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COS cells expression cloning of tyrosine-phosphorylated proteins by immunocytochemistry
1Center for the Prevention of Cardiovascular Disease, Harvard School of Public Health, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA. cbianchi@caregroup.harvard.edu
Abstract:
Tyrosine phosphorylation is an important post-translational modification of proteins, essential in many aspects of the cell economy, particularly in signal transduction pathways. Despite the importance of protein tyrosine phosphorylation, the approaches available for molecular cloning remain limited. We have developed a COS cell-based eukaryotic expression cloning procedure for phosphotyrosine-containing proteins by immunocytochemistry of cell monolayers. The approach takes advantage of the low basal levels of tyrosine phosphorylated, robust transient expression, availability of specific antibodies against tyrosine-phosphorylated residues, and rescue of episomal DNA after immunocytochemistry. The technique is validated by cloning the rat proto-oncogene c-fgr in its tyrosine-phosphorylated form out of a rat kidney cDNA library containing over 10(6) primary recombinants. This technique set the grounds for expression cloning of tyrosine-phosphorylated proteins in eukaryotic cells, and it is anticipated that further modifications and refinements will allow the identification of protein tyrosine phosphatase substrates.
Insights
Researchers developed a new method for cloning phosphotyrosine-containing proteins using eukaryotic expression and immunocytochemistry. This technique enables the identification of novel tyrosine-phosphorylated proteins and potential substrates for protein tyrosine phosphatases.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Tyrosine phosphorylation is a critical post-translational modification regulating cellular processes, especially signal transduction.
- Existing molecular cloning methods for phosphotyrosine-containing proteins are limited, hindering research in this area.
Purpose of the Study:
- To develop a novel eukaryotic expression cloning procedure for identifying phosphotyrosine-containing proteins.
- To overcome limitations in current molecular cloning techniques for studying tyrosine phosphorylation.
Main Methods:
- A COS cell-based eukaryotic expression cloning procedure utilizing immunocytochemistry on cell monolayers.
- Leveraged low basal tyrosine phosphorylation levels, robust transient expression, specific anti-phosphotyrosine antibodies, and episomal DNA rescue.
- Validated the technique by cloning the tyrosine-phosphorylated form of rat proto-oncogene c-fgr from a large cDNA library.
Main Results:
- Successfully established and validated a novel method for expression cloning of phosphotyrosine-containing proteins.
- Demonstrated the technique's efficacy by isolating the tyrosine-phosphorylated c-fgr proto-oncogene.
Conclusions:
- The developed COS cell-based expression cloning procedure provides a powerful new tool for identifying tyrosine-phosphorylated proteins in eukaryotic cells.
- This technique lays the foundation for future refinements to identify protein tyrosine phosphatase substrates.