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The human p50csk tyrosine kinase phosphorylates p56lck at Tyr-505 and down regulates its catalytic activity
M Bergman1, T Mustelin, C Oetken
1Department of Pathology, University of Helsinki, Finland.
Abstract:
Protein tyrosine kinases participate in the transduction and modulation of signals that regulate proliferation and differentiation of cells. Excessive or deregulated protein tyrosine kinase activity can cause malignant transformation. The catalytic activity of the T cell protein tyrosine kinase p56lck is normally suppressed by phosphorylation of a carboxyl-terminal tyrosine, Tyr-505, by another cellular protein tyrosine kinase. Here we characterize a human cytosolic 50 kDa protein tyrosine kinase, p50csk, which specifically phosphorylates Tyr-505 of p56lck and a synthetic peptide containing this site. Phosphorylation of Tyr-505 suppressed the catalytic activity of p56lck. We suggest that p50csk negatively regulates p56lck, and perhaps other cellular src family kinases.
Insights
A newly identified protein tyrosine kinase, p50csk, phosphorylates and suppresses the activity of T cell protein tyrosine kinase p56lck. This discovery reveals a key mechanism in regulating cell signaling and preventing malignant transformation.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Protein tyrosine kinases (PTKs) are crucial for cell signaling, regulating proliferation and differentiation.
- Dysregulated PTK activity is linked to malignant transformation.
- The T cell protein tyrosine kinase, p56lck, is normally inhibited by phosphorylation at Tyr-505.
Purpose of the Study:
- To characterize a human cytosolic PTK, p50csk.
- To investigate the role of p50csk in regulating p56lck activity.
Main Methods:
- Biochemical characterization of p50csk.
- In vitro phosphorylation assays using p56lck and synthetic peptides.
Main Results:
- p50csk specifically phosphorylates Tyr-505 of p56lck.
- Phosphorylation of Tyr-505 by p50csk suppressed the catalytic activity of p56lck.
- p50csk also phosphorylated a synthetic peptide mimicking the Tyr-505 site.
Conclusions:
- p50csk acts as a negative regulator of p56lck.
- p50csk may also regulate other Src family kinases.
- This finding provides insight into the control of T cell signaling pathways.