Intestinal Tumorigenesis in Compound Mutant Mice of both Dpc4(Smad4) and Apc Genes

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Abstract

The DPC4 (SMAD4) gene plays a key role in the TGFbeta signaling pathway. We inactivated its mouse homolog Dpc4 (Smad4). The homozygous mutants were embryonic lethal, whereas the heterozygotes showed no abnormality. We then introduced the Dpc4 mutation into the Apc(delta716) knockout mice, a model for human familial adenomatous polyposis. Because both Apc and Dpc4 are located on chromosome 18, we constructed compound heterozygotes carrying both mutations on the same chromosome by meiotic recombination. In such mice, intestinal polyps developed into more malignant tumors than those in the simple Apc(delta716) heterozygotes, showing an extensive stromal cell proliferation, submucosal invasion, cell type heterogeneity, and in vivo transplantability. These results indicate that mutations in DPC4 (SMAD4) play a significant role in the malignant progression of colorectal tumors.

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Targeted disruption of the mouse transforming growth factor-beta 1 gene results in multifocal inflammatory disease.

M Shull, I Ormsby, A Kier … (1992)

Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.

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S A Hahn, M. Schutte, A Hoque … (1996)

About 90 percent of human pancreatic carcinomas show allelic loss at chromosome 18q. To identify candidate tumor suppressor genes on 18q, a panel of pancreatic carcinomas were analyzed for convergent sites of homozygous deletion. Twenty-five of 84 tumors had homozygous deletions at 18q21.1, a site that excludes DCC (a candidate suppressor gene for colorectal cancer) and includes DPC4, a gene similar in sequence to a Drosophila melanogaster gene (Mad) implicated in a transforming growth factor-beta (TGF-beta)-like signaling pathway. Potentially inactivating mutations in DPC4 were identified in six of 27 pancreatic carcinomas that did not have homozygous deletions at 18q21.1. These results identify DPC4 as a candidate tumor suppressor gene whose inactivation may play a role in pancreatic and possibly other human cancers.

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Transforming growth factor-beta (TGF-beta) is a potent inhibitor of epithelial cell growth. Human colon cancer cell lines with high rates of microsatellite instability were found to harbor mutations in the type II TGF-beta receptor (RII) gene. Eight such examples, due to three different mutations, were identified. The mutations were clustered within small repeated sequences in the RII gene, were accompanied by the absence of cell surface RII receptors, and were usually associated with small amounts of RII transcript. RII mutation, by inducing the escape of cells from TGF-beta-mediated growth control, links DNA repair defects with a specific pathway of tumor progression.