Purified Wnt5a protein activates or inhibits beta-catenin-TCF signaling depending on receptor context.
The Wnts comprise a large class of secreted proteins that control essential developmental processes such as embryonic patterning, cell growth, migration, and differentiation. In the most well-understood "canonical" Wnt signaling pathway, Wnt binding to Frizzled receptors induces beta-catenin protein stabilization and entry into the nucleus, where it complexes with T-cell factor/lymphoid enhancer factor transcription factors to affect the transcription of target genes. In addition to the canonical pathway, evidence for several other Wnt signaling pathways has accumulated, in particular for Wnt5a, which has therefore been classified as a noncanonical Wnt family member. To study the alternative mechanisms by which Wnt proteins signal, we purified the Wnt5a protein to homogeneity. We find that purified Wnt5a inhibits Wnt3a protein-induced canonical Wnt signaling in a dose-dependent manner, not by influencing beta-catenin levels but by downregulating beta-catenin-induced reporter gene expression. The Wnt5a signal is mediated by the orphan tyrosine kinase Ror2, is pertussis toxin insensitive, and does not influence cellular calcium levels. We show that in addition to its inhibitory function, Wnt5a can also activate beta-catenin signaling in the presence of the appropriate Frizzled receptor, Frizzled 4. Thus, this study shows for the first time that a single Wnt ligand can initiate discrete signaling pathways through the activation of two distinct receptors. Based on these and additional observations, we propose a model wherein receptor context dictates Wnt signaling output. In this model, signaling by different Wnt family members is not intrinsically regulated by the Wnt proteins themselves but by receptor availability.
Mikels
Amanda J
AJ
Department of Developmental Biology, Stanford University School of Medicine, Stanford, California, United States of America.
Nusse
Roel
R
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry; D002460:Cell Line; D051157:Frizzled Receptors / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; D015398:Signal Transduction / Q000187:drug effects*; D051820:TCF Transcription Factors / Q000378:metabolism*; D051153:Wnt Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D000071818:Wnt-5a Protein; D051176:beta Catenin / Q000378:metabolism*
D002413:Cations, Divalent; D051157:Frizzled Receptors; D011518:Proto-Oncogene Proteins; D051820:TCF Transcription Factors; D051153:Wnt Proteins; D000071818:Wnt-5a Protein; C438615:Wnt5a protein, mouse; D051176:beta Catenin; D020794:Receptor Protein-Tyrosine Kinases; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; C477010:Ror2 protein, mouse; D002118:Calcium