Glycosyltransferase Function in Core 2-Type Protein O Glycosylation

Abstract

Three glycosyltransferases have been identified in mammals that can initiate core 2 protein O glycosylation. Core 2 O-glycans are abundant among glycoproteins but, to date, few functions for these structures have been identified. To investigate the biological roles of core 2 O-glycans, we produced and characterized mice deficient in one or more of the three known glycosyltransferases that generate core 2 O-glycans (C2GnT1, C2GnT2, and C2GnT3). A role for C2GnT1 in selectin ligand formation has been described. We now report that C2GnT2 deficiency impaired the mucosal barrier and increased susceptibility to colitis. C2GnT2 deficiency also reduced immunoglobulin abundance and resulted in the loss of all core 4 O-glycan biosynthetic activity. In contrast, the absence of C2GnT3 altered behavior linked to reduced thyroxine levels in circulation. Remarkably, elimination of all three C2GnTs was permissive of viability and fertility. Core 2 O-glycan structures were reduced among tissues from individual C2GnT deficiencies and completely absent from triply deficient mice. C2GnT deficiency also induced alterations in I-branching, core 1 O-glycan formation, and O mannosylation. Although the absence of C2GnT and C4GnT activities is tolerable in vivo, core 2 O glycosylation exerts a significant influence on O-glycan biosynthesis and is important in multiple physiological processes.

ACKNOWLEDGMENTS

We thank David Ditto for technical expertise with the hematological assays and Margo Streets and Trang Tran for technical expertise with the behavior assays. Jeffery Long assisted with the statistical analysis of the behavioral data.

This study was funded in part by a Mizutani Foundation for Glycoscience award (J.D.M.), a Veterans Affairs Merit Review Grant (S.B.H.), the University of California San Diego Digestive Disease Research Development Center (S.B.H), and National Institute of Health grants HL057345 (J.D.M.), HL78784 (J.D.M.), GMG2116 (J.D.M.), CA33000 (M.F.), and P01CA71932 (M.F. and J.D.M.). J.D.M. is supported by the Howard Hughes Medical Institute. This study was also funded in part by Biotechnology and Biological Sciences Research Council grant BBF0083091 (A.D.) and Public Health Service grant DK080506 (S.B.H.). M.N.I. is supported by University Science Malaysia, Ministry of Higher Education.

We declare that we have no competing financial interests.