Identification and characterization of a missense mutation in the O-linked β- N-acetylglucosamine ( O-GlcNAc) transferase gene that segregates with X-linked intellectual disability
- J Biol Chem. 2017 May 26;292(21):8948-8963. doi: 10.1074/jbc.M116.771030.
- 1. From the Department of Biochemistry and Molecular Biology, Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602.
- 2. the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University, Baltimore, Maryland 21287.
- 3. the Greenwood Genetic Center, Greenwood, South Carolina 29646.
- 4. Pediatrics (Medical Genetics), Pediatric Pathology, Human Genetics, Obstetrics, and Gynecology, University of Utah School of Medicine, Salt Lake City, Utah 84132.
- 5. the Department of Paediatrics and Robinson Research Institute, University of Adelaide, Adelaide, South Australia 5006, Australia, and.
- 6. the Department of Computational Biophysics and Bioinformatics, Clemson University, Clemson, South Carolina 29634.
- 7. the Greenwood Genetic Center, Greenwood, South Carolina 29646, [email protected].
- 8. From the Department of Biochemistry and Molecular Biology, Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602, [email protected].
O-GlcNAc is a regulatory post-translational modification of nucleocytoplasmic proteins that has been implicated in multiple biological processes, including transcription. In humans, single genes encode Enzymes for its attachment (O-GlcNAc transferase (OGT)) and removal (O-GlcNAcase (OGA)). An X-chromosome exome screen identified a missense mutation, which encodes an amino acid in the tetratricopeptide repeat, in OGT (759G>T (p.L254F)) that segregates with X-linked intellectual disability (XLID) in an affected family. A decrease in steady-state OGT protein levels was observed in isolated lymphoblastoid cell lines from affected individuals, consistent with molecular modeling experiments. Recombinant expression of L254F-OGT demonstrated that the enzyme is active as both a Glycosyltransferase and an HCF-1 protease. Despite the reduction in OGT levels seen in the L254F-OGT individual cells, we observed that steady-state global O-GlcNAc levels remained grossly unaltered. Surprisingly, lymphoblastoids from affected individuals displayed a marked decrease in steady-state OGA protein and mRNA levels. We observed an enrichment of the OGT-containing transcriptional repressor complex mSin3A-HDAC1 at the proximal promoter region of OGA and correspondingly decreased OGA promoter activity in affected cells. Global transcriptome analysis of L254F-OGT lymphoblastoids compared with controls revealed a small subset of genes that are differentially expressed. Thus, we have begun to unravel the molecular consequences of the 759G>T (p.L254F) mutation in OGT that uncovered a compensation mechanism, albeit imperfect, given the phenotype of affected individuals, to maintain steady-state O-GlcNAc levels. Thus, a single amino acid substitution in the regulatory domain (the tetratricopeptide repeat domain) of OGT, which catalyzes the O-GlcNAc post-translational modification of nuclear and cytosolic proteins, appears causal for XLID.