title: Phosphorylation by glycogen synthase kinase-3 controls c-myc proteolysis and subnuclear localization.
abstract: The c-Myc protein is a transcription factor that is a central regulator of cell growth and proliferation. Thr-58 is a major phosphorylation site in c-Myc and is a mutational hotspot in Burkitt's and other aggressive human lymphomas, indicating that Thr-58 phosphorylation restricts the oncogenic potential of c-Myc. Mutation of Thr-58 is also associated with increased c-Myc protein stability. Here we show that inhibition of glycogen synthase kinase-3 (GSK-3) activity with lithium increases c-Myc stability and inhibits phosphorylation of c-Myc specifically at Thr-58 in vivo. Conversely, overexpression of GSK-3 alpha or GSK-3 beta enhances Thr-58 phosphorylation and ubiquitination of c-Myc. Together, these observations suggest that phosphorylation of Thr-58 mediated by GSK-3 facilitates c-Myc rapid proteolysis by the ubiquitin pathway. Furthermore, we demonstrate that GSK-3 binds c-Myc in vivo and in vitro and that GSK-3 colocalizes with c-Myc in the nucleus, strongly arguing that GSK-3 is the c-Myc Thr-58 kinase. We found that c-MycS, which lacks the N-terminal 100 amino acids of c-Myc, is unable to bind GSK-3; however, mutation of Ser-62, the priming phosphorylation site necessary for Thr-58 phosphorylation, does not disrupt GSK-3 binding. Finally, we show that Thr-58 phosphorylation alters the subnuclear localization of c-Myc, enhancing its localization to discrete nuclear bodies together with GSK-3.
authors.affiliation: Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Gregory
authors.forename: Ying
authors.initials: Y
authors.lastname: Qi
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Hann
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D010447:Peptide Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D016271:Proto-Oncogene Proteins c-myc; D025801:Ubiquitin; D038362:Glycogen Synthase Kinase 3; D010447:Peptide Hydrolases