Amyloid Precursor Protein (APP)/APP-like Protein 2 (APLP2) Expression Is Required to Initiate Endosome-Nucleus-Autophagosome Trafficking of Glypican-1-derived Heparan Sulfate

作者：Cheng Fang; Cappai Roberto; Lidfeldt Jon; Belting Mattias; Fransson Lars Ake; Mani Katrin^*

来源：JOURNAL OF BIOLOGICAL CHEMISTRY, 2014, 289(30): 20871-20878.

DOI：10.1074/jbc.M114.552810

Anhydromannose (anMan)-containing heparan sulfate (HS) derived from the proteoglycan glypican-1 is generated in endosomes by an endogenously or ascorbate-induced S-nitrosothiol-catalyzed reaction. Processing of the amyloid precursor protein (APP) and APP-like protein 2 (APLP2) by beta- and gamma-secretases into amyloid beta (A beta) and A beta-like peptides also takes place in these compartments. Moreover, anMan-containing HS suppresses the formation of toxic A beta assemblies in vitro. We showed by using deconvolution immunofluorescence microscopy with an anMan-specific monoclonal antibody as well as S-35 labeling experiments that expression of APP/APLP2 is required for ascorbate-induced transport of HS from endosomes to the nucleus. Nuclear translocation was observed in wild-type mouse embryonic fibroblasts (WT MEFs), Tg2576 MEFs, and N2a neuroblastoma cells but not in APP(-/-) and APLP2(-/-) MEFs. Transfection of APP(-/-) cells with a vector encoding APP restored nuclear import of anMan-containing HS. In WT MEFs and N2a neuroblastoma cells exposed to beta- or gamma-secretase inhibitors, nuclear translocation was greatly impeded, suggesting involvement of APP/APLP2 degradation products. In Tg2576 MEFs, the beta-inhibitor blocked transport, but the gamma-inhibitor did not. During chase in ascorbate-free medium, anMan-containing HS disappeared from the nuclei of WT MEFs. Confocal immunofluorescence microscopy showed that they appeared in acidic, LC3-positive vesicles in keeping with an autophagosomal location. There was increased accumulation of anMan-containing HS in nuclei and cytosolic vesicles upon treatment with chloroquine, indicating that HS was degraded in lysosomes. Manipulations of APP expression and processing may have deleterious effects upon HS function in the nucleus.

• 出版日期2014-7-25