Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Endosomes have recently been identified as one major site of glucagon degradation in intact rat liver. In this study, a cell-free system has been used to assess the role of ATP-dependent acidification in endosomal glucagon degradation and identify the glucagon products generated. Percoll gradient fractionation of Golgi-endosomal fractions prepared 10-30 min after injection of [125I]iodoglucagon showed a time-dependent shift of the radioactivity towards high densities. Regardless of time, the radioactivity was less precipitable by trichloroacetic acid (Cl3Ac) at high densities than at low densities. Chloroquine treatment slightly increased the density shift of the radioactivity and decreased its Cl3Ac-precipitability throughout the gradient. Incubation of endosomal fractions containing [125I]iodoglucagon in 0.15 M-KCl at 30 degrees C resulted in a time- and pH-dependent generation of Cl3Ac-soluble radioactivity, with a maximum at pH 4 (t1/2, 7 min). At pH 5, 1,10-phenanthroline, bacitracin and p-chloromercuribenzoic acid partially inhibited [125I]iodoglucagon degradation. At pH 6-7, ATP stimulated [125I]iodoglucagon degradation by 5-10-fold and caused endosomal acidification as judged from Acridine Orange uptake. The effects of ATP were inhibited by chloroquine, monensin, N-ethylmaleimide and dansylcadaverine. Poly(ethylene glycol) (PEG) precipitation of the radioactivity associated with endosomes showed that lowering the pH below 5.5 caused dissociation of the glucagon-receptor complex, and that, regardless of incubation conditions, all degraded [125I]iodoglucagon diffused extraluminally. On h.p.l.c., at least three products less hydrophobic than [125I]iodoglucagon were identified in incubation mixtures along with monoiodotyrosine. Radiosequence analysis of the products revealed one major cleavage located C-terminally to Tyr-13 and two minor cleavages affecting Thr-5-Phe-6 and Phe-6-Thr-7 bonds. It is concluded that glucagon degradation in liver endosomes is functionally linked to ATP-dependent endosomal acidification and involves several cleavages in the glucagon sequence.
 ...
PMID:Degradation of glucagon in isolated liver endosomes. ATP-dependence and partial characterization of degradation products. 174 49

The uptake and processing of glucagon into liver endosomes were studied in vivo by subcellular fractionation. After injection of [[125I]iodo-Tyr10]glucagon and [[125I]iodo-Tyr13]glucagon to rats, the uptake of radioactivity into the liver was maximum at 2 min (6% of the dose/g of tissue). On differential centrifugation, the radioactivity in the homogenate was recovered mainly in the nuclear (N), microsomal (P) and supernatant (S) fractions, with maxima at 5, 10 and 40 min, respectively; recovery of radioactivity in the mitochondrial-lysosomal (ML) fraction did not exceed 6% and was maximal at 20 min. On density-gradient centrifugation, the radioactivity associated first (2-10 min) with plasma membranes and then (10-40 min) with Golgi-endosomal (GE) fractions, with 2-5-fold and 20-150-fold enrichments respectively. Subfractionation of the GE fractions showed that, unlike the Golgi marker galactosyltransferase, the radioactivity was density-shifted by diaminobenzidine cytochemistry. Subfractionation of the ML fraction isolated at 40 min showed that more than half of the radioactivity was recovered at lower densities than the lysosomal marker acid phosphatase. Throughout the time of study, the [125I]iodoglucagon associated with the P, PM and GE fractions remained at least 80-90% trichloroacetic acid (TCA)-precipitable, whereas that associated with other fractions, especially the S fraction, became progressively TCA-soluble. On gel filtration and h.p.l.c., the small amount of degraded [125I]iodoglucagon associated with GE fractions was found to consist of monoiodotyrosine. Chloroquine treatment of [125I]iodoglucagon-injected rats caused a moderate but significant increase in the late recovery of radioactivity in the ML, P and GE fractions, but had little effect on the association of the ML radioactivity with acid-phosphatase-containing structures. Chloroquine treatment also led to a paradoxical decrease in the TCA-precipitability of the radioactivity associated with the P and GE fractions. Upon h.p.l.c. analysis of GE extracts of chloroquine-treated rats, at least four degradation products less hydrophobic than intact [125I]iodoglucagon were identified. Radio-sequence analysis of four of these products revealed three cleavages, affecting bonds Ser2-Gln3, Thr5-Phe6 and Phe6-Thr7. When GE fractions containing internalized [125I]iodoglucagon were incubated in iso-osmotic KCl at 30 degrees C, a rapid generation of TCA-soluble products was observed, with a maximum at pH 4. We conclude that endosomes are a major site at which internalized glucagon is degraded, endosomal acidification being required for optimum degradation.
 ...
PMID:Fate of injected glucagon taken up by rat liver in vivo. Degradation of internalized ligand in the endosomal compartment. 226 96

Glucagon-like peptide-1(7-36)amide [GLP-1(7-36)amide] is supposed to be an important physiologic incretin. Recently, high affinity receptors for GLP-1(7-36)amide have been demonstrated on rat insulinoma-derived RINm5F cells. The present study examined the internalization and degradation of the GLP-1-receptor complex. Internalization of the peptide was time- and temperature-dependent. At 37 degrees C binding and internalization was rapid. At 60 min 35% of 125I-labeled GLP-1(7-36)amide was internalized. Incubation in the presence of increasing concentrations of non-labeled GLP-1(7-36)amide resulted in a decrease of internalization of 125I-labeled peptide indicating that this process is saturable. Incubation in the presence of 0.2 mM chloroquine, an inhibitor of intracellular hormone degradation, resulted in intracellular accumulation of 125I-GLP-1(7-36)amide. HPLC-supported analysis of cell content after internalization of 125I-GLP-1(7-36)amide during a 60-min incubation period at 37 degrees C revealed an elution profile showing two maxima of radioactivity: one represented intact labeled GLP-1(7-36)amide, the other an intracellular degradation product of the peptide. Chloroquine caused a 5-fold increase of the peak representing intact 125I-GLP-1(7-36)amide thus demonstrating inhibition of degradation of labelled peptide. Furthermore, a 4-fold increase of the other peak occurred possibly mirroring a delay of release of degradation products by chloroquine. It was excluded that chloroquine is able to interfere with GLP-1(7-36)amide-binding to its receptor.
 ...
PMID:Internalization of glucagon-like peptide-1(7-36)amide in rat insulinoma cells. 255 38

To examine the function of islet lysosomal enzymes in islet hormone secretory mechanisms, we investigated the effects of the lysosomotropic drug chloroquine on islet lysosomal enzyme activities and basal as well as stimulated insulin and glucagon secretion. Chloroquine, added to islet homogenates, did not affect the activities of the lysosomal enzymes acid amyloglucosidase, acid alpha-glucosidase, or N-acetyl-beta-D-glucosaminidase. The activity of acid phosphatase, however, was inhibited at a high concentration of chloroquine (10(-3) M). When injected together with glucose, chloroquine (2 or 10 mumol/kg) inhibited the peak plasma insulin response. Similarly, at 24 hrs after chloroquine injection (100 mumol/kg), the plasma insulin response to glucose was reduced. In contrast, islets isolated from mice pretreated 24 hrs before with chloroquine, displayed glucose-stimulated insulin secretion in vitro that was not different from controls. Such islets showed, furthermore, enhanced activities of the enzymes acid phosphatase and neutral alpha-glucosidase but not of acid amyloglucosidase, acid alpha-glucosidase or N-acetyl-beta-D-glucosaminidase. Arginine-stimulated insulin response in vivo displayed a complex pattern; it was increased when arginine was injected together with chloroquine but decreased at 24 hrs after chloroquine administration. Arginine-stimulated glucagon secretion was not affected by chloroquine. We conclude that chloroquine pretreatment 24 hrs prior to glucose injection decreases glucose-stimulated insulin secretion in vivo by mechanisms that are not correlated to an inhibitory action on islet activities of glycogenolytic lysosomal enzymes.
 ...
PMID:Islet hormone secretion and islet lysosomal enzyme activities in the mouse: effects of chloroquine. 307 44

The incidence of nonalcoholic fatty liver disease (NAFLD) keeps rising year by year, and NAFLD is rapidly becoming the most common liver disease worldwide. Clinical studies have found that glucagon-like peptide-1 (GLP-1) analogue, liraglutide (LRG), cannot only reduce glucose levels, but also improve hepatic lipase, especially in patients also with type 2 diabetes mellitus (T2DM). In addition, enhancing autophagy decreases lipid accumulation in hepatocytes. The aim of the present study is to explore the effect of LRG on hepatocyte steatosis and the possible role of autophagy. We set up an obesity mouse model with a high-fat diet (HFD) and induced hepatocyte steatosis with free fatty acids (FFA) in human L-O2 cells. LRG and two inhibitors of autophagy, Chloroquine (CQ) and bafilomycin A1 (Baf), were added into each group, respectively. The lipid profiles and morphological modifications of each group were tested. Immunohistochemistry, immunofluorescence staining and transmission electron microscopy (TEM) were used to measure autophagy in this study. The autophagy protein expression of SQSTM1 (P62), and LC3B, along with the signaling pathway proteins of mTOR, phosphorylated mTOR (p-mTOR), AMPK, phosphorylated AMPK (p-AMPK) and Beclin1, were evaluated by western blot. Our results showed that LRG improved hepatocyte steatosis by inducing autophagy, and the AMPK/mTOR pathway is involved. These findings suggest an important mechanism for the positive effects of LRG on hepatic steatosis, and provide new evidence for clinical use of LRG in NAFLD.
 ...
PMID:GLP-1 analogue improves hepatic lipid accumulation by inducing autophagy via AMPK/mTOR pathway. 2720 76