Trafficking defects and loss of ligand binding are the underlying causes of all reported DDR2 missense mutations found in SMED-SL patients

Hum Mol Genet. 2010 Jun 1;19(11):2239-50. doi: 10.1093/hmg/ddq103. Epub 2010 Mar 10.

Abstract

Spondylo-meta-epiphyseal dysplasia (SMED) with short limbs and abnormal calcifications (SMED-SL) is a rare, autosomal recessive human growth disorder, characterized by disproportionate short stature, short limbs, short broad fingers, abnormal metaphyses and epiphyses, platyspondyly and premature calcifications. Recently, three missense mutations and one splice-site mutation in the DDR2 gene were identified as causative genetic defects for SMED-SL, but the underlying cellular and biochemical mechanisms were not explored. Here we report a novel DDR2 missense mutation, c.337G>A (p.E113K), that causes SMED-SL in two siblings in the United Arab Emirates. Another DDR2 missense mutation, c.2254C>T (p.R752C), matching one of the previously reported SMED-SL mutations, was found in a second affected family. DDR2 is a plasma membrane receptor tyrosine kinase that functions as a collagen receptor. We expressed DDR2 constructs with the identified point mutations in human cell lines and evaluated their localization and functional properties. We found that all SMED-SL missense mutants were defective in collagen-induced receptor activation and that the three previously reported mutants (p.T713I, p.I726R and p.R752C) were retained in the endoplasmic reticulum. The novel mutant (p.E113K), in contrast, trafficked normally, like wild-type DDR2, but failed to bind collagen. This finding is in agreement with our recent structural data identifying Glu113 as an important amino acid in the DDR2 ligand-binding site. Our data thus demonstrate that SMED-SL can result from at least two different loss-of-function mechanisms: namely defects in DDR2 targeting to the plasma membrane or the loss of its ligand-binding activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Child
  • DNA Primers / genetics
  • Discoidin Domain Receptors
  • Endoplasmic Reticulum / metabolism
  • HeLa Cells
  • Humans
  • Immunohistochemistry
  • Male
  • Models, Molecular*
  • Molecular Sequence Data
  • Mutation, Missense / genetics
  • Osteochondrodysplasias / diagnostic imaging
  • Osteochondrodysplasias / genetics*
  • Osteochondrodysplasias / metabolism*
  • Pedigree
  • Protein Binding / genetics
  • Protein Transport / genetics
  • Protein Transport / physiology
  • Radiography
  • Receptor Protein-Tyrosine Kinases / chemistry
  • Receptor Protein-Tyrosine Kinases / genetics*
  • Receptor Protein-Tyrosine Kinases / metabolism*
  • Receptors, Collagen / metabolism
  • Receptors, Mitogen / chemistry
  • Receptors, Mitogen / genetics*
  • Receptors, Mitogen / metabolism*
  • Sequence Analysis, DNA
  • Signal Transduction / genetics
  • Signal Transduction / physiology
  • Transfection
  • United Arab Emirates

Substances

  • DNA Primers
  • Receptors, Collagen
  • Receptors, Mitogen
  • Discoidin Domain Receptors
  • Receptor Protein-Tyrosine Kinases