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The ras-related GTPase rac1 regulates a proliferative pathway selectively utilized by G-protein coupled receptors
E S Burstein1, D J Hesterberg, J S Gutkind
1ACADIA Pharmaceuticals Inc., San Diego, California 92121, USA.
Abstract:
Ras and rac are each members of the superfamily of monomeric GTPases and both function as molecular switches to link cell-surface signals to intracellular responses. Using a novel assay of cellular proliferation called R-SAT (Receptor Selection and Amplification Technology), we examined the roles of ras and rac in mediating the proliferative responses to a variety of cell-surface receptors. Activated, wild-type and dominant-negative mutants of rac and ras were tested for their effects on cellular proliferation either alone or in combination with receptors. Activated rac (rac Q61L, henceforth rac*) and ras (ras G12V, henceforth ras*) each induced strong proliferative responses. Dominant-negative rac (rac T17N, henceforth rac(-)) dramatically suppressed proliferative responses to G-protein coupled receptors (GPCR's) including the m5 muscarinic receptor and the alpha1B adrenergic receptor. In contrast, rac(-) had little or no effect upon responses to the tyrosine kinase receptor TrkC, and only partially suppressed responses to the Janus kinase (JAK/STAT) linked granulocyte macrophage colony stimulating factor (GM-CSF) receptor. Dominant-negative ras (ras T17N, henceforth ras(-)) blocked the proliferative responses to all of the tested receptors. Compared to rac(-) and ras(-), wild-type rac and ras had only modest effects on the tested receptors. Overall these results demonstrate that rac mediates the proliferative effects of G-protein coupled receptors through a pathway that is distinct from the proliferative signaling pathway utilized by tyrosine kinase linked and JAK-linked receptors.
Insights
Ras and Rac proteins act as molecular switches. Rac mediates G-protein coupled receptor proliferation, distinct from pathways used by tyrosine kinase and JAK-linked receptors.
Area of Science:
- Cellular Biology
- Molecular Signaling
- Signal Transduction
Background:
- Ras and Rac are monomeric GTPases that link cell surface signals to intracellular responses.
- Understanding their roles in cellular proliferation is crucial for deciphering signal transduction pathways.
Purpose of the Study:
- To investigate the distinct roles of Ras and Rac in mediating cellular proliferation.
- To differentiate the signaling pathways utilized by various cell-surface receptors.
Main Methods:
- Utilized a novel assay, Receptor Selection and Amplification Technology (R-SAT), for cellular proliferation.
- Employed activated, wild-type, and dominant-negative mutants of Rac and Ras.
- Tested effects on proliferation in combination with G-protein coupled receptors (GPCRs), tyrosine kinase receptors (TrkC), and JAK/STAT-linked receptors (GM-CSF).
Main Results:
- Activated Rac (Rac*) and Ras (Ras*) strongly induced proliferation.
- Dominant-negative Rac (Rac(-)) suppressed proliferation mediated by GPCRs but had minimal effect on tyrosine kinase or JAK/STAT receptors.
- Dominant-negative Ras (Ras(-)) blocked proliferation across all tested receptor types.
Conclusions:
- Rac mediates proliferation for GPCRs via a distinct pathway.
- Tyrosine kinase and JAK-linked receptors utilize a separate signaling pathway for proliferation, independent of Rac's GPCR-mediated effects.
- Ras appears to be a more general mediator of receptor-induced proliferation compared to Rac.