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M Tally

Publications and source records attributed to M Tally.

At least 37 records · Page 2Linked to original sources
PubMed1996

C-peptide stimulates glucose transport in isolated human skeletal muscle independent of insulin receptor and tyrosine kinase activation.

We have previously demonstrated that C-peptide stimulates glucose transport in skeletal muscle from non-diabetic subjects in a dose-dependent manner. To further elucidate the mechanism by which C-peptide activates glucose transport, we investigated the influence of human recombinant C-peptide on receptor and post-receptor events involved in the glucose transport process. Human skeletal muscle specimens were obtained from the vastus lateralis by means of an open biopsy procedure. Stimulation of isolated muscle strips from healthy control subjects with supra-physiological concentrations of insulin (6,000 pmol/l) and C-peptide (2,500 pmol/l), did not further augment the twofold increase in the rate of 3-o-methylglucose transport induced by either stimulus alone. C-peptide did not displace 125I-insulin binding from partially purified receptors, nor did it activate receptor tyrosine kinase activity. Tyrosine-labelled 125I-C-peptide did not bind specifically to crude membranes prepared from skeletal muscle, or to any serum protein other than albumin. The beta-adrenergic receptor stimulation with isoproterenol inhibited insulin- but not C-peptide-mediated 3-o-methylglucose transport by 63 +/- 18% (p < 0.01), whereas the cyclic AMP analogue, Bt2cAMP, abolished the insulin- and C-peptide-stimulated 3-o-methylglucose transport. C-peptide (600 pmol/l) increased 3-o-methylglucose transport 1.8 +/- 0.2-fold in skeletal muscle specimens from patients with insulin-dependent diabetes mellitus. In conclusion, C-peptide stimulates glucose transport by a mechanism independent of insulin receptor and tyrosine kinase activation. In contrast to the effect on insulin-stimulated glucose transport, catecholamines do not appear to have a counter regulatory action on C-peptide-mediated glucose transport.

3-O-Methylglucose↗
PubMed1996

Influence of droloxifene on plasma levels of insulin-like growth factor (IGF)-I, Pro-IGF-IIE, insulin-like growth factor binding protein (IGFBP)-1 and IGFBP-3 in breast cancer patients.

The influence of the novel anti-estrogen droloxifene on the insulin-like growth factor (IGF) system in plasma was studied in two groups of breast cancer patients receiving droloxifene 40 mg o.d. (group 1, n = 6) or 100 mg o.d. (group 2, n = 7). Fasting blood samples were obtained from all patients before treatment and after 3 months (group 1) or 6 months (group 2) on droloxifene treatment, except for two patients in group 2 from whom the second sample was obtained following 2 months on treatment when the drug was to be terminated due to progressive disease. Insulin-like growth factor (IGF)-I, insulin-like growth factor binding protein (IGFBP)-1, IGFBP-3 and pro-IGF-IIE (IGF-IIE) were measured by radioimmunoassay. In patients in group 1, plasma lGF-I levels decreased by a mean value of 20% (P < 0.05) on treatment with droloxifene, while IGFBP-1 increased by a mean value of 45% (P > 0.1). In group 2 we observed a 42% decrease in IGF-I during treatment (P < 0.025), while the level of IGFBP-1 increased by a mean value of 70% (P < 0.025). No significant effect on IGF-IIE or IGFBP-3 was noted in any of the groups. The change in plasma lGF-I and IGFBP-1 observed during treatment with droloxifene resembles what is found in patients treated with tamoxifen. As IGF-I is a potent mitogen for breast cancer cells in vitro, a decrease in the plasma level of this growth factor with an increase in the concentration of IGFBP-1 may contribute to the anti-tumour effects of droloxifene.

Aged↗
PubMed1996

Increased amounts of a high molecular weight insulin-like growth factor II (IGF-II) peptide and IGF-II messenger ribonucleic acid in pancreatic islets of diabetic Goto-Kakizaki rats.

Insulin-like growth factor II (IGF-II), a member of the insulin family, regulates cell growth and differentiation. The IGF-II gene is localized close to the insulin gene in man and rat. IGF-II peptide binds weakly to the insulin receptor and exerts insulin-like effects on the blood glucose level. We studied IGF-II in endocrine pancreas in an animal model of noninsulin-dependent diabetes mellitus, the Goto-Kakizaki (GK) rat. At the age of 2 months, these rats have structural islet changes, with fibrosis and irregular configuration, so-called starfish-shaped islets. Immunohistochemical investigation revealed IGF-II immunoreactivity in the beta-cells in both GK and control rats. Pancreatic extraction, followed by size separation using gel chromatography, disclosed a high mol wt form of IGF-II in all animals, and RIA measurements revealed a considerably larger amount of the IGF-II peptide in the 2-and 6-month-old GK rats than in the 1-month GK and control rats. In situ hybridization of 3-month-old GK rats showed increased IGF-II messenger RNA expression in the starfish-shaped islets of GK rats than in the islets with normal structure in both diabetic and control animals. The reason for the increased amount of IGF-II is unclear. As the animals are diabetic before the islet changes occur, it might be a compensatory effect in response to hyperglycemia, but could also be a cause of the islet fibrosis.

Animals↗
PubMed1995

Relations between sex hormones, sex hormone binding globulin, insulin-like growth factor-I and insulin-like growth factor binding protein-1 in post-menopausal breast cancer patients.

OBJECTIVE: Oestrogens, androgens and anti-endocrine drugs such as tamoxifen and aminoglutethimide influence plasma insulin-like growth factor-I (IGF-I). IGF-I, in turn, has been found to stimulate the peripheral aromatase in vitro. The aim of this study was to examine relations between sex hormones, IGF-I and insulin-like growth factor binding protein-1 (IGFBP-1) in post-menopausal women with breast cancer. DESIGN: To measure plasma sex steroids, sex hormone binding globulin (SHBG), IGF-I, IGFBP-1, insulin and urinary oestrogen metabolites in post-menopausal women with breast cancer not receiving any endocrine therapy. PATIENTS: Thirty-two patients had fasting blood samples obtained between 0800 and 1000 h. A sub-group of 10 patients had 24-hour urine oestrogen metabolites determined. MEASUREMENTS: Plasma steroids and proteins were measured by radioimmunoassays. Urinary oestrogens were measured by GC-MS. RESULTS: SHBG correlated negatively with plasma androstenedione (P < 0.001), insulin (P < 0.001), IGF-I, height and plasma oestrone sulphate (P < 0.025 for all), but positively with plasma IGFBP-1 (P < 0.025). IGFBP-1 correlated negatively with IGF-I (P < 0.001) and the testosterone/SHBG ratio (P < 0.05). Neither IGF-I nor IGFBP-1 correlated with any of the plasma or urinary sex hormones or with the oestrone/androstenedione and oestradiol/testosterone ratios. Multivariate analysis revealed plasma SHBG to correlate positively with IGFBP-1 (P = 0.029) and negatively with insulin (P = 0.031). Plasma IGFBP-1 correlated negatively with IGF-I (P < 0.0001) but not with insulin. CONCLUSION: Our results do not suggest any influence of plasma sex steroids in physiological concentrations on IGF-I or IGFBP-1 in post-menopausal breast cancer patients, nor do they indicate IGF-I at physiological concentrations influences the ratios between plasma oestrogens and their androgen precursors.

Aged↗
PubMed1994

Immunoreactive proinsulin-like growth factor-II levels in healthy subjects, patients with growth hormone deficiency, and patients with type 1 diabetes: effects of insulin-like growth factor-I and insulin.

Proinsulin-like growth factor-II (IGF-IIE), with an E-peptide elongation at the C-terminal, is found in the circulation and in different body fluids with mol wt between 10-16 kilodaltons compared to native 7.4-kilodalton IGF-II. Some tumors overexpress IGF-II and IGF-IIE with increased levels in patients serum, sometimes causing hypoglycemia (nonislet cell tumor-induced hypoglycemia). We have developed a RIA for a 15-amino acid part of the E-peptide. By using the E16-peptide as the labeled ligand, this RIA is unaffected by the presence of IGF-binding protein in the samples. Gel chromatography under acid and neutral conditions revealed that all IGF-IIE was detected without prior separation of serum. Using recombinant IGF-IIE21 as standard, we determined normal levels in 70 males and 67 females between 20-70 yr of age. The average was 46.6 +/- 1.1 micrograms/L, and the 95% confidence interval was between 21.4-71.9 micrograms/L. A significantly higher level was found in males (49.0 +/- 1.6 micrograms/L) compared to females (44.2 +/- 1.3 micrograms/L). In two nonislet cell tumor-induced hypoglycemia patients, levels of immunoreactive (ir) IGF-IIE were 2.5-3 times normal levels. GH-deficient patients had normal levels, but daily sc injections of recombinant human IGF-I decreased serum irIGF-IIE by 40%. Insulin-dependent diabetic patients undergoing liver venous catheterization had normal basal levels of irIGF-IIE in peripheral blood. A 180-min insulin infusion decreased the levels significantly in the vena hepatica, but no splanchnic gradient was observed.

Adult↗
PubMed1991

Characterization of an extended form of recombinant human insulin-like growth factor II.

To investigate the biological role of variants of human insulin-like growth factor II (IGF-II), an extended form designated IGF-IIE21, with a molecular mass of 9.8 kDa, was produced in Escherichia coli as a stable and soluble secreted fusion protein. After site-specific cleavage of the affinity purified fusion protein, followed by purification using ion exchange and reversed phase chromatography, it could be demonstrated that IGF-IIE21 and IGF-II have similar or identical activities according to radioimmunoassay and radioreceptor assay. However, IGF-IIE21 showed only 1% growth promotion activity as compared with IGF-II in a clonal expansion assay using human K562 cells which lacks IGF-I receptors. These results suggest that this extended variant of IGF-II can bind to the receptor but has limited growth promoting activity.

Amino Acid Sequence↗
PubMed1991

Purification and characterization of recombinant human insulin-like growth factor II (IGF-II) expressed as a secreted fusion protein in Escherichia coli.

Human insulin-like growth factor II (IGF-II) was produced in an Escherichia coli ompT strain as a 22.5-kDa fusion protein. IGF-II was fused to the carboxy-terminal of a synthetic 15-kDa IgG-binding protein, originating from staphylococcal protein A, via a unique methionine linker. During fermentation, the fusion protein was exported to the growth medium at levels exceeding 900 mg/liter and subsequently affinity purified on IgG Sepharose followed by ion exchange on S Sepharose. After chemical cleavage with CNBr, yielding an authentic IGF-II molecule, the recombinant IGF-II was purified to homogeneity by a two step procedure involving ion-exchange and reverse-phase HPLC. A substantial fraction of the secreted protein was found to be biologically active, eliminating the need for complex refolding procedures. The yield of highly purified and biologically active IGF-II was 5-7 mg/liter of fermenter broth. The IGF-II produced by this method displayed biochemical, immunological, receptor binding, and biological activity properties equal to those of native IGF-II isolated from human serum.

Amino Acids↗
PubMed1990

Determination of IGF-II levels in human serum using the erythroleukemia cell line K562.

A homologous radioreceptor assay (RRA) has been developed for Insulin-like Growth Factor II (IGF II) using the human erythroleukemia cell line K562. These cells have binding sites for insulin and IGF-II but not for Insulin-like Growth Factor I (IGF I). All samples were dissociated and separated from binding proteins by gel filtration at acidic pH. In healthy adults the mean serum level of radioreceptor assayable IGF II (RRA-IGF II) and 95% confidence limits were 965 ng/ml and 717-1299 ng/ml, respectively. The mean level in GH deficient patients was significantly lower (p less than 0.001) compared with healthy subjects whereas no change was found in patients with acromegaly and uremia. Slightly lowered levels of RRA-IGF II were found in one patient with a tumor induced hypoglycemia.

Acromegaly↗
PubMed1990

Differential stability of recombinant human insulin-like growth factor II in Escherichia coli and Staphylococcus aureus.

Recombinant human insulin-like growth factor II (IGF-II), produced as a soluble extracellular fusion protein, was shown to be proteolytically degraded in Escherichia coli. In contrast, the fusion protein secreted from Staphylococcus aureus was stable and the full length product could be recovered by affinity chromatography. After site specific cleavage of the fusion protein, soluble IGF-II with biological activity was obtained without refolding procedures. These results demonstrate that a eukaryotic protein unstable in E. coli can be stabilized by expression in a Gram positive host. The full-length fusion protein from S. aureus was used to characterize the protease responsible for the degradation in E. coli. Biochemical and genetic analysis suggests a specific degradation by the outer membrane protease (OmpT).

Amino Acid Sequence↗
PubMed1990

Insulin-like growth factor II effects mediated through insulin-like growth factor II receptors.

Insulin-like growth factor II (IGF-II) resembles the homologous peptide insulin-like growth factor I (IGF-I) in that it stimulates cellular growth in vitro. This effect is generally believed to be mediated through IGF type 1 receptors; the role of the IGF type 2 receptor remains, as yet, unknown. IGF-II has been shown to stimulate clonal expansion in cells from the human erythroleukaemia cell line K562, which displays binding of IGF-II and insulin but not IGF-I. This IGF-II effect was dose-dependent and correlated to the amount of specific binding; IGF-I did not stimulate growth. A similar effect on clonal growth was observed in the human T-cell line Jurkat. Furthermore, IGF-II was found to stimulate the cytotoxic activity of natural killer cells (as does interleukin 2). This effect was not inhibited by addition of IGF binding protein 1. Thus, it can be concluded that IGF-II, besides demonstrating standard IGF properties, exhibits unique biological effects in certain cells.

Cell Line↗
PubMed1989

Dual affinity fusion approach and its use to express recombinant human insulin-like growth factor II.

A dual affinity fusion concept has been developed in which the gene encoding the desired product is fused between two flanking heterologous genes encoding IgG- and albumin-binding domains. Using sequential IgG and serum albumin affinity chromatography, a full-length tripartite fusion protein is obtained. This approach was used to recover a full-length fusion product in Escherichia coli containing the human insulin-like growth factor II (IGF-II). Surprisingly, the recombinant IGF-II showed increased stability against proteolytic degradation in E. coli when produced as a dual affinity fusion protein, as compared to an N-terminal fusion protein. After site-specific cleavage of the tripartite fusion protein, IGF-II molecules with immunological and receptor binding activity were obtained without renaturation steps. The results demonstrate that proteins can fold into biologically active structures, even if provided with large flanking heterologous protein domains. The concept was further used to characterize the specific degradation of recombinant IGF-II in this heterologous host.

Amino Acid Sequence↗
PubMed1988

An effective method for the separation of insulin-like growth factors 1 and 2 during the purification process.

The separation of human insulin-like growth factors hIGF-1 and hIGF-2 was greatly improved by an additional purification step using the cation exchanger Mono-S (FPLC) compared to previous studies. Cross-reactions between hIGF-1 and hIGF-2 were strongly reduced. The more highly purified hIGF-1 had a cross-reaction of less than 1% in the RIA for hIGF-2, and was equivalent to recombinant hIGF-1. The pure hIGF-2 had a cross-reaction of less than 1% in the RIA for hIGF-1. In the human placental hIGF-2 radioreceptor assay, the hIGF-1 polypeptide completed less than 1% with hIGF-2 when the type 1 IGF receptor was blocked with insulin.

Cation Exchange Resins↗
PubMed1987

IGF-2 stimulated growth mediated by the somatomedin type 2 receptor.

Human Insulinlike Growth Factor 2 (IGF-2) can promote cell proliferation via the type 2 receptor in K562 cells, a human erythroleukemia cell line with IGF-2/type 2 receptors and insulin receptors but lacking IGF-1/type 1 receptors. Cells are grown in semi-solid agar in the absence and presence of increasing amounts of insulin, IGF-1 and IGF-2. Two strains of K562 cells have been studied, with different concentrations of insulin and IGF-2 receptors. The effect of IGF-2 is proportional to the IGF-2 receptor concentration.

Cell Division↗
PubMed1987

The specificity of the human IGF-2 receptor.

The specificity of the type 2 insulinlike growth factor (IGF) receptor is evaluated in human placenta membranes and the human cell line K562. K562 cells have type 2 but not type 1 IGF receptors. Native IGF-2 isolated from human plasma and synthetic IGF-2 were equipotent in competing with labeled IGF-2 in both systems. Pure IGF-1 isolated from plasma, synthetic IGF-1 and recombinant IGF-1 could not crossreact with the type 2 IGF receptor in concentrations up to 1 microgram/ml in both systems. Studies on placenta membrane were done in the presence of 300 ug/ml insulin to block the type 1 IGF receptors. It is concluded that IGF-1, as well as insulin, cannot crossreact with the human type 2 IGF receptor.

Binding, Competitive↗
PubMed1987

Involvement of transferrin in the reduction of iron by the transplasma membrane electron transport system.

Nonpermeable electron acceptors can be reduced by a transplasma membrane electron transport system in suspensions of intact cells. Here we report that diferric transferrin is reduced by HeLa S3 cells. The reduction is recorded spectrophotometrically as the formation of the ferrous complex of bathophenanthroline disulfonate. Ferric ammonium citrate can also be used as an electron acceptor and the presence of low concentrations of diferric transferrin greatly stimulates the reduction of trivalent iron under these conditions. Likewise very low concentrations of ferricyanide, which does not give rise to a ferrous bathophenanthroline disulfonate complex formation, have a strong stimulatory effect on the complex formation when ferric ammonium citrate is the source of ferric iron. Apotransferrin is a potent inhibitor of the reaction. The inhibition occurs at the concentration necessary for complete occupancy of the transferrin receptors. The inhibition can be demonstrated also when high concentrations of ferricyanide are used as electron acceptor. The possible mechanism behind the reported phenomena is discussed, and it is concluded that the transplasma membrane electron transport system can be involved in the process of cellular iron uptake.

Apoproteins↗