LAUSR

ABSTRACT The recycling, S‐nitrosylated heparan sulfate (HS) proteoglycan glypican‐1 releases anhydromannose (anMan)‐containing HS chains by a nitrosothiol‐catalyzed cleavage in endosomes that can be constitutive or induced by ascorbate. The HS‐anMan chains are then transported to the nucleus. A specific nuclear target for HS‐anMan has not been identified. We have monitored endosome‐to‐nucleus trafficking of HS‐anMan by deconvolution and confocal immunofluorescence microscopy using an anMan‐specific monoclonal antibody in non‐growing, ascorbate‐treated, and growing, untreated, wild‐type mouse embryonic fibroblasts and hypoxia‐exposed Alzheimer mouse Tg2576 fibroblasts and human U87 glioblastoma cells. In all cells, nuclear HS‐anMan targeted a limited number of sites of variable size where it colocalized with DNA and nucleolin, an established marker for nucleoli. HS‐anMan also colocalized with ethynyl uridine‐tagged nascent RNA and two acetylated forms of histone H3. Acute hypoxia increased the formation of HS‐anMan in both Tg2576 and U87 cells. A portion of HS‐anMan colocalized with nucleolin at small discrete sites, while most of the nucleolin and nascent RNA was dispersed. In U87 cells, HS‐anMan, nucleolin and nascent RNA reassembled after prolonged hypoxia. Nucleolar HS may modulate synthesis and/or release of rRNA.