Genetic Dissection of Differential Signaling Threshold Requirements for the Wnt/β-Catenin Pathway In Vivo

Abstract

Contributions of null and hypomorphic alleles of Apc in mice produce both developmental and pathophysiological phenotypes. To ascribe the resulting genotype-to-phenotype relationship unambiguously to the Wnt/β-catenin pathway, we challenged the allele combinations by genetically restricting intracellular β-catenin expression in the corresponding compound mutant mice. Subsequent evaluation of the extent of resulting Tcf4-reporter activity in mouse embryo fibroblasts enabled genetic measurement of Wnt/β-catenin signaling in the form of an allelic series of mouse mutants. Different permissive Wnt signaling thresholds appear to be required for the embryonic development of head structures, adult intestinal polyposis, hepatocellular carcinomas, liver zonation, and the development of natural killer cells. Furthermore, we identify a homozygous Apc allele combination with Wnt/β-catenin signaling capacity similar to that in the germline of the Apcmin mice, where somatic Apc loss-of-heterozygosity triggers intestinal polyposis, to distinguish whether co-morbidities in Apcmin mice arise independently of intestinal tumorigenesis. Together, the present genotype–phenotype analysis suggests tissue-specific response levels for the Wnt/β-catenin pathway that regulate both physiological and pathophysiological conditions.

Essential requirement for β-arrestin2 in mouse intestinal tumors with elevated Wnt signaling

“…The interplay between Arrb2 and the Wnt pathway detected in our study is likely to play a role in this effect. In Apc-mutated mice, partial or complete inactivation of the second Apc allele is the earliest event of tumor initiation (4), and threshold levels of Tcf-4 activity must be attained to initiate intestinal tumors (21). Our results indicate that the reduction of Arrb2 is only effective to decrease β-catenin/Tcf-4 activity and colony formation in soft agar when Wnt activity is experimentally increased in Apc Min/+ cells.…”

WNT signaling drives cholangiocarcinoma growth and can be pharmacologically inhibited

“…However, the function of WNT signaling in both homeostasis and tumorigenesis is not simple, as WNT signaling appears to have different functions at different signaling levels, and so the well-described on-off model of WNT signaling is unlikely to be borne out in complex cellular environments (36,62). Understanding how the WNT signaling cascade is regulated in a complex cellular environment, where multiple cellular components will influence the growth of the cancer and WNT activity, will be important for the development of therapeutic approaches to the treatment of WNT-dependent cancers.…”

Association of β-catenin with P-Smad3 but not LEF-1 dissociates in vitro profibrotic from anti-inflammatory effects of TGF-β1

“…Wild-type (Buchert et al, 2010) b-catenin (WT b-cat) construct: Flag-tagged WT b-cat fused into pcDNA3. E-cadherin promoter luciferase reporter constructs: pmoEcad (2201 to 2131)/GL3, with mouse Ecadherin promoter 2201 to 2131 driving firefly luciferase reporter gene.…”