title: Direct inhibition of GSK3beta by the phosphorylated cytoplasmic domain of LRP6 in Wnt/beta-catenin signaling.
abstract: Wnt/beta-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. Binding of Wnts to the coreceptors Frizzled and LRP6/5 leads to phosphorylation of PPPSPxS motifs in the LRP6/5 intracellular region and the inhibition of GSK3beta bound to the scaffold protein Axin. However, it remains unknown how GSK3beta is specifically inhibited upon Wnt stimulation. Here, we show that overexpression of the intracellular region of LRP6 containing a Ser/Thr rich cluster and a PPPSPxS motif impairs the activity of GSK3beta in cells. Synthetic peptides containing the PPPSPxS motif strongly inhibit GSK3beta in vitro only when they are phosphorylated. Microinjection of these peptides into Xenopus embryos confirms that the phosphorylated PPPSPxS motif potentiates Wnt-induced second body axis formation. In addition, we show that the Ser/Thr rich cluster of LRP6 plays an important role in LRP6 binding to GSK3beta. These observations demonstrate that phosphorylated LRP6/5 both recruits and directly inhibits GSK3beta using two distinct portions of its cytoplasmic sequence, and suggest a novel mechanism of activation in this signaling pathway.
authors.affiliation: College of Pharmacy and Research Institute for Drug Development, Pusan National University, Busan, Korea.
authors.forename: Shunfu
authors.initials: S
authors.lastname: Piao
authors.forename: Sun-Hye
authors.initials: SH
authors.lastname: Lee
authors.forename: Hyunjoon
authors.initials: H
authors.lastname: Kim
authors.forename: Soohwan
authors.initials: S
authors.lastname: Yum
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Stamos
authors.forename: Yongbin
authors.initials: Y
authors.lastname: Xu
authors.forename: Su-Jin
authors.initials: SJ
authors.lastname: Lee
authors.forename: Jaewon
authors.initials: J
authors.lastname: Lee
authors.forename: Sangtaek
authors.initials: S
authors.lastname: Oh
authors.forename: Jin-Kwan
authors.initials: JK
authors.lastname: Han
authors.forename: Bum-Joon
authors.initials: BJ
authors.lastname: Park
authors.forename: William I
authors.initials: WI
authors.lastname: Weis
authors.forename: Nam-Chul
authors.initials: NC
authors.lastname: Ha
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004625:Embryo, Nonmammalian; D047108:Embryonic Development / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D026502:LDL-Receptor Related Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D060488:Low Density Lipoprotein Receptor-Related Protein-6; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology; D051153:Wnt Proteins / Q000502:physiology*; D014981:Xenopus / Q000196:embryology; D051176:beta Catenin / Q000502:physiology*
chemical_list: 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; D051153:Wnt Proteins; D051176:beta Catenin; D011494:Protein Kinases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3