title: Calreticulin destabilizes glucose transporter-1 mRNA in vascular endothelial and smooth muscle cells under high-glucose conditions.
abstract: 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 (CAE(2181-2190)) 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 CAE(2181-2190)-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.
authors.affiliation: Department of Pharmacology, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Israel.
authors.forename: Hana
authors.initials: H
authors.lastname: Totary-Jain
authors.forename: Tally
authors.initials: T
authors.lastname: Naveh-Many
authors.forename: Yael
authors.initials: Y
authors.lastname: Riahi
authors.forename: Nurit
authors.initials: N
authors.lastname: Kaiser
authors.forename: Jürgen
authors.initials: J
authors.lastname: Eckel
authors.forename: Shlomo
authors.initials: S
authors.lastname: Sasson
mesh_terms: D020413:3' Untranslated Regions / Q000378:metabolism; D000818:Animals; D037282:Calreticulin / Q000502:physiology*; D002417:Cattle; D002478:Cells, Cultured; D015536:Down-Regulation; D042783:Endothelial Cells / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000235:genetics*; D006943:Hyperglycemia / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D037282:Calreticulin; D051272:Glucose Transporter Type 1; D012333:RNA, Messenger; D009569:Nitric Oxide