title: Sumoylation induced by the Arf tumor suppressor: a p53-independent function.
abstract: The mouse p19(Arf) protein has both p53-dependent and p53-independent tumor-suppressive activities. Arf triggers sumoylation of many cellular proteins, including Mdm2 and nucleophosmin (NPM/B23), with which p19(Arf) physically interacts in vivo, and this occurs equally well in cells expressing or lacking functional p53. In an Arf-null NIH 3T3 cell derivative (MT-Arf cells) engineered to reexpress an Arf transgene driven by a zinc-inducible metallothionein promoter, sumoylation of endogenous Mdm2 and NPM proteins was initiated as p19(Arf) was induced and was observed before p53-dependent cell cycle arrest. Predominately nucleoplasmic molecules visualized by immunofluorescence with antibodies to small ubiquitin-like modifier (SUMO) 1 localized to nucleoli as p19(Arf) accumulated there. Two Arf mutants, one of which binds to Mdm2 and NPM but is excluded from nucleoli and the other of which enters nucleoli but is handicapped in binding to Mdm2 and NPM, were defective in inducing sumoylation of these two target proteins and did not localize bulk sumoylated molecules to nucleoli. The CELO adenovirus protein, Gam1, which inhibits the SUMO activating enzyme (E1) and leads to down-regulation of the SUMO conjugating enzyme (E2/Ubc9), had no overt effect on the ability of p19(Arf) to activate p53 or the p53-responsive genes encoding Mdm2 and p21(Cip1), despite the fact that Arf-induced sumoylation of Mdm2 was blocked. Reduction of Ubc9 levels with short hairpin RNAs rendered similar results. We suggest that Arf's p53-independent effects on gene expression and tumor suppression might depend on Arf-induced sumoylation.
authors.affiliation: Howard Hughes Medical Institute, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Kenji
authors.initials: K
authors.lastname: Tago
authors.forename: Susanna
authors.initials: S
authors.lastname: Chiocca
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Sherr
mesh_terms: D000818:Animals; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000378:metabolism; D000090243:Nucleophosmin; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D014162:Transfection; D019076:Transgenes / Q000235:genetics; D025803:Tumor Suppressor Protein p14ARF / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism
chemical_list: C105052:CELO protein, adenovirus; C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D017931:DNA Primers; C000716967:NPM1 protein, human; C000715570:Npm1 protein, mouse; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D025841:Small Ubiquitin-Related Modifier Proteins; D025803:Tumor Suppressor Protein p14ARF; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D014764:Viral Proteins; D000090243:Nucleophosmin; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2