Colorectal cancer (CRC) is the second most common cause of cancer death in the United States. It is relatively uncommon before the age of 50 but the incidence rises after that age. CRC arises as a consequence of stepwise mutations in key genes with critical roles in regulating cell growth. These genes include tumor suppressor genes and oncogenes. Studies have shown that somatic or germ-line mutations in adenomatous polyposis coli (APC), p53, and genes involved in DMA mismatch repair such as MLH1 and MSH2, and oncogenic activation of KRAS and BRAF are important in the development of CRC. ARC regulates ?-catenin levels through the Wnt pathway and acts as a negative regulator of ?-catenin signaling in colonic epithelial cells. Activating mutations of ?-catenin or truncation of APC occur in colon cancer, which increase the stability and transcriptional activity of ?-catenin. Kr?ppel-like factor 4 [KLF4;also called gut-enriched Kr?ppel-like factor (GKLF)] was previously identified by our group as a zinc finger-containing transcription factor expressed in the epithelial cells of the gastrointestinal tract. KLF4 negatively regulates cellular proliferation by up-regulating the cyclin-dependent kinase inhibitor, p21WAF1/Cip1. Recent work from our lab indicated that KLF4 is a potential tumor suppressor for colorectal cancer. In addition, mice with homozygous deletion of the Klf4 gene had a significant reduction in the number of goblet cells in the intestine. On the other hand, goblet cell differentiation in the intestine has been shown to be suppressed by Notch signaling. Several reports have shown the existence of cross-talk between Notch and Wnt pathways and that Wnt increases Notch1 expression. The central HYPOTHESIS of this research proposal is that KLF4 plays an important role in intestinal adenoma formation and in goblet cell formation and maturation. Moreover, preliminary studies show that loss of a single Klf4 allele in presence of ApcMin mutation significantly reduces the number of mature goblet cells in the colon. Thus we also hypothesize that Notch signaling plays an important role in negatively regulating KLF4 expression and/or its transcriptional activity. We proposed 3 SPECIFIC AIMS to test these hypotheses: (1) To investigate the relationship between KLF4 and Notch signaling in the formation of goblet cells, (2) To investigate whether Notch negatively regulates KLF4, (3) To investigate the relationship between Notch, KLF4 and APC in intestinal adenoma formation, cell proliferation and apoptosis. The further elucidation of the functions of KLF4 in CRC may lead to new insights into the mechanism of intestinal tumorigenesis.
