G Protein-coupled receptor kinases phosphorylate LRP6 in the Wnt pathway

J Biol Chem. 2009 Dec 11;284(50):35040-8. doi: 10.1074/jbc.M109.047456. Epub 2009 Oct 2.

Abstract

Wnt ligands conduct their functions in canonical Wnt signaling by binding to two receptors, the single transmembrane low density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) and seven transmembrane (7TM) Frizzled receptors. Subsequently, phosphorylation of serine/threonine residues within five repeating signature PPPSP motifs on LRP6 is responsible for LRP6 activation. GSK3beta, a cytosolic kinase for phosphorylation of a downstream effector beta-catenin, was proposed to participate in such LRP6 phosphorylation. Here, we report a new class of membrane-associated kinases for LRP6 phosphorylation. We found that G protein-coupled receptor kinases 5 and 6 (GRK5/6), traditionally known to phosphorylate and desensitize 7TM G protein-coupled receptors, directly phosphorylate the PPPSP motifs on single transmembrane LRP6 and regulate Wnt/LRP6 signaling. GRK5/6-induced LRP6 activation is inhibited by the LRP6 antagonist Dickkopf. Depletion of GRK5 markedly reduces Wnt3A-stimulated LRP6 phosphorylation in cells. In zebrafish, functional knock-down of GRK5 results in reduced Wnt signaling, analogous to LRP6 knock-down, as assessed by decreased abundance of beta-catenin and lowered expression of the Wnt target genes cdx4, vent, and axin2. Expression of GRK5 rescues the diminished beta-catenin and axin2 response caused by GRK5 depletion. Thus, our findings identify GRK5/6 as novel kinases for the single transmembrane receptor LRP6 during Wnt signaling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Axin Protein
  • Cells, Cultured
  • Fibroblasts / cytology
  • Fibroblasts / physiology
  • Frizzled Receptors / genetics
  • Frizzled Receptors / metabolism
  • G-Protein-Coupled Receptor Kinase 5 / genetics
  • G-Protein-Coupled Receptor Kinase 5 / metabolism*
  • G-Protein-Coupled Receptor Kinases / genetics
  • G-Protein-Coupled Receptor Kinases / metabolism*
  • HeLa Cells
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism
  • Humans
  • Low Density Lipoprotein Receptor-Related Protein-6
  • Mice
  • Mice, Knockout
  • Molecular Sequence Data
  • Oligonucleotides, Antisense / genetics
  • Oligonucleotides, Antisense / metabolism
  • Phosphorylation
  • Receptors, LDL / genetics
  • Receptors, LDL / metabolism*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Signal Transduction / physiology
  • Wnt Proteins / genetics
  • Wnt Proteins / metabolism*
  • Zebrafish / embryology
  • Zebrafish / genetics
  • Zebrafish / metabolism
  • Zebrafish Proteins / genetics
  • Zebrafish Proteins / metabolism
  • beta Catenin / genetics
  • beta Catenin / metabolism

Substances

  • Axin Protein
  • Frizzled Receptors
  • Homeodomain Proteins
  • LRP6 protein, human
  • Low Density Lipoprotein Receptor-Related Protein-6
  • Lrp6 protein, mouse
  • Oligonucleotides, Antisense
  • Receptors, LDL
  • Repressor Proteins
  • Wnt Proteins
  • Zebrafish Proteins
  • beta Catenin
  • G-Protein-Coupled Receptor Kinase 5
  • G-Protein-Coupled Receptor Kinases
  • G-protein-coupled receptor kinase 6

Associated data

  • GENBANK/GQ903573
  • GENBANK/GQ903574