Comparative genetic screens in human cells reveal new regulatory mechanisms in WNT signaling
- Stanford University School of Medicine, United States
- Vanderbilt University Medical Center, United States
- Geisel School of Medicine at Dartmouth College, United States
- University of Colorado, Boulder, United States
Abstract
The comprehensive understanding of cellular signaling pathways remains a challenge due to multiple layers of regulation that may become evident only when the pathway is probed at different levels or critical nodes are eliminated. To discover regulatory mechanisms in canonical WNT signaling, we conducted a systematic forward genetic analysis through reporter-based screens in haploid human cells. Comparison of screens for negative, sensitizing and positive regulators of WNT signaling, mediators of R-spondin-dependent signaling and suppressors of constitutive signaling induced by loss of the tumor suppressor APC or casein kinase 1α uncovered new regulatory features at many levels of the pathway. These include a requirement for the transcription factor TFAP4, a role for the DAX domain of AXIN2 in controlling β-catenin activity, a contribution of GPI anchor biosynthetic enzymes and glypicans to R-spondin-potentiated signaling, and two different mechanisms that regulate signaling when distinct components of the β-catenin destruction complex are lost.
Data availability
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Comparative genetic screens in human cells reveal new regulatory mechanisms in WNT signalingPublicly available at the Sequence Read Archive NCBI website (accession no: SRP094861).
Article and author information
Author details
Funding
National Institutes of Health (DP2 AI104557,DP2 GM105448,R01 GM081635,R01 GM103926,RO1 CA105038)
- Yashi Ahmed
- Ethan Lee
- Jan E Carette
- Rajat Rohatgi
National Science Foundation (DBI-1039423)
- Yashi Ahmed
David and Lucile Packard Foundation (Fellow Award)
- Jan E Carette
Helen Hay Whitney Foundation (Novartis Fellowship)
- Andres M Lebensohn
Stanford University School of Medicine (Josephine Q. Berry Fellowship)
- Rajat Rohatgi
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Utpal Banerjee, University of California, Los Angeles, United States
Version history
- Received: September 13, 2016
- Accepted: December 7, 2016
- Accepted Manuscript published: December 20, 2016 (version 1)
- Accepted Manuscript updated: December 22, 2016 (version 2)
- Version of Record published: January 23, 2017 (version 3)
- Version of Record updated: February 1, 2017 (version 4)
Copyright
© 2016, Lebensohn et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Comparative genetic screens in human cells reveal new regulatory mechanisms in WNT signaling
eLife 5:e21459.
https://doi.org/10.7554/eLife.21459
Further reading
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Adenine phosphoribosyltransferase (APRT) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT) are two structurally related enzymes involved in purine recycling in humans. Inherited mutations that suppress HGPRT activity are associated with Lesch–Nyhan disease (LND), a rare X-linked metabolic and neurological disorder in children, characterized by hyperuricemia, dystonia, and compulsive self-injury. To date, no treatment is available for these neurological defects and no animal model recapitulates all symptoms of LND patients. Here, we studied LND-related mechanisms in the fruit fly. By combining enzymatic assays and phylogenetic analysis, we confirm that no HGPRT activity is expressed in Drosophila melanogaster, making the APRT homolog (Aprt) the only purine-recycling enzyme in this organism. Whereas APRT deficiency does not trigger neurological defects in humans, we observed that Drosophila Aprt mutants show both metabolic and neurobehavioral disturbances, including increased uric acid levels, locomotor impairments, sleep alterations, seizure-like behavior, reduced lifespan, and reduction of adenosine signaling and content. Locomotor defects could be rescued by Aprt re-expression in neurons and reproduced by knocking down Aprt selectively in the protocerebral anterior medial (PAM) dopaminergic neurons, the mushroom bodies, or glia subsets. Ingestion of allopurinol rescued uric acid levels in Aprt-deficient mutants but not neurological defects, as is the case in LND patients, while feeding adenosine or N6-methyladenosine (m6A) during development fully rescued the epileptic behavior. Intriguingly, pan-neuronal expression of an LND-associated mutant form of human HGPRT (I42T), but not the wild-type enzyme, resulted in early locomotor defects and seizure in flies, similar to Aprt deficiency. Overall, our results suggest that Drosophila could be used in different ways to better understand LND and seek a cure for this dramatic disease.
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