O-Glycosylation Modulates Proprotein Convertase Activation of Angiopoietin-like Protein 3

Abstract

The angiopoietin-like protein 3 (ANGPTL3) is an important inhibitor of the endothelial and lipoprotein lipases and a prom-ising drug target. ANGPTL3 undergoes proprotein convertase processing (RAPR 224 2TT) for activation, and the processing site contains two potential GalNAc O-glycosylation sites imme-diately C-terminal (TT 226). We developed an in vivo model sys-tem in CHO ldlD cells that was used to show that O-glycosyla-tion in the processing site blocked processing of ANGPTL3. Genome-wide SNP association studies have identified the polypeptide GalNAc-transferase gene, GALNT2, as a candidate gene for low HDL and high triglyceride blood levels. We hypoth-esized that the GalNAc-T2 transferase performed critical O-gly-cosylation of proteins involved in lipid metabolism. Screening of a panel of proteins known to affect lipid metabolism for poten-tial sites glycosylated by GalNAc-T2 led to identification of Thr 226 adjacent to the proprotein convertase processing site in ANGPTL3. We demonstrated that GalNAc-T2 glycosylation of Thr 226 in a peptide with the RAPR 224 2TT processing site blocks in vitro furin cleavage. The study demonstrates that ANGPTL3 activation is modulated by O-glycosylation and that this step is probably controlled by GalNAc-T2.