Yumi Tohyama
Himeji Dokkyo University
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Publication
Featured researches published by Yumi Tohyama.
Journal of Biological Chemistry | 2013
Patrick Ejlerskov; Izabela Rasmussen; Troels Tolstrup Nielsen; Ann-Louise Bergström; Yumi Tohyama; Poul Henning Jensen; Frederik Vilhardt
Background: The mechanism of unconventional secretion of α-synuclein is unknown. Results: Autophagy of α-synuclein followed by exocytosis of autophagy intermediates (exophagy) are increased by expression of TPPP/p25α. Conclusion: Exophagy of α-synuclein is increased by lysosomal dysfunction and/or altered trafficking of autophagosomes. Significance: Exophagy of α-synuclein might represent the first step in inter-neuronal spread of Lewy body disease. Aggregation of α-synuclein can be promoted by the tubulin polymerization-promoting protein/p25α, which we have used here as a tool to study the role of autophagy in the clearance of α-synuclein. In NGF-differentiated PC12 catecholaminergic nerve cells, we show that de novo expressed p25α co-localizes with α-synuclein and causes its aggregation and distribution into autophagosomes. However, p25α also lowered the mobility of autophagosomes and hindered the final maturation of autophagosomes by preventing their fusion with lysosomes for the final degradation of α-synuclein. Instead, p25α caused a 4-fold increase in the basal level of α-synuclein secreted into the medium. Secretion was strictly dependent on autophagy and could be up-regulated (trehalose and Rab1A) or down-regulated (3-methyladenine and ATG5 shRNA) by enhancers or inhibitors of autophagy or by modulating minus-end-directed (HDAC6 shRNA) or plus-end-directed (Rab8) trafficking of autophagosomes along microtubules. Finally, we show in the absence of tubulin polymerization-promoting protein/p25α that α-synuclein release was modulated by dominant mutants of Rab27A, known to regulate exocytosis of late endosomal (and amphisomal) elements, and that both lysosomal fusion block and secretion of α-synuclein could be replicated by knockdown of the p25α target, HDAC6, the predominant cytosolic deacetylase in neurons. Our data indicate that unconventional secretion of α-synuclein can be mediated through exophagy and that factors, which increase the pool of autophagosomes/amphisomes (e.g. lysosomal disturbance) or alter the polarity of vesicular transport of autophagosomes on microtubules, can result in an increased release of α-synuclein monomer and aggregates to the surroundings.
Journal of Biochemistry | 2009
Yumi Tohyama; Hirohei Yamamura
Spleen tyrosine kinase (Syk) is a non-receptor protein tyrosine kinase expressed in a wide range of haematopoietic cells. At the initial stage of investigation, main exploring was toward its functions in platelets and in classical immunoreceptor signalling. However, Syk has now been recognized as a key player in both innate and adaptive immunity. Especially, in phagocytosis, Syk plays essential roles in signalling evoked by various types of receptors such as FcgammaR, CR3, Dectin-1 and apoptotic cell-recognizing receptor. A variety of upstream immunoreceptor tyrosine-based activation motif-like molecules have been found and are still in the course of new studies. On the contrary, downstream effectors to explain diverse function of Syk are still under exploration. As its novel function, we propose the role of Syk in the regulation of alpha-tubulin acetylation. Further investigation on the effectors of Syk would give us more information in relation to therapeutic molecular targets.
Journal of Biological Chemistry | 2006
Rina Kurihara; Yumi Tohyama; Satoshi Matsusaka; Hiromu Naruse; Emi Kinoshita; Takayuki Tsujioka; Yoshinao Katsumata; Hirohei Yamamura
The possible role of the peripheral cannabinoid receptor (CB2) in neutrophil migration was investigated by using human promyelocytic HL60 cells differentiated into neutrophil-like cells and human neutrophils isolated from whole blood. Cell surface expression of CB2 on HL60 cells, on neutrophil-like HL60 cells, and on human neutrophils was confirmed by flow cytometry. Upon stimulation with either of the CB2 ligands JWH015 and 2-arachidonoylglycerol (2-AG), neutrophil-like HL60 cells rapidly extended and retracted one or more pseudopods containing F-actin in different directions instead of developing front/rear polarity typically exhibited by migrating leukocytes. Activity of the Rho-GTPase RhoA decreased in response to CB2 stimulation, whereas Rac1, Rac2, and Cdc42 activity increased. Moreover, treatment of cells with RhoA-dependent protein kinase (p160-ROCK) inhibitor Y27632 yielded cytoskeletal organization similar to that of CB2-stimulated cells. In human neutrophils, neither JWH015 nor 2-AG induced motility or morphologic alterations. However, pretreatment of neutrophils with these ligands disrupted N-formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLP)-induced front/rear polarization and migration and also substantially suppressed fMLP-induced RhoA activity. These results suggest that CB2 might play a role in regulating excessive inflammatory response by controlling RhoA activation, thereby suppressing neutrophil migration.
Annals of Human Genetics | 2013
Dian Kesumapramudya Nurputra; Poh San Lai; Nur Imma Fatimah Harahap; Satoru Morikawa; Tomoto Yamamoto; Noriyuki Nishimura; Yuji Kubo; Atsuko Takeuchi; Toshio Saito; Yasuhiro Takeshima; Yumi Tohyama; Stacey K.H. Tay; Poh Sim Low; Kayoko Saito; Hisahide Nishio
Spinal muscular atrophy (SMA) is a common neuromuscular disorder with autosomal recessive inheritance, resulting in the degeneration of motor neurons. The incidence of the disease has been estimated at 1 in 6000–10,000 newborns with a carrier frequency of 1 in 40–60. SMA is caused by mutations of the SMN1 gene, located on chromosome 5q13. The gene product, survival motor neuron (SMN) plays critical roles in a variety of cellular activities. SMN2, a homologue of SMN1, is retained in all SMA patients and generates low levels of SMN, but does not compensate for the mutated SMN1. Genetic analysis demonstrates the presence of homozygous deletion of SMN1 in most patients, and allows screening of heterozygous carriers in affected families. Considering high incidence of carrier frequency in SMA, population‐wide newborn and carrier screening has been proposed. Although no effective treatment is currently available, some treatment strategies have already been developed based on the molecular pathophysiology of this disease. Current treatment strategies can be classified into three major groups: SMN2‐targeting, SMN1‐introduction, and non‐SMN targeting. Here, we provide a comprehensive and up‐to‐date review integrating advances in molecular pathophysiology and diagnostic testing with therapeutic developments for this disease including promising candidates from recent clinical trials.
Leukemia | 2010
Akihito Matsuoka; A Tochigi; Mitsuyo Kishimoto; T Nakahara; Toshinori Kondo; Takayuki Tsujioka; Taizo Tasaka; Yumi Tohyama; Kaoru Tohyama
Myelodysplastic syndromes (MDS) are a group of hematopoietic stem cell disorders characterized by refractory cytopenias and susceptibility to leukemic transformation. On a subset of MDS patients with deletion of the long arm of chromosome5 (del(5q)), lenalidomide exerts hematological and cytogenetic effects, but the underlying pharmacological mechanisms are not fully understood. In this study, we have investigated the in vitro effects of lenalidomide on an MDS-derived cell line, MDS-L, which carries del(5q) and complex chromosome abnormalities. We found that the growth of MDS-L cells was specifically suppressed mainly by apoptosis, and in addition, multinucleated cells were frequently formed and finally died out in the presence of lenalidomide. Time-lapse microscopic observation and the DNA ploidy analysis revealed that lenalidomide does not affect DNA synthesis but inhibits cytokinesis of MDS-L cells. The gene expression profile showed decreased expression of M phase-related genes such as non-muscle myosin heavy-chain 10, polo-like kinase 1, aurora kinase B, citron kinase and kinesin family member 20A(KIF20A). Interestingly, KIF20A is located at 5q31. These data contribute to the understanding of action mechanisms of lenalidomide on MDS with del(5q) and complex abnormalities.
Current Pharmaceutical Design | 2004
Yumi Tohyama; Tomoko Takano; Hirohei Yamamura
B-lymphocytes are exposed to a reduction/oxidation environment during activation or inflammatory process, and the antioxidant systems are functional to protect themselves against harmful reactive oxygen species (ROS). The crucial roles of thioredoxin-2 (Trx-2) and a DNA repair enzyme APE/Ref-1 in mitochondria are reported in B-lymphocytes. Furthermore, ROS stimulate different signaling pathways in many cellular responses. Their effects often cause some diseases or are utilized for the treatment of other diseases. For example, the cells derived from Fanconi anemia (FA) patients are intolerant of oxidative stress and the therapeutic effect of anti-CD20 monoclonal antibody rituximab on B cell lymphoproliferative disorders is due to the generation of ROS. To clarify the oxidative stress-induced signaling pathways, we stimulated a B cell line with various concentrations of H(2)O(2). As a result, a protein tyrosine kinase, Syk was involved in the induction of G2/M arrest and protection of cells from apoptosis. Syk might inhibit the activation of caspase-9 through Akt thereby protecting cells from oxidative stress-induced apoptosis. On the other hand, Syk-dependent PLC-gamma2 activation was required for acceleration towards apoptosis following oxidative stress. These findings suggest that oxidative stress-induced Syk activation triggers the activation of different pathways, such as pro-apoptotic or survival pathways, and that the balance of these pathways is a key factor in determining the fate of the cells exposed to oxidative stress. In contrast, the stimulation with the millimolar concentrations of H(2)O(2) rapidly led to necrosis in which tyrosine phosphorylation of FAK was involved at the downstream of Lyn and Syk.
Genes to Cells | 2004
Jinsong He; Yumi Tohyama; Ken Yamamoto; Masahiko Kobayashi; Yuhong Shi; Tomoko Takano; Kaoru Tohyama; Hirohei Yamamura
To investigate the mechanism of B cell receptor (BCR)‐mediated apoptosis, we utilized immature B cell lines, DT40 and WEHI‐231. In both cell lines, BCR‐crosslinking caused the increase in lysosomal pH with early apoptotic changes characterized by chromatin condensation and phosphatidylserine exposure. This increase was detected in c‐Abl‐deficient DT40 cells but not in Syk‐deficient cells, which corresponded to the fact that the former cells but not the latter revealed BCR‐induced apoptosis. In contrast, BCR‐crosslinking caused no apparent change in mitochondrial transmembrane potential. Therefore, the lysosomal change might be a primary event in BCR‐induced apoptosis in DT40 cells. The increased activity of cathepsin B and apoptosis‐preventing effect of a cathepsin inhibitor suggested a significant role of lysosomal enzymes in this apoptosis. By microscopic studies, lysosomes of wild‐type DT40 cells fused to BCR‐carrying endosomes became enlarged and accumulated one another. In contrast, these changes of lysosomal dynamics did not occur in Syk‐deficient cells but transfer of wild‐type Syk restored the lysosomal changes and apoptosis. These results demonstrated that the lysosomal change accompanied with the activation of lysosomal enzymes is a primary step in BCR‐crosslinking‐mediated apoptosis and Syk is responsible for this step through the fusion of BCR‐carrying endosomes to lysosomes.
Journal of Biological Chemistry | 2010
Taketoshi Kajimoto; Seishiro Sawamura; Yumi Tohyama; Yasuo Mori; Alexandra C. Newton
Conventional and novel protein kinase C (PKC) isozymes transduce the abundance of signals mediated by phospholipid hydrolysis; however redundancy in regulatory mechanisms confounds dissecting the unique signaling properties of each of the eight isozymes constituting these two subgroups. Previously, we created a genetically encoded reporter (C kinase activity reporter (CKAR)) to visualize the rate, amplitude, and duration of agonist-evoked PKC signaling at specific locations within the cell. Here we designed a reporter, δCKAR, that specifically measures the activation signature of one PKC isozyme, PKC δ, in cells, revealing unique spatial and regulatory properties of this isozyme. Specifically, we show two mechanisms of activation: 1) agonist-stimulated activation at the plasma membrane (the site of most robust PKC δ signaling), Golgi, and mitochondria that is independent of Src and can be triggered by phorbol esters and 2) agonist-stimulated activation in the nucleus that requires Src kinase activation and cannot be triggered by phorbol esters. Translocation studies reveal that the G-protein-coupled receptor agonist UTP induces the translocation of PKC δ into the nucleus by a mechanism that depends on the C2 domain and requires Src kinase activity. However, translocation from the cytosol into the nucleus is not required for the Src-dependent regulation of nuclear activity; a construct of PKC δ prelocalized to the nucleus continues to be activated by UTP by a mechanism dependent on Src kinase activity. These data identify the nucleus as a signaling hub for PKC δ that is driven by receptor-mediated signaling pathways (but not phorbol esters) and differs from signaling at plasma membrane and Golgi in that it is controlled by Src family kinases.
Iubmb Life | 2006
Yumi Tohyama; Hirohei Yamamura
Phagocytosis is a central event in the innate immune responses that are triggered by the association between ligands on the surface of pathogens and receptors on the membrane of phagocytes. Particularly, complement‐mediated phagocytosis is accomplished by specific recognition of bound complement components by the corresponding complement receptors on the phagocytes. The protein‐tyrosine kinase, Syk, plays a central role in Fcγ receptor‐mediated phagocytosis in the adaptive immune system. From recent studies using a macrophage‐like differentiated cell line and serum‐treated zymosan, it was found that Syk also plays an essential role in complement‐mediated phagocytosis in innate immunity. Serum‐treated zymosan particles promptly attached to the cells and were subsequently engulfed via complement receptor3. During this process, Syk became tyrosine‐phosphorylated and accumulated around the nascent phagosomes. The transfer of Syk‐siRNA or dominant‐negative Syk (DN‐Syk) into macrophages resulted in impaired engulfment of pathogen. Collectively, Syk is required for the engulfment of pathogen in complement‐mediated phagocytosis. iubmb Life, 58: 304‐308, 2006
Molecular and Cellular Biology | 2004
S. M. Shahjahan Miah; Kiyonao Sada; P. T. Tuazon; K. Maeno; S. Kyo; Xiujuan Qu; Yumi Tohyama; J. A. Traugh; Hirohei Yamamura
ABSTRACT The p21-activated serine/threonine protein kinase Pak2/γ-PAK and the nonreceptor type of protein tyrosine kinase Syk are known to be activated when the cells are exposed to osmotic stress. The purpose of the present study was to examine whether Pak2 and Syk functionally cooperate in cellular signaling. Cotransfection studies revealed that Pak2 associates with Syk in COS cells. The constitutively active form of Cdc42 increases the association of Pak2 with Syk. Pak2 coexpressed with an inactive form of Cdc42 or kinase-inactive Pak2 interacts to a lesser extent with Syk, suggesting that Pak2-Syk association is enhanced by Pak2 activation. Interaction with Pak2 enhances the intrinsic kinase activity of Syk. This is supported by in vitro studies showing that Pak2 phosphorylates and activates Syk. Treatment of cells with sorbitol to induce hyperosmolarity results in the translocation of Pak2 and Syk to the region surrounding the nucleus and in dramatic enhancement of their association. Furthermore, cotransfection of Pak2 and Syk leads to the activation of c-Jun N-terminal kinase (JNK) under hyperosmotic conditions. Pak2 short interfering RNA suppresses sorbitol-mediated activation of endogenous Syk and JNK, thus identifying a novel pathway for JNK activation by Cdc42. These results demonstrate that Pak2 and Syk positively cooperate to regulate cellular responses to stress.