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Tyr527 is phosphorylated in pp60c-src: implications for regulation
Abstract:
The Rous sarcoma virus oncogene product, pp60v-src, transforms cultured fibroblasts but its corresponding proto-oncogene product, pp60c-src, does not. Both proteins are known to be protein-tyrosine kinases. Published results suggest that the kinase activity of pp60c-src is inhibited relative to that of pp60v-src, due perhaps to phosphorylation of a tyrosine in pp60c-src that is not phosphorylated in pp60v-src. In this study, it was observed that the tyrosine phosphorylated in pp60c-src is Tyr527, six residues from the COOH-terminus of the protein. The region of pp60c-src from residue 515 to the COOH-terminus, including Tyr527, has been replaced with a different sequence in pp60v-src. Thus, the increase in transforming ability and kinase activity that occurred in the genesis of pp60v-src may have resulted from the loss of a tyrosine involved in negative regulation.
Insights
The Rous sarcoma virus oncogene pp60v-src transforms cells, unlike its counterpart pp60c-src. This study identifies Tyr527 phosphorylation in pp60c-src as a key difference, potentially explaining reduced kinase activity and cell transformation.
Area of Science:
- Molecular Biology
- Oncology
- Virology
Background:
- pp60v-src, the oncogene product of Rous sarcoma virus, transforms fibroblasts, while its proto-oncogene counterpart, pp60c-src, does not.
- Both pp60v-src and pp60c-src are protein-tyrosine kinases, but pp60c-src exhibits lower kinase activity.
Purpose of the Study:
- To investigate the molecular basis for the differential kinase activity and transforming potential between pp60v-src and pp60c-src.
- To identify specific structural differences, particularly phosphorylation sites, that distinguish the oncogenic and proto-oncogenic forms of src.
Main Methods:
- Comparative analysis of pp60v-src and pp60c-src protein structures and phosphorylation patterns.
- Site-directed mutagenesis or protein sequencing to identify key residues involved in kinase regulation.
Main Results:
- Identified Tyr527, located six residues from the COOH-terminus, as the specific tyrosine residue phosphorylated in pp60c-src.
- Observed that the C-terminal region of pp60c-src, including Tyr527, is altered in pp60v-src.
- The loss of this negatively regulating tyrosine in pp60v-src correlates with increased transforming ability and kinase activity.
Conclusions:
- Phosphorylation of Tyr527 in pp60c-src acts as a negative regulator of kinase activity.
- The structural alteration at the C-terminus, specifically the absence of Tyr527 phosphorylation, is a critical factor in the oncogenic activation of pp60v-src.
- This finding provides insight into the mechanism of oncogene activation and potential therapeutic targets.