Nuclear beta-catenin displays GSK-3beta- and APC-independent proteasome sensitivity in melanoma cells.
Colon carcinoma and melanoma cells containing either a deletion of the adenomatous polyposis coli tumor suppressor protein (APC) or mutation of the site in beta-catenin phosphorylated by glycogen synthase kinase-3beta (GSK-3beta) display elevated levels of detergent-soluble beta-catenin due to insensitivity of the cytosolic protein to proteasome-dependent degradation. In this study, we have examined the effect of beta-catenin mutation (S37F) or APC loss on the proteasome sensitivity of additional subcellular beta-catenin pools in melanoma cells. In contrast to detergent-soluble beta-catenin, the detergent-insoluble protein remains proteasome-sensitive irrespective of S37F mutation or APC status. This insoluble component appears associated primarily with nuclear cytoskeletal elements. In addition, DNase I treatment solubilized a portion of detergent-insoluble beta-catenin, suggesting that this fraction also contains chromatin-associated protein, and correlating with a proteasome-sensitive elevation in beta-catenin-stimulated reporter activity. Since the detergent-insoluble nuclear component of beta-catenin displays GSK-3beta- and APC-independent proteasome sensitivity, distinct from the soluble nuclear and cytosolic pools of this protein, regulation of beta-catenin proteasome sensitivity and the contribution of this process to beta-catenin function may be more complex than previously appreciated.
Bonvini
P
P
Department of Cell and Cancer Biology, Medicine Branch, NCI, NIH, 9610 Medical Center Drive, Suite 300, Rockville, MD 20850, USA.
Hwang
S G
SG
El-Gamil
M
M
Robbins
P
P
Kim
J S
JS
Trepel
J
J
Neckers
L
L
D025601:Adenomatous Polyposis Coli Protein; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003902:Detergents / Q000737:chemistry; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006801:Humans; D008545:Melanoma; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D012995:Solubility; D013347:Subcellular Fractions / Q000378:metabolism; D015534:Trans-Activators; D014407:Tumor Cells, Cultured; D051176:beta Catenin
D025601:Adenomatous Polyposis Coli Protein; C495270:CTNNB1 protein, human; D002843:Chromatin; D003598:Cytoskeletal Proteins; D003902:Detergents; D009097:Multienzyme Complexes; D015534:Trans-Activators; D051176:beta Catenin; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex