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P F Pilch

Publications and source records attributed to P F Pilch.

At least 55 records · Page 3Linked to original sources
PubMed1994

gp160, a tissue-specific marker for insulin-activated glucose transport.

We have isolated and partially sequenced a M(r) 160,000 glycoprotein whose rate of cycling to and from the adipocyte cell surface is enhanced by insulin in a manner apparently identical to the effect of insulin on GLUT4 cycling. Based on the protein sequence, we have prepared an antipeptide antibody against this protein, gp160. The antibody recognizes a M(r) 160,000 protein whose subcellular distribution is identical to that of GLUT4. This was determined by three separate criteria: (i) Western blotting of fractionated adipocyte membranes from cells exposed to insulin or not, (ii) adsorption of vesicles with anti-GLUT4 antibodies followed by Western blotting, and (iii) separation of microsomal vesicles by sucrose velocity and density gradients. By all three criteria, GLUT4 and gp160 are completely colocalized in rat fat cells. Moreover, gp160 can be detected by Western blot only in fat and cardiac and skeletal muscles and was absent from all other tissues tested. Thus, gp160 is an additional marker for physiologically important, insulin-sensitive glucose transport. Its further study at the protein and DNA level may reveal information about the mechanistic details of insulin-activated GLUT4 translocation as well as information concerning the tissue-specific expression of GLUT4 and gp160.

Adipocytes↗
PubMed1994

Identification and isolation of glycoproteins that translocate to the cell surface from GLUT4-enriched vesicles in an insulin-dependent fashion.

It has previously been shown that in fat cells, the intracellular reservoir of the glucose transporter isoform GLUT4 consists of a membrane vesicle population highly enriched in this transporter (approximately 15% of the protein content) that has a relatively simple protein pattern as revealed by SDS-polyacrylamide gel electrophoresis and silver staining (Zorzano, A., Wilkinson, W., Kotliar, N., Thoidis, G., Wadzinski, B. E., Ruoho, A. E., and Pilch, P. F. (1989) J. Biol. Chem. 264, 12358-12363). Upon exposure of adipocytes to insulin, the cell-surface (plasma membrane) content of GLUT4 is dramatically enhanced, and this transporter appears to continually cycle from intracellular vesicles to the plasma membrane. To identify other proteins that may recycle in a similar fashion to GLUT4 and that may participate in the insulin-dependent alteration in the cellular location of GLUT4 and other membrane proteins, we performed immunoadsorption of GLUT4-enriched vesicles together with biotinylation of membranes using a cell-impermeant analog of biotin. We find that immunoadsorbed GLUT4-containing vesicles can be fractionated into Triton X-100-soluble and -insoluble fractions. The first includes three major glycoprotein components with molecular masses of 110, 160, and 230 kDa and a few minor polypeptides with lower molecular masses. A Triton X-100-resistant fraction consists of GLUT4 and an approximately 25-kDa protein. All three major Triton-soluble proteins (110, 160, and 230 kDa) isolated from the immunoimmobilized vesicles on wheat germ agglutinin-agarose are strongly biotinylated in an insulin-dependent fashion, i.e. they cycle to and from the cell surface in an apparently identical manner to GLUT4. Sequence analysis of two tryptic fragments from p160 reveals that it is a novel protein containing sequence with no homology to known proteins.

Adipocytes↗
PubMed1994

The insulin receptor: structure, function, and signaling.

The insulin receptor is a member of the ligand-activated receptor and tyrosine kinase family of transmembrane signaling proteins that collectively are fundamentally important regulators of cell differentiation, growth, and metabolism. The insulin receptor has a number of unique physiological and biochemical properties that distinguish it from other members of this large well-studied receptor family. The main physiological role of the insulin receptor appears to be metabolic regulation, whereas all other receptor tyrosine kinases are engaged in regulating cell growth and/or differentiation. Receptor tyrosine kinases are allosterically regulated by their cognate ligands and function as dimers. In all cases but the insulin receptor (and 2 closely related receptors), these dimers are noncovalent, but insulin receptors are covalently maintained as functional dimers by disulfide bonds. The initial response to the ligand is receptor autophosphorylation for all receptor tyrosine kinases. In most cases, this results in receptor association of effector molecules that have unique recognition domains for phosphotyrosine residues and whose binding to these results in a biological response. For the insulin receptor, this does not occur; rather, it phosphorylates a large substrate protein that, in turn, engages effector molecules. Possible reasons for these differences are discussed in this review. The chemistry of insulin is very well characterized because of possible therapeutic interventions in diabetes using insulin derivatives. This has allowed the synthesis of many insulin derivatives, and we review our recent exploitation of one such derivative to understand the biochemistry of the interaction of this ligand with the receptor and to dissect the complicated steps of ligand-induced insulin receptor autophosphorylation. We note possible future directions in the study of the insulin receptor and its intracellular signaling pathway(s).

Animals↗
PubMed1993

Immunological analysis of GLUT4-enriched vesicles. Identification of novel proteins regulated by insulin and diabetes.

In adipocytes and muscle, insulin stimulates the translocation of glucose transporter proteins from an intracellular vesicle pool to the plasma membrane. To study the molecular basis of this process, we used the anti-GLUT4 antibody 1F8 to isolate intracellular vesicles from rat adipocytes that are enriched in the muscle/fat glucose transporter isoform. These vesicles were then used as immunogens to generate monoclonal antibodies against their protein components. We isolated an antibody, 3F8, that recognizes three polypeptides, designated GTV3, migrating in the 36-40-kDa range as analyzed by SDS-polyacrylamide gel electrophoresis and Western blotting. These proteins are enriched in GLUT4-containing vesicles, and the two smallest of the polypeptides recognized by 3F8 translocate to the cell surface in response to insulin. GTV3 proteins are also present in plasma membranes of fat cells and liver as well as in a wide number of tissues, red blood cells being the only exception. In adipocytes from streptozotocin-induced diabetic rats, GTV3 protein levels decrease dramatically and return to normal levels when animals are treated with insulin. The localization of GTV3 in glucose transporter-containing vesicles as well as their wide tissue distribution suggests that these proteins may be involved in vesicle mediated transport and regulated trafficking between membrane compartments.

Adipose Tissue↗
PubMed1993

BpaB25 insulins. Photoactivatable analogues that quantitatively cross-link, radiolabel, and activate the insulin receptor.

Benzoylphenylalanine (Bpa), a photoactivatable amino acid was incorporated into the 25 position of the insulin B-chain by a combination of chemical synthesis and enzymatic semisynthesis. BpaB25 insulin binds specifically to the insulin receptor with an affinity approximately 40% that of native insulin. Addition of biotin or epsilon-amino-hexanoic acid-iminobiotin at the epsilon-LysB29 position to form BpaB25,B29 epsilon-biotinyl (BBpa) or BpaB25,B29 epsilon-(Aha-iminobiotin) analogues had little adverse effect on receptor binding affinity and provided a convenient handle for affinity purification, gel shift assays, and blotting of cross-linked complexes with avidin. The analogues were readily 125I-iodinated with the majority of 125I being incorporated at the TyrA14 position; the monoiodo-A14 derivative was easily separated from other forms by high performance liquid chromatography. Photolysis of a complex of the insulin receptor and either BpaB25 insulin or [125I]iodo-TyrA14,BpaB25 insulin yields a covalent insulin-receptor complex. The efficiency of cross-linking with these reagents was unusually high, ranging from 60 to 100%. Furthermore, cross-linking to the insulin receptor results in kinase activation in vitro, and in intact cells insulin receptor phosphorylation and internalization were both activated. Notably, even at saturating concentrations one molecule of BpaB25 insulin covalently cross-linked each alpha 2 beta 2 receptor, demonstrating that holoreceptor activation occurs with one high affinity insulin binding site occupied and, if a second insulin binds with lower affinity it must be in a different orientation. Bpa insulin analogues form a new class of photoaffinity reagents which facilitate studies relating insulin-insulin receptor structure and function.

Affinity Labels↗
PubMed1993

Insulin receptor autophosphorylation occurs asymmetrically.

The unoccupied insulin receptor is a structurally symmetric, disulfide-linked dimer, comprising two alpha beta halves, each with a potential insulin binding alpha subunit and a kinase active beta subunit. In the accompanying paper (Shoelson, S. E., Lee, J., Lynch, C. S., Backer, J. M., and Pilch, P. F. (1993) J. Biol. Chem. 268, 4085-4091), we described the utility of a novel insulin analogue, L-benzoylphenylalanineB25,B29 epsilon-biotin insulin (BBpa insulin)1 as a probe for receptor behavior, and we determined that binding and cross-linking of one BBpa insulin molecule could fully stimulate insulin receptor autophosphorylation. Here we use this analogue to determine the symmetry of the autophosphorylation reaction. The alpha beta half-receptor that does not covalently couple to BBpa insulin incorporates 50% more orthophosphate than the alpha beta half that becomes coupled to the insulin analogue. Phosphopeptide mapping of each receptor half shows minimal differences in the phosphorylation sites or their relative contribution to the phosphate content of each half. The kinetics of 32P incorporation into each receptor half are essentially identical over a 10-20-min time course. Phosphopeptide mapping analysis reveals that the phosphate incorporation patterns do not change between the two alpha beta half-receptor forms (BBpa insulin-linked and unlinked, respectively) at different time points or concentrations of ATP ranging from 12 to 200 microM. Based on these and other data, we propose a model of insulin receptor activation whereby binding of one insulin molecule can trigger autophosphorylation in an asymmetric fashion.

3T3 Cells↗
PubMed1993

Insulin-responsive human adipocytes express two glucose transporter isoforms and target them to different vesicles.

We have characterized the insulin-dependent increase in glucose transport in human adipocytes using subcellular fractionation and antibodies specific for the two isoforms of the glucose transporter that are expressed in these cells. Plasma membranes isolated from untreated human fat cells contain the erythroid/GLUT1 isoform of the glucose transporter almost exclusively whereas the muscle-fat/GLUT4 transporter isoform is most abundant in intracellular microsomal membranes in resting cells. After exposure of adipocytes to insulin, the muscle-fat isoform is dramatically increased in the plasma membrane whereas the erythroid isoform barely changes in response to insulin. Thus, the total insulin-mediated increase in plasma membrane glucose transporters, confirmed by affinity labeling of both transporter isoforms, must be due to the increase in the muscle-fat/GLUT4 transporter. The two isoforms exist in different vesicle populations as shown by immunoadsorption of the muscle fat isoform-containing vesicles which are essentially devoid of the erythroid transporter. These data indicate that the insulin-mediated increases in glucose transport in human fat cells is a result of the translocation of vesicles uniquely containing the muscle-fat glucose transporter isoform.

Adipose Tissue↗
PubMed1992

Differential regulation of glucose transporter 1 and 2 mRNA expression by epidermal growth factor and transforming growth factor-beta in rat hepatocytes.

We have examined by Northern blot analysis the expression of two members of the glucose transporter family of genes (GLUT-1 and GLUT-2) in regenerating liver and in hepatocytes cultured under various conditions. GLUT-1, although thought to be a growth-associated gene, is not expressed in normal or regenerating liver, whereas GLUT-2, a liver-specific gene, is abundant in normal liver and gradually up-regulated during liver regeneration. Conversely, in hepatocytes cultured conventionally on dried rat tail collagen (RTC) in the presence of EGF and insulin, which potentiate proliferation, GLUT-1 mRNA is rapidly and abundantly expressed, whereas GLUT-2 is depressed. To investigate the causes of this "switch" in glucose transporter expression seen when hepatocytes are removed from the liver and cultured under the conventional proliferative conditions, we examined the effects of specific growth factors and extracellular matrices on cultured hepatocytes. EGF, a potent liver mitogen, although causing a threefold induction of GLUT-1, was found to have no effect on GLUT-2 expression, suggesting that the increase in GLUT-2 seen in regenerating liver is not due to EGF. Inhibition of protein synthesis by cycloheximide in cultured hepatocytes does not prevent the induction of GLUT-1 mRNA. In addition, treatment of cells with cycloheximide appears to stabilize the GLUT-2 mRNA, preventing the usual down-regulation of this gene in cultured hepatocytes. The expression of the two glucose transporter mRNAs also differed when the hepatocytes were adherent to particular cell matrices. Culture of hepatocytes on a reconstituted basement membrane gel matrix (EHS) is known to restrain their growth and mediate high levels of differentiated hepatocytic functions that are lost under conventional culture conditions. Unlike cells on RTC, hepatocytes on EHS expressed low levels of GLUT-1 mRNA, and decreased GLUT-2 mRNA. TGF-beta, an attenuator of DNA synthesis, when added to cultures on RTC, substantially down-regulated GLUT-2 but had no effect on GLUT-1. We propose that the effectors, EGF, TGF-beta and basement membrane components, play a significant role in the regulation of expression of GLUT-1 and GLUT-2 in hepatocytes.

Animals↗
PubMed1992

Alteration in the expression of GLUT-1 and GLUT-4 protein and messenger RNA levels in denervated rat muscles.

Denervation induces insulin resistance of the glucose transport process in skeletal muscle. To determine whether this is due to alterations in the expression of muscle glucose transporters (GLUT) in different fiber types, we evaluated the amount of GLUT-1 and GLUT-4 protein and messenger RNA (mRNA) in extensor digitorum longus (EDL) and soleus at 1, 2, and 3 days after sciatotomy. Denervation elevated the basal rate of 2-[1,2-3H]deoxy-D-glucose (2-DOG) uptake in the EDL and decreased the insulin-stimulated DOG uptake in both muscles. Denervation after 1 day did not modify the GLUT-1 or the GLUT-4 protein level in either muscle. However, it increased GLUT-1 mRNA by 66% and decreased GLUT-4 mRNA by 70% in the EDL, but not in the soleus (P < 0.05). After 2 days of denervation, by which time GLUT-1 mRNA was increased 2-fold and GLUT-4 mRNA was reduced by 70%, we observed a 2-fold increase in GLUT-1 protein (P < 0.01) in the EDL and a 40-45% decrease in GLUT-4 protein in both muscles (P < 0.01). These results indicate that modifications in the expression of GLUT-1 and GLUT-4 protein cannot explain the insulin resistance of the glucose transport process in the EDL or soleus 1 day after denervation. After 2 days of denervation, however, alterations in GLUT-1 and GLUT-4 protein levels may contribute to the change in basal and insulin-stimulated DOG uptake in both the EDL and the soleus muscles.

Animals↗
PubMed1992

Expression of the glucose transporter isoform GLUT 4 is insufficient to confer insulin-regulatable hexose uptake to cultured muscle cells.

Glucose transporter isoform expression was studied in the skeletal muscle-like cell line, C2C12. Northern and Western blot analysis showed that the insulin-responsive muscle/fat glucose transporter isoform, GLUT 4, was expressed in these cells at very low levels, whereas the erythrocyte isoform, GLUT 1, was expressed at readily detectable levels. Insulin did not stimulate glucose transport in this cultured muscle cell line. The C2C12 cells were then transfected separately with either GLUT 1 or GLUT 4, and stable cell lines expressing high levels of mRNA and protein were isolated. GLUT 1-transfected cells exhibited a 3-fold increase in the amount of the GLUT 1 transporter protein which was accompanied by a 2- to 3-fold increase in the glucose uptake rate. However, despite at least a 10-fold increase in GLUT 4 mRNA and protein detected after GLUT 4 cDNA transfection, the glucose uptake of these cells was unchanged and remained insulin-insensitive. By laser confocal immunofluorescence imaging, it was established that the transfected GLUT 4 protein was localized almost entirely in cytoplasmic compartments. In contrast, the GLUT 1 isoform was detected both at the plasma membrane as well as in intracellular compartments. These results suggest that acute insulin stimulation of glucose transport is not solely dependent on the presence of the insulin receptor and the GLUT 4 protein, and that the presence of some additional protein(s) must be required.

Animals↗
PubMed1991

Autophosphorylation within insulin receptor beta-subunits can occur as an intramolecular process.

The insulin receptor is a complex membrane-spanning glycoprotein composed of two alpha-subunits and two beta-subunits connected to form an alpha 2 beta 2 holoreceptor. Insulin binding to the extracellular alpha-subunits activates intracellular beta-subunit autophosphorylation and substrate kinase activity. The current study was designed to differentiate mechanisms of transmembrane signaling by the insulin receptor, specifically whether individual beta-subunits undergo cis- or trans-phosphorylation. We compared relative kinase activities of trypsin-truncated receptors, alpha beta-half receptors, and alpha 2 beta 2 holoreceptors under conditions that allowed us to differentiate intermolecular and intramolecular events. Compared to the insulin-stimulated holoreceptors, the trypsin-truncated receptor undergoes autophosphorylation at similar tyrosine residues and catalyzes substrate phosphorylation in the absence of insulin at a comparable rate. The truncated receptor sediments on a sucrose gradient at a position consistent with a structure comprising a single beta-subunit attached to a fragment of the alpha-subunit and undergoes autophosphorylation in this form in the absence of insulin. Autophosphorylation of the truncated insulin receptor is independent of receptor concentration, and immobilization of the truncated receptor on a matrix composed of an anti-receptor antibody bound to protein A-Sepharose diminishes neither autophosphorylation nor receptor-catalyzed substrate phosphorylation. Therefore, true intramolecular (cis) phosphorylations, which occur within individual beta-subunits derived from trypsin-truncated receptors, lead to kinase activation. However, insulin-stimulated autophosphorylation of insulin receptor alpha beta heterodimers is concentration-dependent, and both autophosphorylation and kinase activity are markedly reduced following immobilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Phosphatidylinositol 4-kinase is a component of glucose transporter (GLUT 4)-containing vesicles.

We recently developed a procedure for immunoisolating insulin-responsive membrane vesicles that contain the muscle/fat glucose transporter isoform, GLUT 4, from rat adipocytes. Utilizing this methodology, we are analyzing the components of these vesicles to gain an understanding of how they are regulated by insulin. In this report we identify a phosphatidylinositol (PtdIns) 4-kinase as a constituent of glucose transporter vesicles (GTVs). This kinase has the biochemical and immunological properties of a type II PtdIns 4-kinase as classified by Endeman et al. (Endemann, G., Dunn, S. N., and Cantley, L. C. (1987) Biochemistry 26, 6845-6852). A monoclonal antibody, 4C5G, which specifically inhibits the type II PtdIns 4-kinase, suppresses 80% of the GTV-PtdIns 4-kinase activity. In addition, the GTVs-PtdIns 4-kinase is maximally activated by the nonionic detergent Triton X-100, at a concentration of 0.2% and is inhibited by adenosine with a Ki of approximately 20-30 microM. We find that the GTVs do not contain any PtdIns4P 5-kinase or diacylglycerol kinase activities, whereas these activities were detected in the plasma membrane. An analysis of the subcellular distribution of PtdIns 4-kinase activity in the rat adipocyte shows that there are similar levels of activity in GTVs, plasma membranes, and the high and low density microsomal fractions, whereas the mitochondria- and nuclei-containing fractions have less than 5% of the activity seen in other fractions. Low density microsomes were subfractionated by sucrose density gradient centrifugation and PtdIns 4-kinase activity was found to correlate closely with the distribution of membrane protein, indicating that the activity is equally distributed throughout this heterogenous population of membranes. PtdIns 4-kinase activity measured in GTVs, plasma membranes, and low density microsomes, was not affected by prior treatment of the intact adipocytes with 35 nM insulin. We postulate that while the GTV-PtdIns 4-kinase is not regulated by insulin, it may play a role in defining the fusogenic properties necessary to mediate membrane movement between the GTVs, plasma membranes, and microsomes.

1-Phosphatidylinositol 4-Kinase↗
PubMed1991

Decreased expression of glucose transporter in muscle from insulin-resistant patients.

We have observed that in vitro incubated human muscle fiber strips from obese patients with or without non-insulin-dependent diabetes mellitus (NIDDM) have reduced insulin-stimulated glucose transport rates compared with nonobese control patients. To investigate if the decrease in glucose transport is associated with a depletion of glucose transport protein, we performed Western blot analysis of muscle samples from nonobese control, obese nondiabetic, and obese NIDDM patients to measure the levels of the muscle-adipose tissue glucose transporter (GLUT-4) protein. Glucose transporter protein was depressed by 23% in the obese nondiabetic and 18% in the obese NIDDM group. The results were essentially the same in the rectus abdominus and vastus lateralis muscles. These data suggest that the decreased glucose transport rate observed in muscle of these obese patients with or without NIDDM may be due, at least in part, to a decreased expression of the "insulin-sensitive" (GLUT-4) glucose transporter. This alteration may play a role in the insulin resistance seen in obesity and diabetes.

Diabetes Mellitus↗
PubMed1991

Adipose tissue glucose transporters in NIDDM. Decreased levels of muscle/fat isoform.

We investigated the mechanism of peripheral insulin resistance in the adipose tissue of obese and non-insulin-dependent diabetes mellitus (NIDDM) patients at the level of the glucose-transport effector system. Freshly isolated adipocytes from obese nondiabetic and obese NIDDM subjects had decreased insulin sensitivity and responsiveness for glucose-transport stimulation compared with control subjects, with more pronounced changes associated with obese NIDDM patients. The relative abundance of muscle/fat glucose-transporter isoform in the three groups of subjects was determined by Western-blot analysis of detergent-soluble adipose tissue extracts with monoclonal antibody 1F8. Obesity per se had no effect on adipose tissue muscle/fat glucose-transporter isoform (3150 +/- 660 vs. 4495 +/- 410 counts/min [cpm]/mg protein). Furthermore, decreased levels of muscle/fat isoform in adipose tissue of NIDDM patients were also reflected in isolated adipocytes. Our results demonstrate that insulin resistance in isolated adipocytes of NIDDM patients could at least partly be due to a significant depletion of adipose tissue muscle/fat glucose-transporter isoform.

Adipose Tissue↗
PubMed1990

The endogenous functional turkey erythrocyte and rat liver insulin receptor is an alpha 2 beta 2 heterotetrameric complex.

Previous studies have indicated that turkey erythrocyte and rat liver membranes contain endogenous alpha beta heterodimeric insulin receptors in addition to the disulphide-linked alpha 2 beta 2 heterotetrameric complexes characteristic of most cell types. We utilized 125I-insulin affinity cross-linking to examine the structural properties of insulin receptors from rat liver and turkey erythrocyte membranes prepared in the absence and presence of sulphydryl alkylating agents. Rat liver membranes prepared in the absence of sulphydryl alkylating agents displayed specific labelling of Mr 400,000 and 200,000 bands, corresponding to the alpha 2 beta 2 heterotetrameric and alpha beta heterodimeric insulin receptor complexes respectively. In contrast, affinity cross-linking of membranes prepared with iodoacetamide (IAN) or N-ethylmaleimide identified predominantly the alpha 2 beta 2 heterotetrameric insulin receptor complex. Similarly, affinity cross-linking and solubilization of intact turkey erythrocytes in the presence of IAN resulted in exclusive labelling of the alpha 2 beta 2 heterotetrameric insulin receptor complex, whereas in the absence of IAN both alpha 2 beta 2 and alpha beta species were observed. Turkey erythrocyte alpha 2 beta 2 heterotetrameric insulin receptors from IAN-protected membranes displayed a 3-4-fold stimulation of beta subunit autophosphorylation and substrate phosphorylation by insulin, equivalent to that observed in intact human placenta insulin receptors. Turkey erythrocyte alpha beta heterodimeric insulin receptors, prepared by defined pH/dithiothreitol treatment of IAN-protected membranes, were also fully competent in insulin-stimulated protein kinase activity compared with alpha beta heterodimeric human placenta receptors. In contrast, endogenous turkey erythrocyte alpha beta heterodimeric insulin receptors displayed basal protein kinase activity which was insulin-insensitive. These data indicate that native turkey erythrocyte and rat liver insulin receptors are structurally and functionally similar to alpha 2 beta 2 heterotetrameric human placenta insulin receptors. The alpha beta heterodimeric insulin receptors previously identified in these tissues most likely resulted from disulphide bond reduction and denaturation of the alpha 2 beta 2 holoreceptor complexes during membrane preparation.

Animals↗
PubMed1990

Intrinsic kinase activity of the insulin receptor.

Since the identification of the insulin receptor by insulin-binding activity almost two decades ago, our understanding of the structure and function of the insulin receptor has progressed tremendously. The importance of the intrinsic tyrosine protein kinase activity of the insulin receptor is implied by the fact that the insulin receptor belongs to a family of receptor tyrosine kinases which play a role in growth control, by experiments demonstrating the intimate association of normal kinase activity and insulin action, and by evidence that the intrinsic kinase activity can be regulated under certain conditions. There are still some major gaps in our knowledge concerning the structure/function of the insulin receptor such as how activation of the intrinsic kinase activity of the receptor leads to altered cellular physiology. The kinase may phosphorylate endogenous substrates or autophosphorylation may simply alter beta subunit conformation so it can then interact with an effector system (i.e. a serine kinase) directly, or indirectly through a G-protein. The truth may lie somewhere between these two pathways.

Animals↗
PubMed1990

Vanadate treatment of streptozotocin diabetic rats restores expression of the insulin-responsive glucose transporter in skeletal muscle.

Streptozotocin-treated rats were diabetic, as assessed by blood glucose and plasma insulin values, while vanadate treatment restored blood glucose values to normal. Immunoblot analysis using a monoclonal antibody to the insulin-responsive glucose transporter demonstrated a 70% decline in transporter expression in skeletal muscle of diabetic rats. Subsequent treatment of diabetic animals with vanadate resulted in renewed expression of the transporter to 87% of control levels. Northern blot analysis of total skeletal muscle RNA from diabetic animals revealed a 55% decline in the steady state level of muscle glucose transporter mRNA, while vanadate treatment led to a 187% increase in transporter mRNA over normal levels. These results support the conclusion that vanadate acts to relieve diabetic hyperglycemia by inducing expression of the insulin-responsive glucose transporter at the pretranslational level.

Animals↗