Modulation of the beta-catenin signaling pathway by the dishevelled-associated protein Hipk1.
BACKGROUND
Wnts are evolutionarily conserved ligands that signal through beta-catenin-dependent and beta-catenin-independent pathways to regulate cell fate, proliferation, polarity, and movements during vertebrate development. Dishevelled (Dsh/Dvl) is a multi-domain scaffold protein required for virtually all known Wnt signaling activities, raising interest in the identification and functions of Dsh-associated proteins.


METHODS
We conducted a yeast-2-hybrid screen using an N-terminal fragment of Dsh, resulting in isolation of the Xenopus laevis ortholog of Hipk1. Interaction between the Dsh and Hipk1 proteins was confirmed by co-immunoprecipitation assays and mass spectrometry, and further experiments suggest that Hipk1 also complexes with the transcription factor Tcf3. Supporting a nuclear function during X. laevis development, Myc-tagged Hipk1 localizes primarily to the nucleus in animal cap explants, and the endogenous transcript is strongly expressed during gastrula and neurula stages. Experimental manipulations of Hipk1 levels indicate that Hipk1 can repress Wnt/beta-catenin target gene activation, as demonstrated by beta-catenin reporter assays in human embryonic kidney cells and by indicators of dorsal specification in X. laevis embryos at the late blastula stage. In addition, a subset of Wnt-responsive genes subsequently requires Hipk1 for activation in the involuting mesoderm during gastrulation. Moreover, either over-expression or knock-down of Hipk1 leads to perturbed convergent extension cell movements involved in both gastrulation and neural tube closure.


CONCLUSIONS
These results suggest that Hipk1 contributes in a complex fashion to Dsh-dependent signaling activities during early vertebrate development. This includes regulating the transcription of Wnt/beta-catenin target genes in the nucleus, possibly in both repressive and activating ways under changing developmental contexts. This regulation is required to modulate gene expression and cell movements that are essential for gastrulation.
Louie
Sarah H
SH
Department of Pharmacology, Howard Hughes Medical Institute, University of Washington School of Medicine, Seattle, Washington, United States of America.
Yang
Xiao Yong
XY
Conrad
William H
WH
Muster
Jeanot
J
Angers
Stephane
S
Moon
Randall T
RT
Cheyette
Benjamin N R
BN
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000072261:Dishevelled Proteins; D004625:Embryo, Nonmammalian / Q000378:metabolism; D054262:Gastrulation; D008969:Molecular Sequence Data; D010641:Phenotype; D010750:Phosphoproteins / Q000378:metabolism*; D010802:Phylogeny; D017346:Protein Serine-Threonine Kinases; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000196:embryology; D051176:beta Catenin / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; C000606586:DVL1 protein, Xenopus; D000072261:Dishevelled Proteins; D010750:Phosphoproteins; D012097:Repressor Proteins; D051153:Wnt Proteins; D029867:Xenopus Proteins; D051176:beta Catenin; C539476:Hipk1 protein, Xenopus; D017346:Protein Serine-Threonine Kinases