The APC protein binds to A/T rich DNA sequences

Abstract

The tumor suppressor protein APC (Adenomatous Polyposis Coli) is localized in the cytosol and in the nucleus. In this study, we demonstrate that the nuclear APC protein level is high in cells in the basal crypt region of the normal colorectal epithelium. Strikingly, the APC protein staining resembles the staining pattern of a nuclear proliferation marker. As a ®rst step towards a possible role of the nuclear APC protein, we provide data showing the direct interaction of the nuclear APC protein with DNA. A nuclear APC isoform precipitates with matrix-immobilized DNA. Vice versa, the immunoprecipitation of APC from nuclear lysates results in coprecipitation of genomic DNA. Using recombinant APC fragments we mapped three DNA binding domains: one within the b-catenin binding and regulatory domain, and two in the carboxyterminal third of the APC protein. All these three domains contain clusters of repetitive S(T)PXX sequence motifs that were described to mediate the DNA interaction of many other DNA binding proteins. In analogy to S(T)PXX proteins, the APC protein binds preferentially to A/T rich DNA sequences rather than to a single DNA sequence motif.

Interaction between Ku80 protein and a widely used antibody to adenomatous polyposis coli

“…Adenomatous polyposis coli has been shown to interact with DNA (Deka et al, 1999), leading to the possibility that interaction with the Ku heterodimer may have occurred indirectly through DNA molecules with double-strand breaks. To eliminate this possibility, the IP was repeated in the presence of DNase.…”

The Adenomatous Polyposis Coli-protein (APC) interacts with the protein tyrosine phosphatase PTP-BL via an alternatively spliced PDZ domain

“…Due to its modular organization, PTP-BL may build up a multiprotein complex recruiting the APC protein within the nucleus, which may be involved in cell cycle regulation. Thus, overexpression of the APC protein blocks the progression from G0 ± G1 to the S phase of the cell cycle Ishidate et al, 2000) and the capability of the APC protein to interact directly with DNA was demonstrated recently (Deka et al, 1999). Although these data suggest an involvement of the APC protein in cell division, the intracellular signaling cascades involved in APC function remain elusive.…”

Subcellular distribution of Wnt pathway proteins in normal and neoplastic colon

“…19). In fact, in both cells and tissue, smaller APC isoforms shown by immunoblot were recognized by antibodies directed against both N-and C-terminal portions of the protein (12,20). In addition, several known splice forms do eliminate exon 1 (21), which might explain the failure of Nterminal antibodies to detect expression in this instance.…”

“…APC expression at lateral cell borders and near apical membranes in mouse and human tissue has been reported (7-10). Nuclear APC was first characterized in tissue culture cells (6), but has also been reported in mouse and human colon tissue (11,12). The subcellular localization of APC thus reflects its function as a regulator of ␤-catenin.…”