Chromosomal instability and APC gene mutations in human sporadic colorectal adenomas

Abstract

The mechanisms by which adenomatous polyposis coli (APC) gene mutations contribute to colorectal tumourigenesis and progression are still not fully understood. Using in vitro mouse embryonic stem cells, APC mutations have been proposed to dysregulate the interactions between kinetochores and microtubules during mitosis, leading to chromosomal instability (CIN) and aneuploidy. A link between APC mutations and aneuploidy in vivo among human sporadic colorectal adenomas has not been reported previously and was therefore investigated in the present series of 61 adenomas. Multi-parameter flow cytometry, based on scattering and fluorescence from the DNA-specific 4,6-diamidino-2-phenylindole-2-hydrochloride (DAPI) dye, which separates epithelial from stromal lymphocyte nuclei, was used to evaluate the DNA index (DI) and to sort epithelial nuclei. Additionally, DNA extracted from these sorted nuclei was used to analyse APC mutations by DNA sequencing. Aneuploidy was present in 20 of 61 adenomas (33%), with 15 of these 20 cases (75%) having a near-diploid DI (DI different from 1 and less than 1.3). APC mutations were detected in 19 adenomas (31%): 12 were within or downstream of the mutation cluster region (MCR), roughly defined by codons 1200-1500, and seven were upstream of the MCR. Overall, the prevalence of aneuploidy in APC wild-type and mutated adenomas was 26% and 47%, respectively, and no statistically significant association was found between APC status and DI (p = 0.142). However, when APC mutations were subdivided into two groups, ie occurring within/downstream of the MCR and upstream of the MCR, the association of APC mutations within and downstream of the MCR with aneuploidy was statistically significant (p = 0.017). In conclusion, the present data suggest that the type of APC mutation may play a role in the origin of CIN in vivo in human sporadic colorectal adenomas and that APC mutations within and downstream of the MCR, and large-scale chromosomal alterations, may co-operate in the progression of a subgroup of adenomas.

H-RAS 81 polymorphism is significantly associated with aneuploidy in follicular tumors of the thyroid

“…At variance with the findings of Giaretti et al, 1995Giaretti et al, , 1998Giaretti et al, , 2004 in colorectal carcinomas, the presence of RAS mutations in thyroid tumors was not significantly associated with the ploidy of the tumors.…”

“…These authors suggested a functional role of K-RAS activation (by mutation) in the control of chromosomal stability (Giaretti et al, 1995(Giaretti et al, , 1998(Giaretti et al, , 2004. Other authors have shown that fibroblasts transfected with mutant H-RAS displayed genomic instability (Denko et al, 1994(Denko et al, , 1995.…”

Reduced ATR or Chk1 Expression Leads to Chromosome Instability and Chemosensitization of Mismatch Repair–deficient Colorectal Cancer Cells

“…It is generally accepted that both CIN and MSI are early events that drive cancer development by allowing cells to rapidly accumulate genetic changes required for the multistep tumorigenic process (Nowak et al, 2002). Although APC truncations were always thought to be the driving force behind CIN initiation, new evidence indicates that ϳ55% of aneuploid colorectal adenomas are found to be APC wild type and only 47% of adenomas with APC mutation are aneuploid (Giaretti et al, 2004). These data point to alternative mechanisms for CIN development in colorectal tumors, independent of APC mutations.…”

Aneuploidy and Epithelial Cancers: The Impact of Aneuploidy on the Genesis, Progression and Prognosis of Colorectal and Breast Carcinomas

“…The second "hit" mutates the remaining wild-type allele, which results in the complete loss of gene function (Knudson 1979). In addition to structural chromosomal aberrations, we also observe alterations of chromosome number, i.e., aneuploidy (Giaretti et al 2004). While one reason for the emergence of structural chromosomal aberrations are deficiencies in the repair of DNA double strand breaks , there is mounting evidence that numeric chromosome imbalances are caused by chromatid segregation errors during mitotic cell division (D'Amours and Jackson 2002;Jallepalli and Lengauer 2001;Loeb and Loeb 2000;Vessey, Norbury, and Hickson 1999).…”