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

Ali BR, Xu H, Akawi NA, John A, Karuvantevida NS, Langer R, Al-Gazali L, Leitinger B - Hum. Mol. Genet. (2010)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.

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.

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Schematic domain structure of homodimeric DDR2. The extracellular domain consists of a collagen-binding discoidin domain, followed by a so-called stalk region. The intracellular domain contains a large cytosolic juxtamembrane domain in addition to the C-terminal tyrosine kinase domain. The position of disease-causing missense mutations is shown at the left.
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DDQ103F1: Schematic domain structure of homodimeric DDR2. The extracellular domain consists of a collagen-binding discoidin domain, followed by a so-called stalk region. The intracellular domain contains a large cytosolic juxtamembrane domain in addition to the C-terminal tyrosine kinase domain. The position of disease-causing missense mutations is shown at the left.

Mentions: The discoidin domain receptors (DDRs), DDR1 and DDR2, comprise a family of receptor tyrosine kinases (RTKs) that function as collagen receptors (1,2). The DDRs are the only RTKs that are activated by a component of the extracellular matrix. Several collagen types, both fibrillar and non-fibrillar types, activate the DDRs, with the two receptors displaying different specificities for certain collagen types (1–4). Structurally, the DDRs are characterized in their extracellular regions by the presence of a collagen-binding discoidin homology domain and a domain unique to the DDRs (stalk region) (Fig. 1). A transmembrane region is followed by a large cytoplasmic juxtamembrane domain, and, finally a C-terminal tyrosine kinase domain. Both DDRs form ligand-independent dimers on the cell surface (5). We have recently defined the mode of collagen recognition by the discoidin domain of DDR2 using X-ray crystallography (6).


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

Ali BR, Xu H, Akawi NA, John A, Karuvantevida NS, Langer R, Al-Gazali L, Leitinger B - Hum. Mol. Genet. (2010)

Schematic domain structure of homodimeric DDR2. The extracellular domain consists of a collagen-binding discoidin domain, followed by a so-called stalk region. The intracellular domain contains a large cytosolic juxtamembrane domain in addition to the C-terminal tyrosine kinase domain. The position of disease-causing missense mutations is shown at the left.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2865377&req=5

DDQ103F1: Schematic domain structure of homodimeric DDR2. The extracellular domain consists of a collagen-binding discoidin domain, followed by a so-called stalk region. The intracellular domain contains a large cytosolic juxtamembrane domain in addition to the C-terminal tyrosine kinase domain. The position of disease-causing missense mutations is shown at the left.
Mentions: The discoidin domain receptors (DDRs), DDR1 and DDR2, comprise a family of receptor tyrosine kinases (RTKs) that function as collagen receptors (1,2). The DDRs are the only RTKs that are activated by a component of the extracellular matrix. Several collagen types, both fibrillar and non-fibrillar types, activate the DDRs, with the two receptors displaying different specificities for certain collagen types (1–4). Structurally, the DDRs are characterized in their extracellular regions by the presence of a collagen-binding discoidin homology domain and a domain unique to the DDRs (stalk region) (Fig. 1). A transmembrane region is followed by a large cytoplasmic juxtamembrane domain, and, finally a C-terminal tyrosine kinase domain. Both DDRs form ligand-independent dimers on the cell surface (5). We have recently defined the mode of collagen recognition by the discoidin domain of DDR2 using X-ray crystallography (6).

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates.

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.

Show MeSH
Related in: MedlinePlus