title: The Axin1 scaffold protein promotes formation of a degradation complex for c-Myc.
abstract: Expression of the c-Myc proto-oncoprotein is tightly regulated in normal cells. Phosphorylation at two conserved residues, threonine58 (T58) and serine62 (S62), regulates c-Myc protein stability. In cancer cells, c-Myc can become aberrantly stabilized associated with altered T58 and S62 phosphorylation. A complex signalling cascade involving GSK3beta kinase, the Pin1 prolyl isomerase, and the PP2A-B56alpha phosphatase controls phosphorylation at these sites. We report here a novel role for the tumour suppressor scaffold protein Axin1 in facilitating the formation of a degradation complex for c-Myc containing GSK3beta, Pin1, and PP2A-B56alpha. Although knockdown of Axin1 decreases the association of c-Myc with these proteins, reduces T58 and enhances S62 phosphorylation, and increases c-Myc stability, acute expression of Axin1 reduces c-Myc levels and suppresses c-Myc transcriptional activity. Moreover, the regulation of c-Myc by Axin1 is impaired in several tested cancer cell lines with known stabilization of c-Myc or loss of Axin1. This study provides critical insight into the regulation of c-Myc expression, how this can be disrupted in three cancer types, and adds to our knowledge of the tumour suppressor activity of Axin1.
authors.affiliation: Department of Molecular and Medical Genetics, Oregon Health and Science University, Portland, OR, USA.
authors.forename: Hugh K
authors.initials: HK
authors.lastname: Arnold
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhang
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Daniel
authors.forename: Deanne
authors.initials: D
authors.lastname: Tibbitts
authors.forename: Julie
authors.initials: J
authors.lastname: Escamilla-Powers
authors.forename: Amy
authors.initials: A
authors.lastname: Farrell
authors.forename: Sara
authors.initials: S
authors.lastname: Tokarz
authors.forename: Charlie
authors.initials: C
authors.lastname: Morgan
authors.forename: Rosalie C
authors.initials: RC
authors.lastname: Sears
mesh_terms: D060466:Axin Protein; D002460:Cell Line; D050703:E2F2 Transcription Factor / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D019696:Peptidylprolyl Isomerase / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D015533:Transcriptional Activation; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000502:physiology*; D054875:Ubiquitination
chemical_list: C555451:AXIN1 protein, human; D060466:Axin Protein; D050703:E2F2 Transcription Factor; C493761:E2F2 protein, human; C489427:MYC protein, human; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins; D025521:Tumor Suppressor Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D054648:Protein Phosphatase 2; C000606846:PIN1 protein, human; D019696:Peptidylprolyl Isomerase