ABSTRACT
Zinc and ring finger 3 (ZNRF3) is a transmembrane E3 ubiquitin ligase that targets Wnt receptors for ubiquitination and lysosomal degradation. Previously, we showed that dephosphorylation of an endocytic tyrosine motif (4Y motif) in ZNRF3 by protein tyrosine phosphatase receptor-type kappa (PTPRK) promotes ZNRF3 internalization and Wnt receptor degradation (Chang et al 2020). However, a responsible protein tyrosine kinase(s) (PTK) phosphorylating the 4Y motif remained elusive. Here we identify the proto-oncogene MET (mesenchymal-epithelial transition factor) as a 4Y kinase. MET binds to ZNRF3 and induces 4Y phosphorylation, stimulated by the MET ligand HGF (hepatocyte growth factor, scatter factor). HGF-MET signaling reduces ZNRF3-dependent Wnt receptor degradation thereby enhancing Wnt/ß-catenin signaling. Conversely, depletion or pharmacological inhibition of MET promotes the internalization of ZNRF3 and Wnt receptor degradation. We conclude that HGF-MET signaling phosphorylates- and PTPRK dephosphorylates ZNRF3 to regulate ZNRF3 internalization, functioning as a rheostat for Wnt signaling that may offer novel opportunities for therapeutic intervention.
Subject(s)
Adenocarcinoma of Lung/enzymology , Lung Neoplasms/enzymology , Proto-Oncogene Proteins c-met/metabolism , Receptor-Like Protein Tyrosine Phosphatases, Class 2/metabolism , Ubiquitin-Protein Ligases/metabolism , Wnt Proteins/metabolism , Wnt Signaling Pathway , Adenocarcinoma of Lung/genetics , Adenocarcinoma of Lung/pathology , Cell Line, Tumor , Endocytosis , Gene Expression Regulation, Neoplastic , HEK293 Cells , Hepatocyte Growth Factor/pharmacology , Humans , Lung Neoplasms/genetics , Lung Neoplasms/pathology , Phosphorylation , Protein Transport , Proteolysis , Proto-Oncogene Mas , Proto-Oncogene Proteins c-met/genetics , Receptor-Like Protein Tyrosine Phosphatases, Class 2/genetics , Receptors, Wnt/metabolism , Ubiquitin-Protein Ligases/genetics , Ubiquitination , Wnt Proteins/genetics , Wnt Signaling Pathway/drug effectsABSTRACT
A hallmark of Spemann organizer function is its expression of Wnt antagonists that regulate axial embryonic patterning. Here we identify the tumor suppressor Protein tyrosine phosphatase receptor-type kappa (PTPRK), as a Wnt inhibitor in human cancer cells and in the Spemann organizer of Xenopus embryos. We show that PTPRK acts via the transmembrane E3 ubiquitin ligase ZNRF3, a negative regulator of Wnt signaling promoting Wnt receptor degradation, which is also expressed in the organizer. Deficiency of Xenopus Ptprk increases Wnt signaling, leading to reduced expression of Spemann organizer effector genes and inducing head and axial defects. We identify a '4Y' endocytic signal in ZNRF3, which PTPRK maintains unphosphorylated to promote Wnt receptor depletion. Our discovery of PTPRK as a negative regulator of Wnt receptor turnover provides a rationale for its tumor suppressive function and reveals that in PTPRK-RSPO3 recurrent cancer fusions both fusion partners, in fact, encode ZNRF3 regulators.
Subject(s)
Gene Expression Regulation, Developmental , Gene Expression Regulation, Neoplastic , Receptor-Like Protein Tyrosine Phosphatases, Class 2/metabolism , Ubiquitin-Protein Ligases/metabolism , Wnt Proteins/antagonists & inhibitors , Animals , Body Patterning/genetics , Endocytosis , Gene Expression Profiling , HEK293 Cells , Humans , Low Density Lipoprotein Receptor-Related Protein-6/metabolism , Organizers, Embryonic/metabolism , Signal Transduction , Xenopus Proteins/metabolism , Xenopus laevis , beta Catenin/metabolismABSTRACT
Casein kinase 1 (CK1) members play key roles in numerous biological processes. They are considered "rogue" kinases, because their enzymatic activity appears unregulated. Contrary to this notion, we have identified the DEAD-box RNA helicase DDX3 as a regulator of the Wnt-ß-catenin network, where it acts as a regulatory subunit of CK1ε: In a Wnt-dependent manner, DDX3 binds CK1ε and directly stimulates its kinase activity, and promotes phosphorylation of the scaffold protein dishevelled. DDX3 is required for Wnt-ß-catenin signaling in mammalian cells and during Xenopus and Caenorhabditis elegans development. The results also suggest that the kinase-stimulatory function extends to other DDX and CK1 members, opening fresh perspectives for one of the longest-studied protein kinase families.
Subject(s)
Casein Kinase 1 epsilon/metabolism , DEAD-box RNA Helicases/metabolism , RNA Helicases/metabolism , Wnt Signaling Pathway , Xenopus Proteins/metabolism , Adaptor Proteins, Signal Transducing/metabolism , Animals , Caenorhabditis elegans/genetics , Caenorhabditis elegans/growth & development , Caenorhabditis elegans/metabolism , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , Casein Kinase 1 epsilon/chemistry , DEAD-box RNA Helicases/chemistry , DEAD-box RNA Helicases/genetics , Dishevelled Proteins , HEK293 Cells , Humans , Phosphoproteins/metabolism , Phosphorylation , Protein Binding , Protein Structure, Tertiary , RNA Helicases/chemistry , RNA Helicases/genetics , Wnt Proteins/metabolism , Xenopus/embryology , Xenopus/genetics , Xenopus/metabolism , Xenopus Proteins/chemistry , Xenopus Proteins/genetics , beta Catenin/metabolismABSTRACT
Wnt/beta-catenin signaling is important in stem cell biology, embryonic development, and disease, including cancer. However, the mechanism of Wnt signal transmission, notably how the receptors are activated, remains incompletely understood. We found that the prorenin receptor (PRR) is a component of the Wnt receptor complex. PRR functions in a renin-independent manner as an adaptor between Wnt receptors and the vacuolar H+-adenosine triphosphatase (V-ATPase) complex. Moreover, PRR and V-ATPase were required to mediate Wnt signaling during antero-posterior patterning of Xenopus early central nervous system development. The results reveal an unsuspected role for the prorenin receptor, V-ATPase activity, and acidification during Wnt/beta-catenin signaling.
