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Ras-dependent activation of MAP kinase pathway mediated by G-protein beta gamma subunits
1Molecular Signalling Unit, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892.
Abstract:
Mitogen-activated protein kinases, MAP kinases or ERKs (extracellular signal-regulated kinases) are rapidly stimulated by growth-promoting factors acting on a variety of cell-surface receptors. In turn, ERKs phosphorylate and regulate key intracellular enzymes and transcription factors involved in the control of cellular proliferation. The tyrosine-kinase class of growth-factor receptors transmits signals to ERKs in a multistep process that involves Ras and a limited number of defined molecules. In contrast, ERK activation by G-protein-coupled receptors is poorly understood, as is the role of ras in this signalling pathway. We have explored in COS-7 cells the mechanism of ERKs activation by m1 and m2 muscarinic receptors, typical examples of receptors coupled through Gq proteins to induce phosphatidylinositol hydrolysis and to G(i) proteins to inhibit adenylyl cyclase, respectively. Here we present evidence that ERK activation is mediated by beta gamma subunits of heterotrimeric G proteins acting on a ras-dependent pathway.
Insights
Mitogen-activated protein kinases (MAPKs/ERKs) are crucial for cell proliferation. This study reveals that beta gamma subunits of G proteins activate ERKs via a Ras-dependent pathway, clarifying signaling from G-protein-coupled receptors.
Area of Science:
- Cellular signaling and molecular biology
- Signal transduction pathways
- G protein-coupled receptor (GPCR) research
Background:
- Mitogen-activated protein kinases (MAPKs), also known as extracellular signal-regulated kinases (ERKs), are key regulators of cellular proliferation.
- ERK activation by tyrosine-kinase growth-factor receptors involves Ras, but the mechanism for G-protein-coupled receptors (GPCRs) and the role of Ras are less understood.
- Muscarinic receptors (m1 and m2) are typical GPCRs coupled to Gq and Gi proteins, respectively, mediating diverse cellular responses.
Purpose of the Study:
- To investigate the mechanism of ERK activation by m1 and m2 muscarinic receptors in COS-7 cells.
- To elucidate the role of Ras in ERK signaling initiated by GPCRs.
- To identify the specific components of the G protein signaling pathway involved in ERK activation.
Main Methods:
- Utilized COS-7 cells to study ERK activation mechanisms.
- Investigated signaling pathways downstream of m1 and m2 muscarinic receptors.
- Examined the involvement of G protein subunits and Ras in ERK activation.
Main Results:
- Demonstrated that beta gamma (βγ) subunits of heterotrimeric G proteins mediate ERK activation.
- Provided evidence for a Ras-dependent pathway in ERK activation downstream of muscarinic receptors.
- Established a link between GPCR signaling and the Ras/ERK pathway.
Conclusions:
- ERK activation by m1 and m2 muscarinic receptors is primarily mediated by G protein βγ subunits.
- This activation occurs through a Ras-dependent signaling cascade.
- The findings clarify a previously poorly understood aspect of GPCR signaling and its connection to the Ras/ERK pathway, crucial for cellular proliferation control.