Isoform-specific regulation of the inositol 1,4,5-trisphosphate receptor by O-linked glycosylation

Abstract

The inositol 1,4,5-trisphosphate receptor (InsP3R), an intracellular calcium channel, has three isoforms with >65% sequence homology, yet the isoforms differ in their function and regulation by post-translational modifications. We showed previously that InsP3R-1 is functionally modified by O-linked >-N-acetylglucosamine glycosylation (O-GlcNAcylation) (Rengifo, J., Gibson, C. J., Winkler, E., Collin, T., and Ehrlich, B. E. (2007) J. Neurosci. 27, 13813-13821). We now report the effect of O-GlcNAcylation on InsP3R-2 and InsP3R-3. Analysis of AR4-2J cells, a rat pancreatoma cell line expressing predominantly InsP 3R-2, showed no detectable O-GlcNAcylation of InsP3R-2 and no significant functional changes despite the presence of the enzymes for addition (O-β-N-acetylglucosaminyltransferase) and removal (O-β-N-acetylglucosaminidase) of the monosaccharide. In contrast, InsP 3R-3 in Mz-ChA-1 cells, a human cholangiocarcinoma cell line expressing predominantly InsP3R-3, was functionally modified byO-GlcNAcylation. Interestingly, the functional impact of O-GlcNAcylation on the InsP3R-3 channel was opposite the effect measured with InsP 3R-1. Addition of O-GlcNAc byO-β-N-acetylglucosaminyltransferase increased InsP3R-3 single channel open probability. Incubation of Mz-ChA-1 cells in hyperglycemic medium caused an increase in the InsP 3-dependent calcium release from the endoplasmic reticulum. The dynamic and inducible nature of O-GlcNAcylation and the InsP3R isoform specificity suggest that this form of modification of InsP3R and subsequent changes in intracellular calcium transients are important in physiological and pathophysiological processes. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.