Biological and biochemical properties of the c-src+ gene product overexpressed in chicken embryo fibroblasts.
The c-src protein isolated from neuronal cells (pp60c-src+) displays a higher level of protein kinase activity than does pp60c-src from nonneural tissues. There are two structural alterations present in the amino-terminal half of pp60c-src+ expressed in neurons which could contribute to the enhanced activity of this form of pp60c-src: (i) a hexapeptide insert located at amino acid 114 of avian pp60c-src+ and (ii) a novel site(s) of serine phosphorylation. We characterized pp60c-src+ expressed in a nonneuronal cell type to identify factors that regulate the activity of the c-src+ protein and the importance of the neuronal environment on this regulation. The c-src+ protein overexpressed in chicken embryo fibroblasts (CEFs) displayed higher kinase activity than did pp60c-src. The major sites of phosphorylation of the c-src+ protein were Ser-17 and Tyr-527. The unique site(s) of serine phosphorylation originally identified in pp60c-src+ expressed in neurons was not detected in the c-src+ protein overexpressed in CEFs. Therefore, the hexapeptide insert is sufficient to cause an elevation in the tyrosine protein kinase activity of pp60c-src+. Our data also indicate that CEFs infected with the Rous sarcoma virus (RSV)c-src+ display phenotypic changes that distinguish them from cultures producing pp60c-src and that pp60c-src+-expressing cells are better able to grow in an anchorage-independent manner. The level of total cellular tyrosine phosphorylation in RSVc-src+-infected cultures was moderately higher than the level observed in cultures infected with RSVc-src. This level was not as pronounced as that observed in cells infected with RSVv-src or oncogenic variants of RSVc-src. Thus, pp60c-src+ could be considered a partially activated c-src variant protein much like other c-src proteins that contain mutations in the amino-terminal domain.
Levy
J B
JB
Department of Microbiology, State University of New York, Stony Brook 11794.
Brugge
J S
JS
D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D005347:Fibroblasts / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010641:Phenotype; D010748:Phosphopeptides / Q000032:analysis; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D010957:Plasmids; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src); D011994:Recombinant Proteins / Q000378:metabolism
D009419:Nerve Tissue Proteins; D010748:Phosphopeptides; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D010768:Phosphoserine; D011505:Protein-Tyrosine Kinases; D016392:Proto-Oncogene Proteins pp60(c-src)