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Inhibition of hepatocytic autophagy by adenosine, aminoimidazole-4-carboxamide riboside, and N6-mercaptopurine riboside. Evidence for involvement of amp-activated protein kinase.
- Source :
-
The Journal of biological chemistry [J Biol Chem] 1998 Sep 11; Vol. 273 (37), pp. 23758-63. - Publication Year :
- 1998
-
Abstract
- To examine the role of AMP-activated protein kinase (AMPK; EC 2.7.1. 109) in the regulation of autophagy, rat hepatocytes were incubated with the AMPK proactivators, adenosine, 5-amino-4-imidazole carboxamide riboside (AICAR), or N6-mercaptopurine riboside. Autophagic activity was inhibited by all three nucleosides, AICAR and N6-mercaptopurine riboside being more potent (IC50 = 0.3 mM) than adenosine (IC50 = 1 mM). 2'-Deoxycoformycin, an adenosine deaminase (EC 3.5.4.4) inhibitor, increased the potency of adenosine 5-fold, suggesting that the effectiveness of adenosine as an autophagy inhibitor was curtailed by its intracellular deamination. 5-Iodotubercidin, an adenosine kinase (EC 2.7.1.20) inhibitor, abolished the effects of all three nucleosides, indicating that they needed to be phosphorylated to inhibit autophagy. A 5-iodotubercidin-suppressible phosphorylation of AICAR to 5-aminoimidazole-4-carboxamide riboside monophosphate was confirmed by chromatographic analysis. AICAR, up to 0.4 mM, had no significant effect on intracellular ATP concentrations. Because activated AMPK phosphorylates and inactivates 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (EC 1.1.1.88), the rate-limiting enzyme in cholesterol synthesis, the strong inhibition of hepatocytic cholesterol synthesis by all three nucleosides confirmed their ability to activate AMPK under the conditions used. Lovastatin and simvastatin, inhibitors of HMG-CoA reductase, strongly suppressed cholesterol synthesis while having no effect on autophagic activity, suggesting that AMPK inhibits autophagy independently of its effects on HMG-CoA reductase and cholesterol metabolism.
- Subjects :
- AMP-Activated Protein Kinases
Acetates metabolism
Aminoimidazole Carboxamide pharmacology
Animals
Antimetabolites pharmacology
Autophagy
Cells, Cultured
Cholesterol biosynthesis
Drug Synergism
Hydroxymethylglutaryl-CoA Reductase Inhibitors pharmacology
Kinetics
Liver drug effects
Liver metabolism
Lovastatin pharmacology
Male
Nucleosides metabolism
Nucleotides metabolism
Pentostatin pharmacology
Rats
Rats, Wistar
Simvastatin pharmacology
Tubercidin analogs & derivatives
Tubercidin pharmacology
Adenosine pharmacology
Adenosine Triphosphate metabolism
Aminoimidazole Carboxamide analogs & derivatives
Liver cytology
Multienzyme Complexes metabolism
Protein Kinases metabolism
Protein Serine-Threonine Kinases
Ribonucleotides pharmacology
Thioinosine pharmacology
Subjects
Details
- Language :
- English
- ISSN :
- 0021-9258
- Volume :
- 273
- Issue :
- 37
- Database :
- MEDLINE
- Journal :
- The Journal of biological chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 9726984
- Full Text :
- https://doi.org/10.1074/jbc.273.37.23758