Gastroenterology

Gastroenterology

Volume 131, Issue 4, October 2006, Pages 1096-1109
Gastroenterology

Basic–alimentary tract
APC and Oncogenic KRAS Are Synergistic in Enhancing Wnt Signaling in Intestinal Tumor Formation and Progression

https://doi.org/10.1053/j.gastro.2006.08.011Get rights and content

Background & Aims: Synchronous activation of the Wnt signaling pathway, mostly because of loss of function of the APC tumor suppressor, and of the oncogenic KRAS-signaling pathway is very frequent in colorectal cancer and is associated with poor prognosis. Methods: We have generated a compound transgenic mouse model, KRASV12G/Apc+/1638N, to recapitulate the human disease and compared it with single transgenic littermates. Results: Compound mutant mice are characterized by a 10-fold increase in tumor multiplicity and by accelerated tumor progression, resulting in strongly enhanced morbidity and mortality. Tumors from compound mutant mice proliferate faster and show decreased levels of apoptosis. Several lines of evidence indicate that the observed increase in tumor multiplicity and malignant transformation is caused by the synergistic activation of Wnt signaling in cells with oncogenic KRAS and loss-of-function Apc mutations. Activated KRAS is known to induce tyrosine phosphorylation of β-catenin, leading to its release from E-cadherin at the adherens junction. This results in an increased β-catenin pool in the cytoplasma, its subsequent translocation to the nucleus, and the transcriptional activation of Wnt downstream target genes. Accordingly, intestinal tumors from KRASV12G/Apc+/1638N mice show a significant increase in cells with nuclear accumulation of β-catenin when compared with Apc+/1638N animals. Moreover, Apc/KRAS-mutant embryonic stem cells show a significantly enhanced β-catenin/T-cell factor–mediated transcriptional activation, accompanied by increased β-catenin nuclear localization. Conclusions: This KRAS-induced increase in Wnt/β-catenin signaling may enhance the plasticity and self-renewal capacity of the tumor, thus resulting in the drastically augmented tumor multiplicity and malignant behavior in compound mutant animals.

Section snippets

Animal Models

All experiments on mice were performed in accordance with institutional and national guidelines and regulations. The Apc1638N mouse lineage in the inbred C57Bl/6J background21 was bred with the transgenic model22 pVillin-KRASV12G in the genetic background B6D2 (C57Bl/6J × DBA/2). To control for genetic background effects, littermates were always used as controls. Mice were maintained under a 12-hour light-dark cycle and fed with standard diet and water ad lib. Genotyping was performed on DNA

Intestinal Tumor Multiplicity and Progression Is Significantly Increased in KRASV12G/Apc+/1638N Mice

To study the interaction between oncogenic KRAS and deregulated Wnt pathway, we bred transgenic mice expressing the activated human KRASV12G oncogene driven by the intestine-specific villin promoter22 with Apc+/1638N mice carrying a targeted nonsense mutation at the endogenous Apc gene.21 Compound mutant mice showed significant increase in morbidity and mortality when compared with the single transgenic littermates (Figure 1A, see Supplementary Table 1 online at www.gastrojournal.org). In fact,

Discussion

We have generated a compound mouse model that recapitulates the tumor-specific mutations characteristic of the majority of human CRC patients20 by combining loss of Apc tumor suppressor function with intestine-specific expression of oncogenic KRAS. Compound KRASV12G/Apc+/1638N mice displayed an average of 30 intestinal tumors, a 15-fold and a 7-fold increase over the pvill-KRASV12G and Apc+/1638N littermates, respectively. Rather than simply adding up the tumor phenotypes of the parental

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    Supported by grants from the Deutsche Forschungsgemeinschaft and the KKF/MRI (to K-P.J.); from the ARC/Biologie du développement et physiologie intégrative (to S.R.); and from the NWO/Vici, the Dutch Cancer Society (KWF), and the BSIK program of the Dutch Government (to R.F.; BSIK 03038).

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    K-P.J. and P.A. have contributed equally to this work.

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