Search PubMed⌕ Search

Biomedical subjects

R Ishikawa

Publications and source records attributed to R Ishikawa.

At least 55 records · Page 3Linked to original sources
PubMed1993

Calvasculin, as a factor affecting the microfilament assemblies in rat fibroblasts transfected by src gene.

Cell transformations accompany alterations in cell morphology and microfilament patterns. Calvasculin encodes mRNA termed pEL-98, 18A2, 42A, p9Ka, or mts1, found to be elevated in several metastatic cell lines. We report the elevation of calvasculin expression in SR-3Y1 cells, which show disappearance of ordered microfilaments, compared to that in 3Y1 cells and that the similar distribution of calvasculin to that of actin filaments. Interestingly, calvasculin co-sediments with F-actin and bundles actin filaments in a Ca(2+)-dependent manner. This activity, along with the elevation of calvasculin following transformation, suggests that the disorganization of filaments in SR-3Y1 cell is due to the cross-linking activity of calvasculin.

Actin Cytoskeleton↗
PubMed1993

IFN induction and associated changes in splenic leukocyte distribution.

Our studies were undertaken to evaluate early events associated with IFN expression and IFN-induced cellular changes in the spleen. Polyinosinic-polycytidylic acid (poly(I:C)) was used to induce IFN in C57BL/6 mice. Biologically active IFN was present in spleens and sera of poly(I:C)-treated mice as early as 3 h and peaked at 6 to 12 h posttreatment. Neutralization assays and Northern blot analyses demonstrated that IFN-beta was the form of IFN preferentially induced in the spleens. Immunohistochemical staining and in situ hybridization studies of splenic tissue sections demonstrated that, although many cells were induced to express low levels of IFN-beta, low frequency cells were particularly potent expressers of IFN-beta. Perivascular cells expressed high levels of IFN-beta. Other positive cells were localized in red pulp at early times and in white pulp at later times posttreatment. Histologic examination of splenic sections showed that the IFN production was accompanied by dramatic architectural changes. There were significant 1.4-fold increases in the proportion of white pulp area and > 50% decreases in red pulp leukocyte number. These architectural changes appeared at 6 h and lasted through 36 h after poly(I:C) treatment. They were not due to increased cell proliferation as splenic weights and cell yields were not elevated. The changes in splenic leukocyte distribution were shown to be a result of IFN induction as: 1) treatment with anti-IFN antibodies inhibited poly(I:C)-induced depletion of red pulp leukocytes, and 2) administration of purified IFN-beta induced both an increase in white pulp area and a decrease in red pulp leukocytes. Splenic leukocytes were labeled with the lipophilic fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate, to evaluate cell traffic after IFN induction. Poly(I:C) enhanced accumulation of cells in white pulp regions. In contrast to the 76 +/- 2 labeled cells that accumulated in 0.5 mm2 of white pulp area in control PBS-treated mice, 131 +/- 4 labeled cells accumulated in 0.5 mm2 of white pulp area in poly(I:C)-treated mice. The poly(I:C)-enhanced leukocyte accumulation in short term cell migration to white pulp regions was dependent on preexposure of both splenic leukocytes and recipient environments to the IFN inducer. These data demonstrate that poly(I:C) is a potent and rapid inducer of IFN-beta production by splenic cells and that IFN induces cellular redistribution in the spleen. The results suggest that margination of leukocytes into splenic white pulp may be another important immunoregulatory function of IFN.

Animals↗
PubMed1993

Does the gender difference in interferon production seen in picornavirus-infected spleen cell cultures from ICR Swiss mice have any in vivo significance?

Splenocyte cultures from female ICR Swiss mice produced greater interferon (IFN) levels, particularly IFN-gamma, than did cultures from males by 12 h post-infection (pi) with the D variant of encephalomyocarditis virus (EMCV-D). This early IFN-gamma is produced by natural killer (NK)-like cells and is dependent on plastic adherent cells and IFN-alpha/beta. In this study, we evaluated the significance of this observation on the innate resistance of ICR Swiss females to EMCV-D-mediated disease. Treatment of females with rabbit anti-mouse IFN-alpha/beta serum rendered them susceptible to the diabetogenicity of EMCV-D. Although sera from both sexes of ICR Swiss mice exhibited peak IFN levels day 3 pi, IFN-gamma was present in the sera of males at only 1 day pi and in the sera of females at days 1-3 pi. Females cleared virus from the circulation by day 2 pi, 1 day earlier than did males. Flow cytometric evaluations of lymphoid cell phenotypes in spleens and pancreata of infected mice revealed that percentages of L3T4+ cells were significantly decreased only in spleens from males at day 1 pi and were diminished along with Ly2+ cells in pancreata of males at 7 days pi, suggesting that T-cell responses were impaired in virus-infected males.

Animals↗
PubMed1993

Stimulatory effect of calponin on myosin ATPase activity.

Calponin, a calmodulin-binding protein of smooth muscle that inhibits the actin-myosin interaction by binding to actin, was shown to bind to myosin and to stimulate the ATPase activity of myosin to some extent. Actin abolished this myosin-linked, stimulatory effect of calponin. Ca(2+)-calmodulin affected neither the myosin-binding activity nor the stimulatory effect of calponin. We further presented a few data which suggest that calponin may exert regulatory activity toward myosin in quite a different way from caldesmon, another smooth muscle protein that binds to myosin, actin, and calmodulin.

Animals↗
PubMed1993

Role of myosin in the stimulatory effect of caldesmon on the interaction between actin, myosin, and ATP.

We have previously shown that caldesmon at low concentrations stimulates the interaction between actin, myosin, and ATP, while at high concentrations it inhibits the interaction [Ishikawa, R., Okagaki, T., Higashi-Fujime, S., & Kohama, K. (1991) J. Biol. Chem. 266, 21784-21790]. When the effect of caldesmon at low concentrations was monitored by measuring myosin ATPase activity in the absence of actin, the effect was slightly but significantly stimulatory; and at higher concentrations no inhibitory effect was observed. Therefore, we related the stimulatory effect with the myosin-binding property of caldesmon. In the presence of actin, a low concentration of caldesmon was not enough to evince the stimulatory effect: myosin concentration must also be low. This is because the stimulatory effect was obscured when myosin concentration was elevated. Ca(2+)-calmodulin abolished the stimulatory effect of caldesmon. However, the concentration of calmodulin required to abolish the stimulation was higher than that required to abolish the inhibition.

Actins↗
PubMed1993

[An experience of dissecting cerebral aneurysm of the anterior cerebral artery].

Intracranial dissecting aneurysms have been reported occasionally in recent years. However, excluding dissecting aneurysms which extend from the proximal intracranial carotid artery, dissecting aneurysms arising merely in ACA are found only rarely. We are reporting here a case of a 42 year-old gentleman who did not present any particular causative etiology such as trauma or other basic diseases causing arteritis. Our patient is the 8th case, as far as we could find in the literature, in which the dissection of the arterial wall originated at the ACA. The patient was thought to have a tiny saccular aneurysm at the A 1-2 junction of the right ACA associated with vasospasm in the distal ACA on the angiogram. The patient had motor weakness on the left side and headache as well as a low density area in the territory of the ACA on the CT scan. A craniotomy was performed verifying the aneurysm to be dissecting in type without any sign of recent subarachnoid hemorrhage in the surrounding structures. No aggressive surgical treatment such as trapping of the aneurysm was done because the collateral blood circulation in that territory of the distal right ACA seemed to be poor and the patient no longer had neurological deficit at the time of operation. The patient was treated successfully with antiplatelet therapy. On the follow-up angiogram performed 3.5 months after the onset of the illness, we noted the disappearance of the abnormal angiographical findings of the dissecting aneurysm and distal arterial narrowing (pearl and string sign).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

A novel regulatory effect of myosin light chain kinase from smooth muscle on the ATP-dependent interaction between actin and myosin.

The actin-binding activity of myosin light chain kinase (MLCK) from smooth muscle was studied with special reference to the ATP-dependent interaction between actin and myosin. MLCK in the presence of calmodulin endowed sensitivity to Ca2+ on the movement of actin filaments on phosphorylated myosin from smooth muscle that was fixed on a coverslip. This regulatory effect was not attributable to the kinase activity of MLCK but could be explained by its actin-binding activity. The importance of the actin-binding activity was further substantiated by results of an experiment with Nitellopsis actin-cables in which MLCK regulated the interaction under conditions where MLCK was exclusively associated with the actin-cables.

Actins↗
PubMed1992

A novel regulatory protein that affects the functions of caldesmon and myosin light chain kinase.

A caldesmon (CaD)-binding protein of about 65 kDa (by SDS-PAGE) was purified from smooth muscle of chicken gizzard. The 65-kDa protein prevented the inhibitory effect of CaD on the ATP-dependent interaction between actin and myosin. Unlike the case with calmodulin (CaM), Ca2+ was not required for this effect. As reported in the preceding communication, myosin light chain kinase (MLCK), another well characterized protein that binds CaM, has CaD-like activity that modulates the interaction by binding to actin. The 65-kDa protein was also effective in relieving the modulation, while leaving unaffected the kinase activity that phosphorylates the light chain of smooth muscle myosin.

Actins↗
PubMed1992

The binding of nonmuscle caldesmon from brain to microtubules. Regulations by Ca(2+)-calmodulin and cdc2 kinase.

Nonmuscle caldesmon from bovine brain bound to microtubules with a stoichiometry of five tubulin dimers to one molecule of caldesmon with values of Ka 4.5 x 10(5) M-1. The binding of caldesmon to microtubules was inhibited in the presence of Ca2+ and calmodulin. The phosphorylation of caldesmon by cdc2 kinase also eliminated the microtubule-binding activity. These results suggest that caldesmon may play a physiological role in the functions of microtubules.

Animals↗
PubMed1992

Injury-induced reduction of acidic fibroblast growth factor levels in the distal parts of rat sciatic nerve.

Acidic fibroblast growth factor (aFGF) level in sciatic nerve after lesioning was measured by enzyme immunoassay to determine if aFGF functions as a neurotrophic factor like nerve growth factor (NGF). Whereas the NGF level increased in distal segments, the aFGF level there decreased after transection or crushing and recovered to the original level by 10 weeks after crushing. The amount of aFGF mRNA in the sciatic nerve was extremely low to supply the high level of protein found in the sciatic nerve. Sympathetic ganglia, dorsal root ganglia, and spinal cord, which contain neuronal cell bodies extending their axons into the sciatic nerve, showed a greater or similar level of aFGF as sciatic nerve. These results imply that aFGF is synthesized in neuronal cell bodies and distributed anterogradely into their axons. Difference of injury-induced changes in levels between aFGF and NGF suggests distinct mechanisms of the effects elicited from these factors on regeneration of the sciatic nerve.

Animals↗
PubMed1992

Characterization of smooth muscle caldesmon as a microtubule-associated protein.

We have previously shown that nonmuscle caldesmon copurified with brain microtubules binds to microtubules in vitro [Ishikawa et al.: FEBS Lett. 299:54-56, 1992]. To explore the role of caldesmon in the functions of microtubules, further characterization was performed using smooth muscle caldesmon, whose molecular structure and function have been best-characterized in all caldesmon species. Smooth muscle caldesmon bound to microtubules with a stoichiometry of five tubulin dimers to one molecule of caldesmon with the binding constant of 1.1 x 10(6) M-1. The binding of caldesmon to microtubules was inhibited in the presence of Ca2+ and calmodulin. Partial digestion of the caldesmon with alpha-chymotrypsin revealed that the binding site of the caldesmon for microtubules lay in the 34-kDa C-terminal domain. When the caldesmon was in the dimeric form in the absence of a reducing agent, the caldesmon cross-linked microtubules to form bundles. Further, the caldesmon potentiated the polymerization of tubulin, and inhibited the in vitro movement of microtubules on dynein. These results suggest that caldesmon may be involved in the regulation by Ca2+ of the functions of microtubules.

Animals↗
PubMed1992

Pollen-derived rice calli that have large deletions in plastid DNA do not require protein synthesis in plastids for growth.

Albino rice plants derived from pollen contain plastid genomes that have suffered large-scale deletions. From the roots of albino plants, we obtained several calli containing homogeneous plastid DNA differing in the size and position of the deletion. DNA differing in the size and position of the deletion. Southern blotting and pulsed field gel electrophoresis experiments revealed that the DNAs were linear molecules having a hairpin structure at both termini, existing as monomers (19 kb) or dimers, trimers and tetramers linked to form head-to-head and tail-to-tail multimers. This characteristic form is similar to that of the vaccinia virus, in which the replication origin is thought to lie at or near the hairpin termini. Furthermore, polymerase chain reaction experiments revealed complete loss of the ribosomal RNA genes of the plastid DNA. The results suggest that plant cells can grow without translation occurring in plastids. All of the deleted plastid DNAs commonly retained the region containing the tRNA(Glu) gene (trnE), which is essential for biosynthesis of porphyrin. As porphyrin is the precursor of heme for mitochondria and other organelles, it is considered that trnE on the remnant plastid genome may be transcribed by an RNA polymerase encoded on nuclear DNA.

Base Sequence↗
PubMed1992

Regulation by Ca(2+)-calmodulin of the actin-bundling activity of Physarum 210-kDa protein.

From the plasmodia of a lower eukaryote, Physarum polycephalum, we have previously purified a 210-kDa protein that showed similar properties to those of smooth muscle caldesmon. Further characterization of the 210-kDa protein revealed that it bundled actin filaments. This bundling activity was inhibited by calmodulin in the presence of Ca2+. Unlike smooth muscle caldesmon, the 210-kDa protein bundled actin filaments whether or not a reducing agent, such as dithiothreitol, was present. The protein was shown to have two (or more) different actin-binding sites which were classified into salt-sensitive and salt-insensitive sites. Electron microscopy revealed that the 210-kDa protein was an elongated molecule (mean length, 97 +/- 25 nm) which was bent in the middle. The Stokes radius and sedimentation coefficient of the 210-kDa protein were 130 A and 2.9 S, respectively. An immunofluorescence study revealed that the 210-kDa protein colocalized with the bundles of actin filaments in thin-spread preparations of Physarum plasmodia, suggesting that the 210-kDa protein was regulating the appearance and disappearance of the actin bundles that are associated with the contraction-relaxation cycle of the plasmodia.

Actins↗
PubMed1991

Stimulation of the interaction between actin and myosin by Physarum caldesmon-like protein and smooth muscle caldesmon.

We have purified an actin-binding protein from the plasmodia of a lower eukaryote, Physarum polycephalum, with an apparent molecular mass of 210,000 daltons on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This protein bound to actin filaments with a stoichiometry of 1:7-8 in a Ca(2+)-calmodulin-dependent manner. Antibody raised against caldesmon from smooth muscle cross-reacted with the 210-kDa protein. In vitro motility assay revealed that the 210-kDa protein increased the sliding velocity of actin filaments on Physarum myosin. The 210-kDa protein more than doubled the actin-activated ATPase activity of Physarum myosin under comparative conditions of in vitro motility assay. Further increases in the concentration of the 210-kDa protein decreased its stimulatory effects. Ca(2+)-calmodulin prevented the stimulatory effects of the 210-kDa protein. Unexpectedly, smooth muscle caldesmon also increased the sliding velocity of actin filaments on smooth muscle myosin at lower concentrations. The well-known inhibitory effect of smooth muscle caldesmon on the actin-myosin interaction was observed with this motility assay when the concentration of the caldesmon was increased further. The stimulatory and inhibitory effects were confirmed by measurements of actin-activated ATPase activity of smooth muscle myosin. From estimations of the intracellular concentrations of the 210-kDa protein and smooth muscle caldesmon in vivo, it appears that effects of the former and the latter on actin-myosin interactions in vivo are stimulatory and inhibitory, respectively.

Actins↗