Biomedical subjects

N Shiina

Publications and source records attributed to N Shiina.

12 recordsLinked to original sources

PubMed1994

Microtubule severing by elongation factor 1 alpha.

An activity that severs stable microtubules is thought to be involved in microtubule reorganization during the cell cycle. Here, a 48-kilodalton microtubule-severing protein was purified from Xenopus eggs and identified as translational elongation factor 1 alpha (EF-1 alpha). Bacterially expressed human EF-1 alpha also displayed microtubule-severing activity in vitro and, when microinjected into fibroblasts, induced rapid and transient fragmentation of cytoplasmic microtubule arrays. Thus, EF-1 alpha, an essential component of the eukaryotic translational apparatus, appears to have a second role as a regulator of cytoskeletal rearrangements.

Adenosine Triphosphate↗

PubMed1993

Microtubule nucleating activity of centrosomes in cell-free extracts from Xenopus eggs: involvement of phosphorylation and accumulation of pericentriolar material.

We have studied the regulation of microtubule nucleating activity of the centrosome using cell-free extracts from Xenopus eggs. We found that the number of microtubules per centrosome increases dramatically with time during incubation of isolated centrosomes in interphasic egg extracts prepared 20-30 minutes after electric activation of cytostatic factor (CSF)-arrested eggs. The increase in microtubule nucleation was still conspicuous even when KCl-treated centrosomes (centrosomes stripped of their microtubule nucleating activity by 1 M KCl treatment) were incubated in interphasic extracts. Electron microscopy and immunostaining by anti-gamma-tubulin and 5051 human anti-centrosome antibodies revealed that pericentriolar material (PCM) was accumulated during the increase in microtubule nucleation from centrosomes in interphasic extracts, suggesting regulation of centrosomal activity by PCM accumulation. The ability of egg extracts to activate microtubule nucleation from centrosomes was also assumed to be regulated by phosphorylation, since addition of protein kinase inhibitors into interphasic extracts totally blocked the increase in microtubule nucleation from the KCl-treated centrosome. The ability of CSF-arrested mitotic extracts to increase microtubule nucleation from KCl-treated centrosomes was 3.5- to 5-fold higher than that of interphasic extracts, while PCM accumulation in mitotic extracts seemed to be similar to that in interphasic extracts. The increase in microtubule nucleation from KCl-treated centrosomes was strikingly enhanced by the addition of purified p34cdc2/cyclin B complex to interphasic extracts, but not by MAP kinase, which is activated downstream of p34cdc2/cyclin B. These results suggest two pathways activating centrosomal activity in egg extracts: accumulation of PCM and phosphorylation mediated by p34cdc2/cyclin B.

Alkaloids↗

PubMed1992

Regulation of a major microtubule-associated protein by MPF and MAP kinase.

The interphase-M phase transition of microtubule dynamics is thought to be induced by phosphorylation reactions mediated by MPF and by MAP kinase functioning downstream of MPF. We have now identified and purified from Xenopus eggs a major microtubule-associated protein, p220, that may be a target protein for these two M phase-activated kinases. p220, when purified from interphase cells, potently bound to microtubules and stimulated tubulin polymerization, whereas p220 purified from M phase cells showed little or no such activities. Cell staining with a monoclonal anti-p220 antibody revealed that p220 is localized on cytoplasmic microtubule networks during interphase, while it is distributed rather diffusely throughout the cell during M phase. We have further found that p220 is phosphorylated specifically in M phase. Moreover, p220 purified from interphase cells served as a good substrate for MAP kinase and MPF in vitro, and two-dimensional phosphopeptide mapping pattern of the p220 phosphorylated in vitro was very similar to that of p220 phosphorylated at M phase in vivo. These results suggest that the drastic change in p220 activity during the transition from interphase to M phase may be induced by its phosphorylation in M phase probably catalyzed by MAP kinase and MPF.

Animals↗

PubMed1992

A novel homo-oligomeric protein responsible for an MPF-dependent microtubule-severing activity.

An activity that severs stable microtubules has previously been detected in M phase extracts, but not in interphase extracts, of Xenopus eggs. We show that incubation of interphase extracts with purified MPF rapidly increases the microtubule-severing activity. We then report the identification and purification of a novel protein factor responsible for this MPF-dependent microtubule-severing activity. The purified microtubule-severing factor is a homo-oligomeric protein composed of 56 kDa polypeptide subunits. These subunits appear to assemble into a pentagonal loop, forming a doughnut-shaped molecule whose overall contours resemble a flattened ball. The microtubule-severing activity of the purified factor does not require ATP or divalent cations, and is inhibited by monomeric tubulin. The purified factor is capable of binding to both monomeric tubulin and microtubules. This factor is thus a novel kind of microtubule-binding protein in both structure and function, and may play an important role in the cell cycle-dependent change in microtubule organization.

Animals↗

PubMed1991

In vitro effects on microtubule dynamics of purified Xenopus M phase-activated MAP kinase.

The protein kinase MAP kinase, also called MAP2 kinase, is a serine/threonine kinase whose activation and phosphorylation are induced by a variety of mitogens, and which is thought to have a critical role in a network of protein kinases in mitogenic signal transduction. A burst in kinase activation and protein phosphorylation may also be important in triggering the dramatic reorganization of the cell during the transition from interphase to mitosis. The interphase-metaphase transition of microtubule arrays is under the control of p34cdc2 kinase, a central control element in the G2-M transition of the cell cycle. Here we show that a Xenopus kinase, closely related to the mitogen-activated mammalian MAP kinase, is phosphorylated and activated during M phase of meiotic and mitotic cell cycles, and that the interphase-metaphase transition of microtubule arrays can be induced by the addition of purified Xenopus M phase-activated MAP kinase or mammalian mitogen-activated MAP kinase to interphase extracts in vitro.

Animals↗

PubMed1989

[Clinical study on the prognosis of complete denture wearers covering 10 years. 4. Masticatory efficiency].

The purpose of this study was to estimate masticatory efficiency of complete denture wearers. The subjects were 72 patients, treated before 5-10 years at students' clinic of Tsurumi University, School of Dental Medicine. The masticatory efficiencies with peanuts and Kamaboko were calculated. Results 1. The mean masticatory efficiency with peanuts for 63 patients was 35.8%, and with Kamaboko (steamed fishpast) for 64 patients was 94.5%, in comparison with natural dentition. 2. The mean masticatory efficiency with peanuts was 124.3%, and with Kamaboko was 99.6%, for complete denture wearers. 3. Comparing the measured value of masticatory efficiency with 5 to 10 years wearing period, there was significant difference in the masticatory efficiency between peanuts and Kamaboko. 4. There was significant difference in the masticatory efficiency with peanuts between the group needed new denture and the group not needed but there was not significant difference with Kamaboko.

Denture, Complete↗

PubMed1989

[Clinical study on the prognosis of complete denture wearers covering 10 years. 3. Fitness test of the complete denture base].

The purpose of this study was to estimate the clinical condition of complete denture wearers. 72 patients came to our Dental Hospital according to our recall. The examination consisted of a questionnaire and clinical examinations. For objective evaluation, the fitness test of lower complete denture base was taken place and was classified into four groups by the thickness of the white-silicone film (A-zone 0-30 microns, B-zone 30-70 microns, C-zone 70-130 microns, D-zone 130 microns-). Results 1. The average ratio of four groups of the white-silicone film were A-zone 9.3%, B-zone 35.8%, C-zone 24.5% and D-zone 30.4%. 2. The fitness of anterior portion was ill fit in comparison with posterior portion. 3. There was statistically significant difference between the fitness of lower complete denture and dentist's judgment diagnosed as ill fit denture. 4. There was significant difference between the fitness test and the patients who complained about loose fit of the denture.

Denture Bases↗

PubMed1988