Functional definition of the mutation cluster region of adenomatous polyposis coli in colorectal tumours.
The mutation cluster region (MCR) of adenomatous polyposis coli (APC) is located within the central part of the open reading frame, overlapping with the region encoding the 20 amino acid repeats (20R) that are beta-catenin-binding sites. Each mutation in the MCR leads to the synthesis of a truncated APC product expressed in a colorectal tumour. The MCR extends from the 3' border of the first 20R coding region to approximately the middle of the third 20R coding region, reflecting both positive and negative selections of the N- and C-terminal halves of the APC protein in colon cancer cells, respectively. In contrast, the second 20R escapes selection and can be either included or excluded from the truncated APC products found in colon cancer cells. To specify the functional outcome of the selection of the mutations, we investigated the beta-catenin binding capacity of the first three 20R in N-terminal APC fragments. We found in co-immunoprecipitation and intracellular co-localization experiments that the second 20R is lacking any beta-catenin binding activity. Similarly, we also show that the tumour-associated truncations abolish the interaction of beta-catenin with the third 20R. Thus, our data provide a functional definition of the MCR: the APC fragments typical of colon cancer are selected for the presence of a single functional 20R, the first one, and are therefore equivalent relative to beta-catenin binding.
Kohler
Eva Maria
EM
Nikolaus-Fiebiger-Center for Molecular Medicine, University Erlangen-Nürnberg, Glückstrasse 6, 91054 Erlangen, Germany.
Derungs
Adrian
A
Daum
Gabriele
G
Behrens
Jürgen
J
Schneikert
Jean
J
D025601:Adenomatous Polyposis Coli Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D005810:Multigene Family; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D017384:Sequence Deletion; D051176:beta Catenin / Q000378:metabolism*
D025601:Adenomatous Polyposis Coli Protein; D001426:Bacterial Proteins; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D051176:beta Catenin; C054562:yellow fluorescent protein, Bacteria