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Vol. 19, Issue 10, 4076-4085, October 2008

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Interaction between Tumor Suppressor Adenomatous Polyposis Coli and Topoisomerase II: Implication for the G2/M Transition

Yang Wang^*, Yoshiaki Azuma^*, David Moore, Neil Osheroff, and Kristi L. Neufeld^*

*Department of Molecular Biosciences and KU Microscopy and Analytical Imaging Laboratory, University of Kansas, Lawrence, KS 66045; and Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232

Submitted January 2, 2008; Revised June 3, 2008; Accepted July 8, 2008
Monitoring Editor: Yixian Zheng

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 II (topo II) was identified as a potential binding partner of APC. Topo II is a critical regulator of G2/M transition. Evidence supporting an interaction between endogenous APC and topo II was obtained by coimmunoprecipitation, colocalization, and Förster resonance energy transfer (FRET). The 15-amino acid repeat region of APC (M2-APC) interacted with topo II 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 β-catenin binding domain, biochemical studies failed to implicate β-catenin in the observed phenotype. Finally, purified recombinant M2-APC enhanced topo II activity in vitro. Together, these data support a novel role for APC in the G2/M transition, potentially through association with topo II.

Address correspondence to: Kristi L. Neufeld (klneuf{at}ku.edu)

Abbreviations used: APC, adenomatous polyposis coli; FRET, Förster resonance energy transfer; NLS, nuclear localization signal; topo II, topoisomerase II; FACS, fluorescence activated cell sorting; GFP, green fluorescent protein.