Bars, mean,*p <0

Bars, mean,*p <0.05 by Student'st test. activity compared to Rabbit polyclonal to TP53INP1 tumors lacking Apc protein, which could lead to context-dependent inhibition of tumorigenesis. Keywords:Apc truncation, Apc null, colon cancer, mouse model Colorectal malignancy is one of the leading causes of cancer death in the Western world. Upwards of 80% of colorectal cancers have mutations in theAdenomatous Polyposis Coli(APC) gene, which is known to occur early in tumor development. Most of theseAPCgene alterations, found both in the germline in individuals with hereditary Familial Adenomatous Polyposis (FAP) and in sporadic colon cancers, fall in a region ofAPCtermed the mutation cluster region (MCR) and result in retained expression of an N-terminal fragment of the APC protein (Kinzler & Vogelstein, 1996). Genotype-phenotype correlations including germlineAPCmutations suggest that different lengths and levels of APC expression can influence the number of polyps in the gut, the distribution of polyps, and extra-colonic manifestations of the disease (Nieuwenhuis & Vasen, 2007;Soravia et al., 1998). Specifically, patients that present clinically with attenuated FAP (AFAP) have reduced polyp counts and a later age of colon cancer development. Interestingly, germlineAPCmutations associated with AFAP fall 5 and 3 of the MCR, presumably resulting in APC truncations bearing different protein domains than in classical FAP and/or hypomorphic APC expression. These observations suggest a gain-of-function or dominant-negative role for APC truncated at the MCR. Paradoxically, patients with whole-gene APC deletions, albeit rare, have been found to present with classical FAP (Herrera et al., 1986;Sieber et LMD-009 al., 2002). More thorough analysis of the phenotypic effects of different heritableAPCalleles is usually hampered by the low frequency of FAP and AFAP as well as the presence of numerous genetic and environmental modifiers of the disease (de la Chapelle, 2004). Thus, we as well as others have turned to mouse models that faithfully recapitulate human disease as a tool to examine the consequences of variousApcmutations. ApcMinwas the first heritable mutant allele ofApcdeveloped in the mouse (Su et al., 1992).ApcMinmice develop multiple intestinal neoplasias (Min) resembling human FAP. TheApcMinallele, which was discovered in an ethylnitrosourea mutagenesis screen, comprises a nonsense mutation in codon 850 ofApcand gives rise to a stable, truncated Apc protein much like those found in human colon cancers. Since the characterization of theApcMinmouse, additional alleles ofApchave been generated, including truncations both 5′ and 3′ to the Min mutation (Colnot et al., 2004;Gaspar et al., 2009;Oshima et al., 1995;Pollard et al., 2009;Smits et al., 1999). As observed in human patients bearing mutations inAPC, these alleles have yielded different phenotypic effects relating LMD-009 to intestinal tumorigenesis (Fodde & Smits, 2001). The basis for these genotype-phenotype correlations remains largely unknown. The APC/Apc gene product is a critical negative regulator of the canonical Wnt signaling pathway. Apc forms a complex with Axin and Gsk-3 that phosphorylates -catenin on N-terminal residues, allowing for subsequent ubiquitination and proteosomal degradation. When the ability of Apc to interact with this destruction complex is compromised, -catenin accumulates in the cytoplasm and translocates into the nucleus where it binds to Tcf/Lef transcription factors to regulate target genes, such asc-mycandAxin2(Clevers, 2006). Moreover, mutations in -catenin that lead to protein stabilization are observed in human colon cancer and comparable mutations can initiate intestinal tumorigenesis in mice (Harada et al., 1999;Morin et al., 1997). Beyond -catenin deregulation, mutant APC has been suggested to contribute to colon tumorigenesis through other mechanisms. First, the vast majority of sporadic colon cancers in humans have mutations inAPC, whereas other cancers with deregulated WNT signaling have an equal or greater proportion of mutations in-Cateninor other WNT pathway components (Giles, 2003). This observation points to a special role forAPCmutation specifically LMD-009 in colon cancer. Second, Apc is usually a relatively large protein of approximately 312 kDa and has a quantity of protein binding motifs. In fact, Apc has been shown to interact with a variety of proteins outside of the Wnt pathway and has been found in numerous sub-cellular locations (Aoki & Taketo, 2007;Fodde et al., 2001;Mccartney & Nathke, 2008). Furthermore, the majority ofAPCmutations result in a stable, truncated polypeptide, lacking most -catenin and Axin binding domains, which lie in the middle portion of the protein. In these mutant proteins, the microtubule-binding domain name and EB1-binding site at the C-terminus of APC are also lost, but the N-terminal armadillo repeats and oligomerization domains are retained (Nathke, 2004). We required a genetic approach to dissect the role of truncated Apc in.