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Focal adhesion kinase promotes phospholipase C-gamma1 activity
X Zhang1, A Chattopadhyay, Q S Ji
1Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Abstract:
The nonreceptor tyrosine kinase FAK ("focal adhesion kinase") is a key mediator of integrin signaling events controlling cellular responses to the extracellular matrix, including spreading, migration, proliferation, and survival. Integrin-ligand interactions stimulate FAK tyrosine phosphorylation and activation of FAK signaling functions. Here evidence is presented that the FAK autophosphorylation site Tyr-397 mediates a direct interaction with the C-terminal Src homology 2 domain of phospholipase C (PLC)-gamma1 and that this is required for both adhesion-dependent association of the two molecules and increased inositol phosphate production in mouse embryo fibroblasts. Overexpression of FAK and PLC-gamma1 in COS-7 cells increases PLC-gamma1 enzymatic activity and tyrosine phosphorylation, also dependent on FAK Tyr-397. However, FAK appears incapable of directly phosphorylating PLC-gamma1. These observations suggest a role for FAK in recruiting PLC-gamma1 to the plasma membrane at sites of cell-matrix adhesion and there promoting its enzymatic activity, possibly by releasing the repression caused by intramolecular interactions of the PLC-gamma1 Src homology domains and/or by positioning it for phosphorylation by associated Src-family kinases. These findings expand the known signaling functions of FAK and provide mechanistic insight into integrin-stimulation of PLC-gamma1.
Insights
Focal adhesion kinase (FAK) directly binds phospholipase C gamma 1 (PLCγ1) at Tyr-397, promoting PLCγ1 activity at cell-matrix adhesion sites. This interaction is crucial for integrin signaling and cell responses.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase central to integrin signaling.
- Integrin-ligand interactions activate FAK, influencing cell adhesion, migration, proliferation, and survival.
- Phospholipase C gamma 1 (PLCγ1) is involved in signal transduction pathways.
Purpose of the Study:
- To investigate the direct interaction between FAK and PLCγ1.
- To determine the role of FAK's autophosphorylation site Tyr-397 in this interaction.
- To elucidate the mechanism by which FAK influences PLCγ1 activity.
Main Methods:
- Co-immunoprecipitation assays to assess protein interactions.
- Measurement of inositol phosphate production.
- Overexpression studies in COS-7 cells.
Main Results:
- FAK Tyr-397 directly interacts with the SH2 domain of PLCγ1.
- This interaction is essential for adhesion-dependent association of FAK and PLCγ1.
- FAK promotes PLCγ1 enzymatic activity and tyrosine phosphorylation, dependent on FAK Tyr-397.
- FAK does not directly phosphorylate PLCγ1.
Conclusions:
- FAK recruits PLCγ1 to the plasma membrane at cell-matrix adhesion sites.
- FAK promotes PLCγ1 enzymatic activity, potentially by relieving intramolecular repression or facilitating phosphorylation by Src-family kinases.
- These findings reveal a novel mechanism for FAK in integrin-stimulated PLCγ1 activation.