title: Interaction between tumor suppressor adenomatous polyposis coli and topoisomerase IIalpha: implication for the G2/M transition.
abstract: The tumor suppressor adenomatous polyposis coli (APC) is implicated in regulating multiple stages of the cell cycle. APC participation in G1/S is attributed to its recognized role in Wnt signaling. APC function in the G2/M transition is less well established. To identify novel protein partners of APC that regulate the G2/M transition, APC was immunoprecipitated from colon cell lysates and associated proteins were analyzed by matrix-assisted laser desorption ionization/time of flight (MALDI-TOF). Topoisomerase IIalpha (topo IIalpha) was identified as a potential binding partner of APC. Topo IIalpha is a critical regulator of G2/M transition. Evidence supporting an interaction between endogenous APC and topo IIalpha was obtained by coimmunoprecipitation, colocalization, and Förster resonance energy transfer (FRET). The 15-amino acid repeat region of APC (M2-APC) interacted with topo IIalpha when expressed as a green fluorescent protein (GFP)-fusion protein in vivo. Although lacking defined nuclear localization signals (NLS) M2-APC predominantly localized to the nucleus. Furthermore, cells expressing M2-APC displayed condensed or fragmented nuclei, and they were arrested in the G2 phase of the cell cycle. Although M2-APC contains a beta-catenin binding domain, biochemical studies failed to implicate beta-catenin in the observed phenotype. Finally, purified recombinant M2-APC enhanced topo IIalpha activity in vitro. Together, these data support a novel role for APC in the G2/M transition, potentially through association with topo IIalpha.
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Azuma
authors.forename: David
authors.initials: D
authors.lastname: Moore
authors.forename: Neil
authors.initials: N
authors.lastname: Osheroff
authors.forename: Kristi L
authors.initials: KL
authors.lastname: Neufeld
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism*; D000951:Antigens, Neoplasm / Q000378:metabolism*; D002455:Cell Division; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005434:Flow Cytometry; D031541:Fluorescence Resonance Energy Transfer; D016195:G2 Phase; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D051176:beta Catenin / Q000378:metabolism
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D051176:beta Catenin; D049452:Green Fluorescent Proteins; D004250:DNA Topoisomerases, Type II