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pp60v-src phosphorylates and activates low molecular weight phosphotyrosine-protein phosphatase
S Rigacci1, D Degl'Innocenti, M Bucciantini
1Department of Biochemical Sciences, University of Firenze, Italy.
Abstract:
Low M(r) phosphotyrosine-protein phosphatase belongs to the non-receptor cytosolic phosphotyrosine-protein phosphatase subfamily. It has been demonstrated that this enzyme dephosphorylates receptor tyrosine kinases, namely the epidermal growth factor receptor in vitro and the platelet-derived growth factor receptor in vivo. Low M(r) phosphotyrosine-protein phosphatase is constitutively tyrosine-phosphorylated in NIH/3T3 cells transformed by pp60v-src. The same tyrosine kinase, previously immunoprecipitated, phosphorylates this enzyme in vitro as well. Phosphorylation is enhanced using phosphatase inhibitors and phenylarsine oxide-inactivated phosphatase, consistently with the existence of an auto-dephosphorylation process. Intermolecular dephosphorylation is demonstrated adding the active enzyme in a solution containing the inactivated and previously phosphorylated one. This tyrosine phosphorylation correlates with an increase in catalytic activity. Our results provide evidence of a physiological mechanism of low M(r) phosphotyrosine-protein phosphatase activity regulation.
Insights
Low molecular weight phosphotyrosine-protein phosphatase activity is regulated by tyrosine phosphorylation. This phosphorylation enhances the enzyme's catalytic function, revealing a key physiological control mechanism.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Signaling
Background:
- Low molecular weight (M(r)) phosphotyrosine-protein phosphatase is a cytosolic enzyme.
- It dephosphorylates receptor tyrosine kinases like EGFR (in vitro) and PDGFR (in vivo).
Purpose of the Study:
- To investigate the regulation of low M(r) phosphotyrosine-protein phosphatase activity.
- To explore the role of tyrosine phosphorylation in enzyme activity.
Main Methods:
- Studied tyrosine phosphorylation of low M(r) phosphotyrosine-protein phosphatase in NIH/3T3 cells transformed by pp60v-src.
- Utilized immunoprecipitation to identify the tyrosine kinase responsible for phosphorylation.
- Investigated auto-dephosphorylation and intermolecular dephosphorylation using phosphatase inhibitors and phenylarsine oxide.
Main Results:
- Low M(r) phosphotyrosine-protein phosphatase is constitutively tyrosine-phosphorylated in pp60v-src transformed cells.
- pp60v-src phosphorylates the enzyme in vitro.
- Phosphorylation is enhanced by phosphatase inhibitors and inactivated phosphatase, suggesting auto-dephosphorylation.
- Intermolecular dephosphorylation was also observed.
- Tyrosine phosphorylation correlates with increased catalytic activity.
Conclusions:
- Tyrosine phosphorylation is a physiological mechanism for regulating low M(r) phosphotyrosine-protein phosphatase activity.
- This phosphorylation enhances the enzyme's catalytic function.