Tyrosine 706 and 807 phosphorylation site mutants in the murine colony-stimulating factor-1 receptor are unaffected in their ability to bind or phosphorylate phosphatidylinositol-3 kinase but show differential defects in their ability to induce early response gene transcription.
The receptor for colony-stimulating factor-1 (CSF-1) is a receptor protein-tyrosine kinase. To study the possible function of CSF-1 receptor autophosphorylation, two autophosphorylation sites, Tyr-706, located in the kinase insert, and Tyr-807, a residue conserved in all protein-tyrosine kinases, were changed independently to either phenylalanine or glycine. Wild-type and mutant receptors were stably expressed in Rat-2 cells. In response to CSF-1, cells expressing Phe- or Gly-706 mutant receptors showed increased growth rate and altered cell morphology. Both the Phe- and Gly-706 mutant receptors associated with and phosphorylated phosphatidylinositol-3 kinase at levels comparable with those of wild-type receptors. However, these mutant receptors differed subtly from each other and from the wild-type receptor in their ability to induce different aspects of the response to CSF-1. The Phe-706 mutant receptor was most strongly affected in its ability to increase growth rate or elevate the levels of c-fos and NGF1A mRNAs, whereas the Gly-706 mutant receptor was most markedly affected in its ability to induce a change in cell morphology or increase the levels of c-jun and NGF1A mRNAs. These findings indicate that Tyr-706 itself, or this region of the receptor, may be important for interaction of the CSF-1 receptor with different signalling pathways. Gly-807 mutant receptors lacked protein-tyrosine kinase activity, failed to respond to CSF-1, and were defective in biosynthetic processing. Phe-807 mutant receptors had 40 to 60% reduced protein-tyrosine kinase activity in vitro. Although cells expressing Phe-807 receptors were able to respond to CSF-1, the changes in growth rate and cell morphology were significantly less than seen with wild-type receptors, and the induction of early response genes was also slightly lower than for the wild-type receptor. In contrast, Phe-807 receptors were equivalent to wild-type receptors when tested for their ability to interact with phosphatidylinositol-3 kinase. These findings indicate that phosphorylation of Tyr-807 may be important for full activation of the receptor.
van der Geer
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P
Molecular Biology and Virology Laboratory, Salk Institute, San Diego, California 92186.
Hunter
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T
D019870:1-Phosphatidylinositol 4-Kinase; D000818:Animals; D001483:Base Sequence; D002455:Cell Division; D002478:Cells, Cultured; D004247:DNA; D005786:Gene Expression Regulation; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010449:Peptide Mapping; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014443:Tyrosine / Q000378:metabolism*
D014443:Tyrosine; D004247:DNA; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D016186:Receptor, Macrophage Colony-Stimulating Factor