Published online before print October 6, 2005, doi: 10.1161/01.RES.0000189260.46084.e5
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© 2005 American Heart Association, Inc.
Molecular Medicine |
Calreticulin Destabilizes Glucose Transporter-1 mRNA in Vascular Endothelial and Smooth Muscle Cells Under High-Glucose Conditions
From the Department of Pharmacology (H.T.-J., Y.R., S.S.), School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Israel; The Nephrology (T.N.-M.) and Endocrinology & Metabolism (N.K.) Services, Department of Medicine, Hadassah-Hebrew University Medical Center, Jerusalem, Israel; and Department of Clinical Biochemistry and Pathobiochemistry (J.E.), German Diabetes Center, Düsseldorf, Germany.
Correspondence to Shlomo Sasson, Dept of Pharmacology, The Hebrew University Faculty of Medicine, PO Box 12272, Jerusalem 91120, Israel. E-mail sassolo{at}cc.huji.ac.il
Substrate autoregulation of glucose transporter-1 (GLUT-1) mRNA and protein expression provides vascular endothelial and smooth muscle cells a sensitive mechanism to adapt their rate of glucose transport in response to changing glycemic conditions. Hyperglycemia-induced downregulation of glucose transport is particularly important in protecting these cells against an excessive influx of glucose and consequently increased intracellular protein glycation and generation of free radicals; both are detrimental in the development of vascular disease in diabetes. We aimed to investigate the molecular mechanism of high glucose–induced downregulation of GLUT-1 mRNA expression in primary bovine aortic vascular endothelial (VEC) and smooth muscle (VSMC) cell cultures. Using RNA mobility shift, UV cross-linking, and in vitro degradation assays, followed by mass-spectrometric analysis, we identified calreticulin as a specific destabilizing trans-acting factor that binds to a 10-nucleotide cis-acting element (CAE2181-2190) in the 3'-untranslated region of GLUT-1 mRNA. Pure calreticulin accelerated the rate of GLUT-1 mRNA-probe degradation in vitro, whereas overexpression of calreticulin in vascular cells decreased significantly the total cell content of GLUT-1 mRNA and protein. The expression of calreticulin was augmented in vascular cells exposed to high glucose in comparison with low-glucose conditions. Similarly, increased expression of calreticulin was observed in aortae of diabetic Psammomys obesus in comparison with normoglycemic controls. These data suggest that CAE2181-2190–calreticulin complex, which is formed in VSMC and VEC exposed to hyperglycemic conditions, renders GLUT-1 mRNA susceptible to degradation. This interaction underlies the process of downregulation of glucose transport in vascular cells under high-glucose conditions.
Key Words: calreticulin • glucose transporter-1 • hyperglycemia • mRNA turnover • vascular smooth muscle cells • vascular endothelial cells
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Circ. Res. 2005 97: 961-963.
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