Wnt-3a utilizes a novel low dose and rapid pathway that does not require casein kinase 1-mediated phosphorylation of Dvl to activate beta-catenin.
The current view of canonical Wnt signalling is that following Wnt binding to its receptors (Frizzled-Lrp5/6), dishevelled (Dvl) becomes hyperphosphorylated, and the signal is transduced to the APC-GSK3beta-axin-beta-catenin multiprotein complex, which subsequently dissociates. As a result beta-catenin is not phosphorylated, escapes proteosomal degradation and activates its target genes after translocation to the nucleus. Here, we analyzed the importance of the Wnt-3a-induced phosphorylation and shift in electrophoretic migration of Dvl (PS-Dvl) for the activation of beta-catenin. Analysis of Wnt-3a time- and dose-responses in a dopaminergic cell line showed that beta-catenin is activated rapidly (within minutes) and at a low dose of Wnt-3a (1 ng/ml). Surprisingly, PS-Dvl appeared only after 30 min and at greater doses (> or =20 ng/ml) of Wnt-3a. Moreover, we found that a casein kinase 1 inhibitor (D4476) or siRNA for casein kinase 1 delta/epsilon (CK1delta/epsilon) blocked the Wnt-3a-induced PS-Dvl. Interestingly, CK1 inhibition or siRNA for CK1delta/epsilon did not ablate the activation of beta-catenin by Wnt-3a, indicating that there is a PS-Dvl-independent path to activate beta-catenin. The increase in beta-catenin activation by Wnt-3a (PS-Dvl-dependent or -independent) were blocked by Dickkopf1 (Dkk1), suggesting that the effect of Wnt-3a is in both cases mediated by Lrp5/6 receptors. Thus, our results show that Wnt-3a rapidly induce a partial activation of beta-catenin in the absence of PS-Dvl at low doses, while at high doses induce a full activation of beta-catenin in a PS-Dvl-dependent manner.
Bryja
Vítezslav
V
Karolinska Institutet, Department Medical Biochemistry and Biophysics, Laboratory Molecular Neurobiology, S-171 77 Stockholm, Sweden.
Schulte
Gunnar
G
Arenas
Ernest
E
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D047389:Casein Kinase I / Q000378:metabolism*; D002460:Cell Line; D000072261:Dishevelled Proteins; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D014162:Transfection; D051153:Wnt Proteins / Q000494:pharmacology*; D060508:Wnt3 Protein; D051176:beta Catenin / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D000072261:Dishevelled Proteins; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D051153:Wnt Proteins; D060508:Wnt3 Protein; D051176:beta Catenin; D047389:Casein Kinase I