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Acute Myeloid Leukemia
LEF-1 drives aberrant β-catenin nuclear localization in myeloid leukemia cells
Ferrata Storti Foundation
Haematologica 2018 Volume 104(7):1365-1377
Rhys G. Morgan,1,2 Jenna Ridsdale,3 Megan Payne,1 Kate J. Heesom,4 Marieangela C. Wilson,4 Andrew Davidson,1 Alexander Greenhough,1 Sara Davies,3 Ann C. Williams,1 Allison Blair,1 Marian L. Waterman,5 Alex Tonks3 and Richard L. Darley3
1School of Life Sciences, University of Sussex, Brighton, UK; 2School of Cellular and Molecular Medicine, University of Bristol, UK; 3Department of Haematology, Division of Cancer and Genetics, School of Medicine, Cardiff University, UK; 4University of Bristol Proteomics Facility, UK and 5Department of Microbiology and Molecular Genetics, University of California, Irvine, CA, USA
ABSTRACT
Canonical Wnt/β-catenin signaling is frequently dysregulated in myeloid leukemias and is implicated in leukemogenesis. Nuclear- localized β-catenin is indicative of active Wnt signaling and is fre- quently observed in acute myeloid leukemia (AML) patients; however, some patients exhibit little or no nuclear β-catenin even where cytosolic β-catenin is abundant. Control of the subcellular localization of β-catenin therefore represents an additional mechanism regulating Wnt signaling in hematopoietic cells. To investigate the factors mediating the nuclear-local- ization of β-catenin, we carried out the first nuclear/cytoplasmic proteomic analysis of the β-catenin interactome in myeloid leukemia cells and identi- fied putative novel β-catenin interactors. Comparison of interacting factors between Wnt-responsive cells (high nuclear β-catenin) versus Wnt-unre- sponsive cells (low nuclear β-catenin) suggested the transcriptional partner, LEF-1, could direct the nuclear-localization of β-catenin. The relative levels of nuclear LEF-1 and β-catenin were tightly correlated in both cell lines and in primary AML blasts. Furthermore, LEF-1 knockdown perturbed β- catenin nuclear-localization and transcriptional activation in Wnt-respon- sive cells. Conversely, LEF-1 overexpression was able to promote both nuclear-localization and β-catenin-dependent transcriptional responses in previously Wnt-unresponsive cells. This is the first β-catenin interactome study in hematopoietic cells and reveals LEF-1 as a mediator of nuclear β- catenin level in human myeloid leukemia.
Introduction
Canonical Wnt signaling is an evolutionary conserved signal transduction path- way strictly controlled during normal development but frequently dysregulated in cancer.1 In the absence of a Wnt ligand, the central mediator of this signaling path- way, β-catenin, is constitutively phosphorylated by a destruction complex (DC) consisting of GSK3β, CK1, Axin and APC, priming it for subsequent degradation by the proteasome. Upon Wnt ligand binding to the Wnt receptors (Frizzled and LRP5/6), the DC becomes saturated with phosphorylated β-catenin (which cannot be degraded) resulting in cytosolic accumulation of non-phosphorylated β-catenin.2 Following nuclear translocation, β-catenin complexes with the T-cell factor (TCF)/lymphoid enhancer factor (LEF) transcriptional regulators and pro- motes activation of proto-oncogenic Wnt target genes, like c-myc, cyclinD1 and sur- vivin (http://web.stanford.edu/group/nusselab/cgi-bin/wnt/target_genes). Thus, Wnt sig- naling activation is dependent on the movement of β-catenin into the nucleus, yet this remains a poorly understood process in blood cells. β-Catenin lacks canonical nuclear-localization or -export sequences and its subcellular distribution has instead been associated with multiple factors in context-dependent settings.3
β-Catenin is frequently over-expressed in acute myeloid leukemia (AML)4 where its expression correlates with inferior patient survival.5 β-Catenin has been shown
Correspondence:
RICHARD DARLEY
darley@cardiff.ac.uk
RHYS MORGAN
rhys.morgan@sussex.ac.uk
Received: July 26, 2018. Accepted: January 3, 2019. Pre-published: January 10, 2019.
doi:10.3324/haematol.2018.202846
Check the online version for the most updated information on this article, online supplements, and information on authorship & disclosures: www.haematologica.org/content/104/7/1365
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