title: Second cysteine-rich domain of Dickkopf-2 activates canonical Wnt signaling pathway via LRP-6 independently of dishevelled.
abstract: Recent evidence suggests that members of the Dickkopf (Dkk) family can directly bind to LDL-related protein (LRP)-6, resulting in inhibition of Wnt-activated signaling. To further characterize the interactions between Dkk and LRP proteins, conditioned media containing individually conserved cysteine-rich domains of Dkk-1 and Dkk-2 were prepared. Although full-length Dkk-1 and Dkk-2 and the second cysteine-rich domains of both Dkk molecules inhibited Wnt-3a-induced activation of lymphoid enhancing factor (LEF)-1, a downstream target of the canonical pathway, we found that the second cysteine-rich domain of Dkk-2 (Dkk-2C2) was able to stimulate the canonical pathway when LRP-6 was ectopically expressed in NIH3T3 cells. This effect of Dkk-2C2 could be blocked by a monoclonal antibody specific to the second YWTD repeat domain of LRP-5/6, suggesting that Dkk-2C2 acts via LRP-6. We also showed that while both Axin and the DIX domain of Dishevelled (Dvl) could inhibit Dkk-2C2-induced activation of LEF-1, the DEP domain of Dvl, which inhibited Wnt-induced activation of LEF-1, failed to inhibit the activation of LEF-1 by Dkk-2C2 or by an activated form of LRP-5, LRPC2. In addition, glycogen synthase kinase-3 beta, a potent inhibitor for both Dvl and Wnt, also failed to inhibit LRPC2 or Dkk-2C2. Furthermore, knocking-down the expression of Dvl molecules by short interfering RNAs specific to Dvl inhibited Wnt-induced, but not LRPC2-induced, activation of LEF-1. All the evidence indicates that Dkk-2C2 signals through LRP proteins, which does not require Dvl, while Wnt protein may employ both Dvl, presumably through Fz, and LRP to achieve more efficient signal transduction.
authors.affiliation: Department of Genetics and Developmental Biology, University of Connecticut, Farmington, Connecticut 06030, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Li
authors.forename: Junhao
authors.initials: J
authors.lastname: Mao
authors.forename: Le
authors.initials: L
authors.lastname: Sun
authors.forename: Wenzhong
authors.initials: W
authors.lastname: Liu
authors.forename: Dianqing
authors.initials: D
authors.lastname: Wu
mesh_terms: D016475:3T3 Cells; D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D000818:Animals; D002460:Cell Line; D003545:Cysteine; D000072261:Dishevelled Proteins; D004789:Enzyme Activation; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011973:Receptors, LDL / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D051153:Wnt Proteins; D029961:Zebrafish Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C498622:DKK2 protein, human; D000072261:Dishevelled Proteins; C405060:Dkk2 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; C555475:LRP6 protein, human; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555476:Lrp6 protein, mouse; D010750:Phosphoproteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011973:Receptors, LDL; D011994:Recombinant Proteins; D051153:Wnt Proteins; D029961:Zebrafish Proteins; D011505:Protein-Tyrosine Kinases; D003545:Cysteine