Biomedical subjects

Masaaki Tokuda

Publications and source records attributed to Masaaki Tokuda.

29 records · Page 2Linked to original sources

PubMed2003

Post-synaptic density-95 promotes calcium/calmodulin-dependent protein kinase II-mediated Ser847 phosphorylation of neuronal nitric oxide synthase.

Post-synaptic density-95 (PSD-95) is a neuronal scaffolding protein that associates with N -methyl-D-aspartate (NMDA) receptors and links them to intracellular signalling molecules. In neurons, neuronal nitric oxide synthase (nNOS) binds selectively to the second PDZ domain (PDZ2) of PSD-95, thereby exhibiting physiological activation triggered via NMDA receptors. We have demonstrated previously that Ca(2+)/calmodulin-dependent protein kinase IIalpha (CaM-K IIalpha) directly phosphorylates nNOS at residue Ser(847), and can attenuate the catalytic activity of the enzyme in neuronal cells [Komeima, Hayashi, Naito and Watanabe (2000) J. Biol. Chem. 275, 28139-28143]. In the present study, we examined how CaM-K II participates in the phosphorylation by analysing the functional interaction between nNOS and PSD-95 in cells. The results showed that PSD-95 directly promotes the nNOS phosphorylation at Ser(847) induced by endogenous CaM-K II. In transfected cells, this effect of PSD-95 required its dual palmitoylation and the PDZ2 domain, but did not rely on its guanylate kinase domain. CaM-K Ialpha and CaM-K IV failed to phosphorylate nNOS at Ser(847) in transfected cells. Thus PSD-95 mediates cellular trafficking of nNOS, and may be required for the efficient phosphorylation of nNOS at Ser(847) by CaM-K II in neuronal cells.

Animals↗

PubMed2003

A novel inhibitory effect of D-allose on production of reactive oxygen species from neutrophils.

The rare sugar D-allose produced from D-psicose using an immobilized L-rhamnose isomerase bioreactor was shown to have weak scavenging activity toward reactive oxygen species (ROS) and potent inhibitory effect on production of ROS from stimulated neutrophils. These findings may have important implications in understanding the ameliorative effect of D-allose in transplantation and ischemia/reperfusion injury.

Journal Article↗

PubMed2002

Role of oxidative stress in germ cell apoptosis induced by di(2-ethylhexyl)phthalate.

Phthalate esters have been used extensively as plasticizers of synthetic polymers. Recent studies have revealed that these esters induce atrophy of the testis, although its pathogenesis remains unknown. The present study describes the possible involvement of oxidative stress in the pathogenesis of atrophy of the rat testis induced by di(2-ethylhexyl)phthalate (DEHP). Biochemical and immunohistochemical analysis revealed that oral administration of DEHP increased the generation of reactive oxygen species, with concomitant decrease in the concentration of glutathione and ascorbic acid in the testis, and selectively induced apoptosis of spermatocytes, thereby causing atrophy of this organ. Oxidative stress was selectively induced in germ cells, but not in Sertoli cells, treated with mono(2-ethylhexyl)phthalate (MEHP), a hydrolysed metabolite of DEHP. Furthermore, MEHP selectively induced the release of cytochrome c from mitochondria of the testis. These results indicate that oxidative stress elicited by MEHP principally injured mitochondrial function and induced the release of cytochrome c, thereby inducing apoptosis of spermatocytes and causing atrophy of the testis.

Animals↗

PubMed2002

Clinical relevance of cyclin B1 overexpression in laryngeal squamous cell carcinoma.

Cyclin B1 is a key molecule for G2/M phase transition during the cell cycle and is overexpressed in various human tumors. However, the expression status of cyclin B1 in laryngeal squamous cell carcinoma (LSCC) and its clinical significance remain unknown. We used immunohistochemical studies to examine the expression of cyclin B1 in 102 patients with LSCC. The results showed that cyclin B1 overexpression was observed in 40 cases (39.2%) of LSCCs and was significantly correlated with the tumor site (P=0.031), tumor size (P<0.0001), and advanced stage (P=0.003). In addition, cyclin B1 overexpression was associated with patients' overall survival, but not with disease-free survival using Kaplan-Meier analysis. On multivariate analysis, cyclin B1 expression was not recognized as an independent prognostic factor. These findings indicate that cyclin B1 overexpression may be associated with the malignant biological behavior of LSCC.

Carcinoma, Squamous Cell↗

PubMed2002

Phosphorylation of neuronal nitric oxide synthase at Ser847 by CaM-KII in the hippocampus of rat brain after transient forebrain ischemia.

The authors previously demonstrated that Ca2+/calmodulin (CaM)-dependent protein kinase IIalpha (CaM-KIIalpha) can phosphorylate neuronal nitric oxide synthase (nNOS) at Ser847 and attenuate NOS activity in neuronal cells. In the present study, they established that forebrain ischemia causes an increase in the phosphorylation of nNOS at Ser847 in the hippocampus. This nNOS phosphorylation appeared to be catalyzed by CaM-KII: (1) it correlated with the autophosphorylation of CaM-KIIalpha; (2) it was blocked by the CaM-KII inhibitor, KN-93; and (3) nNOS and CaM-KIIalpha were found to coexist in the hippocampus. Examination of the spatial relation between nNOS and CaM-KIIalpha in the brain revealed coexistence in the hippocampus but not in the cortex during reperfusion, with a concomitant increase in autophosphorylation of CaM-KIIalpha. The phosphorylation of nNOS at Ser847 probably takes place in nonpyramidal hippocampal neurons, which increased after 30 minutes of reperfusion in the hippocampus, whereas no significant increase was detected in the cortex. An intraventricular injection of KN-93 significantly decreased the phosphorylation of nNOS in the hippocampus. These results point to CaM-KII as a protein kinase, which by its colocalization may attenuate the activity of nNOS through its Ser847 phosphorylation, and may thus contribute to promotion of tolerance to postischemic damage in hippocampal neurons.

Animals↗

PubMed2002

Survivin expression and its correlation with cell proliferation and prognosis in epithelial ovarian tumors.

Survivin is a new member of the inhibitors of apoptosis proteins (IAP) family, selectively overexpressed in common human cancers but not in normal adult tissues, and associated with aggressiveness of the disease and unfavorable outcomes. Recent study also found that survivin expression is associated with cell proliferation. In order to gain insight into the role of survivin in ovarian tumors, we investigated the expression of survivin in a group of epithelial ovarian tumors, and examined the relationship of its expression with cell proliferation and clinical outcome. Immunohistochemical analysis was performed in 103 cases of epithelial ovarian tumors. Twenty-six of the 103 cases were evaluated by Western blot analysis. The results showed that survivin overexpression was detected in 21.2% (7 of 33) of benign tumors, 47.8% (11 of 23) of borderline tumors, and 51.1% (24 of 47) of ovarian carcinomas. The positive ratio was significantly higher in malignant or borderline tumors than in benign tumors, and the overexpression of survivin was significantly correlated with the size of residual disease. A positive correlation between survivin expression and proliferative activity of tumor cell measured by PCNA index was found. Kaplan-Meier analysis demonstrated that the patients with survivin overexpression have a short overall survival. These findings suggest that survivin overexpression may play a pivotal role in the progression of ovarian tumors and may provide an important prognostic implication for epithelial ovarian carcinomas.

Adenocarcinoma, Clear Cell↗

PubMedDate not supplied

Aberrant expression of cyclin A in laryngeal squamous cell carcinoma.

The expression of cyclin A protein was retrospectively investigated in 102 patients with human laryngeal squamous cell carcinoma (LSCC) by using immunohistochemistry. Out of 102 tumors, 41 (40.2%) exhibited positive-staining in cancer cells with this antibody. No association between cyclin A overexpression and the patients' clinicopathological parameters was found. However, cyclin A overexpression was significantly associated with CDK2 and PCNA expression (p = 0.01 and p = 0.001, respectively). Kaplan-Meier analysis showed that patients with overexpression of cyclin A were associated with poor disease-free survival (p = 0.046), but it was not associated with overall survival (p = 0.106). Additionally, patients with both lymph node metastasis and cyclin A overexpression were significantly associated with worse disease-free survival (p < 0.0001). The multivariate analysis showed that tumor size, lymph node metastasis and cyclin A overexpression are significantly independent prognostic factors of disease-free survival. These findings suggest that cyclin A overexpression is associated with recurrence of LSCC.

Adult↗

PubMedDate not supplied

Survivin expression in laryngeal squamous cell carcinomas and its prognostic implications.

We examined the expression of survivin using immunohistochemistry in 102 cases of laryngeal squamous cell carcinoma (LSCC). Overall, 65.7% (67 out of 102) of tumors were positive for survivin expression and significantly associated with tumor site, poor differentiation, tumor size, lymph node metastasis and advanced stage. Kaplan-Meier analysis showed that survivin expression was significantly associated with shorter disease-free and overall survival respectively. When survivin expression and clinical stage were combined, patients with both survivin-positive and advanced stage (III, IV) revealed poorer disease-free and overall survival when compared with the other cases (p = 0.0002 and p = 0.0002, respectively). Additionally, in early stage (I, II) cases, survivin expression also showed a significant prognostic trend for disease-free and overall survival (p = 0.0727 and p = 0.0701, respectively). By the multivariate analysis, tumor size, lymph node metastasis and survivin expression were independent prognostic factors both in disease-free and overall survival. These findings indicate that survivin expression is associated with unfavorable clinicopathological parameters and represents an independent marker for prognosis of LSCC.

Adult↗

PubMedDate not supplied

Expression of p57kip2 and its clinical relevance in epithelial ovarian tumors.

BACKGROUND: The aim of this study was to elucidate the expression of p57kip2 in a series of benign, borderline and malignant ovarian tumors, to evaluate its relationship with other G1 regulators of the cell cycle and to determine whether p57kip2 expression is associated with progression and prognosis of epithelial ovarian tumors. MATERIALS AND METHODS: Immunohistochemical analysis was performed in 103 cases of epithelial ovarian tumors. Twenty-six of the 103 cases were evaluated by Western blot analysis. RESULTS: The study demonstrated that high p57kip2 expression was detected in 63.6% (21 out of 33) of benign tumors, 52.2% (12 out of 23) of borderline tumors and 40.4% (19 out of 47) of ovarian carcinomas. The positive ratio of p57kip2 expression was decreased from benign to borderline to malignant tumors, whilst statistical significance was observed between benign and malignant tumors. Low p57kip2 expression was significantly associated with high tumor grades, advanced clinical stages and cyclin E overexpression. Kaplan-Meier analysis demonstrated that the patients with low p57kip2 expression had a short overall survival. When the combined phenotype of p57kip2 and p27kip1 was analyzed, the patients with both p57kip2 and p27kip1 low expression had a lower overall survival rate. CONCLUSION: These findings suggest that decreased p57kip2 expression may play a pivotal role in the progression of ovarian tumors and provide an important prognostic implication for epithelial ovarian carcinomas.

Blotting, Western↗

PubMedDate not supplied

S-phase kinase-associated protein 2 expression in laryngeal squamous cell carcinomas and its prognostic implications.

The F-box protein S-phase kinase-associated protein 2 (Skp2) positively regulates the G1-S transition by controlling the stability of several G1 regulators, such as the cell cycle inhibitor p27kip1. However, the clinical significance of Skp2 in patients with laryngeal squamous cell carcinoma (LSCC) remains unknown. In this study, a potential distribution of Skp2 in LSCC and its clinical implications was investigated by an immunohistochemical study. Overall, Skp2 overexpression was observed in 36.7% (37 of 102) patients and was significantly associated with lymph node metastasis (p=0.002) and was inversely associated with p27kip1 expression (p=0.026). Survival analysis using the Kaplan-Meier method showed that Skp2 overexpression was significantly associated with shorter disease-free and overall survival (p=0.0051 and p=0.0002, respectively). When Skp2 expression and p27kip1 expression were combined, patients with both Skp2 overexpression and reduced expression of p27kip1 revealed poorest disease-free and overall survival as compared to the other cases (p=0.0017 and p<0.0001, respectively). Additionally, in early stage (I, II) cases, Skp2 expression was also revealed to possess a significant prognostic factor in overall survival (p=0.0234), but not in disease-free survival (p=0.2055). By multivariate analysis using the Cox proportional hazards model, tumor grade, tumor size, clinical stage and Skp2 expression were independent prognostic factors both in disease-free and overall survival. These findings indicated that Skp2 expression was closely associated with tumor progression and represented an independent marker for prognosis of LSCC.

Carcinoma, Squamous Cell↗

PubMedDate not supplied

Growth inhibitory effect of D-allose on human ovarian carcinoma cells in vitro.

BACKGROUND: D-allose is a rare sugar found in nature and, because of its very limited amount and of the high cost associated with its synthesis, its physiological functions remain virtually unknown. The aim of the current study was to investigate the effect of D-allose on the proliferation of human ovarian carcinoma cells in vitro. MATERIALS AND METHODS: Human ovarian carcinoma cells (OVCAR-3 cell line) were exposed to rare sugars including D-allose, D-altrose, D-psicose and D-talitol. Cell growth was evaluated by MTT assay. Cell cycle analysis was carried out by flow cytometric assay. The expression of cell cycle regulatory proteins was determined by Western blot analysis. TUNEL assay was employed for the detection of apoptotic cells. RESULTS: D-allose had a significant inhibitory effect on ovarian cancer cell proliferation in a dose-dependent manner, and caused a moderate G2/M arrest in the cell cycle, up-regulation of Cdk inhibitors p21 and p27 levels, and the induction of apoptosis in OVCAR-3 cells. CONCLUSION: Our results show, for the first time, that D-allose inhibits the growth of ovarian carcinoma cells in vitro. Although the exact mechanisms remain unclear, these findings suggest that D-allose possesses a novel inhibitory property on ovarian carcinoma cell proliferation, and may represent a new class of compounds with possible therapeutic potential.

Adenocarcinoma↗