Long-term interleukin-1alpha treatment inhibits insulin signaling via IL-6 production and SOCS3 expression in 3T3-L1 adipocytes

Proinflammatory cytokines are well-known to inhibit insulin signaling to result in insulin resistance. IL-1alpha is also one of the proinflammatory cytokines, but the mechanism of how IL-1alpha induces insulin resistance remains unclear. We have now examined the effects of IL-1alpha on insulin signaling in 3T3-L1 adipocytes. Prolonged IL-1alpha treatment for 12 to 24 hours partially decreased the protein levels as well as the insulin-stimulated tyrosine phosphorylation of IRS-1 and Akt phosphorylation. mRNA for SOCS3, an endogenous inhibitor of insulin signaling, was dramatically augmented 4 hours after IL-1alpha treatment. Concomitantly, the level of IL-6 in the medium and STAT3 phosphorylation were increased by the prolonged IL-1alpha treatment. Addition of anti-IL-6 neutralizing antibody to the medium or overexpression of dominant-negative STAT3 decreased the IL-1alpha-stimulated STAT3 activation and SOCS3 induction, and ameliorated insulin signaling. These results suggest that the IL-1alpha-mediated deterioration of insulin signaling is largely due to the IL-6 production and SOCS3 induction in 3T3-L1 adipocytes.

A case of retropharyngeal abscess caused by penicillin-resistant Streptococcus pneumoniae

We report here a case of a 1-year-old girl with retropharyngeal abscess caused by penicillin-resistant Streptococcus pneumoniae (PRSP). Computed tomography disclosed a retropharyngeal mass lesion (4 cm x 3 cm in diameter), and the diagnosis was confirmed by needle aspiration of the retropharyngeal space, which yielded PRSP. To our knowledge, this is the first report of a young subject in whom retropharyngeal abscess was caused by this organism. Retropharyngeal abscess is most common in children younger than 3 or 4 years of age, during which period a high carriage rate of PRSP is also shown. This patient was successfully treated with panipenem/betamipron.

Tyrosine phosphorylation-dependent and -independent role of Shc in the regulation of IGF-1-induced mitogenesis and glycogen synthesis

To examine the functional role of Shc tyrosine phosphorylation in IGF-1 signaling, wild-type (WT)-Shc and Y239,240,317F (3F)-Shc were transiently transfected into L6 myoblasts. IGF-1 signaling was compared among the transfected cells. IGF-1-induced tyrosine phosphorylation of Shc and its subsequent association with Grb2 were increased in WT-Shc cells, whereas they were decreased in 3F-Shc cells compared with those in parental L6 cells. Consistent with their changes, IGF-1-induced MAPK activation and thymidine incorporation were enhanced in WT-Shc cells, whereas they were again decreased in 3F-Shc cells. It is possible that Shc and insulin receptor substrate (IRS)-1 can interact competitively, via their phosphotyrosine binding (PTB) domains, with the activated IGF-1 receptor. In this regard, IGF-1-induced tyrosine phosphorylation of IRS-1 was decreased by overexpressing both WT-Shc and 3F-Shc cells. Consistent with the decrease, IGF-1-induced IRS-1 association with the p85 subunit of PI3K and activation of PI3K and Akt were reduced in both WT-Shc and 3F-Shc cells. As a result, IGF-1-induced glycogen synthesis was also decreased in both cells. Furthermore, expression of Shc PTB domain alone inhibited IGF-1 stimulation of Akt and glycogen synthesis. These results indicate that tyrosine phosphorylation of Shc is important for IGF-1 stimulation of MAPK leading to mitogenesis and that Shc, via its PTB domain, negatively regulates IGF-1-induced glycogen synthesis by competing with IRS-1, which is not relevant to Shc tyrosine phosphorylation.

[A pediatric case of acute focal bacterial nephritis; comparison with the reports in Japanese child cases]

We report an 8-year-old boy with acute focal bacterial nephritis (AFBN). At the age of 3 months, he had a history of urinary tract infection and vesicoureteral reflux. He was admitted to our hospital because of high fever and costovertebral angle pain. Although acute pyelonephritis was suspected, neither pyuria nor cultures of blood and urine were positive. An initial ultrasonogram (US) of his kidneys was normal except for bilateral hydronephrosis. Two days later, however, a computed tomography (CT) revealed a poorly enhanced mass in the upper pole of the right kidney. Similar findings were also observed by US. Under the diagnosis of AFBN, he received antibiotics for 3 weeks. Voiding cystourethrogram showed both-sided vesicoureteral reflux and he underwent an operation. At present the mass of the kidney still remains, albeit its size tends to decrease. We suggest that an early examination of US or enhanced CT is necessary in cases with fever of unknown origin, considering the possibility of AFBN even if neither pyuria nor cultures of urine are positive.

SH2-containing inositol phosphatase 2 negatively regulates insulin-induced glycogen synthesis in L6 myotubes

AIMS/HYPOTHESIS

PI(3,4,5)P3 produced by PI3-kinase seems to be a key mediator for insulin's metabolic actions. We have recently cloned rat SHIP2 cDNA which is abundantly expressed in target tissues of insulin. Here, we clarify the role of SHIP2 possessing 5'-phosphatase activity toward PI(3,4,5)P3 in insulin signalling in the skeletal muscle.

METHODS

The role of SHIP2 in insulin-induced glycogen synthesis was studied by expressing wild-type (WT)-SHIP2 and a 5'-phosphatase defective (Delta IP)-SHIP2 into L6 myotubes by means of adenovirus mediated gene transfer.

RESULTS

The early events of insulin signalling including tyrosine phosphorylation of the insulin receptor and IRS-1, IRS-1 association with the p85 subunit, and PI3-kinase activity were not affected by expression of WT- and Delta IP-SHIP2. Although PI(3,4,5)P3 and PI(3,4)P2 are known to possibly activate a downstream molecule of PI3-kinase Akt in vitro, overexpression of WT-SHIP2 inhibited insulin-induced phosphorylation and activation of Akt. Conversely, Akt activity was increased by expression of Delta IP-SHIP2. GSK3 beta located downstream of Akt is an important molecule to further transmit insulin signal for glycogen synthesis in skeletal muscles. In accordance with the results of Akt, insulin-induced phosphorylation and inactivation of GSK3 beta, subsequent activation of glycogen synthase and glycogen synthesis were decreased by expression of WT-SHIP2, whereas these events were increased by expression of Delta IP-SHIP2.

CONCLUSION/INTERPRETATION

Our results indicate that SHIP2 plays a negative regulatory role via the 5'-phosphatase activity in insulin signalling, and that PI(3,4,5)P3 rather than PI(3,4)P2 is important for in vivo regulation of insulin-induced Akt activation leading to glycogen synthesis in L6 myotubes.

[Surveillance of various enteropathogenic bacteria from diarrheal cases during 1989-1999 in Kobe City]

Incidence of various enteropathogenic bacteria was examined from diarrheal faecal samples that were collected from the patients of Kobe City General Hospital and some station hospitals (23,862), and from overseas travelers (2,855) over a period of decade (1989-1999) in Kobe. A total of 1,580 strains were isolated from domestic and 331 strains from overseas travelers. The results are as follows. 1) Thirteen kinds of enteropathogenic bacteria were isolated from domestic diarrheal cases (6.6%). Salmonella was the most predominant bacteria followed by Campylobacter, Vibrio parahaemolyticus, enteropathogenic Escherichia coli and Shigella. 2) Eleven kinds of enteropathogenic bacteria were isolated from overseas diarrheal travelers (11.6%). The most frequently isolated species was Salmonella, followed by Vibrio parahaemolyticus, Shigella and Plesiomonas shigelloides. 3) Of Salmonella strains isolated from domestic and overseas diarrheal cases, serovar Enteritidis was the most predominant. Other frequent serovars in both cases were Typhimurium, Tennessee, Hadar, Infantis, Blockley and Montevideo. 4) Antibiotics resistant rate of the isolated Salmonella strains was 42.6% for domestic samples and 29.3% for overseas diarrheal cases. In domestic cases. Enteritidis was resistance to streptomycin only and the multiple antibiotic resistance was observed in Typhimurium serovars. In overseas samples, the multiple antibiotic resistance was seen in a few Typhimurium, Anatum and Blockley strains. 5) Among Shigella, S. sonnei was isolated from both domestic and overseas cases. The frequency of acquiring infection was the highest in India, followed by Indonesia, Thailand and Nepal. 6) With reference to the incidence of the members of the genus Vibrio, Aeromonas and Plesiomonas, V. parahaemolyticus were abundant from domestic samples where as V. parahaemolyticus, P. shigelloides, Vibrio cholerae non-O1 and Vibrio cholerae O1 were isolated more frequently from overseas samples. The frequency of acquiring infection was the highest in Thailand, followed by Indonesia and India.

Mammalian target of rapamycin pathway regulates insulin signaling via subcellular redistribution of insulin receptor substrate 1 and integrates nutritional signals and metabolic signals of insulin

A pathway sensitive to rapamycin, a selective inhibitor of mammalian target of rapamycin (mTOR), down-regulates effects of insulin such as activation of Akt (protein kinase B) via proteasomal degradation of insulin receptor substrate 1 (IRS-1). We report here that the pathway also plays an important role in insulin-induced subcellular redistribution of IRS-1 from the low-density microsomes (LDM) to the cytosol. After prolonged insulin stimulation, inhibition of the redistribution of IRS-1 by rapamycin resulted in increased levels of IRS-1 and the associated phosphatidylinositol (PI) 3-kinase in both the LDM and cytosol, whereas the proteasome inhibitor lactacystin increased the levels only in the cytosol. Since rapamycin but not lactacystin enhances insulin-stimulated 2-deoxyglucose (2-DOG) uptake, IRS-1-associated PI 3-kinase localized at the LDM was suggested to be important in the regulation of glucose transport. The amino acid deprivation attenuated and the amino acid excess enhanced insulin-induced Ser/Thr phosphorylation and subcellular redistribution and degradation of IRS-1 in parallel with the effects on phosphorylation of p70 S6 kinase and 4E-BP1. Accordingly, the amino acid deprivation increased and the amino acid excess decreased insulin-stimulated activation of Akt and 2-DOG uptake. Furthermore, 2-DOG uptake was affected by amino acid availability even when the degradation of IRS-1 was inhibited by lactacystin. We propose that subcellular redistribution of IRS-1, regulated by the mTOR-dependent pathway, facilitates proteasomal degradation of IRS-1, thereby down-regulating Akt, and that the pathway also negatively regulates insulin-stimulated glucose transport, probably through the redistribution of IRS-1. This work identifies a novel function of mTOR that integrates nutritional signals and metabolic signals of insulin.

Growth hormone induces cellular insulin resistance by uncoupling phosphatidylinositol 3-kinase and its downstream signals in 3T3-L1 adipocytes

Growth hormone (GH) is well known to induce in vivo insulin resistance. However, the molecular mechanism of GH-induced cellular insulin resistance is largely unknown. In this study, we demonstrated that chronic GH treatment of differentiated 3T3-L1 adipocytes reduces insulin-stimulated 2-deoxyglucose (DOG) uptake and activation of Akt (also known as protein kinase B), both of which are downstream effects of phosphatidylinositol (PI) 3-kinase, despite enhanced tyrosine phosphorylation of insulin receptor substrate (IRS)-1, association of IRS-1 with the p85 subunit of PI 3-kinase, and IRS-1-associated PI 3-kinase activity. In contrast, chronic GH treatment did not affect 2-DOG uptake and Akt activation induced by overexpression of a membrane-targeted form of the p110 subunit of PI 3-kinase (p110(CAAX)) or Akt activation stimulated by platelet-derived growth factor. Fractionation studies indicated that chronic GH treatment reduces insulin-stimulated translocation of Akt from the cytosol to the plasma membrane. Interestingly, chronic GH treatment increased insulin-stimulated association of IRS-1 with p85 and IRS-1-associated PI 3-kinase activity preferentially in the cytosol. These results indicate that cellular insulin resistance induced by chronic GH treatment in 3T3-L1 adipocytes is caused by uncoupling between activation of PI 3-kinase and its downstream signals, which is specific to the insulin-stimulated PI 3-kinase pathway. This effect of GH might result from the altered subcellular distribution of IRS-1-associated PI 3-kinase.

Potential role of Gab1 and phospholipase C-gamma in osmotic shock-induced glucose uptake in 3T3-L1 adipocytes

Osmotic shock induces GLUT4 translocation and glucose uptake through a mechanism independent of PI 3-kinase, but dependent on tyrosine phosphorylation of cellular proteins. To identify the tyrosine phosphorylated proteins required for osmotic shock-stimulated glucose uptake, we examined tyrosine phosphorylation of candidate proteins, and found that the 60-80kDa species including paxillin and the 120-130kDa species including p130Cas, PYK2, FAK and Gab1 were tyrosine-phosphorylated in response to osmotic shock. Inhibition of actin polymerization by cytochalasin D significantly decreased the tyrosine phosphorylation of paxillin, p130Cas, PYK2 and FAK but not Gab1, but had no effect on 2-deoxyglucose (DOG) uptake, suggesting a role for Gab1 in osmotic shock-induced glucose transport. Also, we found that osmotic shock increases the association of phospholipase C-gamma (PLC-gamma) with Gab1 and stimulates tyrosine phosphorylation of PLC-gamma itself. The PLC inhibitor, U73122, inhibited osmotic shock-induced 2-DOG uptake. These results suggest that tyrosine phosphorylation of Gab1 and subsequent recruitment and activation of PLC-gamma may play a role in osmotic shock-induced glucose transport.

Pioglitazone ameliorates tumor necrosis factor-alpha-induced insulin resistance by a mechanism independent of adipogenic activity of peroxisome proliferator--activated receptor-gamma

Tumor necrosis factor (TNF)-alpha is one of the candidate mediators of insulin resistance associated with obesity, a major risk factor for the development of type 2 diabetes. The insulin resistance induced by TNF-alpha is antagonized by thiazolidinediones (TZDs), a new class of insulin-sensitizing drugs. The aim of the current study was to dissect the mechanism whereby pioglitazone, one of the TZDs, ameliorates TNF-alpha-induced insulin resistance in 3T3-L1 adipocytes. Pioglitazone restored insulin-stimulated 2-deoxyglucose (DOG) uptake, which was reduced by TNF-alpha, with concomitant restorations in tyrosine phosphorylation and protein levels of insulin receptor (IR) and insulin receptor substrate (IRS)-1, as well as association of the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase with IRS-1 and PI 3-kinase activity. Adenovirus-mediated gene transfer of either wild-type human peroxisome proliferator-activated receptor (PPAR)-gamma2 or a mutant carrying a replacement at the consensus mitogen-activated protein kinase phosphorylation site (hPPAR-gamma2-S112A) promoted adipogenesis of 3T3-L1 fibroblasts and restored TNF-alpha-induced decrease of triglyceride in adipocytes as effectively as pioglitazone. Overexpression of the PPAR-gamma proteins in TNF-alpha-treated adipocytes restored protein levels of IR/IRS-1, but did not improve insulin-stimulated tyrosine phosphorylation of IR/IRS-1 or insulin-stimulated 2-DOG uptake. These results indicate that the ability of pioglitazone to restore insulin-stimulated tyrosine phosphorylation of IR/IRS-1, which is necessary for amelioration of TNF-alpha-induced insulin resistance, may be independent of the adipogenic activity of PPAR-gamma that regulates protein levels of IR/IRS-1.

Oxidative stress in childhood meningitis: measurement of 8-hydroxy-2'-deoxyguanosine concentration in cerebrospinal fluid

To examine the involvement of reactive oxygen species, we measured the concentration of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative stress, in cerebrospinal fluid samples from 63 children with and without meningitis. We observed that the mean concentration of 8-OHdG in samples obtained during the early phase of bacterial meningitis, but not aseptic meningitis, was significantly higher than that in control samples. Clinical and laboratory improvement was associated with a fall in the 8-OHdG concentration in the patients with bacterial meningitis. Our findings suggest the presence of enhanced oxidative stress in the central nervous system of children with bacterial meningitis.

Overexpression of SH2-containing inositol phosphatase 2 results in negative regulation of insulin-induced metabolic actions in 3T3-L1 adipocytes via its 5'-phosphatase catalytic activity

Phosphatidylinositol (PI) 3-kinase plays an important role in various metabolic actions of insulin including glucose uptake and glycogen synthesis. Although PI 3-kinase primarily functions as a lipid kinase which preferentially phosphorylates the D-3 position of phospholipids, the effect of hydrolysis of the key PI 3-kinase product PI 3,4,5-triphosphate [PI(3,4,5)P3] on these biological responses is unknown. We recently cloned rat SH2-containing inositol phosphatase 2 (SHIP2) cDNA which possesses the 5'-phosphatase activity to hydrolyze PI(3,4,5)P3 to PI 3,4-bisphosphate [PI(3,4)P2] and which is mainly expressed in the target tissues of insulin. To study the role of SHIP2 in insulin signaling, wild-type SHIP2 (WT-SHIP2) and 5'-phosphatase-defective SHIP2 (Delta IP-SHIP2) were overexpressed in 3T3-L1 adipocytes by means of adenovirus-mediated gene transfer. Early events of insulin signaling including insulin-induced tyrosine phosphorylation of the insulin receptor beta subunit and IRS-1, IRS-1 association with the p85 subunit, and PI 3-kinase activity were not affected by expression of either WT-SHIP2 or Delta IP-SHIP2. Because WT-SHIP2 possesses the 5'-phosphatase catalytic region, its overexpression marked by decreased insulin-induced PI(3,4,5)P3 production, as expected. In contrast, the amount of PI(3,4,5)P3 was increased by the expression of Delta IP-SHIP2, indicating that Delta IP-SHIP2 functions in a dominant-negative manner in 3T3-L1 adipocytes. Both PI(3,4,5)P3 and PI(3,4)P2 were known to possibly activate downstream targets Akt and protein kinase C lambda in vitro. Importantly, expression of WT-SHIP2 inhibited insulin-induced activation of Akt and protein kinase C lambda, whereas these activations were increased by expression of Delta IP-SHIP2 in vivo. Consistent with the regulation of downstream molecules of PI 3-kinase, insulin-induced 2-deoxyglucose uptake and Glut4 translocation were decreased by expression of WT-SHIP2 and increased by expression of Delta IP-SHIP2. In addition, insulin-induced phosphorylation of GSK-3beta and activation of PP1 followed by activation of glycogen synthase and glycogen synthesis were decreased by expression of WT-SHIP2 and increased by the expression of Delta IP-SHIP2. These results indicate that SHIP2 negatively regulates metabolic signaling of insulin via the 5'-phosphatase activity and that PI(3,4,5)P3 rather than PI(3,4)P2 is important for in vivo regulation of insulin-induced activation of downstream molecules of PI 3-kinase leading to glucose uptake and glycogen synthesis.

A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1

Insulin receptor substrate-1 (IRS-1) is a major substrate of the insulin receptor and acts as a docking protein for Src homology 2 domain containing signaling molecules that mediate many of the pleiotropic actions of insulin. Insulin stimulation elicits serine/threonine phosphorylation of IRS-1, which produces a mobility shift on SDS-PAGE, followed by degradation of IRS-1 after prolonged stimulation. We investigated the molecular mechanisms and the functional consequences of these phenomena in 3T3-L1 adipocytes. PI 3-kinase inhibitors or rapamycin, but not the MEK inhibitor, blocked both the insulin-induced electrophoretic mobility shift and degradation of IRS-1. Adenovirus-mediated expression of a membrane-targeted form of the p110 subunit of phosphatidylinositol (PI) 3-kinase (p110CAAX) induced a mobility shift and degradation of IRS-1, both of which were inhibited by rapamycin. Lactacystin, a specific proteasome inhibitor, inhibited insulin-induced degradation of IRS-1 without any effect on its electrophoretic mobility. Inhibition of the mobility shift did not significantly affect tyrosine phosphorylation of IRS-1 or downstream insulin signaling. In contrast, blockade of IRS-1 degradation resulted in sustained activation of Akt, p70 S6 kinase, and mitogen-activated protein (MAP) kinase during prolonged insulin treatment. These results indicate that insulin-induced serine/threonine phosphorylation and degradation of IRS-1 are mediated by a rapamycin-sensitive pathway, which is downstream of PI 3-kinase and independent of ras/MAP kinase. The pathway leads to degradation of IRS-1 by the proteasome, which plays a major role in down-regulation of certain insulin actions during prolonged stimulation.

Retinoblastoma protein phosphorylation via PI 3-kinase and mTOR pathway regulates adipocyte differentiation

In the early phase of adipocyte differentiation, transient increase of DNA synthesis, called clonal expansion, and transient hyperphosphorylation of retinoblastoma protein (Rb) are observed. We investigated the role of these phenomena in insulin-induced adipocyte differentiation of 3T3-L1 cells. Insulin-induced clonal expansion, Rb phosphorylation and adipocyte differentiation were all inhibited by the PI 3-kinase inhibitors and rapamycin, but not the MEK inhibitor, whereas the MEK inhibitor, but not PI 3-kinase inhibitors or rapamycin, decreased c-fos induction. We conclude that insulin induces hyperphosphorylation of Rb via PI 3-kinase and mTOR dependent pathway, which promotes clonal expansion and adipocyte differentiation of 3T3-L1 cells.

A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1

Insulin receptor substrate-1 (IRS-1) is a major substrate of the insulin receptor and acts as a docking protein for Src homology 2 domain containing signaling molecules that mediate many of the pleiotropic actions of insulin. Insulin stimulation elicits serine/threonine phosphorylation of IRS-1, which produces a mobility shift on SDS-PAGE, followed by degradation of IRS-1 after prolonged stimulation. We investigated the molecular mechanisms and the functional consequences of these phenomena in 3T3-L1 adipocytes. PI 3-kinase inhibitors or rapamycin, but not the MEK inhibitor, blocked both the insulin-induced electrophoretic mobility shift and degradation of IRS-1. Adenovirus-mediated expression of a membrane-targeted form of the p110 subunit of phosphatidylinositol (PI) 3-kinase (p110CAAX) induced a mobility shift and degradation of IRS-1, both of which were inhibited by rapamycin. Lactacystin, a specific proteasome inhibitor, inhibited insulin-induced degradation of IRS-1 without any effect on its electrophoretic mobility. Inhibition of the mobility shift did not significantly affect tyrosine phosphorylation of IRS-1 or downstream insulin signaling. In contrast, blockade of IRS-1 degradation resulted in sustained activation of Akt, p70 S6 kinase, and mitogen-activated protein (MAP) kinase during prolonged insulin treatment. These results indicate that insulin-induced serine/threonine phosphorylation and degradation of IRS-1 are mediated by a rapamycin-sensitive pathway, which is downstream of PI 3-kinase and independent of ras/MAP kinase. The pathway leads to degradation of IRS-1 by the proteasome, which plays a major role in down-regulation of certain insulin actions during prolonged stimulation.

[Clinical evaluation of pioglitazone]

Pioglitazone is the second thiazolidinedione derivative to be clinically used for type 2 diabetes in Japan. It is ten times more potent than troglitazone in glucose-lowering effect. Favourable effects against abnormal lipid levels including decreasing blood triglyceride levels, free fatty acid levels and increasing HDL-cholesterol is advantage to treat obese diabetic patient who may develop atherosclerosis. Up to now, there has been no report of severe hepatic dysfunction due to pioglitazone treatment. Pioglitazone should be carefully monitored in its clinical treatment regarding possible its side effect of hepatic dysfunction.

Role of the Src homology 2 (SH2) domain and C-terminus tyrosine phosphorylation sites of SH2-containing inositol phosphatase (SHIP) in the regulation of insulin-induced mitogenesis

To examine the role of SHIP in insulin-induced mitogenic signaling, we used a truncated SHIP lacking the SH2 domain (deltaSH2-SHIP) and a Y917/1020F-SHIP (2F-SHIP) in which two tyrosines contributing to Shc binding were mutated to phenylalanine. Wild-type (WT)-, deltaSH2-, and 2F-SHIP were transiently transfected into Rat1 fibroblasts overexpressing insulin receptors (HIRc). Insulin-stimulated tyrosine phosphorylation of WT-SHIP and deltaSH2-SHIP, whereas tyrosine phosphorylation of 2F-SHIP was not detectable, indicating that 917/1020-Tyr are key phosphorylation sites on SHIP. Although SHIP can bind via its 917/1020-Tyr residues and SH2 domain to Shc PTB domain and 317-Tyr residue, respectively, insulin-induced SHIP association with Shc was more greatly decreased in 2F-SHIP cells than that in deltaSH2-SHIP cells. Insulin stimulation of Shc association with Grb2, which is important for p21ras-MAP kinase activation, was decreased by overexpression of WT- and 2F-SHIP. Importantly, insulin-induced Shc x Grb2 association was not detectably reduced in deltaSH2-SHIP cells. In accordance with the extent of Shc association with Grb2, insulin-induced MAP kinase activation was relatively decreased in both WT-SHIP and 2F-SHIP cells, but not in deltaSH2-SHIP cells. To examine the functional role of SHIP in insulin's biological action, insulin-induced mitogenesis was compared among these transfected cells. Insulin stimulation of thymidine incorporation and bromodeoxyuridine incorporation was decreased in WT-SHIP cells compared with that of control HIRc cells. Expression of 2F-SHIP also significantly reduced insulin-induced mitogenesis, whereas it was only slightly affected by overexpression of deltaSH2-SHIP. Furthermore, the reduction of insulin-induced mitogenesis in WT-SHIP cells was partly compensated by coexpression of Shc. These results indicate that SHIP plays a negative regulatory role in insulin-induced mitogenesis and that the SH2 domain of SHIP is important for its negative regulatory function.

Differential effects of palmitate on glucose uptake in rat-1 fibroblasts and 3T3-L1 adipocytes

Non-esterified fatty acids are thought to be one of the causes for insulin resistance. However, the molecular mechanism of fatty acid-induced insulin resistance is not clearly known. In this study, we first examined the effect of palmitate on insulin signaling in 3T3-L1 adipocytes. We found that 1h treatment with 1 mmol/l palmitate had no effect on insulin binding, tyrosine phosphorylation of insulin receptors, 185 kDa proteins and Shc, and PI3 kinase activity in 3T3-L1 adipocytes. Then, the effects of palmitate on MAP kinase activity and glucose uptake in fully differentiated 3T3-L1 adipocytes were compared with those in poorly differentiated 3T3-L1 cells and in HIRc-B cells. Palmitate treatment had no effect on MAP kinase activity in fully differentiated 3T3-L1 adipocytes, while it inhibited MAP kinase in poorly differentiated 3T3-L1 cells and HIRc-B cells. Glucose transport in 3T3-L1 adipocytes treated with palmitate for 1 h, 4 h and 16 h was higher than that in control cells, but palmitate treatment caused a rightward shift of the insulin-dose responsive curve for glucose uptake in HIRc-B cells. Palmitate treatment did not significantly affect basal and insulin-stimulated GLUT4 translocation. When the cells were treated with PD98059, a specific MEK inhibitor, insulin-stimulated glucose uptake was not affected in 3T3-L1 adipocytes, while it was almost completely inhibited in HIRc-B cells. These results suggest the primary effect of palmitate on adipocytes may not involve insulin resistance of adipocytes themselves.

Synergistic role of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase cascade in the regulation of insulin receptor trafficking

To examine the molecular mechanism of insulin receptor trafficking, we investigated the intracellular signaling molecules that regulate this process in Rat1 fibroblasts overexpressing insulin receptors. Cellular localization of insulin receptors was assessed by confocal laser microscopy with indirect immunofluorescence staining. Insulin receptors were visualized diffusely in the basal state. Insulin treatment induced the change of insulin receptor localization to perinuclear compartment. This insulin-induced insulin receptor trafficking was not affected by treatment of the cells with PI3-kinase inhibitor (wortmannin), whereas treatment with MEK [mitogen-activated protein (MAP) kinase-Erk kinase] inhibitor (PD98059) partly inhibited the process in a dose-dependent manner. Interestingly, treatment with both wortmannin and PD98059 almost completely inhibited insulin receptor trafficking. The functional importance of PI3-kinase and MAP kinase in the trafficking process was directly assessed by using single cell microinjection analysis. Microinjection of p85-SH2 and/or catalytically inactive MAP kinase ([K71A]Erk1) GST fusion protein gave the same results as treatment with wortmannin and PD98059. Furthermore, to determine the crucial step for the requirement of PI3-kinase and MAP kinase pathways, the effect of wortmannin and PD98059 on insulin receptor endocytosis was studied. Insulin internalization from the plasma membrane and subsequent insulin degradation were not affected by treatment with wortmannin and PD98059. In contrast, insulin receptor down-regulation from the cell surface and insulin receptor degradation, after prolonged incubation with insulin, were markedly impaired by the treatment. These results suggest that PI3-kinase and MAP kinase pathways synergistically regulate insulin receptor trafficking at a step subsequent to the receptor internalization.

Molecular cloning of rat SH2-containing inositol phosphatase 2 (SHIP2) and its role in the regulation of insulin signaling

SH2-containing inositol 5'-phosphatase (SHIP) plays a negative regulatory role in hematopoietic cells. We have now cloned the rat SHIP isozyme (SHIP2) cDNA from skeletal muscle, which is one of the most important target tissue of insulin action. Rat SHIP2 cDNA encodes a 1183-amino-acid protein that is 45% identical with rat SHIP. Rat SHIP2 contains an amino-terminal SH2 domain, a central 5'-phosphoinositol phosphatase activity domain, and a phosphotyrosine binding (PTB) consensus sequence and a proline-rich region at the carboxyl tail. Specific antibodies to SHIP2 were raised and the function of SHIP2 was studied by stably overexpressing rat SHIP2 in Rat1 fibroblasts expressing human insulin receptors (HIRc). Endogenous SHIP2 underwent insulin-mediated tyrosine phosphorylation and phosphorylation was markedly increased when SHIP2 was overexpressed. Although overexpression of SHIP2 did not affect insulin-induced tyrosine phosphorylation of the insulin receptor beta-subunit and Shc, subsequent association of Shc with Grb2 was inhibited, possibly by competition between the SH2 domains of SHIP2 and Grb2 for the Shc phosphotyrosine. As a result, insulin-stimulated MAP kinase activation was reduced in SHIP2-overexpressing cells. Insulin-induced tyrosine phosphorylation of IRS-1, IRS-1 association with the p85 subunit of PI3-kinase, and PI3-kinase activation were not affected by overexpression of SHIP2. Interestingly, although both PtdIns-(3,4,5)P3 and PtdIns(3,4)P2 have been implicated in the regulation of Akt activity in vitro, overexpression of SHIP2 inhibited insulin-induced Akt activation, presumably by its 5'-inositol phosphatase activity. Furthermore, insulin-induced thymidine incorporation was decreased by overexpression of SHIP2. These results indicate that SHIP2 plays a negative regulatory role in insulin-induced mitogenesis, and regulation of the Shc. Grb2 complex and of the downstream products of PI3-kinase provides possible mechanisms of SHIP2 action in insulin signaling.

[Causative organisms of acute otitis media and acute sinusitis in children and their susceptibility of oral beta-lactam antibiotics]

The clinical efficacy of cefditoren pivoxil (CDTR-PI) was evaluated for 43 pediatric patients with acute otitis media or acute sinusitis. The causative organisms were identified and their susceptibilities to 6 oral beta-lactam antibiotics were measured; ampicillin (ABPC), cefaclor (CCL), cefdinir (CFDN), cefditoren pivoxil (CDTR-PI), cefteram pivoxil (CFTM-PI) and cefpodoxime proxetil (CPDX-PR). The ages of 43 patients were distributed from 4 months to 10 years and 7 months, and especially children under 4 years accounted for 72% (31 cases). In 22 cases (51%), Haemophilus influenzae or Streptococcus pneumoniae were identified as the pathogens, but in 18 cases, no causative organisms were defined. Treatment by CDTR-PI was successful in 12 cases out of 15 evaluable cases in which H. influenzae or S. pneumoniae were identified as the main causative organisms. From the susceptibility testing of them, some strains of H. influenzae were found to be ABPC-resistant and some strains of S. pneumoniae were benzylpenicillin (PCG)-resistant. To support above clinical evaluation of CDTR-PI, susceptibility testings on clinically isolated H. influenzae (81 strains) and S. pneumoniae (79 strains) were performed using above mentioned 6 oral beta-lactam antibiotics. The MIC80s against H. influenzae were; CDTR-PI 0.06 microgram/ml, CCL 2 micrograms/ml, CPDX-PR 0.125 microgram/ml, CFTM-PI 0.03 microgram/ml, CFDN 1 microgram/ml and ABPC 1 microgram/ml. Those against S. pneumoniae were; CDTR-PI 0.5 microgram/ml, CCL > 4 micrograms/ml, CPDX-PR 2 micrograms/ml, CFTM-PI 1 microgram/ml, CFDN 2 micrograms/ml and ABPC 1 microgram/ml. From those results, it was concluded that CDTR-PI or CFTM-PI may be preferable for the treatment of acute otitis media and acute sinusitis in children.

The functional role of CrkII in actin cytoskeleton organization and mitogenesis

Crk is a member of a family of adapter proteins predominantly composed of Src homology 2 and 3 domains, whose role in signaling pathways is presently unclear. Using an in situ electroporation system which permits the introduction of glutathione S-transferase (GST) fusion proteins into cells, we found that c-CrkII bound to p130(cas), but not to paxillin in serum-starved rat-1 fibroblasts overexpressing the human insulin receptor (HIRc cells) in vivo. 17 nM insulin stimulation dissociated the binding of c-CrkII to p130(cas), whereas 13 nM insulin-like growth factor-I, 16 nM epidermal growth factor (EGF), and 10% serum each showed little or no effect. We found that stress fiber formation is consistent with a change in the p130(cas).c-CrkII interactions before and after growth factor stimulation. Microinjection of either GST-Crk-SH2 or -Crk-(N)SH3 domains, or anti-Crk antibody each inhibited stress fiber formation before and after insulin-like growth factor-I, EGF, and serum stimulation. Insulin stimulation by itself caused stress fiber breakdown and there was no additive effect of microinjection. Microinjection of anti-p130(cas) antibody also blocked stress fiber formation in quiescent cells. Microinjection of the Crk-inhibitory reagents also inhibited DNA synthesis after insulin-like growth factor-I, EGF, and serum stimulation, but not after insulin. These data suggest that the complex containing p130(cas).c-CrkII may play a crucial role in actin cytoskeleton organization and in anchorage-dependent DNA synthesis.

Relative involvement of Shc tyrosine 239/240 and tyrosine 317 on insulin induced mitogenic signaling in rat1 fibroblasts expressing insulin receptors

Shc is phosphorylated on Tyr-239/240 and/or Tyr-317, which serves as a docking site for Grb2. To clarify the relative involvement of Shc Tyr-239/240 and Tyr-317 in insulin-induced mitogenesis, we generated expression vectors for Y317F (1F)-Shc, Y239/240F (2F)-Shc, and Y239/240/317F (3F)-Shc, and stably transfected them into Rat1 fibroblasts expressing insulin receptors (HIRc). Insulin-induced Shc phosphorylation and subsequent association with Grb2 was enhanced in wild-type (WT)-Shc cell. In contrast, insulin-stimulated Shc phosphorylation and Shc.Grb2 association were significantly decreased in 1F-Shc and 3F-Shc cells, while these were only slightly affected and almost comparable in 2F cells compared with those in parental HIRc cells. The kinetics of MAP kinase activation closely paralleled the kinetics of Shc phosphorylation and Shc.Grb2 association. Thus, insulin stimulation of MAP kinase activation occurred more rapidly in WT-Shc cells, and the activation was delayed in 1F-Shc and 3F-Shc cells, while it was comparable in 2F-Shc cells compared with that in HIRc cells. Furthermore, WT-Shc cells displayed enhanced sensitivity to insulin stimulation of thymidine incorporation. Importantly, the sensitivity was significantly decreased in 1F-Shc and 3F-Shc cells, while it was almost comparable in 2F-Shc cells compared with that in HIRc cells. These results indicate that Shc Tyr-317 is more predominant insulin-induced phosphorylation site than Tyr-239/240 for coupling with Grb2 leading to MAP kinase activation and mitogenesis in Rat1 fibroblasts.

[Transferability of tazobactam/piperacillin (TAZ/PIPC) to cerebrospinal fluid of rabbit with meningitis caused by Staphylococcus aureus]

The transferability of tazobactam/piperacillin (TAZ/PIPC) to cerebrospinal fluid (CSF) was studied employing rabbits with experimental meningitis caused by Staphylococcus aureus. 125 or 250 mg/kg of TAZ/PIPC was intravenously administered to rabbits with experimental meningitis then concentrations of TAZ and PIPC in CSF and serum were measured. In the group to which 125 mg/kg of TAZ/PIPC was administered, mean concentration of TAZ in CSF was 7.3 and 2.4 micrograms/ml at 30 and 60 min after administration, respectively, and concerning PIPC, it was 10.1 and 3.5 micrograms/ml, respectively. CSF/serum ratio of TAZ was 29.4% and 31.4%, respectively, and that of PIPC was 24.3 and 35.6%, respectively. In the group to which 250 mg/kg of TAZ/PIPC was administered, mean concentration of TAZ in CSF was 16.5 and 12.6% micrograms/ml, respectively, and concerning PIPC, it was 25.6 and 18.2 micrograms/ml, respectively. CSF/serum ratio of TAZ was 22.1 and 56.1%, respectively, and that of PIPC was 12.2 and 51.9%, respectively. Addition of TAZ did not make significant change of transferability of PIPC to CSF. Considering the antibacterial effect of TAZ/PIPC against main causative organism of meningitis, this agent was thought to be effective for the treatment of purulent meningitis.

Association of the insulin receptor with phospholipase C-gamma (PLCgamma) in 3T3-L1 adipocytes suggests a role for PLCgamma in metabolic signaling by insulin

Phospholipase C-gamma (PLCgamma) is the isozyme of PLC phosphorylated by multiple tyrosine kinases including epidermal growth factor, platelet-derived growth factor, nerve growth factor receptors, and nonreceptor tyrosine kinases. In this paper, we present evidence for the association of the insulin receptor (IR) with PLCgamma. Precipitation of the IR with glutathione S-transferase fusion proteins derived from PLCgamma and coimmunoprecipitation of the IR and PLCgamma were observed in 3T3-L1 adipocytes. To determine the functional significance of the interaction of PLCgamma and the IR, we used a specific inhibitor of PLC, U73122, or microinjection of SH2 domain glutathione S-transferase fusion proteins derived from PLCgamma to block insulin-stimulated GLUT4 translocation. We demonstrate inhibition of 2-deoxyglucose uptake in isolated primary rat adipocytes and 3T3-L1 adipocytes pretreated with U73122. Antilipolytic effect of insulin in 3T3-L1 adipocytes is unaffected by U73122. U73122 selectively inhibits mitogen-activated protein kinase, leaving the Akt and p70 S6 kinase pathways unperturbed. We conclude that PLCgamma is an active participant in metabolic and perhaps mitogenic signaling by the insulin receptor in 3T3-L1 adipocytes.

Involvement of heat shock protein 90 in the degradation of mutant insulin receptors by the proteasome

We previously reported three families with type A insulin-resistant syndrome who had mutations, either Asp1179 or Leu1193, in the kinase domain of the insulin receptor. The extreme insulin resistance of these patients was found to be caused by the decreased number of insulin receptors on the cell surface, due to the intracellular rapid degradation (Imamura, T., Takata, Y., Sasaoka, T., Takada, Y., Morioka, H., Haruta, T., Sawa, T., Iwanishi, M., Yang, G. H., Suzuki, Y., Hamada, J., and Kobayashi, M. (1994) J. Biol. Chem. 269, 31019-31027). In the present study, we first examined whether these mutations caused rapid degradation of unprocessed proreceptors, using the exon 13 deleted mutant insulin receptors (DeltaEx13-IR), which were accumulated in the endoplasmic reticulum as unprocessed proreceptors. The addition of Asp1179 or Leu1193 mutation to DeltaEx13-IR caused accelerated degradation of the unprocessed DeltaEx13-IR in the transfected COS-7 cells. Next, we tested whether these mutant receptors were degraded by the proteasome. Treatment with proteasome inhibitors Z-Leu-Leu-Nva-H (MG-115) or Z-Leu-Leu-Leu-H (MG-132) prevented the accelerated degradation of these mutant receptors, resulting in increased amounts of the mutant receptors in the COS-7 cells. Essentially the same results were obtained in the patient's transformed lymphocytes. Finally, we found that these mutant receptors bound to heat shock protein 90 (Hsp90). To determine whether Hsp90 played an important role in the accelerated receptor degradation, we examined the effect of anti-Hsp90 antibody on the mutant receptor degradation. The microinjection of anti-Hsp90 antibody into cells prevented the accelerated degradation of both Asp1179 and Leu1193 mutant insulin receptors. Taken together, these results suggest that Hsp90 is involved in dislocation of the mutant insulin receptors out of the endoplasmic reticulum into the cytosol, where the mutant receptors are degraded by the proteasome.

Nitric oxide in septic and aseptic meningitis in children

To investigate the involvement of nitric oxide (NO) in childhood meningitis, we measured the concentrations of NO2- (a stable metabolite of NO) in serial samples of cerebrospinal fluid (CSF) from 11 children with septic and 7 with aseptic meningitis and 26 control patients without meningitis. The mean concentration of NO2- in samples obtained during the early stages of septic meningitis, but not aseptic meningitis, was significantly higher than in control samples. Clinical and laboratory improvement following administration of antibiotics and dexamethasone was associated with a fall in CSF [NO2-] to normal levels in these patients. CSF [NO2-] remained almost consistently within the normal range in patients with aseptic meningitis. Our findings indicate that NO production is enhanced in the CSF compartment of children with septic meningitis and support the hypothesis that NO is involved in the pathophysiology of septic meningitis.

Ligand-independent GLUT4 translocation induced by guanosine 5'-O-(3-thiotriphosphate) involves tyrosine phosphorylation

To delineate the signaling pathway leading to glucose transport protein (GLUT4) translocation, we examined the effect of microinjection of the nonhydrolyzable GTP analog, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS), into 3T3-L1 adipocytes. Thirty minutes after the injection of 5 mM GTPgammaS, 40% of injected cells displayed surface GLUT4 staining indicative of GLUT4 translocation compared with 55% for insulin-treated cells and 10% in control IgG-injected cells. Treatment of the cells with the phosphatidylinositol 3-kinase inhibitor wortmannin or coinjection of GST-p85 SH2 fusion protein had no effect on GTPgammaS-mediated GLUT4 translocation. On the other hand, coinjection of antiphosphotyrosine antibodies (PY20) blocked GTPgammaS-induced GLUT4 translocation by 65%. Furthermore, microinjection of GTPgammaS led to the appearance of tyrosine-phosphorylated proteins around the periphery of the plasma membrane, as observed by immunostaining with PY20. Treatment of the cells with insulin caused a similar phosphotyrosine-staining pattern. Electroporation of GTPgammaS stimulated 2-deoxy-D-glucose transport to 70% of the extent of insulin stimulation. In addition, immunoblotting with phosphotyrosine antibodies after electroporation of GTPgammaS revealed increased tyrosine phosphorylation of several proteins, including 70- to 80-kDa and 120- to 130-kDa species. These results suggest that GTPgammaS acts upon a signaling pathway either downstream of or parallel to activation of phosphatidylinositol 3-kinase and that this pathway involves tyrosine-phosphorylated protein(s).

The small guanosine triphosphate-binding protein Rab4 is involved in insulin-induced GLUT4 translocation and actin filament rearrangement in 3T3-L1 cells

Insulin's stimulation of glucose transport involves the translocation of vesicles containing the glucose transporter GLUT4 to the plasma membrane. Small GTP-binding proteins have been implicated in the regulation of vesicular traffic. We studied the effects of microinjection of wild-type Rab4 glutathione S-transferase fusion protein (WT Rab4), a GTP-binding defective mutant (Rab4 N121I), a guanosine triphosphatase-defective mutant (Rab4 Q67L), and a Rab4 antibody on insulin-induced GLUT4 translocation in 3T3-L1 adipocytes. Microinjection of Rab4 N121I and Rab4 antibodies had no effect on basal GLUT4 staining, but inhibited insulin-induced GLUT4 translocation by 50% compared with that in control IgG-injected cells. WT Rab4 and Rab4 Q67L microinjection had no effect on either basal or insulin-induced GLUT4 translocation. Premixing and coinjection of the Rab4 antibody with WT Rab4 almost completely abolished its inhibitory effect on insulin-induced GLUT4 translocation. In contrast, microinjection of an antibody directed against the highly conserved region of Rab3 proteins had no effect on insulin-induced GLUT4. These results point to a direct role of Rab4 in insulin-induced GLUT4 translocation, and that this effect is dependent on nucleotide binding to the protein. We also studied the effect of microinjection of the same proteins on insulin-induced actin filament rearrangement (membrane ruffling) in the same cell line. Microinjection of Rab4 N121I and Rab4 antibodies inhibited insulin-induced membrane ruffling by 40%, whereas WT Rab4 or a Rab3 antibody injection had no effect on cytoskeletal rearrangement. In summary, 1) Rab4 is a necessary component of the insulin/GLUT4 translocation signaling pathway; 2) the function of Rab4 in this pathway requires GTP binding; 3) Rab4 also participates in the process of insulin-induced membrane ruffling; and 4) Rab3 proteins do not seem to be involved in these processes.

[Usefulness of Helicobacter pylori detection from feces specimens of the patients with peptic ulcer by polymerase chain reaction]

Detection of Helicobacter pylori was studied on the feces and biopsy specimens of 91 patients with gastric ulcer by using cultured and polymerase chain reaction methods. Number of samples from feces and biopsy specimens were 1 (1.1%) and 56 (61.5%) by culture method, on the other hands 49 (53.8%) and 70 (76.9%) in polymerase chain reaction method, respectively. Sensitivity of polymerase chain reaction applied to feces and biopsy specimens were 68.1 and 97.2, respectively. Noninvasive diagnosis such as detection of organisms from feces is effective for patients who have difficulty in collecting the gastric biopsy specimens. Infection route was not clarified, however, fecal-to-oral transmission was strongly suggested by the fact that the organisms were detected from feces samples in this study.

Functional importance of heat shock protein 90 associated with insulin receptor on insulin-stimulated mitogenesis

The role of stress proteins on the function of insulin receptor is not well understood. In the rat-1 fibroblasts overexpressing human insulin receptors, heat shock protein (Hsp) 90 was co-immunoprecipitated with insulin receptors and the association was not affected by insulin stimulation. A GST-fusion protein containing the intracellular insulin receptor beta subunit was associated with Hsp 90 in vitro, suggesting the direct interaction of this protein with insulin receptor beta-subunit. Furthermore, microinjection of anti-Hsp 90 antibody into these cells completely inhibited insulin-stimulated mitogenesis. However, neither epidermal growth factor-stimulated nor serum-stimulated mitogenic signal in the cells was affected by the antibody microinjection. These results suggest that Hsp 90 constitutively binds to insulin receptor beta-subunit, which may be necessary for insulin signaling in mitogenesis.

Ca2+-dependent interaction of the growth-associated protein GAP-43 with the synaptic core complex

The synaptic vesicle exocytosis occurs by a highly regulated mechanism: syntaxin and 25 kDa synaptosome-associated protein (SNAP-25) are assembled with vesicle-associated membrane protein (VAMP) to form a synaptic core complex and then synaptotagmin participates as a Ca2+ sensor in the final step of membrane fusion. The 43 kDa growth-associated protein GAP-43 is a nerve-specific protein that is predominantly localized in the axonal growth cones and presynaptic terminal membrane. In the present study we have examined a possible interaction of GAP-43 with components involved in the exocytosis. GAP-43 was found to interact with syntaxin, SNAP-25 and VAMP in rat brain tissues and nerve growth factor-dependently differentiated PC12 cells, but not in undifferentiated PC12 cells. GAP-43 also interacted with synaptotagmin and calmodulin. These interactions of GAP-43 could be detected only when chemical cross-linking of proteins was performed before they were solubilized from the membranes with detergents, in contrast with the interaction of the synaptic core complex, which was detected without cross-linking. Experiments in vitro showed that the interaction of GAP-43 with these proteins occurred Ca2+-dependently; its maximum binding with the core complex was observed at 100 microM Ca2+, whereas that of syntaxin with synaptotagmin was at 200 microM Ca2+. These values of Ca2+ concentration are close to that required for the Ca2+-dependent release of neurotransmitters. Furthermore we observed that the interaction in vitro of GAP-43 with the synaptic core complex was coupled with protein kinase C-mediated phosphorylation of GAP-43. Taken together, our results suggest a novel function of GAP-43 that is involved in the Ca2+-dependent fusion of synaptic vesicles.

The dominant negative effect of a kinase-defective insulin receptor on insulin-like growth factor-I-stimulated signaling in Rat-1 fibroblasts

To study the interaction between insulin receptor (IR) and insulin-like growth factor-I (IGF-I) receptor (IGF-IR) tyrosine kinases, we examined IGF-I action in Rat-1 cells expressing a naturally occurring tyrosine kinase-deficient mutant IR (Asp 1048 IR). IGF-I normally stimulated receptor autophosphorylation, IRS-I phosphorylation, and glycogen synthesis in cells expressing Asp 1048 IR. However, the Asp 1048 IR inhibited IGF-I-stimulated thymidine uptake by 45% to 52% and amino acid uptake (aminoisobutyric acid [AIB]) by 58% in Asp 1048 IR cells. Furthermore, IGF-I-stimulated tyrosine kinase activity toward synthetic polymers, Shc phosphorylation, and mitogen-activated protein (MAP) kinase activity was inhibited. The inhibition of mitogenesis and AIB uptake was restored with the amelioration of the impaired tyrosine kinase activity and Shc phosphorylation by the introduction of abundant wild-type IGF-IR in Asp 1048 IR cells. These results suggest that the Asp 1048 IR causes a dominant negative effect on IGF-IR in transmitting signals to Shc and MAP kinase activation, which leads to decreased IGF-I-stimulated DNA synthesis, and that the kinase-defective insulin receptor does not affect IGF-I-stimulated IRS-I phosphorylation, which leads to the normal IGF-I-stimulated glycogen synthesis.

Enhancing effects of unsaturated fatty acids with various structures on the permeation of indomethacin through rat skin

Effects of straight-chain, cis-type, unsaturated fatty acids with various structures (alkyl chain lengths, numbers of double bonds, position of double bonds, and cis- and trans-positional isomers) on the skin permeation of indomethacin were examined by using rat skins in-vitro. Furthermore, the disordering degrees of the intercellular lipid domain in the stratum corneum, which were treated with preparations of unsaturated fatty acids, were measured by the Fourier transform infrared (FT-IR) method using excised rabbit ear skins. Unsaturated fatty acids enhanced the permeation of indomethacin through rat skins. These permeation-enhancing effects by unsaturated fatty acids were affected by changes of their alkyl chain length from C14 to C22. The lag-times on the permeation of indomethacin were shortened by unsaturated fatty acids in the following order: C20 = C18 = C22 < C16 < C14. These fluxes were increased by unsaturated fatty acids in the following order: C20 > C22 = C18 = C16 > C14. Therefore, gondoic acid (cis-11-eicosenoic acid; C20H38O2) mostly enhanced the skin permeation of indomethacin. However, the enhancing effects of unsaturated fatty acids (C18 chain) were not affected by their differences of position and numbers of double bonds. These permeation-enhancing effects which were evaluated by flux were related to the degrees of wave-number shift in the frequency of the antisymmetric CH bond stretching absorbance (near 2920 cm-1) on FT-IR spectra of the fatty acid-treated stratum corneum. Therefore, the perturbation increase of lipid domain in the stratum corneum by these fatty acids probably was the cause of the enhancing effects of permeation of indomethacin.

[Therapeutic efficacy of azithromycin in pediatrics]

Azithromycin (AZM), a newly developed azalide antibiotic, was administered at a standard dose of 10 mg/kg once daily for 3 days to pediatric patients with bacterial infections and the therapeutic efficacy of AZM was investigated. 1. A total of 12 patients with the following diseases was evaluated: pharyngitis in two, tonsillitis in four, bronchitis in one, Mycoplasma pneumonia in one, scarlet fever in two and enteritis in two. The drug was rated "excellent" in eight cases and "good" in four. 2. Eleven strains were isolated from patients: five strains of Streptococcus pyogenes, four strains of Haemophilus influenzae, and two strains of Haemophilus parainfluenzae. Isolated bacteria were eradicated in eight strains and persisting in one, resulting in 88.9% in eradication rate. No follow-up examinations in post-treatment were performed in two cases. 3. No adverse reaction was reported, while one case of eosinophilia was noted as an abnormal laboratory test value. 4. As far as compliance is concerned, patients claimed that the formulation of the drug is "easy to take" or "ordinary". With the results presented as above, we have concluded that AZM is a useful antibiotic in pediatric patients with bacterial infections.

Evidence for an insulin receptor substrate 1 independent insulin signaling pathway that mediates insulin-responsive glucose transporter (GLUT4) translocation

Interaction of the activated insulin receptor (IR) with its substrate, insulin receptor substrate 1 (IRS-1), via the phosphotyrosine binding domain of IRS-1 and the NPXY motif centered at phosphotyrosine 960 of the IR, is important for IRS-1 phosphorylation. We investigated the role of this interaction in the insulin signaling pathway that stimulates glucose transport. Utilizing microinjection of competitive inhibitory reagents in 3T3-L1 adipocytes, we have found that disruption of the IR/IRS-1 interaction has no effect upon translocation of the insulin-responsive glucose transporter (GLUT4). The activity of these reagents was demonstrated by their ability to block insulin stimulation of two distinct insulin bioeffects, membrane ruffling and mitogenesis, in 3T3-L1 adipocytes and insulin-responsive rat 1 fibroblasts. These data suggest that phosphorylated IRS-1 is not an essential component of the metabolic insulin signaling pathway that leads to GLUT4 translocation, yet it appears to be required for other insulin bioeffects.

Activated phosphatidylinositol 3-kinase is sufficient to mediate actin rearrangement and GLUT4 translocation in 3T3-L1 adipocytes

Insulin stimulation of 3T3-L1 adipocytes causes rapid translocation of actin and the GLUT4 glucose transporter to the plasma membrane. Both processes depend on the activity of phosphatidylinositol 3-kinase. Using single cell microinjection, we have transiently expressed a constitutively activated mutant of phosphatidylinositol 3-kinase, p110*, in 3T3-L1 adipocytes. Fluorescent detection of GLUT4 protein and actin within these cells demonstrates that expression of p110* is sufficient to cause translocation of GLUT4 to the plasma membrane and the formation of actin membrane ruffles. These effects are inhibited by wortmannin in the p110*-expressing cells, indicating that the phosphatidylinositol 3-kinase activity of the protein is required. Overexpression of an identical protein containing a point mutation in the kinase domain, p110*Deltakin, was incapable of mediating either action, confirming that neither the microinjection process nor a nonspecific effect of the protein was responsible for the observed effects. These data suggest that although insulin is capable of inducing numerous signaling pathways, the isolated activation of phosphatidylinositol 3-kinase can initiate the signaling cascade leading to both actin rearrangement and GLUT4 translocation in the absence of insulin stimulation.

Stability of free Mg2+ concentration and increased concentration of free Ca2+ in vascular smooth muscle cells during dietary magnesium deficiency in rat

Intracellular free calcium and magnesium ion concentrations ([Ca2+]i and [Mg2+]i respectively) were estimated in thoracic aorta smooth muscle strips isolated from magnesium-deficient and control rats using fura-2/AM and mag-fura-2/AM, respectively. Adult male Wistar rats were fed a magnesium-deficient diet (10 mg Mg/kg diet) or a control diet (700 mg Mg/kg diet) for 30 days. Plasma magnesium level in magnesium-deficient rats was half of that in control rats at 30th day. Therefore, thoracic aorta strips, denuded of endothelium, were loaded with fura-2/AM or mag-fura-2/AM in the presence of 0.5 or 1.0 mM Mg2+, and [Ca2+]i or [Mg2+]i was measured under the same Mg2+ conditions. The [Ca2+]i in the aorta strips isolated from magnesium-deficient rats in the presence of 0.5 mM Mg2+ (254.9 +/- 13.1 nM) was approximately three times greater than in those from control rats in the presence of 1.0 mM Mg2+ (86.5 +/- 9.2 nM). The [Mg2+]i was not significantly different between the two groups at either Mg2+ level. The muscle tension and [Ca2+]i increased after [Mg2+]o was exchanged from 1.0 to 0.5 mM; however, [Mg2+]i showed no change. The total calcium content increased and total magnesium content decreased in thoracic aorta strips isolated from magnesium-deficient rats. These results suggest that [Mg2+]i is stable, but that [Ca2+]i increases in vascular smooth muscle cells of thoracic aortas isolated from dietary magnesium-deficient rats.

[Transferability of cefozopran to cerebrospinal fluid in rabbits with meningitis caused by Staphylococcus aureus]

The transferability of cefozopran (CZOP) to cerebrospinal fluid (CSF) was studied employing rabbits with experimental meningitis caused by Staphylococcus aureus. The mean plasma concentration was 293 +/- 17.6 micrograms/ml at 15 minutes after intravenous administration of CZOP at a dose level of 100 mg/kg. The mean concentration in CSF reached its maximum, 16.5 +/- 2.74 micrograms/ml at 60 minutes after administration. Pharmacokinetic parameters calculated from these values were as follows: Cmax (CSF/plasma) 5.72%, AUC (CSF/plasma) 6.61% between 15 and 60 minutes, 9.38% between 15 and 120 minutes and 11.2% between 15 and 180 minutes, T 1/2 for CZOP in CSF: 138 minutes, T 1/2 (CSF/plasma): 2.81. In comparison to those of beta-lactams that were obtained in the same way, the transferability of CZOP to CSF was moderate but concentration in CSF was high, hence, in consideration of the antimicrobial potency against the main pathogens of meningitis, it appears worthwhile of running clinical trials for CZOP.

Hsp70 family molecular chaperones and mutant insulin receptor: differential binding specificities of BiP and Hsp70/Hsc70 determines accumulation or degradation of insulin receptor

We have examined the binding specificities of Hsp70 family molecular chaperones, BiP and Hsp70/Hsc70, to wild-type or mutant insulin receptors. BiP bound to proreceptor of wild-type insulin receptor, but not to mature receptor. A mutant insulin receptor, which lacked 47 amino acid residues (delta Ex13 IR) corresponding to exon 13 of insulin receptor gene, accumulated in the endoplasmic reticulum as uncleaved proreceptor with immature oligosaccharide chains. This deletion mutant bound to BiP more tightly than wild type. Introduction of two types of mutations, Asp1179 or Leu1193, into delta Ex13 IR led to accelerated degradation, and these double mutants bound weakly to BiP. In contrast, Ser735 insulin receptor was normally transported to the plasma membrane and normally bound to BiP. Furthermore, Asp1179, Leu1193 insulin receptors and delta Ex13 IR combination mutant with either Asp1179 or Leu1193 bound more tightly to Hsp70/Hsc70 compared with wild-type, Ser735, and delta Ex13 IR. These results suggest that the binding specificity of mutant insulin receptors to two molecular chaperones, i.e., BiP and Hsp70/Hsc70, plays an important role for their posttranslational processing that may lead to the accumulation in the endoplasmic reticulum or the degradation of insulin receptors.

Insulin-stimulated GLUT4 translocation is mediated by a divergent intracellular signaling pathway

Insulin stimulates glucose transport largely by mediating translocation of the insulin-sensitive glucose transporter (GLUT4) from an intracellular compartment to the plasma membrane. Using single cell microinjection of 3T3-L1 adipocytes, coupled with immunofluorescence detection of GLUT4 proteins, we have determined that inhibition of endogenous p21ras or injection of oncogenic p21ras has no effect on insulin-stimulated GLUT4 translocation. On the other hand, microinjection of anti-phosphotyrosine antibodies or inhibition of endogenous phosphatidylinositol 3-kinase by microinjection of a GST-p85 SH2 fusion protein markedly inhibits this biologic effect of insulin. These data suggest that the p21ras/mitogen-activated protein kinase pathway is not involved in this metabolic effect of insulin, whereas tyrosine phosphorylation and stimulation of phosphatidylinositol 3-kinase activity are critical components of this signaling pathway.