Biomedical subjects

K Yokote

Publications and source records attributed to K Yokote.

At least 19 recordsLinked to original sources

PubMed2001

NK-104, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, reduces osteopontin expression by rat aortic smooth muscle cells.

1. It has been suggested that osteopontin promotes the development of atherosclerosis, especially under diabetic conditions. 2. In the present study, we found that NK-104, a new potent synthetic inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, reduced osteopontin expression both at protein and mRNA levels in cultured rat aortic smooth muscle cells. 3. The inhibitory effect of NK-104 was almost completely reversed by mevalonate, suggesting that mevalonate or its metabolites play important roles in the regulation of osteopontin expression. 4. Furthermore, oral administration of NK-104 (3 mg kg(-1) day(-1) for 7 days) effectively suppressed abnormally upregulated expression of osteopontin mRNA in the aorta and kidney of streptozotocin-induced diabetic rats. 5. These data support a notion that NK-104 is a suitable drug for the treatment of diabetic patients with hypercholesterolaemia.

Administration, Oral↗

PubMed2001

Enhanced intra-abdominal visceral fat accumulation in patients with Werner's syndrome.

OBJECTIVE: Studies were made on the abnormality of glucose and lipid metabolism and its cause in four patients with Werner's syndrome to infer the reason for accelerated atherogenesis in this syndrome. RESULTS: Of these four patients, hypercholesterolemia was found in three, hypertriglyceridemia in four, hypoalphalipoproteinemia in two and hypertension in two. All the patients had insulin-resistant diabetes mellitus and three of them had apparent hyperinsulinemia. Abdominal computed tomography revealed that all of them had visceral fat obesity, namely augumented intra-abdominal adipose tissue. CONCLUSION: The clinical features of these patients resemble those recently designated as insulin resistant syndrome (syndrome X) or visceral fat syndrome. The metabolic abnormality may be one of important factors in the accelerated atherogenesis in this syndrome.

Abdomen↗

PubMed2000

Differential interaction of CrkII adaptor protein with platelet-derived growth factor alpha- and beta-receptors is determined by its internal tyrosine phosphorylation.

CrkII is an intracellular adaptor protein involved in signal transduction by various growth factors. Activation of PDGF alpha-receptor resulted in its association with CrkII in vivo. In contrast, binding of CrkII to the PDGF beta-receptor was negligible, despite its becoming prominently phosphorylated. Bacterially expressed GST-CrkII SH2 domain specifically bound to Tyr-762 and Tyr-771 in the activated PDGF alpha- and beta- receptors, respectively. GST fusion protein of full-length CrkII also bound to the activated PDGF beta-receptor. However, tyrosine phosphorylation of GST-CrkII diminished its binding to the beta-receptor. CrkI, a truncated version of CrkII lacking the phosphorylatable tyrosine residue, could bind to both PDGF alpha- and beta-receptors in vivo. In conclusion, tyrosine phosphorylation of CrkII negatively affects its binding to the PDGF receptors. The differential binding of CrkII to the PDGF alpha- and beta- receptors may be a rationale for functional diversity between the two receptors.

Animals↗

PubMed2000

Marked decrease in plasma apolipoprotein A-I and high density lipoprotein-cholesterol in a case with Werner syndrome.

The patient was a 39-year-old Japanese male with a body height of 160 cm and weight of 48 kg who was diagnosed as Werner syndrome of homozygote for mutation 4. His plasma total cholesterol (TC), triglycerides (TGs), high density lipoprotein-cholesterol (HDL-C) and apolipoprotein A-I (apo A-I) levels were 7.2, 2.1, 1 mmol/l and 128 mg/dl, respectively. During the clinical course of treatment of this patient, his plasma levels of HDL-C and apo A-I declined drastically to levels of as low as 0.2 mmol/l and 10 mg/dl, respectively, with concurrent reciprocal increase in plasma TG levels. Plasma HDL-C, apo A-I and TG levels gradually returned to original values. Lipoprotein lipase activity and mass in post-heparin plasma were markedly low when the apo A-I and HDL-C levels decreased to 10 mg/dl and 0.21 mmol/l, respectively, and these values improved when the apo A-I and HDL-C levels returned to more normal values of 106 mg/dl and 0.94 mmol/l, respectively. The result of direct sequence of the exon 3 and 4, and the promoter region of the apo A-I gene of the patient revealed no single nucleotide changes. These results suggest that in the present patient, impaired hydrolysis of TGs in TG-rich lipoproteins, is due at least in part to a decreased LPL enzyme level, reduced the formation of nascent HDL, resulting in unusually low plasma levels of HDL-C and apo A-I.

Adult↗

PubMed2000

Increased atherogenesis in Otsuka Long-Evans Tokushima fatty rats before the onset of diabetes mellitus: association with overexpression of PDGF beta-receptors in aortic smooth muscle cells.

The mechanism of diabetic macroangiopathy was studied from the view point of phenotypic change of arterial smooth muscle cells (SMC). Otsuka Long-Evans Tokushima fatty (OLETF) rat, an animal model of non-insulin dependent diabetes mellitus (NIDDM), develops spontaneous persistent hyperglycemia after the age of 18 weeks. Medial SMC in OLETF rats expressed more platelet-derived growth factor (PDGF) beta-receptor and fibronectin at the protein level than those from control, Long-Evans Tokushima Otsuka (LETO) rats, not only after but also before the onset of diabetes mellitus. Cultured SMC from OLETF rats more strongly responded specifically to the mitogenic stimuli of PDGF-AB and PDGF-BB and also expressed PDGF beta-receptor more intensely compared with those from LETO rats. PDGF is known to be the main contributor to the intimal thickening induced by balloon catheter injury, which is one of several forms of arterial injuries. Intimal thickening of carotid arteries in OLETF rats after balloon catheter injury increased compared with that in LETO rats before the onset of diabetes mellitus. In in vitro culture system, fibronectin synthesis was stimulated by transforming growth factor-beta1(TGF-beta1) in SMC from OLETF rats, but not in those from LETO rats, suggesting that SMC from OLETF rats respond to TGF-beta1. These results indicate that overexpression of PDGF beta-receptor and fibronectin in medial SMC plays an important role in the accelerated intimal thickening before the onset of diabetes mellitus in OLETF rats.

Animals↗

PubMed2000

Enhanced expression of osteopontin by high glucose. Involvement of osteopontin in diabetic macroangiopathy.

Atherosclerotic vascular disease is a major complication of diabetic patients. Osteopontin has recently been implicated in the development of atherosclerosis. In the present study, we have investigated the effects of high glucose on expression of osteopontin in cultured rat aortic smooth muscle cells. High concentrations of glucose increased osteopontin secretion from the cells, and the increased secretion was completely inhibited by an inhibitor of protein kinase C, GF109203X. Northern blot analysis confirmed the enhanced effect of glucose on expression of osteopontin mRNA. Promoter activity of osteopontin, measured using the osteopontin promoter/luciferase expression vector system, was increased by high glucose, and the enhanced effect was completely inhibited by GF109203X. Glucosamine also increased the promoter activity of osteopontin. Azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase, the key enzyme of the hexosamine pathway, profoundly inhibited high glucose-mediated increase in the promoter activity. Taken together, these data indicate that high glucose enhances the expression of osteopontin at the transcriptional level possibly through the activation of protein kinase C as well as the hexosamine pathway. Our results suggest that osteopontin could play a role in the development of diabetic vascular complications.

Animals↗

PubMed2000

Enhanced expression of osteopontin in human diabetic artery and analysis of its functional role in accelerated atherogenesis.

We have previously reported that high glucose stimulates osteopontin (OPN) expression through protein kinase C-dependent pathways as well as hexosamine pathways in cultured rat aortic smooth muscle cells. The finding prompted us to study in vivo expression of OPN in diabetes mellitus. In the present study, we found by immunohistochemistry that medial layers of the carotid arteries of streptozotocin-induced diabetic rats and the forearm arteries of diabetic patients stained positively for OPN antibodies, whereas the staining from arteries of control rats and nondiabetic patients was negative. We also found that OPN stimulated the migration and enhanced platelet-derived growth factor (PDGF)-mediated DNA synthesis of cultured rat aortic smooth muscle cells. OPN and PDGF synergistically activated focal adhesion kinase as well as extracellular signal-regulated kinase; this finding seems to explain the OPN-induced enhancement of PDGF-mediated DNA synthesis. Taken together, our present results raise a possibility that OPN plays a role in the development of diabetic vascular complications.

Adult↗

PubMed2000

[A case of pulmonary actinomycosis radiologically mimicking a lung cancer].

A 59-year-old male clerk consulted in general practitioner due to cough and hemoptysis. A mass shadow was pointed out in the left upper lung field on a chest radiograph. Patient was referred to our hospital for further treatment. Any definitive daiagnosis could not be made after examinations including sputum culture, cytology and TBLB. Because a lung cancer was strongly suspected, an exploratory thoracotomy was performed. Actinomyces was detected by pathological study of excised specimen, with no evidence of cancer. ABPC was administered for two months postoperatively. The patient is doing well without recurrence of actinomycosis 2.5 years after the surgery. Pulmonary actinomycosis presenting a mass shadow on a radiograph may mimick a pulmonary tumor, especially a lung cancer. Pulmonary actinomycosis should be considered in a differential diagnosis of pulmonary lesion thought to be malignant.

Actinomycosis↗

PubMed1999

Enhanced expression of osteopontin by high glucose in cultured rat aortic smooth muscle cells.

Atherosclerotic vascular disease is a major complication of diabetic patients, and osteopontin has recently been implicated in the development of atherosclerosis. In the present study, we have investigated the effects of high glucose on expression of osteopontin in cultured rat aortic smooth muscle cells. High concentrations of glucose increased osteopontin secretion from the cells, and the increased secretion was completely inhibited by an inhibitor of protein kinase C, GF109203X. Northern blot analysis confirmed the enhanced effect of glucose on expression of osteopontin mRNA. Promoter activity of osteopontin, measured using the osteopontin promoter/luciferase expression vector system, was increased by high glucose, and the enhanced effect was completely inhibited by GF109203X. Glucosamine also increased the promoter activity of osteopontin, and azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase (the key enzyme of the hexosamine pathway), profoundly inhibited high glucose-mediated increase in the promoter activity. Taken together, these data indicate that high glucose enhances the expression of osteopontin at the transcriptional level possibly through the activation of protein kinase C as well as the hexosamine pathway. Our results suggest that osteopontin could play a role in the development of diabetic vascular complications.

Animals↗

PubMed1999

Platelet-derived growth factor activates p38 mitogen-activated protein kinase through a Ras-dependent pathway that is important for actin reorganization and cell migration.

Members of the mitogen activated protein (MAP) kinase family, extracellular signal-regulated kinase, stress-activated protein kinase-1/c-Jun NH2-terminal kinase, and p38, are central elements that transduce the signal generated by growth factors, cytokines, and stressing agents. It is well known that the platelet-derived growth factor (PDGF) activates extracellular signal-regulated kinase, which leads to cellular mitogenic response. On the other hand, the role of the other MAP kinases in mediating the cellular function of PDGF remains unclear. In the present study, we have investigated the functional role of the other MAP kinases in PDGF-mediated cellular responses. We show that ligand stimulation of PDGF receptors leads to the activation of p38 but not stress-activated protein kinase-1/c-Jun NH2-terminal kinase. Experiments using a specific inhibitor of p38, SB203580, show that the activation of p38 is required for PDGF-induced cell motility responses such as cell migration and actin reorganization but not required for PDGF-stimulated DNA synthesis. Analyses of tyrosine residue-mutated PDGF receptors show that Src homology 2 domain-containing proteins including Src family kinases, phosphatidylinositol 3-kinase, the GTPase-activating protein of Ras, the Src homology 2 domain-containing phosphatase SHP-2, phospholipase C-gamma, and Crk do not play a major role in mediating the PDGF-induced activation of p38. Finally, the expression of dominant-negative Ras but not dominant-negative Rac inhibited p38 activation by PDGF, suggesting that Ras is a potent mediator in the p38 activation pathway downstream of PDGF receptors. Taken together, our present study proposes the existence of a Ras-dependent pathway for the activation of p38, which is important for cell motility responses elicited by PDGF stimulation.

Actins↗

PubMed1999

[Werner's syndrome associated with progressive subcortical vascular encephalopathy of the Binswanger type].

A 56-year-old woman with Werner's syndrome was admitted to our hospital because of intractable foot ulcer and malnutrition. She presented dementia consisting of childish behaviour, loss of intelligence, and severe amnesia. Brain CT revealed diffuse periventricular low density areas, and brain MRI also disclosed periventricular high intensity areas under T2-intensified conditions. These findings gave a diagnosis of progressive subcortical vascular encephalopathy of the Binswanger type, which seemed to be the cause of her dementia. She finally died of heart failure due to acute myocardial infarction. Mild to moderate demyelinization was found in the subcortical area of the autopsied cerebrum, confirming the clinical diagnosis. Generalized atherosclerosis characteristic of Werner's syndrome may have predisposed this patient to Binswanger's encephalopathy.

Brain↗

PubMed1999

[Effects of aging and hyperlipidemia on plasma osteopontin level].

In order to elucidate a possible mechanism for accelerated atherogenesis as well as enhanced vascular calcification observed during the normal aging process, we measured plasma osteopontin (OPN) levels and examined their relation to aging and certain disease parameters. In all cases examined, no significant relation was found between the plasma OPN level and age, body mass index, blood pressure, plasma levels of glucose and insulin, serum levels of creatinine, triglyceride, and high density lipoprotein cholesterol. On the other hand, a significant negative correlation was found between the plasma OPN level and serum total cholesterol concentration (n = 78, r = -0.355, p = 0.0014). The serum level of low density lipoprotein (LDL) cholesterol, calculated by the formula of Friedewald, also showed a significant negative correlation to the plasma OPN level (n = 78, r = -0.301, p = 0.0075). In cases without diabetes mellitus and hypertension, a significant positive correlation was found between the plasma OPN level and age (n = 22, r = 0.445, p = 0.0378). It is postulated that OPN plays a negative regulatory role in the development of vascular calcification. Therefore, the observed negative relationship between the plasma OPN level and the serum levels of total cholesterol and LDL cholesterol, suggests a possibility that hypercholesterolemia facilitates vascular calcification by suppressing OPN synthesis. On the other hand, in non-diabetic and normotensive cases, the positive relationship between the plasma OPN level and age may reflect a defense mechanism against age-related increase of vascular calcification.

Aging↗

PubMed1998

Fibronectin stimulates transcription of the platelet-derived growth factor beta-receptor in cultured rat aortic smooth muscle cells.

Fibronectin seems to play an important role in promoting the characteristic changes of vascular smooth muscle cells in diabetes mellitus including overexpression of the platelet-derived growth factor beta-receptor. To determine the regulatory mechanism of the beta-receptor by fibronectin, we have analyzed the effect of fibronectin on the expression of the beta-receptor in cultured rat aortic smooth muscle cells using the beta-receptor promoter/luciferase expression vector system. Fibronectin was found to stimulate the expression of the beta-receptor at the transcriptional level. Both a MEK1 inhibitor PD98059 and a tyrosine kinase inhibitor herbimycin A significantly inhibited the fibronectin-stimulated receptor transcription. Herbimycin A also completely inhibited the fibronectin-stimulated increase in tyrosine phosphorylation of focal adhesion kinase. These data suggest the involvement of the integrin-mediated mitogen-activated protein kinase pathway downstream of fibronectin stimulation in the activation process of the beta-receptor promoter.

Animals↗

PubMed1998

Fibroblast growth factor receptor-1 mediates chemotaxis independently of direct SH2-domain protein binding.

Endothelial cells expressing fibroblast growth factor receptor-1 (FGFR-1) migrate and proliferate in response to treatment with FGF. We analysed ligand-induced migration and proliferation of porcine aortic endothelial cells expressing wild-type FGFR-1, point-mutated Y766F FGFR-1, unable to activate phospholipase C-gamma1 (PLC-gamma1), or carboxyl-terminally truncated FGFR-1, lacking either 48 (from amino acid 774 in the FGFR-1 sequence) or 63 (from amino acid 759) amino acid residues of the C-terminal tail. The truncated CT63 FGFR-1 mutant failed to mediate chemotaxis, but was in response to ligand stimulation capable of mediating proliferation of the cells, stimulation of MAP kinase activity and tyrosine phosphorylation of FRS2, an FGFR-1 specific signaling molecule. The defect in migration-capacity of CT63 was not due to loss of Y766, and thereby PLC-gamma1 activation, since cells expressing the mutant Y766F FGFR-1 migrated as efficiently as the wild-type receptor cells. Induction of phospholipase A2 (PLA2) activity by the activated FGFR-1 was dependent on the presence of Y766, and was therefore also not critical for the chemotactic response. Although the FGFR-1 only very inefficiently mediates activation of phosphatidylinositol 3' kinase (PI 3-kinase), the PI 3-kinase inhibitor wortmannin suppressed wild-type FGFR-1 mediated migration. We conclude that the signal transduction pathway for FGFR-1 mediated migration is independent of phosphotyrosine residues in the receptor and requires activation of a wortmannin-sensitive enzyme.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Identification of Tyr-762 in the platelet-derived growth factor alpha-receptor as the binding site for Crk proteins.

Tyr-762 is an autophosphorylation site in the human platelet-derived growth factor (PDGF) alpha-receptor. In order to investigate whether phosphorylated Tyr-762 serves as a docking site for downstream signal transduction molecules, affinity purification using an immobilized synthetic peptide containing phosphorylated Tyr-762 and its surrounding amino acid residues was performed. Proteins in HeLa cell lysate of molecular sizes 27, 38 and 40 kDa bound to the phosphorylated, but not to the unphosphorylated peptide. Analyses of partial amino acid sequences of the purified proteins indicated that they were identical to CrkI, CrkII and CrkL respectively. The wild-type PDGF alpha-receptor, when expressed in porcine aortic endothelial cells, formed complexes with CrkII and CrkL upon ligand stimulation, which was specifically inhibited by a synthetic peptide containing phosphorylated Tyr-762. Replacement of Tyr-762 with a phenylalanine residue in the PDGF alpha-receptor abrogated ligand-induced binding of Crk proteins. Tyrosine phosphorylation of CrkII and CrkL increased by 1.8- and 1.3-fold, respectively, upon ligand stimulation of the wild-type alpha-receptor. In contrast, the Y762F mutant PDGF alpha-receptor failed to induce tyrosine phosphorylation of Crk proteins. CrkII and CrkL constitutively formed complex with the guanine nucleotide exchange factor C3G, in unstimulated as well as PDGF-stimulated cells. Moreover, the activated wild-type PDGF alpha-receptor but not the Y762F mutant receptor was found in a C3G immunoprecipitate, suggesting that a ternary complex between the activated PDGF alpha-receptor, Crk and C3G was formed. DNA synthesis stimulated by PDGF-BB as well as PDGF-induced MAP kinase activation was similar in cells expressing wild-type and mutant receptors. Interestingly, the activated PDGF beta-receptor was found not to bind Crk proteins. Instead, Tyr-771 of the beta-receptor, which is localized at an analogous position to Tyr-762 in the alpha-receptor, binds RasGAP. RasGAP is not bound to the alpha-receptor. Thus, this region in the kinase inserts of the two receptors may be important for the divergency in signaling from the two PDGF receptors.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Administration of a small amount of lard enhances intimal thickening in the balloon catheter injury model without affecting serum lipids.

Effects of fatty acids on intimal thickening induced by a balloon catheter injury model were investigated by feeding rabbits a small amount of either lard [L] or fish oil [F]. Serum lipids of these groups were not different from those of basal diet-fed rabbits [controls] after 4 weeks of feeding. Serum saturated fatty acids such as 14:0, 16:0, and 18.0 were significantly greater in the L-fed rabbits compared with controls, but those of the aorta were not significantly different. Fatty acid composition of the F-fed rabbits was only different from that of the controls in that n-3 fatty acids slightly increased. The mean and maximum intimal thickening 2 weeks after ballooning, carried out 2 weeks after feeding, were significantly higher in the carotid arteries of the L-fed rabbits than in the controls. The intimal thickening of the F-fed rabbits did not significantly differ from that of the controls. These results suggest that lard promotes the formation of the smooth muscle cell dominant type of arteriosclerosis without affecting serum lipid levels.

Animal Feed↗

PubMed1998

PDGF alpha-receptor mediated cellular responses are not dependent on Src family kinases in endothelial cells.

Two novel autophosphorylation sites in the juxtamembrane region of the PDGF alpha-receptor, Tyr-572 and Tyr-574, were identified. A Y572/574F mutant PDGF (alpha)-receptor was generated and stably expressed in porcine aortic endothelial cells. In contrast to the wild-type receptor, the mutant receptor was unable to associate with or activate Src family tyrosine kinases. Tyrosine phosphorylated synthetic peptides representing the juxtamembrane sequence of the receptor dose-dependently inhibited the binding of Src family tyrosine kinases to the autophosphorylated PDGF alpha-receptor. The mutant receptor showed similar PDGF-induced kinase activity and ability to mediate mitogenicity, actin reorganization and chemotaxis as the wild-type receptor. Thus activation of Src family kinases by the PDGF alpha-receptor is not essential for PDGF-induced mitogenicity or actin reorganization.

Actins↗

PubMed1997

Involvement of phosphatidylinositide 3'-kinase and Rac in platelet-derived growth factor-induced actin reorganization and chemotaxis.

Previous work has suggested a role for phosphatidylinositide 3'-kinase (PI3-kinase) in platelet-derived growth factor (PDGF)-induced actin reorganization and chemotaxis. In support of this notion, we show in this report that the PI3-kinase inhibitor wortmannin inhibits chemotaxis of PDGF beta-receptor expressing porcine aortic endothelial (PAE/PDGFR-beta) cells. Treatment with wortmannin resulted in a dose-dependent decrease in chemotaxis with an IC50 value of about 15-20 nM. Higher concentrations of wortmannin also reduced basal random migration of transfected cells in the absence of PDGF. We also investigated the role of Rac in PDGF-induced actin reorganization and cell motility. Overexpression of wt Rac in PAE/PDGFR-beta cells led to an increased cell motility and edge ruffling in response to PDGF-BB, compared to control cells. In PAE/PDGFR-beta cells transfected with inducible V12Rac (a constitutively active Rac mutant), membrane ruffling occurred in the absence of PDGF stimulation and was independent of PI3-kinase activity. On the other hand, PAE/PDGFR-beta cells transfected with inducible N17Rac (a dominant negative Rac mutant) failed to show membrane ruffling in response to PDGF stimulation. Together with previous observations, these data indicate that activation of PI3-kinase is crucial for initiation of PDGF-induced cell motility responses and that Rac has a major role downstream of PI3-kinase, in this pathway.

Actins↗