Methods to assess Myc function in intestinal homeostasis, regeneration, and tumorigenesis.

Within the intestinal epithelium, c-Myc has been characterized as a target of ß-catenin-TCF signalling (He et al., Science 281:1509-1512, 1998). Given the most commonly mutated tumor suppressor gene within colorectal cancer (CRC) is the APC (Adenomatous Polyposis Coli) gene, a negative regulator of ß-catenin-TCF signalling (Korinek et al., Science 275:1784-1787, 1997), loss of APC leads to Myc deregulation in the vast majority of CRC. This probably explains the numerous studies investigating c-Myc function within the intestinal epithelium. These have shown that c-Myc inhibition or deletion in the adult intestine results in proliferative defects (Muncan et al., Mol Cell Biol 26:8418-8426, 2006; Soucek et al., Nature 455:679-683, 2008). Importantly, intestinal enterocytes are able to survive in the absence of c-Myc which has allowed us (and others) to test the role of c-Myc in intestinal regeneration and tumorigenesis. Remarkably c-Myc deletion suppresses all the phenotypes of the Apc tumor suppressor gene loss and stops intestinal regeneration (Ashton et al., Dev Cell 19:259-269, 2010; Sansom et al., Oncogene 29:2585-2590, 2007). This suggests a clear therapeutic rationale for targeting c-Myc in CRC. Moreover haploinsufficiency for c-Myc in this tissue also reduces intestinal tumorigenesis (Athineos and Sansom, Oncogene 29:2585-2590, 2010; Yekkala and Baudino, Mol Cancer Res 5:1296-1303, 2007), and overexpression of c-Myc affects tissue homeostasis (Finch et al., Mol Cell Biol 29:5306-5315, 2009; Murphy et al., Cancer Cell 14:447-457, 2008). In this chapter we will provide an overview of our current laboratory protocols to characterize c-Myc function in intestinal homeostasis, regeneration, and tumorigenesis in vivo and in vitro.