Rabbit brain glucose transporter responds to insulin when expressed in insulin-sensitive Chinese hamster ovary cells

Transfection of Chinese hamster ovary cells with the expression vector containing rabbit brain HepG2-type glucose transporter cDNA resulted in a dramatic over-expression (approximately 10-fold) of glucose transporter as assessed by either immunoblotting with antipeptide antibody against rabbit brain glucose transporter or photoaffinity labeling with [3H]cytochalasin B. 2-Deoxyglucose uptake was also increased 4-fold in the transfected cells, while no increase in transport activity or transporter amount was observed in cells that were transfected with the expression vector alone without glucose transporter cDNA. Significantly, insulin (10(-7) M) increased 2-deoxyglucose uptake in both control and transfected cells, but the increased amount of the transported 2-deoxyglucose by insulin in the transfected cells was 4.2-fold greater than that in control cells, indicating that the expressed rabbit brain HepG2-type glucose transporter responded to insulin. In addition, we have recently demonstrated that the HepG2-type glucose transporter exists in rat adipocytes and responds to insulin in a fashion similar to a majority of other types of glucose transporters (Oka, Y., Asano, T., Shibasaki, Y., Kasuga, M., Kanazawa, Y., and Takaku, F. (1988) J. Biol. Chem. 263, 13432-13439). In contrast, insulin did not stimulate glucose transport activity in HepG2 cells or IM-9 lymphocytes that have a significant amount of the HepG2-type glucose transporter. Thus, the results in this study further support the notion that insulin regulation of glucose transport activity depends on a tissue-specific signaling mechanism.

Stimulation of the phosphorylation of cytoskeletal 350-kDa and 300-kDa proteins by insulin-like growth factor-I, platelet-derived growth factor and phorbol ester in rat 3Y1 cells

Insulin-like growth factor-I (IGF-I) stimulated the phosphorylation of cytoskeletal 350-kDa and 300-kDa proteins which were immunoprecipitated with antibodies against brain high molecular weight microtubule-associated proteins in quiescent rat 3Y1 cells. The data on the effective concentrations of IGF-I and 125I-labeled IGF-I binding indicated that type I IGF receptors mediate this IGF-I effect. Platelet-derived growth factor (PDGF) as well as phorbol ester (TPA) also stimulated the phosphorylation of these proteins. These proteins, whether immunoprecipitated from cells stimulated by insulin, IGF-I, TPA, PDGF, or epidermal growth factor, produced very similar phosphopeptide mapping patterns irrespective of the stimulant. The results suggest the possibility that these growth factors and phorbol esters may activate a common protein kinase which is responsible for the phosphorylation of the 350-kDa and 300-kDa proteins in cells.

Insulin-induced tyrosine-phosphorylation in intact rat adipocytes

Insulin-induced tyrosine-phosphorylation in intact isolated rat adipocytes was studied using immunoblotting method with antiphosphotyrosine antibodies. Insulin-stimulated adipocytes were solubilized with Triton X-100. The lysate was incubated with wheat germ agglutinin, then with hydroxylapatite. Insulin stimulated tyrosine-phosphorylation of a 95 KDa protein which adsorbs to wheat germ agglutinin and appears to be the beta-subunit of the insulin receptor. Among the proteins adsorbed to hydroxylapatite, tyrosine-phosphorylation of 170 KDa and 60 KDa proteins was stimulated. 170 KDa was also stimulated by polyclonal anti-insulin receptor antibodies B-10 Ig G, IGF-I and H2O2. The detection of these proteins in rat adipocytes may lead to the elucidation of a common signal transduction pathway in insulin-responsive cells.

Studies with antipeptide antibody suggest the presence of at least two types of glucose transporter in rat brain and adipocyte

Three antipeptide antibodies were prepared by immunizing rabbits with synthesized short peptides corresponding to residues 215-226, 466-479, and 478-492 predicted from the cDNA of both the human hepatoma HepG2 and rat brain glucose transporters. All three antibodies were found to precipitate quantitatively the [3H]cytochalasin B photoaffinity-labeled human erythrocyte glucose transporter. Each antibody also recognized the rat brain protein of Mr 45,000 on immunoblots, and a similar molecular weight protein was labeled with [3H]cytochalasin B in a D-glucose-inhibitable manner, suggesting that this protein is glucose transporter. However, only up to 30% of the labeled rat brain glucose transporters were precipitated, even by repeated rounds of immunoprecipitation. In addition, these antibodies were observed to be unable to immunoprecipitate significantly the [3H]cytochalasin B-labeled rat adipocyte glucose transporter. Further, one-dimensional peptide maps of [3H]cytochalasin B-labeled human erythrocyte and adipocyte glucose transporters generated distinct tryptic fragments. Although Mr 45,000 protein in rat adipocyte low density microsomes was detected on immunoblots and its amount was decreased in insulin-treated cells, the rat adipocyte low density microsomes were much less reactive on immunoblots than the rat brain membranes in spite of the fact that the rat adipocyte low density microsomes contained more [3H]cytochalasin B-labeled glucose transporters. In addition, the ratio of cytochalasin B-labeled glucose transporter per unit HepG2-type glucose transporter mRNA was more than 10-fold higher in rat adipocyte than in rat brain. These results indicate that virtually all the human erythrocyte glucose transporters are of the HepG2 type, whereas this type of glucose transporter constitutes only approximately 30 and 3% of all the glucose transporters present in rat brain and rat adipocyte, respectively; and the rest, of similar molecular weight, is expressed by a different gene.

Rapid stimulation of fluid-phase endocytosis and exocytosis by insulin, insulin-like growth factor-I, and epidermal growth factor in KB cells

Effects of growth factors on fluid-phase endocytosis and exocytosis in human epidermoid carcinoma KB cells were examined by measuring horseradish peroxidase (HRP) as a marker. Insulin, insulin-like growth factor-I (IGF-I), and epidermal growth factor (EGF) promoted HRP accumulation. They also stimulated the efflux of the preloaded HRP from the cells. From these results it follows that these growth factors stimulate the influx as well as the efflux of HRP, because the accumulation rate is the sum of the influx rate and the efflux rate. The stimulation of both HRP accumulation and HRP efflux was rapidly induced within 2-4 min of the addition of growth factors and persisted for at least 60 min. The concentrations eliciting half-maximal stimulatory effects of insulin, IGF-I, and EGF were about 5 X 10(-7), 1 X 10(-9), and 5 X 10(-10) M, respectively. aIR-3 (anti-type I IGF receptor antibody) completely blocked the stimulation of HRP accumulation by IGF-I but very slightly inhibited the stimulation by insulin. The 528 IgG (anti-EGF receptor antibody) inhibited the stimulation of HRP accumulation by EGF. These results indicated that each of these growth factors stimulates the HRP accumulation mediated by the corresponding (homologous) growth factor receptors. The rapid stimulation of fluid-phase influx and efflux may constitute one of the common early cellular responses to growth factors.

Requirement for receptor-intrinsic tyrosine kinase activities during ligand-induced membrane ruffling of KB cells. Essential sites of src-related growth factor receptor kinases

We have prepared site-specific antibodies toward human insulin, insulin-like growth factor-I, and epidermal growth factor receptors with chemically synthesized peptides derived from the cDNA-predicted amino acid sequences of these receptors. Two classes of antibodies were produced toward each receptor: one toward the carboxyl termini and the other against the kinase domains containing sequences homologous to the tyrosyl phosphorylation site of the product of src gene (pp60v-src). Both classes of antibodies specifically immunoprecipitated the appropriate 125I-ligand-receptor complexes and [35S]methionine-labeled receptors with almost equal potencies. Antibodies toward the kinase domains inhibited both autophosphorylation and tyrosine kinase activity of the corresponding receptors in a cell-free system, whereas antibodies toward the carboxyl termini did not. Microinjection of the kinase-inhibitory antibodies into the cytoplasm of human epidermoid carcinoma KB cells blocked the ability of the corresponding ligand to induce membrane ruffling. In contrast, these inhibitory antibodies did not block the ability of noncorresponding ligands to induce the same response. Furthermore, control immunoglobulin and antibodies toward the carboxyl termini did not block this biological response. These results support a role for the tyrosine-specific protein kinase activities of these growth factor receptors in mediating their biological effects and suggest that the regions homologous to the tyrosyl phosphorylation site of pp60v-src are important for these kinase activities both in cell-free and intact cell systems.

Long-term comparison of oral hypoglycemic agents in diabetic retinopathy. Gliclazide vs. other sulfonylureas

Gliclazide has been reported to possess the properties of preventing the progression of diabetic retinopathy and of controlling blood glucose levels. This report describes a long-term comparative clinical trial of this agent to assess its efficacy against diabetic retinopathy. One hundred and fifty-nine NIDDM patients with no retinopathy or with simple retinopathy entered this trial. One hundred and nineteen patients receiving other sulfonylurea agents were randomly allocated to two groups (G: gliclazide, SU: other sulfonylureas). Forty patients continued to be treated with diet alone (D group). Finally a total of 60 patients, that is, 21 patients in the G group, 19 patients in the SU group, and 20 patients in the D group, were followed with funduscopic examinations for more than 4 years. The results are summarized as follows. (1) Distribution of background factors between the two drug therapy groups was balanced, but in the D group more male patients and relatively milder cases were involved than in the drug therapy groups. (2) Fasting blood glucose control in the three groups was not significantly different. (3) Funduscopic deterioration was observed less frequently, though not significantly, in the G group than in the other groups. (4) Progression to preproliferative retinopathy was significantly less frequent in the G group than in the SU group. Thus, gliclazide seems to have additional properties compared with other sulfonylurea drugs in preventing deterioration of diabetic retinopathy, and particularly in preventing progression to proliferative retinopathy.

Alteration in growth, cell morphology, and cytoskeletal structures of KB cells induced by epidermal growth factor and transforming growth factor-beta

Long-term biological effects of epidermal growth factor (EGF), insulin, insulin-like growth factor-I (IGF-I), and transforming growth factor-beta (TGF-beta) were examined with human epidermoid carcinoma KB cells. EGF inhibited the growth of KB cells in both serum-containing and serum-free synthetic media by reducing the growth rate and by lowering the saturation density. The cells cultured with EGF showed relatively high motility and grew dispersely as single cells, whereas the cells cultured in the absence of EGF grew in clusters. Although TGF-beta itself did not inhibit the growth of KB cells, it augmented the growth inhibition by EGF. TGF-beta also affected the cell morphology. In the presence of TGF-beta, the cells became flattened and actin stress fibers were well developed compared to those cultured in its absence. The effects of EGF on growth, cell motility, and cell morphology were reversible. Tyrosine phosphorylation of EGF receptors was continuously observed for at least 50 h in the presence of EGF. TGF-beta did not increase the phosphorylation induced by EGF. These results suggested that signals continuously transmitted through EGF receptors caused the changes in cell growth and morphology and that TGF-beta did not act on the cells by modulating binding of EGF to its receptors or activation of the receptor kinase. In contrast to EGF and TGF-beta, neither insulin nor IGF-I affected cell morphology or growth, although KB cells express their receptors and the receptor kinases were also continuously activated during exposure of the cells to insulin or IGF-I.

Induction of the receptor for erythropoietin in murine erythroleukemia cells after dimethyl sulfoxide treatment

Biologically active 125I-labeled human recombinant erythropoietin (EPO) was used to demonstrate specific receptors for this erythroid-specific hemopoietic growth factor on the cell surface of murine erythroleukemia cell clone B8. The binding of radioiodinated EPO to these cells was time and temperature dependent, specific, saturable, and reversible. During erythroid differentiation by dimethyl sulfoxide, B8 cells displayed a rapid and marked increase in the amount of specific 125I-EPO binding before the appearance of hemoglobin-containing cells. Scatchard analysis of the saturation binding data revealed that B8 cells had a single class and low number (350 to 650) of EPO receptors per cell with an apparent Kd of 1.2 to 1.4 nM. In addition, the number of EPO receptors on B8 cells was increased twice by induction with DMSO for 1 day, but the binding affinity of EPO toward its receptors did not change significantly. Affinity cross-linking experiments with disuccinimidyl suberate demonstrated two radiolabeled components with apparent molecular weights of 145,000 and 130,000 under both reducing and nonreducing conditions. Labeling of the two components was inhibited by incubation of cells with unlabeled EPO. These results suggest that some murine erythroleukemia cells potentially express EPO receptors as a differentiation marker of erythroid lineage, which contain two polypeptides with molecular weights of 109,000 and 94,000.

Multiple endocrine neoplasia type I with Cushing's disease, primary hyperparathyroidism, and insulin-glucagonoma

A case of multiple endocrine neoplasia type I (MEN I) consisting of Cushing's disease, primary hyperparathyroidism, and insulin-glucagonoma is described. This condition was treated successfully by transsphenoidal pituitary adenomectomy, subtotal parathyroidectomy, and enucleation of pancreatic tumors. Histologic features showed a basophilic adenoma in the pituitary, chief cell hyperplasia in the parathyroid, and islet cell adenomas in the pancreas. The rarity of multiple endocrine hyperfunctioning states and the pathophysiology created by the combination of these three diseases in this patient are of interest.

Hydrogen peroxide stimulates tyrosine phosphorylation of the insulin receptor and its tyrosine kinase activity in intact cells

H-35 rat hepatoma cells were labelled with [32P]orthophosphate and their insulin receptors isolated on wheat germ agglutinin (WGA)-agarose and anti-(insulin receptor) serum. The incubation of these cells with 10 mM-H2O2 for 10 min increased the phosphorylation of both the serine and tyrosine residues of the beta subunit of the insulin receptor. Next, insulin receptors were purified on WGA-agarose from control and H2O2-treated H-35 cells and the purified fractions incubated with [gamma-32P]ATP and Mn2+. Phosphorylation of the beta subunit of insulin receptors obtained from H2O2-treated cells was 150% of that of control cells. The kinase activity of the WGA-purified receptor preparation obtained from H2O2-treated cells, as measured by phosphorylation of src-related synthetic peptide, was increased about 4-fold over control cells. These data suggest that in intact cell systems, H2O2 may increase the insulin receptor kinase activity by inducing phosphorylation of the beta subunit of insulin receptor.

Glucocorticoids increase insulin binding and the amount of insulin-receptor mRNA in human cultured lymphocytes

The effect of steroid hormones on insulin binding and the amount of insulin-receptor mRNA was examined in IM-9 lymphocytes. Cortisol and cortexolone, but not oestrogen, increased both the binding of insulin and the amount of insulin-receptor mRNA in a time- and dose-dependent manner. Cortisol was most potent, and induced a 2-fold increase in insulin binding and a 4-fold increase in mRNA. The elevation in binding was due to an increased number of insulin receptors at the cell surface. The increase in mRNA involved all four of the insulin-receptor mRNAs and could not be inhibited by cycloheximide. The cortisol-induced increase in mRNA was associated with a 3-4-fold increase in the synthesis of pro-receptor. The relative potency of the three steroids indicated that these effects were mediated by an interaction with the glucocorticoid receptor. The results of this study suggest that cortisol can increase the number of insulin receptors at the cell surface by increasing the amounts of insulin-receptor mRNA and the synthesis de novo of insulin receptors.

Insulin induces chloroquine-sensitive recycling of insulin-like growth factor II receptors but not of glucose transporters in rat adipocytes

Incubation of insulin-treated rat adipocytes with chloroquine, in a time- and concentration-dependent manner, was observed to inhibit the insulin-stimulated increase in insulin-like growth factor II (IGF-II) binding activity, whereas no significant change in IGF-II binding was observed in the absence of insulin. The incremental increase of insulin-stimulated IGF-II binding was inhibited 50% by 0.2 mM chloroquine within 15 min and was nearly completely abolished by 60 min. Interestingly, IGF-II binding was never observed to decrease below the binding value in cells without insulin treatment even when incubation was extended to 180 min. Scatchard analysis of IGF-II binding as well as the specific binding of an anti-IGF-II receptor antibody demonstrated that the loss of IGF-II binding in the insulin-stimulated chloroquine-treated adipocytes was due to a decrease in the number of cell-surface IGF-II receptors, whereas the total number of cellular IGF-II receptors was unaltered. The effect of chloroquine was observed to be reversible, temperature-dependent, and sensitive to the metabolic poison KCN. Furthermore, NH4Cl was also observed to inhibit insulin-stimulated increase in IGF-II binding. In contrast, chloroquine or NH4Cl did not inhibit the basal or insulin-stimulated glucose transport activity. Photoaffinity labeling of the glucose transporter with [3H]cytochalasin B also demonstrated that the basal and insulin-stimulated subcellular distribution of the glucose transporters was unaltered by chloroquine treatment. These results suggest that 1) insulin induces a constitutive, acidotropic agent-sensitive recycling of IGF-II receptor and 2) the glucose transporter and IGF-II receptor do not share the same insulin-regulated intracellular trafficking pathways.

Interleukin 3-specific tyrosine phosphorylation of a membrane glycoprotein of Mr 150,000 in multi-factor-dependent myeloid cell lines

Tyrosine phosphorylation of cellular proteins induced by various hematopoietic growth factors such as interleukin 3 (IL3), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL4) was studied in several multi-factor-dependent myeloid cell lines. Among the growth factors, IL3 specifically induced rapid tyrosine phosphorylation of a membrane glycoprotein of mol. wt 150 kd (gpp150) in the IL3-dependent cell lines, IC2 and DA-1. The IL3-induced tyrosine phosphorylation of gpp150 was detected within 30 s, reached a maximum at 3 min and decreased thereafter. The concentration of IL3 required for half-maximum stimulation of gpp150 tyrosine phosphorylation with 2.5 x 10(6)/ml cells was approximately 200 pM, which is the same as the dissociation constant for 125I-labeled IL3 binding. gpp150 was constitutively phosphorylated on tyrosine residue(s) in growth factor independent variants, IC2Tr and DA-1Tr, derived from IC2 and DA-1 respectively. Neither variant synthesized IL3. The present findings suggest that tyrosine phosphorylation of gpp150 is a critical event involved in both IL3-dependent and -independent growth.

Tyrosine phosphorylation by the epidermal growth factor receptor kinase induces functional alterations in microtubule-associated protein 2

We have examined the effect of tyrosine phosphorylation of microtubule-associated protein 2 (MAP2) by the epidermal growth factor (EGF) receptor kinase on its functions. Incubation of MAP2 with the EGF receptor in the presence of ATP resulted in a great decrease in the ability of MAP2 to promote tubulin polymerization. Under a variety of conditions, the decrease in the ability correlated with the extent of phosphorylation of MAP2. Furthermore, another function of MAP2, the actin filament cross-linking activity, was also inactivated by the incubation of MAP2 with the EGF receptor and ATP. The loss of this activity also correlated well with the extent of phosphorylation. These data indicate that tyrosine phosphorylation of MAP2 by the EGF receptor kinase inactivates both the tubulin polymerizing activity and actin filament cross-linking activity of MAP2. Thus, this study has clearly shown that tyrosine phosphorylation could modify the function of a cytoskeletal protein.

Binding properties and proliferative potency of insulin-like growth factor I in fetal mouse liver cells

Specific high-affinity receptor(s) for insulin-like growth factor I have been identified in fetal mouse liver cells (FMLC) rich in late erythroid progenitors (CFU-E). Competition for [125I]IGF-I binding by IGFs and insulin demonstrated the presence of Type-I IGF receptors. Scatchard analysis of the binding data revealed a single class of receptors (Kd, 1.2 nM; R0, 600 sites per cell). Erythroid colony formation and DNA synthesis by these cells were enhanced by IGF-I alone or in combination with erythropoietin (Epo). Subfractionations of FMLC using Percoll density gradients showed that a significant part of [125I]IGF-I binding was observed in the CFU-E-enriched fraction and that the erythroid colony formation was mostly enhanced by IGF-I in the same fraction. IGF-I stimulated the phosphorylation of the beta-subunit of the Type-I receptors. These results indicate that IGF-I modulates the Epo-stimulated proliferation and differentiation of erythroid progenitors via its specific receptors.

Identification of erythropoietin receptors on fetal liver erythroid cells

Erythropoietin (EPO) has a central role in the growth and development of erythroid cells. Using a biologically active radioiodinated derivative, EPO receptors were identified on fetal mouse liver cells mostly consisting of erythroid cells. 125I-EPO was cross-linked to two receptors forms with apparent molecular masses of 110 and 95 kilodaltons, respectively and both having similar affinity toward EPO.

Vanadate can replace interleukin 3 for transient growth of factor-dependent cells

A mouse interleukin 3 (IL-3)-dependent cell line, IC2, could survive and proliferate over a 48-h period in the absence of IL-3 when incubated with micromolar concentrations of sodium orthovanadate. The greatest response was obtained at 12.5 microM, as judged by stimulation of cell growth. Vanadate also stimulated synthesis of nucleotides and protein in IC2 cells. After 6 h of culture in the absence of IL-3, the intracellular ATP levels of IC2 cells fell dramatically; this fall was prevented by addition of vanadate to the culture. Studies with recombinant IL-3 revealed that vanadate potentiated the effect of submaximal doses of IL-3 on the growth of IC2 cells, but did not appear to act synergistically with IL-3 to give a maximal proliferative response of the cells. After 48 h of IL-3 replacement with vanadate, IC2 cells could respond to IL-3 with no loss of proliferative integrity. These results suggest that IL-3 dependence of IC2 cells is transiently substituted for by vanadate, and it may be a useful tool to understand the mechanism of action of IL-3.

Tyrosine phosphorylation of common and specific sets of cellular proteins rapidly induced by insulin, insulin-like growth factor I, and epidermal growth factor in an intact cell

KB cells respond to insulin and insulin-like growth factor I (IGF-I) in a closely similar way (induction of membrane ruffling, stimulation of pinocytosis, and amino acid transport) but respond to epidermal growth factors (EGF) in a similar but distinct way. In the KB cells, using phosphotyrosine-specific antibody we have found that: the receptors for insulin (beta subunit), IGF-I (beta subunit), and EGF undergo tyrosine phosphorylation as early as 10 s after addition of their respective ligands; a 185-kDa protein is rapidly (less than 10 s) tyrosine phosphorylated by insulin and IGF-I through their respective receptor kinases but not EGF; tyrosine phosphorylation of a 190-kDa glycoprotein is rapidly (less than 10 s) induced by EGF through EGF receptor kinase; and tyrosine phosphorylation of a 240-kDa protein is stimulated within 30 s by all three growth factors. These patterns of tyrosine phosphorylation could be causally related to biological responses induced by the three growth factors.

Differential effects of DNA tumor virus nuclear oncogene products on adipocyte differentiation

We have introduced SV40 and polyoma large T antigen- and adenovirus-type 12 E1A genes into mouse 3T3-L1 preadipocyte cells to study the ability of various nuclear oncogene products to modulate cell differentiation. Clones expressing E1A products could differentiate into adipocytes faster than the control in spite of the absence of adipogenic inducers, as measured by the appearance of lipid droplets microscopically and by staining accumulated triglycerides with oil red O. However, clones expressing SV40 and polyoma large T antigens could not differentiate even if they were exposed to the inducers.

A Mr = 190,000 glycoprotein phosphorylated on tyrosine residues in epidermal growth factor stimulated KB cells is the product of the c-erbB-2 gene

In human epidermoid carcinoma KB cells, a glycoprotein of Mr = 190,000 (gp190) has been shown to be phosphorylated on tyrosine residues upon EGF stimulation (Kadowaki et al., 1987, J. Biol. Chem. in press). Using a specific antibody to the c-terminal portion of the human c-erbB-2 gene product, we have found that gp190 is the human c-erbB-2 gene product which is structurally closely related to the epidermal growth factor (EGF) receptor. Since monoclonal antibody specific for the EGF receptor abolished both EGF binding to its receptor and tyrosine phosphorylation of the c-erbB-2 gene product, we have concluded that activation of EGF receptor tyrosine kinase activity upon EGF binding leads to the phosphorylation of the c-erbB-2 gene product on its tyrosine residues.