O-Linked β-N-Acetylglucosamine (O-GlcNAc) Regulates Emerin Binding to Barrier to Autointegration Factor (BAF) in a Chromatin- and Lamin B-enriched "Niche"

Background: Nuclear membrane protein emerin binding to nuclear intermediate filaments (lamins) and BAF contributes to forming a nuclear lamina structure. Results: Emerin is O-GlcNAc-modified at eight sites: two (Ser-53 and Ser-54) influence further O-GlcNAcylation, and one (Ser-173) regulates association with BAF in the chromatin/lamin B niche. Conclusion:O-GlcNAc transferase, a nutrient-responsive enzyme, regulates emerin. Significance: Emerin hyper-O-GlcNAcylation may contribute to cardiomyopathy and other conditions. Emerin, a membrane component of nuclear lamina networks with lamins and barrier to autointegration factor (BAF), is highly O-GlcNAc-modified (O-GlcNAcylated) in mammalian cells. Mass spectrometry analysis revealed eight sites of O-GlcNAcylation, including Ser-53, Ser-54, Ser-87, Ser-171, and Ser-173. Emerin O-GlcNAcylation was reduced approximate to 50% by S53A or S54A mutation in vitro and in vivo. O-GlcNAcylation was reduced approximate to 66% by the triple S52A/S53A/S54A mutant, and S173A reduced O-GlcNAcylation of the S52A/S53A/S54A mutant by approximate to 30%, in vivo. We separated two populations of emerin, A-type lamins and BAF; one population solubilized easily, and the other required sonication and included histones and B-type lamins. Emerin and BAF associated only in histone- and lamin-B-containing fractions. The S173D mutation specifically and selectively reduced GFP-emerin association with BAF by 58% and also increased GFP-emerin hyper-phosphorylation. We conclude that -N-acetylglucosaminyltransferase, an essential enzyme, controls two regions in emerin. The first region, defined by residues Ser-53 and Ser-54, flanks the LEM domain. O-GlcNAc modification at Ser-173, in the second region, is proposed to promote emerin association with BAF in the chromatin/lamin B niche. These results reveal direct control of a conserved LEM domain nuclear lamina component by -N-acetylglucosaminyltransferase, a nutrient sensor that regulates cell stress responses, mitosis, and epigenetics.