Beta-catenin is a key activator of Wnt signaling target genes. Aberrant activation of beta-catenin through mutational inactivation of its negative regulators has been implicated in the pathogenesis of several common human cancers. Recent studies from our laboratory have demonstrated that beta-catenin is subject to an autofeedback regulation after the adenomatous polyposis coli (APC) tumor suppressor protein mediated regulatory mechanism failed due to mutation. Functional screening of a cDNA library constructed by enriching beta-catenin induced genes through subtraction has lead to the identification the scaffolding protein Axin2, a target gene of beta-catenin. A homolog of Conductin or mouse Axil, Axin2 was previously identified as a negative regulator of Wnt/beta-catenin signaling by several other laboratories. Our transient expression experiments revealed a novel function of Axin2 in the destruction of beta-catenin that is uniquely different from that of the APC-mediated regulatory mechanism. We hypothesize that auto-feedback regulation of beta-catenin by Axin2 is an important mechanism of canonical Wnt/beta-catenin signaling. Based on this hypothesis, we suggest: 1) downregulation of beta-catenin requires a synergetic effect contributed by both APC and Axin 2; and 2) failure of Axin2-mediated auto-feedback regulation will lead to aberrant activation of beta-catenin and consequently neoplastic transformation. We propose to test this hypothesis using a combination of genetic and biochemical approaches as outlined in the following specific aims.
AIM I : To assess whether synergistic cooperation between APC and Axin2 is required for the downregulation of beta-catenin using a set of genetically engineered colon cancer cell lines as the in vitro model system;
and AIM II : To test whether loss of the auto-feedback function of Axin2 will cause aberrant activation of beta-catenin and tumorigenesis in vivo using genetically engineered mutant mice harboring heterozygous Axin2 allele.
AIM III : To define the contribution of individual protein domains to the Axin2 tumor suppressor function, and use these information to delineate the unique features in Axin2-mediated destruction of beta-catenin. The long term goal of these proposed studies is to gain new mechanistic information concerning the pathogenesis of beta-catenin in human cancer, with the objective of identifying key cellular targets useful for rational cancer prevention and therapy.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA113831-03
Application #
7233225
Study Section
Tumor Cell Biology Study Section (TCB)
Program Officer
Woodhouse, Elizabeth
Project Start
2005-05-01
Project End
2010-03-31
Budget Start
2007-05-01
Budget End
2008-03-31
Support Year
3
Fiscal Year
2007
Total Cost
$250,280
Indirect Cost
Name
University of Pittsburgh
Department
Pathology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Su, YunYun; Fu, Chunjiang; Ishikawa, Shinji et al. (2008) APC is essential for targeting phosphorylated beta-catenin to the SCFbeta-TrCP ubiquitin ligase. Mol Cell 32:652-61