Rat colorectal cancers are genetically determined and progress to invasion without going through a polypoid stage

Department of Genetics, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Cancer Research (Impact Factor: 9.28). 01/2008; 67(24):11594-600. DOI: 10.1158/0008-5472.CAN-07-3242
Source: PubMed

ABSTRACT Growing evidence suggests that flat colorectal cancers (CRC) account for 10% to 20% of all CRCs and that these are frequently associated with more advanced pathologies. However, controversy exists as to the origin and progression of flat CRCs compared with the more common polypoid-type morphology. We report using the azoxymethane mouse model for human CRC that KK/HIJ and I/LNJ mice develop different frequencies of flat and polypoid tumors; 83% of colon tumors in I/LNJ mice are flat compared with only 19% in KK/HIJ mice, indicating a strong genetic predisposition to the development of specific CRC morphologies. Like polypoid tumors, all flat tumors show a significant increase in the level of nuclear beta-catenin (CATNNB1), supported by similar frequencies of mutations in the phosphorylation domain-coding region (codons 32-41) of Catnnb1. However, in contrast to previous reports, tumors bearing higher "oncogenic potential" do not cluster in codon 41 of Catnnb1. There are no differences between flat and polypoid tumors in the frequency of mutations in codons 12 and 13 of Kras or codon 624 of Braf. Similarly, there are no differences between tumor morphologies in their location along the proximal-to-distal colonic axis or in the relative quantity of intratumor stromal myofibroblasts as marked by the expression of alpha-smooth muscle actin. Using a combination of serial colonoscopic and histologic analyses, we definitively show that flat CRCs do not develop de novo but progress through a flat adenomatous stage to invasive carcinoma without transit through an intermediary polypoid stage.

  • Endoskopie heute 03/2009; 22(01):22-29. DOI:10.1055/s-2008-1076948 · 0.13 Impact Factor
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    ABSTRACT: BACKGROUND: The intestinal crypt homeostasis is maintained by a combination of growth factors including Wnt, R-Spondin1, Noggin and the epidermal growth factor (EGF). In human colorectal cancer, the Wnt pathway is constitutively activated through genetic and epigenetic alterations in as many as 11 genes encoding components of this crypt stem-cell maintenance mechanism. Although the proliferation of colon cancer cells does not require Wnt, it is possible that colon cancer cells can still respond to the crypt growth factors in the colonic microenvironment. A number of studies have shown that epithelial cells behave differently in 3-D versus 2-D cultures. Because the 3-D conditions more closely mimic the in vivo environment, we examined the effects of Wnt and other crypt growth factors on colon cancer cell growth in 3-D culture. METHODS: Colon cancer cells were grown in 3-D matrigel supplemented with different combinations of crypt growth factors and colonies were examined for morphology and pathways. RESULTS: When colon cancer cells were cultured in 3-D with EGF, they grew as round spheroid colonies. However, colon cancer cells also grew as flat, disc-like colonies when cultured with EGF plus Wnt, R-Spondin1 and Noggin. Disc colonies were found to have comparable levels of E-cadherin as the spheroid colonies, but showed decreased E-cadherin at the cell-matrix contact sites. Disc colonies also elaborated F-actin rich protrusions (FRP) at the cell-matrix edge, reminiscent of an invasive phenotype but without the expression of vimentin. These E-cadherin and F-actin alterations were not induced by the four growth factors in 2-D culture. Formation of the disc colonies was inhibited by the knockdown of beta-catenin and by protein kinase inhibitors such as gefitinib, imatinib and MK-2206. Furthermore, withdrawal of the crypt growth factors was able to revert the disc colonies to spheroid growth, showing that the invasive phenotype was reversible dependent on the availability of growth factors. CONCLUSIONS: These findings show that colon cancer cells remain responsive to the growth factors in the crypt microenvironment and can be induced to undergo morphological transformation in the more physiologically relevant 3-D culture.
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