of Medical Technology, Kagawa Prefectural University of Health Sciences Hiroshi Tokumitsu Calcium/calmodulin-dependent protein kinase kinase (CaMKK) is an activating kinase for calcium/calmodulin-dependent protein kinase type 1 (CaMKI), calcium/calmodulin-dependent protein kinase type IV (CaMKIV), RAC-alpha serine/threonine-protein kinase (PKB), and AMP-activated protein kinase (AMPK) that has been reported to form an active oligomer in cells. Glutathione S-transferase (GST) pulldown assay from the extracts of COS-7 cells expressing GST- and His6-CaMKKα/1 mutants showed that the C-terminal region containing the autoinhibitory and calmodulin (CaM)-binding sequence (residues 438–463) is required for CaMKKα/1 homo-oligomerization. This was confirmed by the fact that the GST-CaMKKα/1 C-terminal domain (residues 435–505) directly interacted with EGFP-CaMKKα/1 residues 435–505 as well as with wild-type CaMKKα/1. Notably, once oligomerized in cells, CaMKKα/1 is neither exchangeable between the oligomeric complexes nor dissociated by Ca2+/CaM binding. These results support stable oligomerization of CaMKK in the cells by intermolecular self-association of its C-terminal region containing a regulatory domain. No potential conflict of interest relevant to this article was reported.

Nature Portfolio Acta Medica Okayama 2045-2322 14 1 2024 Development of a novel AAK1 inhibitor via Kinobeads-based screening 6723 EN Akari Yoshida Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Fumiya Matsumoto Department of Science Education, Graduate School of Education, Okayama University Tomoyuki Miyagawa Department of Science Education, Graduate School of Education, Okayama University Rei Okino Department of Science Education, Graduate School of Education, Okayama University Yumeya Ikeda Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Natsume Tada Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Akira Gotoh Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ryo Morishita CellFree Sciences Co. Ltd Ayano Satoh Organelle Systems Biotechnology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yukinari Sunatsuki Graduate School of Natural Science and Technology, Okayama University Ulf J. Nilsson Department of Chemistry, Lund University Teruhiko Ishikawa Department of Science Education, Graduate School of Education, Okayama University Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University A chemical proteomics approach using Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor-immobilized sepharose (TIM-063-Kinobeads) identified main targets such as CaMKK alpha/1 and beta/2, and potential off-target kinases, including AP2-associated protein kinase 1 (AAK1), as TIM-063 interactants. Because TIM-063 interacted with the AAK1 catalytic domain and inhibited its enzymatic activity moderately (IC50 = 8.51 mu M), we attempted to identify potential AAK1 inhibitors from TIM-063-derivatives and found a novel AAK1 inhibitor, TIM-098a (11-amino-2-hydroxy-7H-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one) which is more potent (IC50 = 0.24 mu M) than TIM-063 without any inhibitory activity against CaMKK isoforms and a relative AAK1-selectivity among the Numb-associated kinases family. TIM-098a could inhibit AAK1 activity in transfected cultured cells (IC50 = 0.87 mu M), indicating cell-membrane permeability of the compound. Overexpression of AAK1 in HeLa cells significantly reduced the number of early endosomes, which was blocked by treatment with 10 mu M TIM-098a. These results indicate TIM-063-Kinobeads-based chemical proteomics is efficient for identifying off-target kinases and re-evaluating the kinase inhibitor (TIM-063), leading to the successful development of a novel inhibitory compound (TIM-098a) for AAK1, which could be a molecular probe for AAK1. TIM-098a may be a promising lead compound for a more potent, selective and therapeutically useful AAK1 inhibitor. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 1422-0067 23 19 2022 Molecular Mechanisms Underlying Ca2+/Calmodulin-Dependent Protein Kinase Kinase Signal Transduction 11025 EN Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) is the activating kinase for multiple downstream kinases, including CaM-kinase I (CaMKI), CaM-kinase IV (CaMKIV), protein kinase B (PKB/Akt), and 5'AMP-kinase (AMPK), through the phosphorylation of their activation-loop Thr residues in response to increasing the intracellular Ca2+ concentration, as CaMKK itself is a Ca2+/CaM-dependent enzyme. The CaMKK-mediated kinase cascade plays important roles in a number of Ca2+-dependent pathways, such as neuronal morphogenesis and plasticity, transcriptional activation, autophagy, and metabolic regulation, as well as in pathophysiological pathways, including cancer progression, metabolic syndrome, and mental disorders. This review focuses on the molecular mechanism underlying CaMKK-mediated signal transduction in normal and pathophysiological conditions. We summarize the current knowledge of the structural, functional, and physiological properties of the regulatory kinase, CaMKK, and the development and application of its pharmacological inhibitors. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 1742-464X 289 19 2022 Substrate recognition by Arg/Pro‐rich insert domain in calcium/calmodulin‐dependent protein kinase kinase for target protein kinases 5971 5984 EN Riku Kaneshige Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yuhei Harada Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Issei Kawamata Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Calcium/calmodulin-dependent protein kinase kinases (CaMKKs) activate CaMKI, CaMKIV, protein kinase B/Akt, and AMP-activated protein kinase (AMPK) by phosphorylating Thr residues in activation loops to mediate various Ca2+-signaling pathways. Mammalian cells expressing CaMKK alpha and CaMKK beta lacking Arg/Pro-rich insert domain (RP-domain) sequences showed impaired phosphorylation of AMPK alpha, CaMKI alpha, and CaMKIV, whereas the autophosphorylation activities of CaMKK mutants remained intact and were similar to those of wild-type CaMKKs. Liver kinase B1 (LKB1, an AMPK kinase) complexed with STRAD and MO25 and was unable to phosphorylate CaMKI alpha and CaMKIV; however, mutant LKB1 with the RP-domain sequences of CaMKK alpha and CaMKK beta inserted between kinase subdomains II and III acquired CaMKI alpha and CaMKIV phosphorylating activity in vitro and in transfected cultured cells. Furthermore, ionomycin-induced phosphorylation of hemagglutinin (HA)-CaMKI alpha at Thr177, HA-CaMKIV at Thr196, and HA-AMPK alpha at Thr172 in transfected cells was significantly suppressed by cotransfection of kinase-dead mutants of CaMKK isoforms, but these dominant-negative effects were abrogated with RP-deletion mutants, suggesting that sequestration of substrate kinases by loss-of-function CaMKK mutants requires the RP-domain. This was confirmed by pulldown experiments that showed that dominant-negative mutants of CaMKK alpha and CaMKK beta interact with target kinases but not RP-deletion mutants. Taken together, these results clearly indicate that both CaMKK isoforms require the RP-domain to recognize downstream kinases to interact with and phosphorylate Thr residues in their activation loops. Thus, the RP-domain may be a promising target for specific CaMKK inhibitors. No potential conflict of interest relevant to this article was reported.

American Chemical Society (ACS) Acta Medica Okayama 0006-2960 61 7 2022 Conformation-Dependent Reversible Interaction of Ca2+/Calmodulin-Dependent Protein Kinase Kinase with an Inhibitor, TIM-063 545 553 EN Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science & Engineering in Health Systems, Okayama University Taisei Okumura Department of Science Education, Graduate School of Education, Okayama University Yuna Τabuchi Department of Science Education, Graduate School of Education, Okayama University Tomoyuki Miyagawa Department of Science Education, Graduate School of Education, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science & Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science & Engineering in Health Systems, Okayama University Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science & Engineering in Health Systems, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Futoshi Suizu Division of Cancer Biology, Institute for Genetic Medicine, Hokkaido University Teruhiko Ishikawa Department of Science Education, Graduate School of Education, Okayama University Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science & Engineering in Health Systems, Okayama University Ca2+/calmodulin-dependent protein kinase kinase (CaMKK), a Ca2+/CaM-dependent enzyme that phosphorylates and activates multifunctional kinases, including CaMKI, CaMKIV, protein kinase B/Akt, and 5'AMP-activated protein kinase, is involved in various Ca2+-signaling pathways in cells. Recently, we developed an ATP competitive CaMKK inhibitor, TIM-063 (2-hydroxy-3-nitro-7H-benzo-[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one, Ohtsuka et al. Biochemistry 2020, 59, 1701-1710). To gain mechanistic insights into the interaction of CaMKK with TIM-063, we prepared TIM-063-coupled sepharose (TIM-127-sepharose) for association/dissociation analysis of the enzyme/inhibitor complex. CaMKK alpha/beta in transfected COS-7 cells and in mouse brain extracts specifically bound to TIM-127-sepharose and dissociated following the addition of TIM-063 in a manner similar to that of recombinant GST-CaMKK alpha/beta, which could bind to TIM-127sepharose in a Ca2+/CaM-dependent fashion and dissociate from the sepharose following the addition of TIM-063 in a dose dependent manner. In contrast to GST-CaMKK alpha, GST-CaMKK beta was able to weakly bind to TIM-127-sepharose in the presence of EGTA, probably due to the partially active conformation of recombinant GST-CaMKK beta without Ca2+/CaM-binding. These results suggested that the regulatory domain of CaMKK alpha prevented the inhibitor from interacting with the catalytic domain as the GST-CaMKK alpha mutant (residues 126-434) lacking the regulatory domain (residues 438-463) interacted with TIM-127-sepharose regardless of the presence or absence of Ca2+/CaM. Furthermore, CaMKK alpha bound to TIM-127-sepharose in the presence of Ca2+/ CaM completely dissociated from TIM-127-sepharose following the addition of excess EGTA. These results indicated that TIM-063 interacted with and inhibited CaMKK in its active state but not in its autoinhibited state and that this interaction is likely reversible, depending on the concentration of intracellular Ca2+. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0006-291X 587 2022 Oligomerization of Ca2+/calmodulin-dependent protein kinase kinase 160 165 EN Yusei Fukumoto Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yuhei Harada Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ca2+/calmodulin-dependent protein kinase kinases (CaMKKα and β) are regulatory kinases for multiple downstream kinases, including CaMKI, CaMKIV, PKB/Akt, and AMP-activated protein kinase (AMPK) through phosphorylation of each activation-loop Thr residue. In this report, we biochemically characterize the oligomeric structure of CaMKK isoforms through a heterologous expression system using COS-7 cells. Oligomerization of CaMKK isoforms was readily observed by treating CaMKK transfected cells with cell membrane permeable crosslinkers. In addition, His-tagged CaMKKα (His–CaMKKα) pulled down with FLAG-tagged CaMKKα (FLAG–CaMKKα) in transfected cells. The oligomerization of CaMKKα was confirmed by the fact that GST–CaMKKα/His–CaMKKα complex from transiently expressed COS-7 cells extracts was purified to near homogeneity by the sequential chromatography using glutathione-sepharose/Nisepharose and was observed in a Ca2+/CaM-independent manner by reciprocal pulldown assay, suggesting the direct interaction between monomeric CaMKKα. Furthermore, the His-CaMKKα kinase-dead mutant (D293A) complexed with FLAG–CaMKKα exhibited significant CaMKK activity, indicating the active CaMKKα multimeric complex. Collectively, these results suggest that CaMKKα can self-associate in the cells, constituting a catalytically active oligomer that might be important for the efficient activation of CaMKK-mediated intracellular signaling. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0143-4160 96 2021 Regulation of the tubulin polymerization-promoting protein by Ca2+/S100 proteins 102404 EN Seita Doi Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Fujioka Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Rina Kondo Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Maho Yamamoto Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Miwako Denda CellFree Sciences Co., Ltd Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ryo Morishita CellFree Sciences Co., Ltd Takafumi Hasegawa Division of Neurology, Department of Neuroscience and Sensory Organs, Tohoku University Graduate School of Medicine Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University To elucidate S100 protein-mediated signaling pathways, we attempted to identify novel binding partners for S100A2 by screening protein arrays carrying 19,676 recombinant glutathione S-transferase (GST)-fused human proteins with biotinylated S100A2. Among newly discovered putative S100A2 interactants, including TMLHE, TRH, RPL36, MRPS34, CDR2L, OIP5, and MED29, we identified and characterized the tubulin polymerization-promoting protein (TPPP) as a novel S100A2-binding protein. We confirmed the interaction of TPPP with Ca2+/S100A2 by multiple independent methods, including the protein array method, S100A2 overlay, and pulldown assay in vitro and in transfected COS-7 cells. Based on the results from the S100A2 overlay assay using various GST-TPPP mutants, the S100A2-binding region was identified in the C-terminal (residues 111-160) of the central core domain of a monomeric form of TPPP that is involved in TPPP dimerization. Chemical cross-linking experiments indicated that S100A2 suppresses dimer formation of His-tagged TPPP in a dosedependent and a Ca2+-dependent manner. In addition to S100A2, TPPP dimerization is disrupted by other multiple S100 proteins, including S100A6 and S100B, in a Ca2+-dependent manner but not by S100A4. This is consistent with the fact that S100A6 and S100B, but not S100A4, are capable of interacting with GST-TPPP in the presence of Ca2+. Considering these results together, TPPP was identified as a novel target for S100A2, and it is a potential binding target for other multiple S100 proteins, including S100A6 and S100B. Direct binding of the S100 proteins with TPPP may cause disassembly of TPPP dimer formation in response to the increasing concentration of intracellular Ca2+, thus resulting in the regulation of the physiological function of TPPP, such as microtubule organization. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2218-273X 11 4 2021 Identification and Biochemical Characterization of High Mobility Group Protein 20A as a Novel Ca2+/S100A6 Target 510 EN Maho Yamamoto Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Rina Kondo Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Haruka Hozumi Department of Applied Chemistry and Biotechnology, Faculty of Engineering, Okayama University Seita Doi Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Miwako Denda Cell Free Sciences Co., Ltd. Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ryo Morishita Cell Free Sciences Co., Ltd. Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University During screening of protein-protein interactions, using human protein arrays carrying 19,676 recombinant glutathione s-transferase (GST)-fused human proteins, we identified the high-mobility protein group 20A (HMG20A) as a novel S100A6 binding partner. We confirmed the Ca2+-dependent interaction of HMG20A with S100A6 by the protein array method, biotinylated S100A6 overlay, and GST-pulldown assay in vitro and in transfected COS-7 cells. Co-immunoprecipitation of S100A6 with HMG20A from HeLa cells in a Ca2+-dependent manner revealed the physiological relevance of the S100A6/HMG20A interaction. In addition, HMG20A has the ability to interact with S100A1, S100A2, and S100B in a Ca2+-dependent manner, but not with S100A4, A11, A12, and calmodulin. S100A6 binding experiments using various HMG20A mutants revealed that Ca2+/S100A6 interacts with the C-terminal region (residues 311-342) of HMG20A with stoichiometric binding (HMG20A:S100A6 dimer = 1:1). This was confirmed by the fact that a GST-HMG20A mutant lacking the S100A6 binding region (residues 311-347, HMG20A-Delta C) failed to interact with endogenous S100A6 in transfected COS-7 cells, unlike wild-type HMG20A. Taken together, these results identify, for the first time, HMG20A as a target of Ca2+/S100 proteins, and may suggest a novel linkage between Ca2+/S100 protein signaling and HMG20A function, including in the regulation of neural differentiation. No potential conflict of interest relevant to this article was reported.

Academic Press Acta Medica Okayama 0006-291X 525 1 2020 Phosphorylation and dephosphorylation of Ca2+/calmodulin-dependent protein kinase kinase β at Thr144 in HeLa cells 251 257 EN Shota Takabatake Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Yusei Fukumoto Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroshi Tokumitsu pplied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ) acts as a regulatory kinase that phosphorylates and activates multiple downstream kinases including CaMKI, CaMKIV, 5′AMP-activated protein kinase (AMPK) and protein kinase B (PKB), resulting in regulation of wide variety of Ca2+-dependent physiological responses under normal and pathological conditions. CaMKKβ is regulated by Ca2+/calmodulin-binding, autophosphorylation, and transphosphorylation by multiple protein kinases including cAMP-dependent protein kinase (PKA). In this report, we found that phosphorylation of CaMKKβ is dynamically regulated by protein phosphatase/kinase system in HeLa cells. Global phosphoproteomic analysis revealed the constitutive phosphorylation at 8 Ser residues including Ser128, 132, and 136 in the N-terminal regulatory domain of rat CaMKKβ in unstimulated HeLa cells as well as inducible phosphorylation of Thr144 in the cells treated with a phosphatase inhibitor, okadaic acid (OA). Thr144 phosphorylation in CaMKKβ has shown to be rapidly induced by OA treatment in a time- and dose-dependent manner in transfected HeLa cells, indicating that Thr144 in CaMKKβ is maintained unphosphorylated state by protein phosphatase(s). We confirmed that in vitro dephosphorylation of pThr144 in CaMKKβ by protein phosphatase 2A and 1. We also found that the pharmacological inhibition of protein phosphatase(s) significantly induces CaMKKβ-phosphorylating activity (at Thr144) in HeLa cell lysates as well as in intact cells; however, it was unlikely that this activity was catalyzed by previously identified Thr144-kinases, such as AMPK and PKA. Taken together, these results suggest that the phosphorylation and dephosphorylation of Thr144 in CaMKKβ is dynamically regulated by multiple kinases/phosphatases signaling resulting in fine-tuning of the enzymatic property. No potential conflict of interest relevant to this article was reported.

Elsevier Science Acta Medica Okayama 0304-4165 1863 4 2019 Regulation of Ca2+/calmodulin-dependent protein kinase kinase beta by cAMP signaling 672 680 EN Shota Takabatake Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Satomi Ohtsuka Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Takeyuki Sugawara Department of Anatomy, Kitasato University School of Medicine Naoya Hatano Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Naoki Kanayama Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Masaki Magari Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University Hiroyuki Sakagami Department of Anatomy, Kitasato University School of Medicine Hiroshi Tokumitsu Applied Cell Biology, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University BACKGROUND: Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) is a pivotal activator of CaMKI, CaMKIV and 5'-AMP-activated protein kinase (AMPK), controlling Ca2+-dependent intracellular signaling including various neuronal, metabolic and pathophysiological responses. Recently, we demonstrated that CaMKKβ is feedback phosphorylated at Thr144 by the downstream AMPK, resulting in the conversion of CaMKKβ into Ca2+/CaM-dependent enzyme. However, the regulatory phosphorylation of CaMKKβ at Thr144 in intact cells and in vivo remains unclear. METHODS: Anti-phosphoThr144 antibody was used to characterize the site-specific phosphorylation of CaMKKβ in immunoprecipitated samples from mouse cerebellum and in transfected mammalian cells that were treated with various agonists and protein kinase inhibitors. CaMKK activity assay and LC-MS/MS analysis were used for biochemical characterization of phosphorylated CaMKKβ. RESULTS: Our data suggest that the phosphorylation of Thr144 in CaMKKβ is rapidly induced by cAMP/cAMP-dependent protein kinase (PKA) signaling in CaMKKβ-transfected HeLa cells, that is physiologically relevant in mouse cerebellum. We confirmed that the catalytic subunit of PKA was capable of directly phosphorylating CaMKKβ at Thr144 in vitro and in transfected cells. In addition, the basal phosphorylation of CaMKKβ at Thr144 in transfected HeLa cells was suppressed by AMPK inhibitor (compound C). PKA-catalyzed phosphorylation reduced the autonomous activity of CaMKKβ in vitro without significant effect on the Ca2+/CaM-dependent activity, resulting in the conversion of CaMKKβ into Ca2+/CaM-dependent enzyme. CONCLUSION: cAMP/PKA signaling may confer Ca2+-dependency to the CaMKKβ-mediated signaling pathway through direct phosphorylation of Thr144 in intact cells. GENERAL SIGNIFICANCE: Our results suggest a novel cross-talk between cAMP/PKA and Ca2+/CaM/CaMKKβ signaling through regulatory phosphorylation. No potential conflict of interest relevant to this article was reported.