Document Detail

Carcinogen-induced colon tumors in mice are chromosomally stable and are characterized by low-level microsatellite instability.
MedLine Citation:
PMID:  15021908     Owner:  NLM     Status:  MEDLINE    
The azoxymethane (AOM)-induced mouse colon tumor model recapitulates many of the histopathological features associated with the multistage progression of human sporadic colorectal cancers (CRCs). To better define the genetic events associated with tumorigenesis in this murine model, we analysed tumors from A/J mice for chromosomal (CIN) and microsatellite (MSI) instabilities, two fundamental pathways of genomic instability that play a critical role in the pathogenesis of human CRCs. Male A/J mice, 6-week old, were injected with either AOM (n=5) (10 mg/kg b.w., i.p.) or vehicle (n=5) (0.9% NaCl solution) once a week for 6 weeks. At 32 weeks after the last dose, comparative genomic hybridization (CGH) was performed on 16 tumors harvested from five animals. Although 25% of the tumors displayed either a gain of chromosome 2 or loss of Y, the majority (75%) showed no genomic imbalances. Further analysis of chromosomal aberrations, using CGH and spectral karyotyping (SKY) was performed in our recently established A/J colon tumor-derived cell line, AJ02-NM0. Results showed a pseudotetraploid karyotype with loss of only the Y chromosome in these cultured cells, thereby providing additional evidence for the minimal role of CIN in the primary AOM-induced tumors. Interestingly, the majority (81%) of A/J tumors displayed low-level microsatellite instability (MSI-L) when analysed using mono- and dinucleotide repeat markers, and showed a significant expansion to high-level instability (MSI-H) in the AJ02-NM0 cells. This finding in cultured cells additionally provides evidence that a mild mutator pathway may contribute to the development of behaviorally benign carcinomas in situ in A/J mice. To better understand the tumorigenic process in the A/J colons, we screened for mutational alterations in key regions of the K-ras and Apc genes. Results showed a very low frequency (6%) of K-ras activating mutations, together with the absence of Apc truncation mutations in primary tumors and AJ02-NM0 cells. However, these tumors displayed intense nuclear accumulation of beta-catenin protein, indicating activation of the Wnt signaling pathway. Based on our molecular and cytogenetic findings, we propose that carcinogen-induced tumors may develop via mechanisms independent of the 'classical' CIN or MSI pathways.
Kishore Guda; Madhvi B Upender; Glenn Belinsky; Christopher Flynn; Masako Nakanishi; Jillian N Marino; Thomas Ried; Daniel W Rosenberg
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Oncogene     Volume:  23     ISSN:  0950-9232     ISO Abbreviation:  Oncogene     Publication Date:  2004 May 
Date Detail:
Created Date:  2004-05-06     Completed Date:  2004-05-20     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  8711562     Medline TA:  Oncogene     Country:  England    
Other Details:
Languages:  eng     Pagination:  3813-21     Citation Subset:  IM    
Center for Molecular Medicine, University of Connecticut Health Center, Farmington, CT 06030-3101, USA.
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MeSH Terms
Colonic Neoplasms / chemically induced,  genetics*,  pathology
Cytoskeletal Proteins / genetics
Genomic Instability*
Microsatellite Repeats*
Trans-Activators / genetics
beta Catenin
Grant Support
Reg. No./Substance:
0/Catnb protein, mouse; 0/Cytoskeletal Proteins; 0/Trans-Activators; 0/beta Catenin; 25843-45-2/Azoxymethane

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