Probing isoform-specific functions of polypeptide GalNAc-transferases using zinc finger nuclease glycoengineered SimpleCells

Katrine Ter-Borch Gram Schjoldager, Sergey Y Vakhrushev, Yun Kong, Catharina Steentoft, Aaron S Nudelman, Nis Borbye Pedersen, Hans H Wandall, Ulla Mandel, Eric P Bennett, Steven B Levery, Henrik Clausen

Research output: Contribution to journalJournal articleResearchpeer-review

109 Citations (Scopus)

Abstract

Our knowledge of the O-glycoproteome [N-acetylgalactosamine (GalNAc) type] is highly limited. The O-glycoproteome is differentially regulated in cells by dynamic expression of a subset of 20 polypeptide GalNAc-transferases (GalNAc-Ts), and methods to identify important functions of individual GalNAc-Ts are largely unavailable. We recently introduced SimpleCells, i.e., human cell lines made deficient in O-glycan extension by zinc finger nuclease targeting of a key gene in O-glycan elongation (Cosmc), which allows for proteome-wide discovery of O-glycoproteins. Here we have extended the SimpleCell concept to include proteome-wide discovery of unique functions of individual GalNAc-Ts. We used the GalNAc-T2 isoform implicated in dyslipidemia and the human HepG2 liver cell line to demonstrate unique functions of this isoform. We confirm that GalNAc-T2-directed site-specific O-glycosylation inhibits proprotein activation of the lipase inhibitor ANGPTL3 in HepG2 cells and further identify eight O-glycoproteins exclusively glycosylated by T2 of which one, ApoC-III, is implicated in dyslipidemia. Our study supports an essential role for GalNAc-T2 in lipid metabolism, provides serum biomarkers for GalNAc-T2 enzyme function, and validates the use of GALNT gene targeting with SimpleCells for broad discovery of disease-causing deficiencies in O-glycosylation. The presented glycoengineering strategy opens the way for proteome-wide discovery of functions of GalNAc-T isoforms and their role in congenital diseases and disorders.
Original languageEnglish
JournalProceedings of the National Academy of Sciences USA (PNAS)
Volume109
Issue number25
Pages (from-to)9893-8
Number of pages6
ISSN0027-8424
DOIs
Publication statusPublished - Jun 2012

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