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Oligomerization-induced differential dephosphorylation of c-Met receptor tyrosine kinase
Payal R Sheth1, Stanley J Watowich
1Department of Human Biological Chemistry and Genetics and Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, Texas 77555-0645, USA.
Abstract:
Although protein tyrosine phosphatases (PTPs) are significant negative regulators of receptor tyrosine kinase (RTK)-initiated cell signaling, it is unknown how RTK oligomerization modulates the equilibrium established between kinase and phosphatase activity. To determine the impact of oligomerization on the ability of c-MET RTK to undergo dephosphorylation, we examined the relative dephosphorylation kinetics of similarly phosphorylated dimeric TPR-MET and monomeric cytoMET. Notably, we observed that the dephosphorylation kinetics of phosphorylated MET were significantly modulated by its oligomeric state, with the global dephosphorylation rate of TPR-MET severalfold slower than the dephosphorylation rate of monomeric cytoMET. Furthermore, there were important site-specific differences in the dephosphorylation patterns of cytoMET and TPR-MET. Reduced dephosphorylation activity was predicted to eliminate or reduce the requirement of ligand-dependent oligomerization for MET autophosphorylation. This was demonstrated by the rapid phosphorylation of unstimulated c-MET on its activation loop and carboxy-terminal tyrosines following pervanadate treatment of cells expressing c-MET. We conclude that the MET oligomerization state is a critical regulator of its dephosphorylation rate. Thus, oligomerization plays a role in modifying the receptor's kinase and dephosphorylation rates to change the equilibrium levels of phosphorylated and dephosphorylated receptor in response to ligand stimulation, and that this may be a general mechanism utilized by many oligomeric receptor tyrosine kinases for regulation of their activity.
Insights
Receptor tyrosine kinase (RTK) oligomerization slows MET dephosphorylation. This oligomeric state regulates MET kinase and phosphatase activity, impacting cell signaling equilibrium.
Area of Science:
- Cellular signaling
- Molecular biology
- Biochemistry
Background:
- Protein tyrosine phosphatases (PTPs) are key negative regulators of receptor tyrosine kinase (RTK) signaling.
- The influence of RTK oligomerization on the balance between kinase and phosphatase activity remains unclear.
- Understanding this balance is crucial for comprehending RTK-mediated cellular responses.
Purpose of the Study:
- To investigate how the oligomeric state of c-MET RTK affects its dephosphorylation kinetics.
- To determine the impact of dimerization versus monomeric states on MET dephosphorylation.
- To elucidate the role of oligomerization in regulating MET kinase and phosphatase activity equilibrium.
Main Methods:
- Comparative analysis of dephosphorylation rates between dimeric TPR-MET and monomeric cytoMET.
- Examination of site-specific dephosphorylation patterns in different MET oligomeric states.
- Assessment of MET autophosphorylation in response to pervanadate treatment in cells expressing c-MET.
Main Results:
- The dephosphorylation rate of phosphorylated MET was significantly slower in its dimeric form (TPR-MET) compared to its monomeric form (cytoMET).
- Distinct site-specific dephosphorylation patterns were observed between monomeric and dimeric MET.
- Reduced dephosphorylation in oligomeric MET suggests a potential decrease in the requirement for ligand-dependent oligomerization for MET autophosphorylation.
Conclusions:
- The oligomeric state of MET is a critical determinant of its dephosphorylation rate.
- Oligomerization modulates both kinase and dephosphorylation rates, altering the equilibrium of phosphorylated/dephosphorylated MET.
- This mechanism of regulating RTK activity via oligomerization may be broadly applicable to other RTKs.
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