Biomedical subjects

M Shichiri

Publications and source records attributed to M Shichiri.

At least 37 records · Page 2Linked to original sources

PubMed2000

Bradykinin enhances insulin receptor tyrosine kinase in 32D cells reconstituted with bradykinin and insulin signaling pathways.

We have previously shown that bradykinin potentiated insulin-induced glucose uptake through GLUT4 translocation in canine adipocytes and skeletal muscles. The aim of this study was to determine the molecular mechanism of bradykinin enhancement of the insulin signal. For this purpose, 32D cells, which express a limited number of insulin receptors and lack endogenous bradykinin B2 receptor (BK2R) or insulin receptor substrate (IRS)-1 were transfected with BK2R cDNA and/or insulin receptor cDNA and/or IRS-1 cDNA, and analyzed. In 32D cells that expressed BK2R and insulin receptor (32D-BKR/IR), bradykinin alone had no effect on the phosphorylation of the insulin receptor, but it enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor. In 32D cells that expressed BK2R, insulin receptor and IRS-1 (32D-BKR/IR/IRS1), bradykinin also enhanced insulin-stimulated tyrosine phosphorylation of the insulin receptor and IRS-1. An increase in insulin-stimulated phosphorylation of IRS-1 by treatment with bradykinin in 32D-BKR/IR/IRS1 cell was associated with increased binding of 85 kD subunit of phosphatidylinositol 3 (PI 3)-kinase and increased IRS-1 associated PI 3-kinase activity. These effects of bradykinin were not observed in 32D cells which lack the expression of BK2R (32D-IR/IRS1) or insulin receptor (32D-BKR/IRS1). Furthermore, tyrosine phosphatase activity against insulin receptor beta-subunit in plasma membrane fraction of 32D-BKR/IR cells was significantly reduced by bradykinin, suggesting that the effect of bradykinin was in part mediated by inhibition of protein tyrosine phosphatase(s). Our results clearly demonstrated that bradykinin enhanced insulin-stimulated tyrosine kinase activity of the insulin receptor and downstream insulin signal cascade through the BK2R mediated signal pathway.

Animals↗

PubMed2000

Cost-effectiveness of intensive insulin therapy for type 2 diabetes: a 10-year follow-up of the Kumamoto study.

To evaluate the cost and effectiveness of intensive insulin therapy for type 2 diabetes on the prevention of diabetes complications in Japan, we performed economic evaluation based on a randomized controlled trial. A total of 110 patients with type 2 diabetes were randomly assigned into two groups, a multiple insulin injection therapy (MIT) group or a conventional insulin injection therapy (CIT) group, and were followed-up for 10 years. Economic evaluation (cost-consequences analysis) was applied to evaluate both health and economic outcomes. As outcome measures for effectiveness of intensive insulin therapy, the frequency of complications, such as retinopathy, nephropathy, neuropathy, macrovascular event, and diabetes-related death, was used. For estimating costs, a viewpoint of the payer (the National Health Insurance) was adopted. Direct medical costs associated with diabetes care during 10 years were calculated and evaluated. In a base case analysis, all costs were discounted to the present value at an annual rate of 3%. Sensitivity analyses were carried out to assess the robustness of the results to changes in the values of important variables. MIT reduced the relative risk in the progression of retinopathy by 67%, photocoagulation by 77%, progression of nephropathy by 66%, albuminuria by 100% and clinical neuropathy by 64%, relative to CIT. Moreover, MIT prolonged the period in which patients were free of complications, including 2.0 years for progression of retinopathy (P<0.0001), 0.3 years for photocoagulation (P<0.05), 1.5 years for progression of nephropathy (P<0.01) and 2.2 years for clinical neuropathy (P<0.0001). The total cost (discounted at 3%) per patient during the 10-year period for each group was $30310 and 31525, respectively. The reduction of total costs in MIT over CIT was mainly due to reduced costs for management of diabetic complications. Our results show that MIT is more beneficial than CIT in both cost and effectiveness. Therefore, MIT is recommended for the treatment of type 2 diabetic patients who require insulin therapy as early as possible from the perspective of both patients and health policy.

Adult↗

PubMed2000

Involvement of bradykinin in acute exercise-induced increase of glucose uptake and GLUT-4 translocation in skeletal muscle: studies in normal and diabetic humans and rats.

Acute exercise induces glucose uptake in skeletal muscle in vivo, but the molecular mechanism of this phenomenon remains to be identified. In this study, we evaluated the involvement of bradykinin in exercise-induced glucose uptake in humans and rats. In human studies, plasma bradykinin concentrations increased significantly during an ergometer exercise (20 minutes) in 8 healthy normoglycemic subjects and 6 well-controlled type 2 diabetic patients (mean hemoglobin A1c [HbA1c], 6.4% +/- 0.6%), but not in 6 poorly controlled type 2 diabetics (mean HbA1c, 11.6% +/- 2.6%). In rat studies, plasma bradykinin concentrations also significantly increased after 1 hour of swimming in nondiabetic and mildly diabetic (streptozotocin [STZ] 45 mg/kg intravenously [IV]) rats, but not in rats with severe diabetes (STZ 65 mg/kg IV). Glucose influx (maximum velocity [Vmax]) and GLUT-4 translocation in skeletal muscle of nondiabetic rats significantly increased after 1 hour of swimming, but these increases were abrogated by subcutaneous infusion of bradykinin B2 receptor antagonist HOE-140 (400 microg x kg(-1) x d(-1)). Insulin-stimulated tyrosine phosphorylation and phosphatidylinositol (PI) 3-kinase activity in response to insulin injection (20 U/kg IV) in the portal vein were significantly attenuated in exercised rats pretreated with HOE-140 compared with saline-treated exercised rats. Our results suggest that plasma bradykinin concentrations increase in response to acute exercise and this increase is affected by blood glucose status in diabetic patients. Moreover, the exercise-induced increase in bradykinin may be involved in modulating exercise-induced glucose transport through an increase of GLUT-4 translocation, as well as enhancement of the insulin signal pathway, during the postexercise period in skeletal muscle, resulting in a decrease of blood glucose.

Adult↗

PubMed2000

Saccharomyces cerevisiae sigma 1278b has novel genes of the N-acetyltransferase gene superfamily required for L-proline analogue resistance.

We discovered on the chromosome of Saccharomyces cerevisiae Sigma 1278b novel genes involved in L-proline analogue L-azetidine-2-carboxylic acid resistance which are not present in the standard laboratory strains. The 5.4 kb-DNA fragment was cloned from the genomic library of the L-azetidine-2-carboxylic acid-resistant mutant derived from a cross between S. cerevisiae strains S288C and Sigma 1278b. The nucleotide sequence of a 4.5-kb segment exhibited no identity with the sequence in the genome project involving strain S288C. Deletion analysis indicated that one open reading frame encoding a predicted protein of 229 amino acids is indispensable for L-azetidine-2-carboxylic acid resistance. The protein sequence was found to be a member of the N-acetyltransferase superfamily. Genomic Southern analysis and gene disruption showed that two copies of the novel gene with one amino acid change at position 85 required for L-azetidine-2-carboxylic acid resistance were present on chromosomes X and XIV of Sigma 1278b background strains. When this novel MPR1 or MPR2 gene (sigma 1278b gene for L-proline analogue resistance) was introduced into the other S. cerevisiae strains, all of the recombinants were resistant to L-azetidine-2-carboxylic acid, indicating that both MPR1 and MPR2 are expressed and have a global function in S. cerevisiae.

Amino Acid Sequence↗

PubMed2000

Endothelin-1 inhibits apoptosis of vascular smooth muscle cells induced by nitric oxide and serum deprivation via MAP kinase pathway.

Endothelin (ET)-1, an endothelium-derived vasoconstrictor and mitogen, acts as an antiapoptotic factor against serum deprivation-induced apoptosis of endothelial cells and fibroblasts but enhances apoptosis of some cancer cells. In the present study, we examined whether nitric oxide (NO) and ET-1 modulate apoptosis of rat vascular smooth muscle cells (VSMCs) via the mitogen-activated protein (MAP) kinase pathway. Both serum deprivation and NO donors (FK409 and SNAP) caused apoptosis of VSMCs, as demonstrated by TdT-mediated dUTP-biotin nick end-labeling, appearance of fragmented DNA, and induction of caspase-3 activity. ET-1 dose-dependently antagonized apoptosis induced by serum deprivation and NO donors. A selective ET(A) receptor antagonist (BQ123) and a nonselective ET(A/B) receptor antagonist (TAK044), but not a selective ET(B) receptor antagonist (BQ788), inhibited the antiapoptotic effect of ET-1, indicating that the antiapoptotic effect of ET-1 is mediated via the ET(A) receptor. ET-1 activated MAP kinase, whose effect was inhibited by FK409. Transfection with an unphosphorylated wild-type MAP kinase kinase-1 (MAPKK-1) or its constitutively activated mutant protected VSMCs against apoptosis induced by serum deprivation and NO donors. Inhibition of MAP kinase activity with PD98059, a specific inhibitor of MAPKK-1, or by transfection of a dominant-negative MAPKK-1 mutant antagonized the antiapoptotic effect of ET-1, suggesting the involvement of MAP kinase in the antiapoptotic effect. The potent inhibitory effect of ET-1 on apoptosis of VSMCs induced by serum deprivation and NO suggests that the counterbalance between the 2 endothelium-derived factors contributes to the process of vascular remodeling by determining VSMC survival and death, respectively, via a common MAP kinase pathway.

Animals↗

PubMed2000

Regulation of insulin secretion by overexpression of Ca2+/calmodulin-dependent protein kinase II in insulinoma MIN6 cells.

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) may play a key role in Ca2+-induced insulin secretion. We have previously reported that treatment of insulinoma MIN6 cells with secretagogues activated CaM kinase II and increased the phosphorylation of synapsin I, followed by insulin secretion. Here, we identified isoforms of CaM kinase II in MIN6 cells and rat islets. Immunoblot analysis suggested that the major isoforms of CaM kinase II were beta'e and delta2 at the protein level in MIN6 cells. Only the beta'e isoform was detected in rat islets by both RT-PCR and immunoblot analysis. We transiently overexpressed beta'e and delta2 isoforms in MIN6 cells and confirmed that treatment of cells with tolbutamide and glucose activated the isoforms. Immunoblot analysis with an antibody against synapsin I phosphorylated by CaM kinase II demonstrated that treatment with tolbutamide and glucose rapidly increased phosphorylation of synapsin I and that phosphorylation was potentiated by overexpression of the isoforms. The secretagogue-induced insulin secretion was potentiated by overexpression of the isoforms. Our results further support our conclusion that activation of CaM kinase II and the concomitant phosphorylation of synapsin I contribute to insulin secretion from pancreatic beta-cells.

Amino Acid Sequence↗

PubMed2000

Suppression of integrin alpha(v) expression by endothelin-1 in vascular smooth muscle cells.

Both integrins and endothelins (ETs) are known to play important roles in vascular remodeling via proliferation, apoptosis, and migration of vascular smooth muscle cells (VSMCs), whose dysfunctions have been implicated in the pathogenesis of end-organ damage associated with hypertension and arteriosclerosis. However, whether there is any interaction between endothelin-1 (ET-1) and integrins remains unknown. Therefore, the aim of the present study was to elucidate whether ET-1 regulates the expression of integrin alpha(v) in rat VSMCs. ET-1 dose- and time-dependently suppressed the integrin alpha(v) messenger RNA (mRNA) transcripts, as quantified by a real-time quantitative polymerase chain reaction (PCR) method, and decreased the transcriptional activity of integrin alpha(v) gene, as demonstrated by integrin alpha(v)-luciferase assay. The inhibitory effect of ET-1 on integrin alpha(v) gene expression was abrogated by an ETA receptor antagonist (BQ123) but not by an ET(B) receptor antagonist (BQ788). ET-1 also suppressed the cell surface expression of integrin alpha(v)beta5 and the adhesion to vitronectin, but not to fibronectin. These results demonstrate that the adhesion of vitronectin to rat VSMCs is inhibited by ET-1 via the ET(A) receptors by suppressing integrin alpha(v) gene transcription, suggesting that ET-1 is involved in regulation of vascular integrin alpha(v) gene expression.

Animals↗

PubMed2000

Cytokine-activated p42/p44 MAP kinase is involved in inducible nitric oxide synthase gene expression independent from NF-kappaB activation in vascular smooth muscle cells.

Recent evidence suggests the possible involvement of inducible nitric oxide synthase (iNOS) in the development and maintenance of hypertension in certain animal models. Inflammatory cytokines activate nuclear factor (NF)-kappaB, which plays a major role in transactivation of the inducible nitric oxide synthase (iNOS) gene. However, it remains unknown whether cytokine-mediated iNOS expression in vascular smooth muscle cells (VSMCs) requires signaling pathway(s) other than NF-kappaB activation. The purpose of this study was to determine whether the p42/p44 MAP kinase pathway is involved in cytokine-induced NF-kappaB activation and/or iNOS expression in cultured rat VSMCs. Nitrite/nitrate (NOx) production stimulated by interleukin (IL)-1beta or tumor necrosis factor (TNF)-alpha in VSMCs was markedly suppressed by inhibiting MAP kinase by pretreatment with a p42/p44 MAP kinase kinase (MAPKK)-1 inhibitor (PD98059) or by transfecting the dominant-interfering form of the nonphosphorylated MAPKK-1 expressing construct (MAPKK S222A). Inhibition of p42/p44 MAP kinase also antagonized the upregulation of iNOS mRNA and protein, as demonstrated by the quantitative RT-PCR method and Western blot analysis, respectively. Furthermore, rat iNOS promoter activity using an iNOS-luciferase construct stimulated by cytokines was inhibited by MAPKK-1 inhibition. However, kappaB-dependent transcription analysis revealed that cytokine-stimulated NF-kappaB activity was unaffected by MAP kinase inhibition. Western blot analysis using anti-IkappaB-alpha and anti-phospho-IkappaB-alpha antibodies showed that PD98059 had no effect on transient phosphorylation or degradation of IkappaB-alpha by cytokines. An electrophoretic mobility shift assay using synthetic oligonucleotide corresponding to the downstream NF-kappaB site of rat iNOS promoter as a probe showed that MAP kinase inhibition did not block cytokine-stimulated activation of NF-kappaB. These data suggest that the MAP kinase pathway is in part involved in cytokine-induced iNOS expression independent from NF-kappaB activation in rat VSMCs.

Animals↗

PubMed2000

Thymic hyperplasia as a source of ectopic ACTH production.

A 26 year-old man with suspected Cushing's disease underwent transsphenoidal exploration of the pituitary without any evidence of microadenoma or hyperplasia. Progressive hypercortisolism necessitated bilateral adrenalectomy. Postoperatively, skin pigmentation gradually developed with a marked elevation of plasma ACTH levels, and CT scanning uncovered a thymic mass. Following removal of the thymic mass, skin pigmentation disappeared and plasma ACTH levels fell to normal. The excised mass was found to be a benign thymic hyperplasia without epithelial or carcinoid tumor cells. However, gel chromatography showed that the thymic tissue extract contained high ACTH content comparable to that of ectopic ACTH-producing tumors with a major component corresponding to ACTH(1-39). Northern blot analysis and in situ hybridization revealed the expression of proopiomelanocortin transcripts in lymphocytes of thymic hyperplasia. This report suggests that lymphocytes in thymic hyperplasia are the most likely site of deregulated ACTH expression causing ectopic ACTH syndrome.

ACTH Syndrome, Ectopic↗

PubMed2000

Granulocyte/macrophage colony-stimulating factor plays an essential role in oxidized low density lipoprotein-induced macrophage proliferation.

We and other groups have recently demonstrated that oxidized low density lipoprotein (Ox-LDL) induces proliferation of macrophages in vitro. Since previous immunohistochemical studies demonstrated that macrophages and macrophage derived foam cells proliferated in situ in atherosclerotic lesions, it seems reasonable to expect that the Ox-LDL-induced macrophage proliferation might be linked to the development of atherosclerotic lesions. Thus, clarification of the molecular cascades of Ox-LDL-induced macrophage proliferation is expected to enhance our knowledge of the pathogenesis of atherosclerosis. Recently, we demonstrated that the activation of PKC leads to release into the culture medium of granulocyte/macrophage colony-stimulating factor (GM-CSF) which plays an important role in Ox-LDL-induced macrophage proliferation. In this review article, we mainly show the role of GM-CSF in the Ox-LDL-induced macrophage proliferation. Moreover, based on our recent findings, we summarize the Ox-LDL-induced signaling pathway for macrophage proliferation.

Animals↗

PubMed2000

[Decision levels of diabetes mellitus and hyperlipidemia in elderly Japanese subjects].

Decision levels of diabetes mellitus and hyperlipidemia in elderly subjects as well as younger subjects should be determined to prevent complications of these diseases such as microvascular and macrovascular diseases. Therefore, prospective follow-up study is necessary to decide the decision levels. In the case of diabetes mellitus, there are some useful studies such as KUMAMOTO STUDY show that strict glycemic control can prevent microvascular diseases, but there are few studies in elderly subjects. However, hypoglycemia causes macrovascular events, and chronic hypoglycemia leads to dementia and apathy. It is generally accepted that the glycemic control level can be milder than that in younger subjects. We suggest that the following decision levels are reasonable for elderly diabetic subjects, 1. FPG > 140-160 mg/dl, 2. PG(2 h) > 200-250 mg/dl, 3. HbA1c > 7-8%. Decision level of hyperlipidemia in elderly subjects should also be determined to prevent cardiovascular disease. It is demonstrated that anti-hyperlipidemic treatment can prevent CHD even in elderly subjects by many prospective studies. Japan Atherosclerosis Society recommend that the decision levels of hyperlipidemia in elderly subjects can be the same as younger subjects. The decision levels indicating diet therapy and medication for risk factor free subjects(category A) are LDL-C > or = 140 and 160 mg/dl, respectively. Those for subjects without CHD but have some risk factors(category B) are LDL-C > or = 120 and 140 mg/dl, respectively. Those for subjects with CHD(category C) are LDL-C > or = 100 and 120 mg/dl, respectively.

Aged↗

PubMed2000

Long-term results of the Kumamoto Study on optimal diabetes control in type 2 diabetic patients.

OBJECTIVE: To examine whether intensive glycemic control could decrease the frequency or severity of diabetic microvascular complications, an 8-year prospective study of Japanese patients with type 2 diabetes was performed. RESEARCH DESIGN AND METHODS: A total of 110 patients with type 2 diabetes (55 with no retinopathy [the primary prevention cohort] and 55 with simple retinopathy [the secondary intervention cohort]) were randomly assigned to multiple insulin injection therapy (MIT) groups and administered three or more daily insulin injections or assigned to conventional insulin injection therapy (CIT) groups and administered one or two daily intermediate-acting insulin injections. Worsening of microvascular complications was regularly assessed during 8 years. Two or more steps up in the 19 stages of the modified Early Treatment of Diabetic Retinopathy Study classification in retinopathy and one or more stages up among three stages in nephropathy (normoalbuminuria, microalbuminuria, and albuminuria) were defined as worsening of complications. RESULTS: In both primary prevention and secondary intervention cohorts, the cumulative percentages of worsening in retinopathy and nephropathy were significantly lower (P < 0.05) in the MIT group than in the CIT group. In neurological tests after 8 years, the MIT group showed significant improvement (P < 0.05) in the median nerve conduction velocities (motor and sensory nerves), whereas the CIT group showed significant deterioration (P < 0.05) in the nerve conduction velocities and vibration threshold. From this study, the glycemic threshold to prevent the onset and progression of diabetic microvascular complications was as follows: HbA1c < 6.5%, fasting blood glucose concentration < 110 mg/dl, and 2-h postprandial blood glucose concentration < 180 mg/dl. CONCLUSIONS: Intensive glycemic control can delay the onset and progression of the early stages of diabetic microvascular complications in Japanese patients with type 2 diabetes.

Adult↗

PubMed2000

[Endothelin].

Explore the source record for details and available documents.

Endothelins↗

PubMed1999

Cis-acting DNA elements of mouse granulocyte/macrophage colony-stimulating factor gene responsive to oxidized low density lipoprotein.

We previously demonstrated that the induction of granulocyte/macrophage colony-stimulating factor (GM-CSF) played an important role in oxidized low density lipoprotein (Ox-LDL)-induced macrophage growth as a growth priming factor. The present study was undertaken to elucidate the transcriptional regulation of the GM-CSF gene using Raw 264.7 cells, a mouse macrophage cell line. Transient transfection into Raw 264.7 cells of several 5'-flanking regions of GM-CSF gene-luciferase fusion plasmids revealed the presence of two positive regulatory sites in regions spanning from -97 to -59 and from -59 to -37 and one negative regulatory site from -120 to -97 in unstimulated cells. When cells were stimulated by Ox-LDL, there was one positive responsive site from -225 to -120 and one negative responsive site from -97 to -59, which contained the NF-kappaB binding site. Computer analysis revealed the presence of a putative AP-2 binding site from -169 to -160. Mutagenesis of a putative AP-2 binding site and tandem repeat of this site in plasmid resulted in a complete loss and increased responsiveness to Ox-LDL, respectively. Electrophoretic mobility shift assay showed that Ox-LDL increased the binding of certain nuclear protein(s) to a putative AP-2 binding site but decreased their binding to NF-kappaB binding site. Supershift assay showed that nuclear proteins bound to NF-kappaB binding site contained, at least, p50 and p65 but could not demonstrate nuclear protein(s) bound to a putative AP-2 binding site. Our results suggested that a putative AP-2 binding site from -169 to -160 was a positive responsive element to Ox-LDL and that the NF-kappaB binding site from -91 to -82 was a negative responsive element in Ox-LDL-induced GM-CSF transcription.

Animals↗

PubMed1999

Cloning from insulinoma cells of synapsin I associated with insulin secretory granules.

Synapsin I is a synaptic vesicle-associated protein involved in neurotransmitter release. The functions of this protein are apparently regulated by Ca2+/calmodulin-dependent protein kinase II (CaM kinase II). We reported evidence for CaM kinase II and a synapsin I-like protein present in mouse insulinoma MIN6 cells (Matsumoto, K., Fukunaga, K., Miyazaki, J., Shichiri, M., and Miyamoto, E. (1995) Endocrinology 136, 3784-3793). Phosphorylation of the synapsin I-like protein in these cells correlated with the activation of CaM kinase II and insulin secretion. In the present study, we screened the MIN6 cDNA library with the full-length cDNA probe of rat brain synapsin Ia and obtained seven positive clones; the largest one was then sequenced. The largest open reading frame deduced from the cDNA sequence of 3695 base pairs encoded a polypeptide of 670 amino acids, which exhibited significant sequence similarity to rat synapsin Ib. The cDNA contained the same sequence as the first exon of the mouse synapsin I gene. These results indicate that synapsin Ib is present in MIN6 cells. Synapsin I was expressed in normal rat islets, as determined by reverse transcriptase-polymerase chain reaction analysis. Immunoblot analysis after subcellular fractionation of MIN6 cells demonstrated that synapsin Ib and delta subunit of CaM kinase II co-localized with insulin secretory granules. By analogy concerning regulation of neurotransmitter release, our results suggest that phosphorylation of synapsin I by CaM kinase II may induce the release of insulin from islet cells.

Amino Acid Sequence↗

PubMed1999

Genomic organization and expression analysis of the mouse qkI locus.

qkI, encoding a KH domain-containing RNA binding protein, has been isolated as a candidate gene for the mouse neurological mutation quaking. Here, we describe detailed studies on its genomic structure and expression pattern. We isolated approximately 1 Mb of genomic region containing the quaking locus and determined its genomic organization. The qkI locus contains at least 9 exons spanning approximately 65 kb of DNA. It gives rise to six distinct transcripts encoding, theoretically, five different protein isoforms. Exons 1 through 4 are shared by all the transcripts, whereas coding exons and two distinct 3'-UTRs downstream to the exon 4 are differentially utilized. One isoform has a truncated KH domain and may act as an antagonist to the others. These findings and identification of a single transcription initiation site suggest that differential expression of each transcript is regulated by alternative splicing. Expression of each alternative transcript and protein product was also examined. Two types of transcripts, 5 kb-A and B, are most abundant in the brain of newborn mice and are gradually downregulated thereafter. In contrast, the other three messages, 6 kb, 7 kb-A and B, increase as myelination proceeds and peak at 2 weeks of age, corresponding to the most active stage of myelination. Although the qkI messages and their products are abundant in brain and heart, a lower level of expression was found in various other tissues tested. Alternative transcripts that share the same 3'-UTR showed very similar expression patterns, suggesting a regulatory role of the 3'-UTRs in qkI gene expression.

3' Untranslated Regions↗

PubMed1999

Insulin inhibits glucagon secretion by the activation of PI3-kinase in In-R1-G9 cells.

Intracellular mechanisms through which insulin inhibits glucagon secretion remain to be elucidated in glucagon secreting cells. In this study, we confirmed that, in In-R1-G9 cells, a pancreatic alpha cell line, insulin stimulated phosphorylation of insulin receptor substrate-1 (IRS-1) and activated phosphatidylinositol 3-kinase (PI3-kinase). We further studied, using wortmannin, an inhibitor of PI3-kinase, whether the inhibitory effect of insulin on glucagon secretion was mediated through PI3-kinase pathway in these cells. In static incubation studies, insulin significantly inhibited glucagon secretion at 2, 6 and 12 h, which was completely abolished by pretreatment with wortmannin. In perifusion studies, insulin significantly suppressed glucagon secretion after 10 min, which was also blocked by wortmannin. Insulin also reduced glucagon mRNA at 6 and 12 h but not at 2 h. Wortmannin also abolished insulin-induced reduction of glucagon mRNA. Insulin increased the amount of 85 kDa subunit of PI3-kinase in plasma membrane fraction (PM), with a reciprocal decrease of the kinase in cytosol fraction (CY). Insulin also increased PI3-kinase activity in PM, but not in CY. Our results suggest that insulin suppressed glucagon secretion by inhibiting glucagon release and gene expression. Both actions were mediated by activation of PI3-kinase. Recruitment and activation of PI3-kinase in plasma membrane might be relevant at least in part to insulin-induced inhibition of glucagon release.

Androstadienes↗

PubMed1999

Natriuretic peptides and nitric oxide induce endothelial apoptosis via a cGMP-dependent mechanism.

Apoptosis is a mode of cell death in which the cell participates in its own demise. We studied whether endothelium-derived relaxing factor, nitric oxide (NO), and natriuretic peptides affect apoptosis of rat vascular endothelial cells via a cGMP-dependent pathway and whether such effects are antagonized by an endothelium-derived vasoconstrictor, endothelin-1 (ET-1). Three natriuretic peptides (atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide) induced endothelial apoptosis as demonstrated by nucleosomal laddering on agarose gel electrophoresis and by the terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling method. This dose-dependent relation was assessed by quantifying the fragmented and intact DNA contents by the diphenylamine method. The atrial natriuretic peptide-induced endothelial apoptosis was completely blocked by a guanylate cyclase-coupled receptor antagonist (HS-142-1) and an inhibitor of cGMP-dependent protein kinase (KT5823). An NO donor, NOR3 ((+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide; FK409) also induced endothelial apoptosis; the effect of this compound was abrogated by KT5823 and an inhibitor of soluble guanylate cyclase, ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one). A cGMP derivative, 8-bromo-cGMP, but not the cAMP derivative 8-bromo-cAMP, caused endothelial apoptosis; the effect of ODQ was also abrogated by KT5823. Endothelial apoptosis induced by ANP, NOR3, and 8-bromo-cGMP was similarly antagonized by ET-1. ANP, NOR3, and 8-bromo-cGMP caused marked accumulations of the tumor suppressor gene product p53 but not of bcl-2, as determined by Western blot analysis. These results demonstrate for the first time that endothelium-derived NO and natriuretic peptides are proapoptotic factors for endothelial cells, whereas the endothelium-derived vasoconstrictor ET-1 is an antiapoptotic factor, suggesting that the countervailing balance between these vasodilators and vasoconstrictors, in addition to regulation of vascular tonus, may contribute to endothelial cell integrity.

Animals↗