title: Protein kinase C beta2-dependent phosphorylation of core 2 GlcNAc-T promotes leukocyte-endothelial cell adhesion: a mechanism underlying capillary occlusion in diabetic retinopathy.
abstract: Increased leukocyte-endothelial cell adhesion is a key early event in the development of retinopathy and atherogenesis in diabetic patients. We recently reported that raised activity of glycosylating enzyme [beta]1,6 acetylglucosaminyltransferase (core 2 GlcNAc-T) is responsible for increased leukocyte-endothelial cell adhesion and capillary occlusion in retinopathy. Here, we demonstrate that elevated glucose increases the activity of core 2 GlcNAc-T and adhesion of human leukocytes to retinal capillary endothelial cells, in a dose-dependent manner, through diabetes-activated serine/threonine protein kinase C beta2 (PKCbeta2)-dependent phosphorylation. This regulatory mechanism, involving phosphorylation of core 2 GlcNAc-T, is also present in polymorphonuclear leukocytes isolated from type 1 and type 2 diabetic patients. Inhibition of PKCbeta2 activation with the specific inhibitor, LY379196, attenuated serine phosphorylation of core 2 GlcNAc-T and prevented increased leukocyte-endothelial cell adhesion. Raised activity of core 2 GlcNAc-T was associated with a threefold increase in O-linked glycosylation of P-selectin glycoprotein ligand-1 on the surface of leukocytes of diabetic patients compared with age-matched control subjects. PKCbeta2-dependent phosphorylation of core 2 GlcNAc-T may thus represent a novel regulatory mechanism for activation of this key enzyme in mediating increased leukocyte-endothelial cell adhesion and capillary occlusion in diabetic retinopathy.
authors.affiliation: Centre for Cardiovascular Biology & Medicine, Guy's, King's and St. Thomas' School of Biomedical Sciences, King's College London, 2nd Floor New Hunt's House, London SE1 1UL, U.K. rakesh.chibber@kcl.ac.uk
authors.forename: Rakesh
authors.initials: R
authors.lastname: Chibber
authors.forename: Bahaedin M
authors.initials: BM
authors.lastname: Ben-Mahmud
authors.forename: Giovanni E
authors.initials: GE
authors.lastname: Mann
authors.forename: Jin J
authors.initials: JJ
authors.lastname: Zhang
authors.forename: Eva M
authors.initials: EM
authors.lastname: Kohner
mesh_terms: D000818:Animals; D002196:Capillaries / Q000201:enzymology / Q000502:physiology / Q000503:physiopathology*; D002417:Cattle; D002448:Cell Adhesion / Q000502:physiology*; D003922:Diabetes Mellitus, Type 1 / Q000201:enzymology / Q000503:physiopathology*; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology / Q000503:physiopathology*; D003930:Diabetic Retinopathy / Q000201:enzymology / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000502:physiology*; D006442:Glycated Hemoglobin / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007962:Leukocytes / Q000502:physiology*; D017351:N-Acetylglucosaminyltransferases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D064546:Protein Kinase C beta; D012016:Reference Values; D012171:Retinal Vessels / Q000201:enzymology / Q000503:physiopathology; D020298:U937 Cells
chemical_list: D006442:Glycated Hemoglobin; D017351:N-Acetylglucosaminyltransferases; D011493:Protein Kinase C; D064546:Protein Kinase C beta; C063313:alpha-1,6-mannosyl-glycoprotein beta-1,2-N-acetylglucosaminyltransferase; C579054:PRKCB protein, human