title: Topoisomerase IIalpha binding domains of adenomatous polyposis coli influence cell cycle progression and aneuploidy.
abstract: BACKGROUND
  Truncating mutations in the tumor suppressor gene APC (Adenomatous Polyposis Coli) are thought to initiate the majority of colorectal cancers. The 15- and 20-amino acid repeat regions of APC bind beta-catenin and have been widely studied for their role in the negative regulation of canonical Wnt signaling. However, functions of APC in other important cellular processes, such as cell cycle control or aneuploidy, are only beginning to be studied. Our previous investigation implicated the 15-amino acid repeat region of APC (M2-APC) in the regulation of the G2/M cell cycle transition through interaction with topoisomerase IIalpha (topo IIalpha).
  
  
  RESULTS
  We now demonstrate that the 20-amino acid repeat region of APC (M3-APC) also interacts with topo IIalpha in colonic epithelial cells. Expression of M3-APC in cells with full-length endogenous APC causes cell accumulation in G2. However, cells with a mutated topo IIalpha isoform and lacking topo IIbeta did not arrest, suggesting that the cellular consequence of M2- or M3-APC expression depends on functional topoisomerase II. Both purified recombinant M2- and M3-APC significantly enhanced the activity of topo IIalpha. Of note, although M3-APC can bind beta-catenin, the G2 arrest did not correlate with beta-catenin expression or activity, similar to what was seen with M2-APC. More importantly, expression of either M2- or M3-APC also led to increased aneuploidy in cells with full-length endogenous APC but not in cells with truncated endogenous APC that includes the M2-APC region.
  
  
  CONCLUSIONS
  Together, our data establish that the 20-amino acid repeat region of APC interacts with topo IIalpha to enhance its activity in vitro, and leads to G2 cell cycle accumulation and aneuploidy when expressed in cells containing full-length APC. These findings provide an additional explanation for the aneuploidy associated with many colon cancers that possess truncated APC.
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Coffey
authors.forename: Neil
authors.initials: N
authors.lastname: Osheroff
authors.forename: Kristi L
authors.initials: KL
authors.lastname: Neufeld
mesh_terms: D011125:Adenomatous Polyposis Coli / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics*; D000782:Aneuploidy; D000951:Antigens, Neoplasm / Q000378:metabolism*; D001665:Binding Sites; D002453:Cell Cycle; D045744:Cell Line, Tumor; D018389:Codon, Nonsense; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells / Q000473:pathology; D016195:G2 Phase; D006801:Humans; D012091:Repetitive Sequences, Nucleic Acid; D051176:beta Catenin / Q000032:analysis
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D000951:Antigens, Neoplasm; D018389:Codon, Nonsense; D004268:DNA-Binding Proteins; D051176:beta Catenin; D004250:DNA Topoisomerases, Type II