Daniela Diehl1, Doris Oesterle2, Martin W Elmlinger3, Andreas Hoeflich1, Eckhard Wolf1, Harald Lahm1
1Institute of Molecular Animal Breeding and Biotechnology, Ludwig-Maximilians University, Feodor-Lynen-Str. 25, D-81377 Munich, Germany
2Institute of Toxicology, GSF-National Research Center for Environment and Health, Ingolstädter Landstr.1, D-85764 Neuherberg, Germany
3Pediatric Endocrinology, Children’s Hospital, University of Tübingen, Hoppe-Seyler-Str.1, D-72076 Tübingen, Germany
In colorectal cancer insulin-like growth factor II (IGF-II) is frequently overexpressed. To evaluate, whether IGF-II affects different stages of tumorigenesis, we induced neoplastic alterations in the colon of wild-type and IGF-II transgenic mice using 1,2-dimethylhydrazine (DMH). Aberrant crypt foci (ACF) served as markers of early lesions in the colonic mucosa, whereas adenomas and carcinomas characterized the endpoints of tumor development. DMH-treatment led initially to significantly more ACF in IGF-II transgenic than in wild-type mice. This increase in ACF was especially prominent for those consisting of ≥three aberrant crypts (AC). Nevertheless, adenomas and adenocarcinomas of the colon, present after 34 weeks in both genetic groups, were not found at different frequency. Tumor volumes, however, were significantly higher in IGF-II transgenic mice and correlated with serum IGF-II levels. Immunohistochemical staining for markers of proliferation and apoptosis revealed increased cell proliferation rates in tumors of IGF-II transgenic mice without significant affection of apoptosis. Increased proliferation was accompanied by elevated localization of β-catenin in the cytosol and cell nuclei and reduced appearance at the inner plasma membrane. In conclusion, we provide evidence that IGF-II, via activation of the β-catenin signaling cascade, promotes growth of ACF and tumors without affecting tumor numbers.