Colorectal Cancer-Associated Smad4 R361 Hotspot Mutations Boost Wnt/β-Catenin Signaling through Enhanced Smad4-LEF1 Binding.

Autor:	Lanauze CB; Division of Pathobiology, Children's Hospital of Philadelphia, Pennsylvania.; Cell & Molecular Biology Graduate Group, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania., Sehgal P; Division of Pathobiology, Children's Hospital of Philadelphia, Pennsylvania., Hayer K; Division of Pathobiology, Children's Hospital of Philadelphia, Pennsylvania.; Department of Biomedical & Health Informatics, Children's Hospital of Philadelphia., Torres-Diz M; Division of Pathobiology, Children's Hospital of Philadelphia, Pennsylvania., Pippin JA; Division of Human Genetics, Children's Hospital of Philadelphia, Pennsylvania., Grant SFA; Cell & Molecular Biology Graduate Group, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.; Division of Human Genetics, Children's Hospital of Philadelphia, Pennsylvania.; Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania., Thomas-Tikhonenko A; Division of Pathobiology, Children's Hospital of Philadelphia, Pennsylvania. andreit@pennmedicine.upenn.edu.; Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.; Department of Pathology & Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania.
Jazyk:	angličtina
Zdroj:	Molecular cancer research : MCR [Mol Cancer Res] 2021 May; Vol. 19 (5), pp. 823-833. Date of Electronic Publication: 2021 Feb 19.
DOI:	10.1158/1541-7786.MCR-20-0721
Abstrakt:	About 10% to 30% of patients with colorectal cancer harbor either loss of or missense mutations in SMAD4, a critical component of the TGFβ signaling pathway. The pathophysiologic function of missense mutations in Smad4 is not fully understood. They usually map to the MH2 domain, specifically to residues that are involved in heterodimeric complex formation with regulatory Smads (such as Smad2/3) and ensuing transcriptional activation. These detrimental effects suggest that SMAD4 missense mutations can be categorized as loss-of-function. However, they tend to cluster in a few hotspots, which is more consistent with them acting by a gain-of-function mechanism. In this study, we investigated the functional role of Smad4 R361 mutants by re-expressing two R361 Smad4 variants in several Smad4-null colorectal cancer cell lines. As predicted, R361 mutations disrupted Smad2/3-Smad4 heteromeric complex formation and abolished canonical TGFβ signaling. In that, they were similar to SMAD4 loss. However, RNA sequencing and subsequent RT-PCR assays revealed that Smad4mut cells acquired a gene signature associated with enhanced Lef1 protein function and increased Wnt signaling. Mechanistically, Smad4 mutant proteins retained binding to Lef1 protein and drove a commensurate increase in downstream Wnt signaling as measured by TOP/FOP luciferase assay and Wnt-dependent cell motility. Consistent with these findings, human colorectal cancers with SMAD4 missense mutations were less likely to acquire activating mutations in the key Wnt pathway gene CTNNB1 (encoding β-catenin) than colorectal cancers with truncating SMAD4 nonsense mutations. IMPLICATIONS: Our studies suggest that in colorectal cancer hotspot mutations in Smad4 confer enhanced Wnt signaling and possibly heightened sensitivity to Wnt pathway inhibitors. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/5/823/F1.large.jpg. (©2021 American Association for Cancer Research.)
Databáze:	MEDLINE
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