Mutations in the APC tumour suppressor gene cause chromosomal instability

Abstract

Two forms of genetic instability have been described in colorectal cancer: microsatellite instability and chromosomal instability. Microsatellite instability results from mutations in mismatch repair genes; chromosomal instability is the hallmark of many colorectal cancers, although it is not completely understood at the molecular level. As truncations of the Adenomatous Polyposis Coli (APC) gene are found in most colorectal tumours, we thought that mutations in APC might be responsible for chromosomal instability. To test this hypothesis, we examined mouse embryonic stem (ES) cells homozygous for Min (multiple intestinal neoplasia) or Apc1638T alleles. Here we show that Apc mutant ES cells display extensive chromosome and spindle aberrations, providing genetic evidence for a role of APC in chromosome segregation. Consistent with this, APC accumulates at the kinetochore during mitosis. Apc mutant cells form mitotic spindles with an abundance of microtubules that inefficiently connect with kinetochores. This phenotype is recapitulated by the induced expression of a 253-amino-acid carboxy-terminal fragment of APC in microsatellite unstable colorectal cancer cells. We conclude that loss of APC sequences that lie C-terminal to the beta-catenin regulatory domain contributes to chromosomal instability in colorectal cancer.

Chromosomal instability by β-catenin/TCF transcription in APC or β-catenin mutant cells

“…It has been reported that APC binds to the kinetochore, and that its truncation mutations cause polyploidy (Fodde et al, 2001;Kaplan et al, 2001). However, APC is a multifunctional protein and it plays a key role also in the canonical Wnt signaling pathway.…”

“…The interaction between APC and b-catenin suggested that expression of the stable b-catenin in ES cells might cause CIN indirectly through interfering with the kinetochore binding of APC (Fodde et al, 2001;Kaplan et al, 2001). To exclude such a possibility, we chose cells that lack both wild-type APC alleles but show little CIN, that is, DLD-1 cells that are MIN cell line with near-diploid chromosome content, and show minimal CIN (Aoki et al, 2003;Stewenius et al, 2005).…”

“…To exclude such a possibility, we chose cells that lack both wild-type APC alleles but show little CIN, that is, DLD-1 cells that are MIN cell line with near-diploid chromosome content, and show minimal CIN (Aoki et al, 2003;Stewenius et al, 2005). Notably, DLD-1 cells lack full-length APC, but express its C-terminally truncated protein that cannot bind to the kinetochore (Homfray et al, 1998;Fodde et al, 2001). In this cell line, the Wnt transcription is relatively lower than those in other cells with Wnt signal activation (van de Wetering et al, 2002).…”

“…It has been found that truncation mutations in the APC gene cause structural abnormalities of chromosomes (Fodde et al, 2001), aneuploidy (Fodde et al, 2001;Kaplan et al, 2001) and spindle aberrations (Fodde et al, 2001). It has been also reported that APC localizes to the kinetochore (Fodde et al, 2001;Kaplan et al, 2001). These reports suggest that lack of APC is involved in cancer progression through induction of CIN.…”

“…In most colon cancer cells, the pathway is activated through mutations in the adenomatous polyposis coli (APC), AXIN1 or b-catenin (CTNNB1) gene. Recent reports have suggested that APC protein plays additional roles in chromosome segregation and CIN (Fodde et al, 2001;Kaplan et al, 2001;Dikovskaya et al, 2004;Green and Kaplan, 2004;Tighe et al, 2004). It has been found that truncation mutations in the APC gene cause structural abnormalities of chromosomes (Fodde et al, 2001), aneuploidy (Fodde et al, 2001;Kaplan et al, 2001) and spindle aberrations (Fodde et al, 2001).…”