A gain of function mutation in the activation loop of platelet-derived growth factor beta-receptor deregulates its kinase activity

• The platelet-derived growth factor receptors (PDGFRs) are receptor tyrosine kinases implicated in multiple aspects of cell growth, differentiation, and survival. Recently, a gain of function mutation in the activation loop of the human PDGFRalpha has been found in patients with gastrointestinal stromal tumors. Here we show that a mutation in the corresponding codon in the activation loop of the murine PDGFRbeta, namely an exchange of asparagine for aspartic acid at amino acid position 849 (D849N), confers transforming characteristics to embryonic fibroblasts from mutant mice, generated by a knock-in strategy. By comparing the enzymatic properties of the wild-type versus the mutant receptor protein, we demonstrate that the D849N mutation lowers the threshold for kinase activation, causes a dramatic alteration in the pattern of tyrosine phosphorylation kinetics following ligand stimulation, and induces a ligand-independent phosphorylation of several tyrosine residues. These changes result in deregulated recruitment of specific signal transducers. The GTPase-activating protein for Ras (RasGAP), a negative regulator of the Ras mitogenic pathway, displayed a delayed binding to the mutant receptor. Moreover, we have observed enhanced ligand-independent ERK1/2 activation and an increased proliferation of mutant cells. The p85 regulatory subunit of the phosphatidylinositol 3 '-kinase was constitutively associated with the mutant receptor, and this ligand-independent activation of the phosphatidylinositol 3'-kinase pathway may explain the observed strong protection against apoptosis and increased motility in cellular wounding assays. Our findings support a model whereby an activating point mutation results in a deregulated PDGFRbeta with oncogenic predisposition.

Nyckelord

1-Phosphatidylinositol 3-Kinase/metabolism

Actins/metabolism

Animals

Apoptosis

Asparagine/chemistry

Aspartic Acid/chemistry

Binding Sites

COS Cells

Cells; Cultured

Dose-Response Relationship; Drug

Enzyme Activation

Fibroblasts/metabolism

Flow Cytometry

Genetic Vectors

Humans

Kinetics

Mice

Mice; Inbred C57BL

Mice; Mutant Strains

Mitogen-Activated Protein Kinase 1/metabolism

Mitogen-Activated Protein Kinase 3/metabolism

Mutation

NIH 3T3 Cells

Platelet-Derived Growth Factor/metabolism

Point Mutation

Protein Structure; Tertiary

Protein-Serine-Threonine Kinases/metabolism

Proto-Oncogene Proteins/metabolism

Receptor; Platelet-Derived Growth Factor beta/*genetics/metabolism

Research Support; Non-U.S. Gov't

Signal Transduction

Substrate Specificity

Time Factors

Tyrosine/chemistry

Up-Regulation

Wound Healing

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