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Wnt signaling requires sequestration of glycogen synthase kinase 3 inside multivesicular endosomes.

ABSTRACT: Canonical Wnt signaling requires inhibition of Glycogen Synthase Kinase 3 (GSK3) activity, but the molecular mechanism by which this is achieved remains unclear. Here, we report that Wnt signaling triggers the sequestration of GSK3 from the cytosol into multivesicular bodies (MVBs), so that this enzyme becomes separated from its many cytosolic substrates. Endocytosed Wnt colocalized with GSK3 in acidic vesicles positive for endosomal markers. After Wnt addition, endogenous GSK3 activity decreased in the cytosol, and GSK3 became protected from protease treatment inside membrane-bounded organelles. Cryoimmunoelectron microscopy showed that these corresponded to MVBs. Two proteins essential for MVB formation, HRS/Vps27 and Vps4, were required for Wnt signaling. The sequestration of GSK3 extended the half-life of many other proteins in addition to ?-Catenin, including an artificial Wnt-regulated reporter protein containing GSK3 phosphorylation sites. We conclude that multivesicular endosomes are essential components of the Wnt signal-transduction pathway.

SUBMITTER: Taelman VF

PROVIDER: S-EPMC3022472 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Wnt signaling requires sequestration of glycogen synthase kinase 3 inside multivesicular endosomes.

Taelman Vincent F VF Dobrowolski Radoslaw R Plouhinec Jean-Louis JL Fuentealba Luis C LC Vorwald Peggy P PP Gumper Iwona I Sabatini David D DD De Robertis Edward M EM

Cell 20101201 7

Canonical Wnt signaling requires inhibition of Glycogen Synthase Kinase 3 (GSK3) activity, but the molecular mechanism by which this is achieved remains unclear. Here, we report that Wnt signaling triggers the sequestration of GSK3 from the cytosol into multivesicular bodies (MVBs), so that this enzyme becomes separated from its many cytosolic substrates. Endocytosed Wnt colocalized with GSK3 in acidic vesicles positive for endosomal markers. After Wnt addition, endogenous GSK3 activity decrease ...[more]

PMID: 21183076

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Project description:Glycogen synthase kinase-3? (GSK-3?), a serine/threonine protein kinase, may function as a tumor suppressor or an oncogene, depending on the tumor type. We sought to determine the biological function of GSK-3? in osteosarcoma, a rare pediatric cancer for which the identification of new therapeutic targets is urgent.We used cell viability assays, colony formation assays, and apoptosis assays to analyze the effects of altered GSK-3? expression in U2OS, MG63, SAOS2, U2OS/MTX300, and ZOS osteosarcoma cell lines. Nude mice (n = 5-8 mice per group) were injected with U2OS/MTX300, and ZOS cells to assess the role of GSK-3? in osteosarcoma growth in vivo and to evaluate the effects of inhibitors and/or anticancer drugs on tumor growth. We used an antibody array, polymerase chain reaction, western blotting, and a luciferase reporter assay to establish the effect of GSK-3? inhibition on the nuclear factor-?B (NF-?B) pathway. Immunochemistry was performed on primary tumor specimens from osteosarcoma patients (n = 74) to determine the relationship of GSK-3? activity with overall survival.Osteosarcoma cells with low levels of inactive p-Ser9-GSK-3? formed colonies in vitro and tumors in vivo more readily than cells with higher levels and cells in which GSK-3? had been silenced formed fewer colonies and smaller tumors than parental cells. Silencing or pharmacological inhibition of GSK-3? resulted in apoptosis of osteosarcoma cells. Inhibition of GSK-3? resulted in inhibition of the NF-?B pathway and reduction of NF-?B-mediated transcription. Combination treatments with GSK-3? inhibitors, NF-?B inhibitors, and chemotherapy drugs increased the effectiveness of chemotherapy drugs in vitro and in vivo. Patients whose osteosarcoma specimens had hyperactive GSK-3?, and nuclear NF-?B had a shorter median overall survival time (49.2 months) compared with patients whose tumors had inactive GSK-3? and NF-?B (109.2 months).GSK-3? activity may promote osteosarcoma tumor growth, and therapeutic targeting of the GSK-3? and/or NF-?B pathways may be an effective way to enhance the therapeutic activity of anticancer drugs against osteosarcoma.

Dataset Information

Wnt signaling requires sequestration of glycogen synthase kinase 3 inside multivesicular endosomes.

Publications

Wnt signaling requires sequestration of glycogen synthase kinase 3 inside multivesicular endosomes.

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