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PAK1 phosphorylation of MEK1 regulates fibronectin-stimulated MAPK activation
Jill K Slack-Davis1, Scott T Eblen, Maja Zecevic
1Department of Microbiology, University of Virginia Health System, Charlottesville, VA 22908, USA.
Abstract:
Activation of the Ras-MAPK signal transduction pathway is necessary for biological responses both to growth factors and ECM. Here, we provide evidence that phosphorylation of S298 of MAPK kinase 1 (MEK1) by p21-activated kinase (PAK) is a site of convergence for integrin and growth factor signaling. We find that adhesion to fibronectin induces PAK1-dependent phosphorylation of MEK1 on S298 and that this phosphorylation is necessary for efficient activation of MEK1 and subsequent MAPK activation. The rapid and efficient activation of MEK and phosphorylation on S298 induced by cell adhesion to fibronectin is influenced by FAK and Src signaling and is paralleled by localization of phospho-S298 MEK1 and phospho-MAPK staining in peripheral membrane-proximal adhesion structures. We propose that FAK/Src-dependent, PAK1-mediated phosphorylation of MEK1 on S298 is central to the organization and localization of active Raf-MEK1-MAPK signaling complexes, and that formation of such complexes contributes to the adhesion dependence of growth factor signaling to MAPK.
Insights
Cell adhesion to fibronectin triggers a key MEK1 phosphorylation event, essential for MAPK pathway activation and growth factor signaling. This finding reveals a convergence point for integrin and growth factor pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The Ras-MAPK pathway is crucial for cellular responses to growth factors and extracellular matrix (ECM) components.
- Integrin signaling, initiated by cell adhesion to ECM, and growth factor signaling pathways often converge to regulate cellular processes.
Purpose of the Study:
- To investigate the molecular mechanisms underlying the convergence of integrin and growth factor signaling pathways.
- To identify specific phosphorylation sites and kinases involved in integrating adhesion and growth factor signals within the Ras-MAPK pathway.
Main Methods:
- Utilized cell adhesion assays with fibronectin-coated surfaces.
- Employed biochemical techniques including Western blotting and immunofluorescence to detect protein phosphorylation and localization.
- Investigated the roles of p21-activated kinase (PAK), focal adhesion kinase (FAK), and Src in MEK1 phosphorylation and MAPK activation.
Main Results:
- Adhesion to fibronectin induced phosphorylation of MAPK kinase 1 (MEK1) at serine 298 (S298) in a manner dependent on p21-activated kinase (PAK).
- Phosphorylation of MEK1 on S298 was essential for efficient MEK1 activation and subsequent mitogen-activated protein kinase (MAPK) activation.
- FAK and Src signaling pathways influenced the activation of MEK1 and its phosphorylation on S298 upon fibronectin adhesion.
- Phosphorylated MEK1 (p-S298 MEK1) and phosphorylated MAPK (p-MAPK) localized to peripheral adhesion structures.
Conclusions:
- Phosphorylation of MEK1 on S298 by PAK serves as a critical convergence point for integrin (fibronectin) and growth factor signaling.
- FAK/Src-dependent, PAK1-mediated phosphorylation of MEK1 on S298 is central to organizing and localizing active Raf-MEK1-MAPK signaling complexes.
- The formation of these localized signaling complexes contributes to the adhesion-dependent nature of growth factor signaling to MAPK.