Reduced affinity to and inhibition by DKK1 form a common mechanism by which high bone mass-associated missense mutations in LRP5 affect canonical Wnt signaling.
The low-density-lipoprotein receptor-related protein 5 (LRP5), a coreceptor in the canonical Wnt signaling pathway, has been implicated in human disorders of low and high bone mass. Loss-of-function mutations cause the autosomal recessive osteoporosis-pseudoglioma syndrome, and heterozygous missense mutations in families segregating autosomal dominant high bone mass (HBM) phenotypes have been identified. We expressed seven different HBM-LRP5 missense mutations to delineate the mechanism by which they alter Wnt signaling. None of the mutations caused activation of the receptor in the absence of ligand. Each mutant receptor was able to reach the cell surface, albeit at differing amounts, and transduce exogenously supplied Wnt1 and Wnt3a signal. All HBM mutant proteins had reduced physical interaction with and reduced inhibition by DKK1. These data suggest that HBM mutant proteins can transit to the cell surface in sufficient quantity to transduce Wnt signal and that the likely mechanism for the HBM mutations' physiologic effects is via reduced affinity to and inhibition by DKK1.
Ai
Minrong
M
Department of Genetics and Center for Human Genetics, Case School of Medicine and University Hospitals of Cleveland, Cleveland, OH 44106, USA.
Holmen
Sheri L
SL
Van Hul
Wim
W
Williams
Bart O
BO
Warman
Matthew L
ML
D000818:Animals; D001847:Bone Diseases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D026502:LDL-Receptor Related Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D010641:Phenotype; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051153:Wnt Proteins; D051155:Wnt1 Protein
C501126:DKK1 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D018832:Molecular Chaperones; D011506:Proteins; C495247:WNT1 protein, human; D051153:Wnt Proteins; D051155:Wnt1 Protein