Mouse Models of Colon Cancer Makoto Mark Taketo, Winfried Edelmann  Gastroenterology  Volume 136, Issue 3, Pages 780-798 (March 2009) DOI: 10.1053/j.gastro.2008.12.049 Copyright © 2009 AGA Institute Terms and Conditions

Figure 1 Wnt signaling activation in colon cancer cells. Wnt signaling can be activated at various levels, including the ligand binding to the cell surface receptor. In the normal colonic epithelium, glycogen synthase kinase-3β (GSK3β), aided by adenomatous polyposis coli (APC) and Axin proteins, phosphorylates (p) β-catenin, which signals subsequent ubiquitylation and degradation (left). In colon adenoma and carcinoma cells, Wnt signaling is activated mostly through mutations in the APC or β-catenin (CTNNB1) genes. Because failure to phosphorylate β-catenin results in its accumulation, it eventually enters the nucleus and binds to the TCF/LEF complex and activates transcription of Wnt target genes (right). Gastroenterology 2009 136, 780-798DOI: (10.1053/j.gastro.2008.12.049) Copyright © 2009 AGA Institute Terms and Conditions

Figure 2 Histopathology of intestinal tumors in mice with Apc heterozygous mutations and those with Apc/Smad4 compound mutations. (A and B) A relatively early small intestinal adenoma in an ApcΔ716 mouse stained with H&E and silver, respectively, in adjoining serial sections. Note the well-preserved basement membrane stained with silver in B. (C) A representative small intestinal adenocarcinoma in an Apc/Smad4 compound mutant mouse. Green arrowheads show the smooth muscle that forms a triangular shape (trabeculation), into which adenocarcinoma glands are invading (asterisks). (D and E) An invasion front of a colonic poly in an Apc/Smad4 compound mutant mouse (E shows a higher magnification of the squared area in D, arrowhead in E indicates “cap cells”). (F) Immunohistochemical staining of CD34 (green) and CD31 (red) in a section adjoining that in E. Closed arrowheads indicates immature myeloid cells expressing CD34, whereas open arrowheads show normal blood vessels that express both CD34 and CD31 (yellow). The red staining on the left upper corner is muscularis mucosae. Nuclei are stained in blue (D–F reprinted with permission from Kitamura et al57). Gastroenterology 2009 136, 780-798DOI: (10.1053/j.gastro.2008.12.049) Copyright © 2009 AGA Institute Terms and Conditions

Figure 3 Arachidonic acid metabolism and intestinal polyposis. Metabolites of arachidonic acid are shown with the enzymes that catalyze the conversion steps of the metabolites. The receptors for PGE2 are also shown. TX, thromboxane. Gastroenterology 2009 136, 780-798DOI: (10.1053/j.gastro.2008.12.049) Copyright © 2009 AGA Institute Terms and Conditions

Figure 4 Molecular mechanism of colon tumor invasion in the cis-Apc/Smad4 mutant mouse. SMAD4-deficient tumor cells produce the chemokine CCL9 and recruit receptor-expressing cells that promote tumor invasion. The inactivation of the TGF-β family signaling within the tumor epithelium causes increased production of chemokine CCL9, because it is suppressed by TGF-β, activin-A, and BMPs (1). Increased levels of CCL9 recruit immature myeloid cells that carry the CCL9 receptor CCR1 from the bloodstream to the tumor invasion front (2). These immature myeloid cells produce MMP9 and 2 (3), which allow the tumor to invade the stroma (4). Modified with permission from Kitamura and Taketo.58 Gastroenterology 2009 136, 780-798DOI: (10.1053/j.gastro.2008.12.049) Copyright © 2009 AGA Institute Terms and Conditions

Figure 5 Model for mammalian MMR. MMR is initiated by the recognition of mispaired bases by MutSα and MutSβ complexes that act as sliding clamps. The activation of downstream repair events requires the interaction of MutSα and MutSβ with MutLα. In addition, MutLγ participates in the repair of single-base mismatches and 1–base pair IDLs. MutSα bound to a mismatch recruits EXO1, which initiates mismatch excision from 5′ nicks in the template strand. Although the mechanisms that generate 5′ and 3′ single-stranded nicks is not clear, MutLα contains an endonuclease activity (encoded by PMS2) that can introduce 5′ nicks into the template strand carrying the mismatch (not shown). Mismatch excision proceeds past the site of the mismatch, and the resulting gap is stabilized by RPA. In mammalian cells, other exonucleases possibly participate in the removal of mispaired bases whose identity remain unknown. Later repair steps require the interaction of MutS and MutL complexes with DNA replication proteins, including proliferating cell nuclear antigen, replication factor C, RPA, and polymerase δ, to coordinate the transfer of information between mismatch recognition and excision/resynthesis (not shown). Little is known about the nature of these interactions and the precise composition of the late MMR complexes. Gastroenterology 2009 136, 780-798DOI: (10.1053/j.gastro.2008.12.049) Copyright © 2009 AGA Institute Terms and Conditions

Figure 6 Histopathology of tumors in MMR mutant mice. (A) Lymphoma in Msh6 mutant mouse. (B) Higher magnification showing large anaplastic cells admixed with small lymphocytes. (C) Adenoma in Msh2 mutant mouse. (D) Higher magnification showing columnar to cuboidal neoplastic intestinal epithelial cells. (E) Invasive carcinoma in Msh2 mutant mouse with the formation of mucin lakes (asterisks) and desmoplasia (arrows). (F) Higher magnification showing invasive cells at all stages of intestinal epithelial cell maturation (goblet [triangles] and Paneth [arrows] cells). Gastroenterology 2009 136, 780-798DOI: (10.1053/j.gastro.2008.12.049) Copyright © 2009 AGA Institute Terms and Conditions