c phosphorylation and activation of the IGF-I receptor in src-transformed cells.
Using a panel of src mutants partially defective for malignant transformation, our laboratory has previously identified the insulin-like growth factor (IGF-I) receptor as a protein whose tyrosine phosphorylation correlates with transformation by src in embryonic chick cells (Kozma et al., 1990; Kozma and Weber, 1990). It has not been clear, however, whether src-induced phosphorylation altered the enzymatic or signaling properties of the IGF-I receptor and thus whether the IGF-I receptor could be a functionally significant target for pp60v-src. To examine the effect of src expression on the activity of the IGF-I receptor, the human IGF-I receptor was expressed in Rat-1 fibroblasts co-expressing the temperature-sensitive v-src mutant, tsLA29. The IGF-I receptor exhibited an elevated level of tyrosine phosphorylation in src transformed cells even in the absence of IGF-I treatment. Increased receptor phosphorylation occurred rapidly when cells expressing a temperature-conditional src mutant were shifted from the restrictive to the permissive temperature. Src-induced phosphorylation of the receptor was correlated with an increase in the in vitro tyrosine kinase activity of the receptor, both toward itself and exogenous substrates. The src-induced increase in receptor activity was shown to be dependent on tyrosine phosphorylation, as treatment with a tyrosine-specific phosphatase lowered receptor activity. A kinase-defective mutant of the IGF-I receptor also became constitutively phosphorylated in src-transformed cells, ruling out a possible autocrine mechanism for this phosphorylation. Collectively these data indicate that pp60v-src induces ligand-independent phosphorylation and activation of the IGF-I receptor by an intracellular mechanism, consistent with the possibility that receptor phosphorylation could contribute to the genesis of the transformed phenotype.
Peterson
J E
JE
Department of Microbiology, University of Virginia, Charlottesville 22908.
Jelinek
T
T
Kaleko
M
M
Siddle
K
K
Weber
M J
MJ
D000818:Animals; D002460:Cell Line; D002472:Cell Transformation, Viral; D016391:Genes, src; D006801:Humans; D015688:Oncogene Protein pp60(v-src) / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D019000:Phosphotyrosine; D014443:Tyrosine; D020794:Receptor Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D015688:Oncogene Protein pp60(v-src)