A SUBPOPULATION OF ESTROGEN-RECEPTORS ARE MODIFIED BY O-LINKED N-ACETYLGLUCOSAMINE

Estrogen receptors (ER) are ligand-inducible transcription factors reg ulated by Ser(Thr)-O-phosphorylation. Many transcription factors and e ukaryotic RNA polymerase II itself are also dynamically modified by Se r(Thr)-O-linked N-acetylglucosamine moieties (O-GlcNAc). Here we repor t that subpopulations of murine, bovine, and human estrogen receptors are modified by O-GlcNAc. O-GlcNAc moieties were detected on insect ce ll-expressed, mouse ER (mER) by probing with bovine milk galactosyltra nsferase, followed by structural analysis, Wheat germ agglutinin-Sepha rose affinity chromatography also readily detected terminal GlcNAc res idues on subpopulations of ER purified from calf uterus, from human br east cancer cells (MCF-7), or from mER produced by in. vitro translati on. These data suggest that greater than 10% of these populations of e strogen receptors bear O-GlcNAc. Site mapping of insect cell expressed mER localized one major site of O-GlcNAc addition to Thr-575, within a PEST region of the carboxyl-terminal F domain, Based upon their rela tive resistance to both hexosaminidase and to in vitro galactosylation , O-GlcNAc moieties appear to be largely buried on native mER. This dy namic saccharide modification, like phosphorylation, may play a role i n modulating the dimerization, stability, or transactivation functions of estrogen receptors.