Biomedical subjects

K Kotani

Publications and source records attributed to K Kotani.

At least 55 records · Page 3Linked to original sources

PubMed1998

SH2-Balpha is an insulin-receptor adapter protein and substrate that interacts with the activation loop of the insulin-receptor kinase.

We identified SH2-Balpha as an insulin-receptor-binding protein based on interaction screening in yeast hybrid systems and co-precipitation in cells. SH2-Balpha contains pleckstrin-homology ('PH') and Src homology 2 (SH2) domains and is closely related to APS (adapter protein with a PH domain and an SH2 domain) and lnk, adapter proteins first identified in lymphocytes. SH2-Balpha is ubiquitously expressed and is present in rat epididymal adipose tissue, liver and skeletal muscle, physiological sites of insulin action. On SDS/PAGE, SH2-Balpha migrates at a molecular mass of 98 kDa, although the predicted size of SH2-Balpha is 79.6 kDa. Insulin causes an electrophoretic mobility shift. SH2-Balpha can be immunoprecipitated using anti-(insulin receptor) antibody from insulin-stimulated cells. Anti-phosphotyrosine antibody or the growth factor receptor-binding protein 2 (Grb2) SH2 domain precipitate SH2-Balpha after insulin stimulation, suggesting that SH2-Balpha is tyrosine-phosphorylated and may be a substrate for the insulin receptor. The SH2-Balpha SH2 domain did not interact with insulin-receptor substrate (IRS) proteins or epidermal-growth-factor receptor. Mutation of the juxtamembrane and C-terminus of the insulin receptor did not abolish the interaction with the SH2 domain. This was further confirmed using a panel of activation-loop single point mutants where mutation of Tyr1158, Tyr1162 and Tyr1163 abolished interaction. Thus SH2-Balpha is a likely component in the insulin-signalling pathway and may function as an alternative signalling protein by interacting with the activation loop of the insulin-receptor cytoplasmic domain.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Requirement of atypical protein kinase clambda for insulin stimulation of glucose uptake but not for Akt activation in 3T3-L1 adipocytes.

Phosphoinositide (PI) 3-kinase contributes to a wide variety of biological actions, including insulin stimulation of glucose transport in adipocytes. Both Akt (protein kinase B), a serine-threonine kinase with a pleckstrin homology domain, and atypical isoforms of protein kinase C (PKCzeta and PKClambda) have been implicated as downstream effectors of PI 3-kinase. Endogenous or transfected PKClambda in 3T3-L1 adipocytes or CHO cells has now been shown to be activated by insulin in a manner sensitive to inhibitors of PI 3-kinase (wortmannin and a dominant negative mutant of PI 3-kinase). Overexpression of kinase-deficient mutants of PKClambda (lambdaKD or lambdaDeltaNKD), achieved with the use of adenovirus-mediated gene transfer, resulted in inhibition of insulin activation of PKClambda, indicating that these mutants exert dominant negative effects. Insulin-stimulated glucose uptake and translocation of the glucose transporter GLUT4 to the plasma membrane, but not growth hormone- or hyperosmolarity-induced glucose uptake, were inhibited by lambdaKD or lambdaDeltaNKD in a dose-dependent manner. The maximal inhibition of insulin-induced glucose uptake achieved by the dominant negative mutants of PKClambda was approximately 50 to 60%. These mutants did not inhibit insulin-induced activation of Akt. A PKClambda mutant that lacks the pseudosubstrate domain (lambdaDeltaPD) exhibited markedly increased kinase activity relative to that of the wild-type enzyme, and expression of lambdaDeltaPD in quiescent 3T3-L1 adipocytes resulted in the stimulation of glucose uptake and translocation of GLUT4 but not in the activation of Akt. Furthermore, overexpression of an Akt mutant in which the phosphorylation sites targeted by growth factors are replaced by alanine resulted in inhibition of insulin-induced activation of Akt but not of PKClambda. These results suggest that insulin-elicited signals that pass through PI 3-kinase subsequently diverge into at least two independent pathways, an Akt pathway and a PKClambda pathway, and that the latter pathway contributes, at least in part, to insulin stimulation of glucose uptake in 3T3-L1 adipocytes.

3T3 Cells↗

PubMed1997

P110delta, a novel phosphoinositide 3-kinase in leukocytes.

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that have been implicated in signal transduction through tyrosine kinase- and heterotrimeric G-protein-linked receptors. We report herein the cloning and characterization of p110delta, a novel class I PI3K. Like p110alpha and p110beta, other class I PI3Ks, p110delta displays a broad phosphoinositide lipid substrate specificity and interacts with SH2/SH3 domain-containing p85 adaptor proteins and with GTP-bound Ras. In contrast to the widely distributed p110alpha and beta, p110delta is exclusively found in leukocytes. In these cells, p110alpha and delta both associate with the p85alpha and beta adaptor subunits and are similarly recruited to activated signaling complexes after treatment with the cytokines interleukin 3 and 4 and stem cell factor. Thus, these class I PI3Ks appear not to be distinguishable at the level of p85 adaptor selection or recruitment to activated receptor complexes. However, distinct biochemical and structural features of p110delta suggest divergent functional/regulatory capacities for this PI3K. Unlike p110alpha, p110delta does not phosphorylate p85 but instead harbors an intrinsic autophosphorylation capacity. In addition, the p110delta catalytic domain contains unique potential protein-protein interaction modules such as a Pro-rich region and a basic-region leucine-zipper (bZIP)-like domain. Possible selective functions of p110delta in white blood cells are discussed.

Amino Acid Sequence↗

PubMed1997

Two decades of annual medical examinations in Japanese obese children: do obese children grow into obese adults?

OBJECTIVE: To investigate trends in frequency of obese children in Japan over two decades, the frequency of obese children who grow into obese adults and predictive factors for adult obesity. DESIGN: Annual cross-sectional studies for 22 y (1974-1995) with a follow-up study. SUBJECTS: Cross-sectional: Cumulatively 13,186 obese (% of standard body weight (SBW): > or = 120%) schoolchildren including 3158 extremely obese (> or = 140% of SBW) children out of 203,088 schoolchildren (age: 6-14 y) in Izumiohtsu City, Osaka, Japan. FOLLOW-UP: 151 initially obese children (initial age: 6-14 y and age at follow-up: 20-35 y) who lived in Izumiohtsu City. CONTROL: 3552 Japanese men and 4631 Japanese women (age: 20-35 y). MEASUREMENTS: Cross-sectional: height, weight, trunk circumference, skin-fold thickness, blood pressure and blood biochemicals. FOLLOW-UP: height, weight, trunk circumference, skin-fold thickness during childhood, and body height and weight at follow-up. Adulthood obesity: > or = 120% of the average body mass indices (BMI) of the controls. RESULTS: Frequency of obese children increased from 5% to more than 10%, and that of extremely obese children increased from 1% to more than 2% during these 22 y. These increases were most prominent in the schoolboys aged 9-11 y. Prevalence of hyperglycemia and hyperlipidemia in the extremely obese children did not change, and that of hypertension and abnormal liver function gradually decreased during these two decades. After coming of age, 32.2% of the initially obese boys (relative risk: 5.3) and 41.0% of the initially obese girls (relative risk: 6.7) remained obese. BMI, percentage of the SBW and skin-fold thickness at the biceps during childhood were significantly larger in currently-obese girls. Positive correlations were demonstrated between these variables and percentage SBW at follow-up. CONCLUSIONS: Childhood obesity is increasing in Japan, especially in boys aged 9-11 y. Approximately 32% of the obese boys and 41% of the obese girls grow into obese adults, and the degree of obesity is a predictive factor for adult obesity.

Adolescent↗

PubMed1997

Visceral fat accumulation as an important risk factor for obstructive sleep apnoea syndrome in obese subjects.

OBJECTIVES: It is well known that obstructive sleep apnoea-(OSA) is frequently associated with obesity. In the current study, we investigated the correlation between abdominal visceral fat accumulation and the presence of OSA in obese subjects. SUBJECTS: A consecutive series of 37 patients (17 men and 20 women) with primary obesity who were admitted to the Second Department of Internal Medicine. Osaka University Hospital, were investigated Patients with OSA were designated as those whose apnoea index (number of apnoea h-1 of sleep) was more than 5. MAIN OUTCOME MEASURES: The distribution of body fat was determined using computed tomographic sections. The upper airway dimensions were evaluated with indices obtained by cephalometry in both inspiratory and expiratory phases. RESULTS: Visceral adipose tissue (AT) area which was measured at the level of the umbilicus, and its ratio to total AT area were both significantly greater in OSA patients as compared with those in non-OSA patients. All subjects whose visceral AT area measured more than 220 cm2 manifested OSA. These two parameters also closely correlated with an increase in apnoea index. A multiple linear regression analysis revealed that the visceral AT area significantly correlated to apnoea index when age, AT mass and lean body mass were taken into account. The fluctuations of the upper airway were significantly greater in the large visceral fat group than in the small visceral fat group. CONCLUSIONS: These results suggest that visceral fat accumulation is an important risk indicator for OSA in obese subjects.

Adipose Tissue↗

PubMed1997

Phosphoinositide 3-kinase is required for insulin-induced but not for growth hormone- or hyperosmolarity-induced glucose uptake in 3T3-L1 adipocytes.

The(1) regulatory mechanism of glucose uptake in 3T3-L1 adipocytes was investigated with the use of recombinant adenovirus vectors encoding various dominant negative proteins. Infection with a virus encoding a mutant regulatory subunit of phosphoinositide (PI) 3-kinase that does not bind the 110-kDa catalytic subunit (delta p85) inhibited the insulin-induced increase in PI 3-kinase activity co-precipitated by antibodies to phosphotyrosine and glucose uptake in a virus dose-dependent manner. Overexpression of a dominant negative RAS mutant in which Asp57 is replaced with tyrosine (RAS57Y) or of a dominant negative SOS mutant that lacks guanine nucleotide exchange activity (delta SOS) abolished the insulin-induced increase in mitogen-activated protein kinase activity, but had no effect on PI 3-kinase activity or glucose uptake. Although GH and hyperosmolarity attributable to 300 mM sorbitol each promoted glucose uptake and translocation of glucose transporter (GLUT)4 to an extent comparable to that of insulin, these stimuli triggered little or no association of PI 3-kinase activity with tyrosine-phosphorylated proteins. Overexpression of delta p85 or treatment of cells with wortmannin, an inhibitor of PI 3-kinase activity, had no effect on glucose uptake or translocation of GLUT4 stimulated by GH or hyperosmolarity. Moreover, overexpression of delta SOS or RAC17N also did not affect the increase in glucose uptake induced by these stimuli. A serine/threonine kinase Akt, a constitutively active mutant of which was previously shown to stimulate glucose uptake, is activated by insulin, GH, and hyperosmolarity to approximately 4-fold, approximately 2.1-fold, and approximately 2.3-fold over basal level, respectively. These results suggest that insulin-induced but neither GH- or hyperosmolarity-induced glucose uptake is PI 3-kinase-dependent, and neither RAS nor RAC is required for glucose uptake induced by these stimuli in 3T3-L1 adipocytes.

3T3 Cells↗

PubMed1997

[Determination of malondialdehyde-modified LDL(MDA-LDL) and its potential usefulness].

Numerous studies have indicated that oxidative modification of low-density lipoprotein(LDL) plays a critical role in the pathogenesis of atherosclerosis. Malondialdehyde-modified LDL(MDA-LDL) is one of the candidates which is the oxidative product of LDL. However, the existence of MDA-LDL in the circulation has been in dispute. Therefore, for the assessment of oxidized-LDL in human serum, we developed a sensitive enzyme-linked-immunosorbent assay(ELISA) for the detection of MDA-LDL. In our method, monoclonal antibody against MDA-LDL, ML25 was used. ML25 recognized MDA-LDL as well as MDA-modified proteins by a solid-phase competitive enzyme immunoassay. Therefore, to establish an ELISA method which is specific for detection of MDA-LDL, ML25 was combined with apoB-specific antibody (AB16) as the second antibody. Using this method, MDA-LDL was detectable in the sera of 314 healthy individuals. The concentration of MDA-LDL preferably ranged from 20 to 80 units/l when the absorbance with artificially prepared MDA-LDL at the concentration of 1 mg/l was defined as 1 unit/l. Furthermore, assays for lipoprotein subfractions separated by density-gradient ultracentrifugation revealed that MDA-LDL was mainly distributed in the LDL fraction as expected, and MDA-LDL/apoB ratio showed a peak at small, dense LDL fractions. This finding seems to be quite interesting since an elevated level of small, dense LDL has been reported to be associated with an increased risk of atherosclerosis. We concluded that our method is useful for specific detection of MDA-LDL in human serum and might be an elevation method for atherogenicity.

Arteriosclerosis↗

PubMed1997

[Complete cholesteryl ester transfer protein deficiency increases oxidized-LDL in plasma].

Malondialdehyde-modified LDL(MDA-LDL) is one of the major oxidative LDL. MDA-LDL was determined by enzyme immunoassay in patients with complete and partial cholesteryl ester transfer protein(CETP) deficiency. Significantly increased serum MDA-LDL levels and MDA-LDL/apoB ratios in the LDL fraction were observed in patients with complete CETP deficiency but not for those with partial CETP deficiency. The present results may indicate that patients with complete CETP deficiency have a higher risk for atherosclerosis than those with partial CETP deficiency and normal.

Arteriosclerosis↗

PubMed1997

Genetic mutations of butyrylcholine esterase identified from phenotypic abnormalities in Japan.

We have identified 12 kinds of genetic mutations of butyrylcholine esterase (BCHE) from phenotypic abnormalities, showing that BCHE activities were deficient or diminished in sera. These genetic mutations, detected by PCR-single-strand conformation polymorphism analysis and direct sequencing, consisted of one deletion (BCHE*FS4), nine missense (BCHE*24 M, *1005, *250P, *267R, *330I, *365R, *418S, *515C, *539T), and two nonsense mutations (BCHE*119STOP, *465STOP). All of the individuals deficient in serum BCHE activity were homozygous for silent genes (6 of 6). Fifty-eight percent of the individuals (31 of 53) with slightly reduced serum BCHE activity were heterozygous for silent genes. They also showed a higher frequency (47% as allele frequency) of the K-variant than the general population (17.5%). Finally, we confirmed low serum BCHE activity in 10 of 23 individuals heterozygous for silent genes.

Butyrylcholinesterase↗

PubMed1996

Enhanced expression of PAI-1 in visceral fat: possible contributor to vascular disease in obesity.

The presence of obesity increases the risk of thrombotic vascular diseases. The role of fat accumulation and its effect on plasminogen activator inhibitor-1 (PAI-1) levels was investigated in humans and animals. Plasma PAI-1 levels were closely correlated with visceral fat area but not with subcutaneous fat area in human subjects. PAI-1 mRNA was detected in both types of fat tissue in obese rats but increased only in visceral fat during the development of obesity. These data suggest that an enhanced expression of the PAI-1 gene in visceral fat may increase plasma levels and may have a role in the development of vascular disease in visceral obesity.

3T3 Cells↗

PubMed1996

Insulin resistance and body fat distribution.

Body fat distribution can be assessed by computed tomography (CT). The ratio of umbilicus was used to classify obese subjects as having visceral fat obesity (VFO) or subcutaneous fat obesity (SFO). Serum triglyceride and total cholesterol levels and plasma glucose area in an oral glucose tolerance test were higher in patients with VFO than in those with SFO. Significant positive correlations were demonstrated between V/S ratio and plasma glucose area, serum triglyceride level, and total cholesterol level as well as systolic or diastolic blood pressure. VFO was more frequently associated with coronary artery disease. Moreover, VFO was more often accompanied by multiple risk factors than was SFO. Steady-state plasma glucose (SSPG) level was significantly higher in patients with VFO than with SFO, suggesting that insulin resistance may be more remarkable in VFO than in SFO. Furthermore, visceral fat accumulation was also associated with these complications even in nonobese subjects. Visceral fat area (VFA) was significantly correlated with fasting plasma glucose, serum triglyceride, and total cholesterol levels. Animal models such as Goto-Kakizaki (GK) rats with ventromedial hypothalamus (VMH) lesions and Otsuka-Long-Evans-Tokushima-Fatty (OLETF) rats were accompanied by visceral fat accumulation and an early stage of aortic atherosclerosis. Aging, sex hormone, genetic, and dietary factors and physical inactivity may induce visceral fat accumulation. Visceral fat is characterized by its high lipogenic activity as well as its accelerated lipolytic activity. High levels of portal free fatty acids (FFAs) may eventually result in an enhancement of hepatic triglyceride synthesis, causing hyperlipidemia. High portal FFA levels would also induce insulin resistance, thereby causing glucose intolerance, hypertension, and finally atherosclerosis. We propose a term, "visceral fat syndrome," as a highly atherogenic state, which includes visceral fat accumulation, glucose intolerance (insulin resistance), hyperlipidemia, and hypertension.

Adipose Tissue↗

PubMed1996

Visceral fat accumulation and vascular complications associated with VMH lesioning of spontaneously non-insulin-dependent diabetic GK rat.

OBJECTIVE: We have reported that ventromedial hypothalamic (VMH) lesions induced marked hyperglycemia and a distinct reduction in pancreatic insulin content during short-term observation in male Goto-Kakizaki (GK) rats, an animal model for non-insulin-dependent diabetes mellitus (NIDDM) (Metabolism 43: 32-37, 1994). We investigated the long-term effect of VMH lesions on glucose metabolism, pancreatic insulin content, abdominal fat distribution and vascular complications in male GK rats. DESIGN: Metabolic and histological examinations in male GK rats during 16 weeks after making VMH lesions were compared to those in sham operated GK or Wistar rats. SUBJECTS: Eleven 9-week-old male GK rats and 4 male Wistar rats. VMH-lesions were made in 6 GK rats and sham operation were performed on 5 GK rats and 4 Wistar rats as controls. MEASUREMENTS: Food intake, body weight, and plasma glucose, insulin and lipid levels at 2 weeks interval after operation. Urinary protein and albumin levels at 15 weeks after operation. Measurement of pancreatic insulin content, mesenteric fat and abdominal subcutaneous fat weights, and histological examinations of kidney and aorta were performed after 16 weeks. RESULTS: Although food intake increased in VMH-lesioned GK (GK-VMH) rats compared with that in sham-operated GK (GK-sham) rats, the body weight of GK-VMH rats was significantly less than that of GK-sham rats. Plasma glucose was markedly elevated in GK-VMH rats from 2 through 16 weeks after operation, while it was only mildly increased in GK-sham rats. Plasma insulin levels were higher in GK-VMH rats one week after operation and thereafter tended to be lower compared to those in GK-sham rats. Plasma triglyceride levels were significantly increased in GK-VMH rats. The insulin content of pancreas at 16 weeks after operation was markedly decreased in GK-VMH rats. VMH lesions caused a significant 1.2-fold increase in mesenteric fat weight and a 1.3-fold higher ratio of mesenteric fat weight to subcutaneous fat weight in GK rats compared with sham-operated rats at 16 weeks after operation. The urinary excretions of protein and albumin in GK-VMH rats were greater than those in GK-sham rats. Histological examinations of the kidneys in GK-VMH rats revealed that the glomerular basement membranes were thicker than those of GK-sham rats. The descending aorta in GK-VMH rats also showed morphologic changes in the intima characteristic of an early stage of atherosclerosis. CONCLUSION: Male GK-VMH rats may be a useful animal model for non-obese NIDDM with visceral fat accumulation, which develops typical diabetic complications, including both microangiopathy and macroangiopathy.

Adipose Tissue↗

PubMed1996

[Clinical significance of serum cholinesterase concentrations determined by enzyme-linked immunosorbent assay (ELISA)].

We developed a sensitive enzyme-linked immunosorbent assay (ELISA) for measurement of the protein mass of serum cholinesterase (CHE). In our ELISA system, a combination of a monoclonal antibody (a capture antibody) and an anti-CHE rabbit antibody (a second antibody) against CHE were used for the specific determination of CHE. The formed antigen-antibody complexes were detected with an alkaline phosphatase-labeled anti-rabbit IgG antibody. Using this ELISA system, we investigated for a possible relationship between the protein mass value and the catalytic activity of serum CHE in three patients groups with different clinical findings: control subjects selected randomly from outpatients (Group A), individuals with a low serum CHE activity including genetic variants (Group B) and patients with sarin poisoning (Group C). The CHE mass value correlated closely with the CHE activity in Group A, as previously reported. In Group B, a less significant correlation than in Group A was observed because both the CHE mass value and the CHE activity were disturbed at relatively lower levels. However, no discrepant cases were observed. On the other hand, in Group C, patients with serious sarin poisoning showed significant discrepancies between the mass value and activity of CHE before medical treatments, indicating that the inhalation of sarin did not affect the protein mass level but did affect the activity of serum CHE. As the patients recovered during the treatments, their CHE activities increased to the levels expected from the regression curve obtained with Group A, whereas the mass values were almost unchanged. In conclusion, protein mass determination of serum CHE provides valuable information concerning the target value of the serum CHE activity for the treatment of patients with organophosphate insecticide poisoning as well as for investigating the specific activity of genetic variants of serum CHE.

Animals↗

PubMed1995

Cloning and characterization of cell adhesion kinase beta, a novel protein-tyrosine kinase of the focal adhesion kinase subfamily.

A second protein-tyrosine kinase (PTK) of the focal adhesion kinase (FAK) subfamily, cell adhesion kinase beta (CAK beta), was identified by cDNA cloning. The rat CAK beta is a 115.7-kDa PTK that contains N- and C-terminal domains of 418 and 330 amino acid residues besides the central kinase domain. The rat CAK beta has a homology with mouse FAK over their entire lengths except for the extreme N-terminal 88 residues and shares 45% overall sequence identity (60% identical in the catalytic domain), which indicates that CAK beta is a protein structurally related to but different from FAK. The CAK beta gene is less evenly expressed in a variety of rat organs than the FAK gene. Anti-CAK beta antibody immunoprecipitated a 113-kDa protein from rat brain, 3Y1 fibroblasts, and COS-7 cells transfected with CAK beta cDNA. The tyrosine-phosphorylated state of CAK beta was not reduced on trypsinization, nor enhanced in response to plating 3Y1 cells onto fibronectin. CAK beta localized to sites of cell-to-cell contact in COS-7 transfected with CAK beta cDNA, in which FAK was found at the bottom of the cells. Thus, CAK beta is a PTK possibly participating in the signal transduction regulated by cell-to-cell contacts.

Amino Acid Sequence↗

PubMed1995

Ras-independent and wortmannin-sensitive activation of glycogen synthase by insulin in Chinese hamster ovary cells.

Activation of glycogen synthase is one of the major metabolic events triggered by exposure of cells to insulin. The molecular mechanism by which insulin activates glycogen synthase was investigated. The possible role of Ras and mitogen-activated protein kinase cascade was investigated with a stable cell line, CHO-IR-C/S 46, that overexpresses insulin receptors and a catalytically inactive SH-PTP 2 protein phosphatase and in which insulin does not induce the formation of the Ras-GTP complex or the subsequently activation of the mitogen-activated protein kinase cascade. Insulin activated glycogen synthase in this cell line to a similar extent as in parental CHO-IR cells. The importance of heteromeric phosphoinositide (PI) 3-kinase in insulin activation of glycogen synthase was examined in a stable cell line, CHO-IR/delta p85, that overexpresses insulin receptors and a dominant negative mutant (delta p85) of the 85-kDa subunit of PI 3-kinase that lacks the binding site for the catalytic 110-kDa subunit. Insulin-dependent activation of PI-3 kinase and glucose transport, but not the formation of the Ras-GTP complex, are markedly attenuated in this cell line. In CHO-IR/delta p85 cells, insulin activated glycogen synthase to a similar extent as in parental CHO-IR cells. The failure of overproduction of the mutant (delta p85) protein to inhibit insulin activation of glycogen synthase was also confirmed by transient expression in Rat 1 cells with the use of a recombinant vaccinia virus. However, wortmannin abolished insulin activation of glycogen synthase in all cell lines. These data suggest that existence of a Ras-independent and wortmannin-sensitive pathway for activation of glycogen synthase by insulin.

Androstadienes↗

PubMed1995

Requirement for phosphoinositide 3-kinase in insulin-stimulated GLUT4 translocation in 3T3-L1 adipocytes.

Insulin stimulates glucose transport in muscle and fat cells by inducing the redistribution of a specific glucose transporter, GLUT4, from intracellular vesicles to the cell surface. Phosphoinositide (PI) 3-kinase has been implicated as a key intermediate in insulin-stimulated glucose transport by studies that have examined the effects of wortmannin and LY294002, which are thought to be specific inhibitors of this enzyme. However, the specificity of these compounds for PI 3-kinase has recently been questioned. Epidermal growth factor, which activates mitogen-activated protein kinase in mouse 3T3-L1 adipocytes, has now been shown to have no effect on PI 3-kinase activity or GLUT4 translocation in these cells. Furthermore, microinjection of a dominant negative mutant of the 85-kDa subunit of PI 3-kinase, which lacks a binding site for the catalytic 110-kDa subunit, inhibited GLUT4 translocation induced by insulin in 3T3-L1 adipocytes; microinjection of the wild-type protein had no effect. These observations indicate that PI 3-kinase is necessary for insulin-induced GLUT4 translocation and glucose transport in adipocytes.

3T3 Cells↗

PubMed1995

Phosphoinositide 3-kinase as an upstream regulator of the small GTP-binding protein Rac in the insulin signaling of membrane ruffling.

Membrane ruffling and the closely linked response of fluid-phase pinocytosis were investigated in Chinese hamster ovary cells that stably overexpress the human insulin receptor and a mutant 85-kDa subunit of phosphoinositide (PI) 3-kinase (delta p85) that lacks a binding site for the catalytic 110-kDa subunit of this enzyme. Both membrane ruffling and pinocytosis induced by insulin were markedly impaired in these cells. Microinjection of Rac, a Ras-related small GTP-binding protein, induced membrane ruffling in human epidermoid carcinoma KB cells, and this effect of Rac was not blocked by coinjection of delta p85 or by exposure of cells to wortmannin, a specific PI 3-kinase inhibitor. These results suggest that PI 3-kinase is essential not only for insulin-stimulated membrane ruffling but also for pinocytosis, and that PI 3-kinase possibly functions upstream of Rac in the signal transduction pathway.

Animals↗

PubMed1995

Normal activation of p70 S6 kinase by insulin in cells overexpressing dominant negative 85kD subunit of phosphoinositide 3-kinase.

The role of heteromeric phosphoinositide (PI) 3-kinase activity in insulin signal transduction was studied by investigating the effects of (i) overexpression of a dominant negative mutant p85 (delta p85) that lacks the binding site for p110 (delta p85-overexpressing cells) and (ii) inhibition of PI 3-kinase activity by wortmannin (wortmannin-treated cells). The insulin-induced association of PI 3-kinase activity with insulin receptor sustrate-1 (IRS-1) was inhibited in both wortmannin-treated cells and delta p85-overexpressing cells. However, whereas insulin-induced activation of p70 S6 kinase was completely abolished in wortmannin-treated cells, it appeared normal in delta p85-overexpressing cells. These results raise the possibility that a wortmannin-sensitive pathway independent of heteromeric PI 3-kinase is involved in the activation of p70 S6 kinase by insulin.

Amino Acid Sequence↗