A novel set of Wnt-Frizzled fusion proteins identifies receptor components that activate beta -catenin-dependent signaling.
Wnt proteins initiate the canonical (beta-catenin-regulated) signaling cascade by binding to seven-transmembrane spanning receptors of the Frizzled (Fz) family together with the coreceptors LRP5 and -6, members of the low density lipoprotein receptor-related protein family (LRP). Several reports have shown physical and functional associations between various Wnt, LRP, and Frizzled molecules; however, the underlying mechanisms for selectivity remain poorly understood. We present data on a novel set of Wnt-Fz fusion constructs that are useful for elucidating mechanisms of Wnt signal transduction specificity in both Xenopus embryos and 293T cells. In 293T cells, coexpression of several Wnt-Fz fusion proteins with LRP6, but not LRP5, significantly activated a Wnt-responsive promoter, Optimized TOPFlash. Interestingly, Wnt proteins from both the Wnt1 and Wnt5A classes, when fused to the same Frizzled, can synergize with LRP6 to activate signaling and induce secondary axes in Xenopus embryos. However, when several Wnt-Fz constructs containing different Frizzled molecules were tested, it was found that all Frizzled molecules are not equivalent in their ability to activate the canonical Wnt pathway in this context. The data suggest that the distinction between the two Wnt classes lies not in intrinsic differences in the molecules but via the Frizzled molecules with which they interact.
Laboratory of Cell Signaling and Carcinogenesis, Van Andel Research Institute, Grand Rapids, Michigan 49503, USA.
Sheri L
SL
Holmen
Adrian
A
Salic
Cassandra R
CR
Zylstra
Marc W
MW
Kirschner
Bart O
BO
Williams
D000818:Animals; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D051157:Frizzled Receptors; D006801:Humans; D026502:LDL-Receptor Related Proteins; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011973:Receptors, LDL / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation; D051153:Wnt Proteins; D051155:Wnt1 Protein; D014981:Xenopus / Q000196:embryology; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin
C495266:CTNNB1 protein, Xenopus; C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D051157:Frizzled Receptors; D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; C555475:LRP6 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011973:Receptors, LDL; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; C495249:WNT1 protein, Xenopus; C495247:WNT1 protein, human; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin