The Wnt signal transduction pathway directs fundamental cellular processes during development and tissue homeostasis. Deregulation of Wnt signaling results in numerous developmental defects and triggers 90% of colorectal cancers, the vast majority of which result from inactivation of the tumor suppressor, Adenomatous polyposis coli (APC). Although we have known for more than two decades that APC plays a central role in Wnt signaling, the mechanistic basis underlying APC function has remained elusive. Our long-term goal is to understand the mechanisms by which APC regulates Wnt signaling, as this knowledge is critical for devising new strategies that target Wnt-driven diseases. APC and its binding partner, Axin, establish a multiprotein ?destruction complex? that inhibits Wnt signaling by promoting turnover of the transcriptional coactivator, beta- catenin, the key mediator of Wnt pathway activation. Axin plays key roles not only in the destruction complex, but also in assembly of the ?signalosome?, a complex that activates signaling following Wnt stimulation. In the prevailing model for Wnt signaling, the role of APC is limited to promoting beta-catenin degradation and, thus, pathway inhibition in the unstimulated state. However, our unexpected findings in the current funding period force revision of this model, as we have discovered completely novel aspects of APC function. Our new findings indicate that the primary role of APC is to control both of Axin's essential roles: to inhibit signaling in the unstimulated state, and to activate signaling following Wnt stimulation. We found that APC regulates two post-translational modifications critical for Axin function in both the inhibition and the activation of Wnt signaling. In the forthcoming funding period, we propose to elucidate the novel mechanisms by which APC regulates Axin, and thereby controls assembly of both the destruction complex and the signalosome. We have developed innovative experimental systems for in vivo Wnt pathway dissection in Drosophila and cultured mammalian cells as well as in vitro pathway reconstitution with Xenopus egg extracts and purified proteins. We propose to combine our unique genetic and biochemical approaches to interrogate the functions of APC in Wnt pathway regulation. The knowledge gained from these studies on the fundamental mechanisms that underlie APC function will be invaluable in the development of future treatments for Wnt-driven diseases.

Public Health Relevance

PUBLICHEALTHRELEVANCE:TheWntcell-cellpathwaydirectsthedevelopmentof multipletissuesduringembryogenesis.ErrorsinWntsignalingresultinbirthdisorders andincancersinadults.Thus,ourunderstandingofWntsignalingisimportantforthe developmentoftherapiestocombatasignificantnumberofhumandiseases.Thegoals ofthisproposalaretointerrogatethemechanismsbywhichthetumorsuppressor, Adenomatouspolyposiscoli,controlstheactivityoftheWntpathwayinboththe?off?and ?on?states.Wewillusetheinnovativeexperimentalapproachesdevelopedinour laboratoriestoachievethesegoals.Knowledgegainedfromthesestudieswillinformour understandingofthefundamentalmechanismsthatcontrolWntsignalingandfacilitate newstrategiesfortherapyinWnt-drivendiseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM122222-12
Application #
9554959
Study Section
Intercellular Interactions Study Section (ICI)
Program Officer
Melillo, Amanda A
Project Start
2017-09-01
Project End
2021-05-31
Budget Start
2018-06-01
Budget End
2019-05-31
Support Year
12
Fiscal Year
2018
Total Cost
Indirect Cost
Name
Dartmouth College
Department
Other Basic Sciences
Type
Schools of Medicine
DUNS #
041027822
City
Hanover
State
NH
Country
United States
Zip Code
Saito-Diaz, Kenyi; Benchabane, Hassina; Tiwari, Ajit et al. (2018) APC Inhibits Ligand-Independent Wnt Signaling by the Clathrin Endocytic Pathway. Dev Cell 44:566-581.e8
Tian, Ai; Benchabane, Hassina; Ahmed, Yashi (2018) Wingless/Wnt Signaling in Intestinal Development, Homeostasis, Regeneration and Tumorigenesis: A Drosophila Perspective. J Dev Biol 6:
Tacchelly-Benites, Ofelia; Wang, Zhenghan; Yang, Eungi et al. (2018) Axin phosphorylation in both Wnt-off and Wnt-on states requires the tumor suppressor APC. PLoS Genet 14:e1007178
Tian, Ai; Benchabane, Hassina; Wang, Zhenghan et al. (2017) Intestinal stem cell overproliferation resulting from inactivation of the APC tumor suppressor requires the transcription cofactors Earthbound and Erect wing. PLoS Genet 13:e1006870
Wang, Zhenghan; Tacchelly-Benites, Ofelia; Yang, Eungi et al. (2016) Dual Roles for Membrane Association of Drosophila Axin in Wnt Signaling. PLoS Genet 12:e1006494
Tacchelly-Benites, Ofelia; Wang, Zhenghan; Yang, Eungi et al. (2013) Toggling a conformational switch in Wnt/?-catenin signaling: regulation of Axin phosphorylation. The phosphorylation state of Axin controls its scaffold function in two Wnt pathway protein complexes. Bioessays 35:1063-70
Busch, Alexander M; Johnson, Kevin C; Stan, Radu V et al. (2013) Evidence for tankyrases as antineoplastic targets in lung cancer. BMC Cancer 13:211
Benchabane, Hassina; Xin, Nan; Tian, Ai et al. (2011) Jerky/Earthbound facilitates cell-specific Wnt/Wingless signalling by modulating ?-catenin-TCF activity. EMBO J 30:1444-58
Xin, Nan; Benchabane, Hassina; Tian, Ai et al. (2011) Erect Wing facilitates context-dependent Wnt/Wingless signaling by recruiting the cell-specific Armadillo-TCF adaptor Earthbound to chromatin. Development 138:4955-67
Benchabane, Hassina; Ahmed, Yashi (2009) The adenomatous polyposis coli tumor suppressor and Wnt signaling in the regulation of apoptosis. Adv Exp Med Biol 656:75-84