title: c-Myc localization within the nucleus: evidence for association with the PML nuclear body.
abstract: Definitive localization of c-Myc within the nucleus is important to fully understand the regulation and function of this oncoprotein. Studies of c-Myc distribution, however, have produced conflicting results. To overcome technical challenges inherent in c-Myc cytology, we use here three methods to visualize c-Myc and in addition examine the impact of proteasome inhibition. EYFP or HA-tagged Myc was reintroduced by stable transfection into myc null diploid rat fibroblasts, replacing endogenous Myc with tagged Myc expressed at or near normal levels. This tagged Myc is shown to functionally replace the endogenous Myc by restoration of normal cell morphology and growth rate. We were able to confirm key findings using antibodies to the endogenous c-Myc and/or its partner, Max. Contrary to some published reports, by all three methods the c-Myc protein in rat fibroblasts distributes predominantly throughout the nucleus in a dispersed granular pattern, avoiding the nucleolus. Importantly, however, several findings provide evidence for an unanticipated relationship between c-Myc and PML nuclear bodies, which is enhanced under conditions of proteasome inhibition. Evidence of Max concentration within PML bodies is shown both with and without proteasome inhibition, strengthening the relationship between PML bodies and Myc/Max. Some accumulation of Myc and Max in nucleoli upon proteasome inhibition is also observed, although co-localization of ubiquitin was only seen with PML bodies. This work provides a comprehensive study of c-Myc distribution and also presents the first evidence of a relationship between turnover of this oncoprotein and PML nuclear bodies, known to break down in certain cancers.
authors.affiliation: Department of Cell Biology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, Massachusetts 01655, USA. Kelly.smith@umassmed.edu
authors.forename: Kelly P
authors.initials: KP
authors.lastname: Smith
authors.forename: Meg
authors.initials: M
authors.lastname: Byron
authors.forename: Brenda C
authors.initials: BC
authors.lastname: O'Connell
authors.forename: Rose
authors.initials: R
authors.lastname: Tam
authors.forename: Christoph
authors.initials: C
authors.lastname: Schorl
authors.forename: Isil
authors.initials: I
authors.lastname: Guney
authors.forename: Lisa L
authors.initials: LL
authors.lastname: Hall
authors.forename: Pooja
authors.initials: P
authors.lastname: Agrawal
authors.forename: John M
authors.initials: JM
authors.lastname: Sedivy
authors.forename: Jeanne B
authors.initials: JB
authors.lastname: Lawrence
mesh_terms: D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002466:Cell Nucleolus / Q000378:metabolism* / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D004268:DNA-Binding Proteins / Q000378:metabolism; D004171:Diploidy; D005347:Fibroblasts / Q000378:metabolism; D006367:HeLa Cells; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D045586:Intranuclear Inclusion Bodies; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009363:Neoplasm Proteins / Q000502:physiology; D009687:Nuclear Proteins / Q000502:physiology; D000071156:Promyelocytic Leukemia Protein; D061988:Proteasome Inhibitors; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000502:physiology*; D051381:Rats; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology; D014162:Transfection; D025521:Tumor Suppressor Proteins
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D007976:Leupeptins; C499330:MAX protein, human; C499329:Max protein, rat; C067850:Myc associated factor X; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C513293:Pml protein, mouse; D000071156:Promyelocytic Leukemia Protein; D061988:Proteasome Inhibitors; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C068422:Max protein, mouse; C070576:PML protein, human; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde