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CDC25(Mm)/Ras-GRF1 regulates both Ras and Rac signaling pathways
M Innocenti1, R Zippel, R Brambilla
1Department of General Physiology and Biochemistry, University of Milan, Via Celoria 26, 20133, Milano, Italy.
FEBS Letters
|November 2, 1999
Summary
Ras-GRF1, a guanine nucleotide exchange factor, utilizes distinct domains to regulate gene transcription via both external stimuli-regulated kinase (ERK)-dependent and independent pathways. This research elucidates its bifunctional role in cellular signaling.
Area of Science:
- Molecular Biology
- Cell Signaling
- Gene Regulation
Background:
- Ras-GRF1 is a guanine nucleotide exchange factor with multiple domains, including catalytic, pleckstrin homology (PH1, PH2), IQ, and Dbl homology (DH).
- The specific roles of these additional domains in Ras-GRF1 function are not fully elucidated.
- Lysophosphatidic acid (LPA) is a lipid mediator known to activate various intracellular signaling pathways.
Purpose of the Study:
- To investigate the functional significance of the PH1 and IQ domains in Ras-GRF1.
- To determine the contribution of different Ras-GRF1 domains to the activation of gene transcription and extracellular signal-regulated kinase (ERK) pathways.
- To explore potential ERK-independent mechanisms of gene induction mediated by Ras-GRF1.
Main Methods:
- Site-directed mutagenesis was used to create a Ras-GRF1 mutant lacking the PH1 and IQ domains.
- Reporter gene assays were employed to measure c-fos promoter activity in response to LPA.
- Western blotting or kinase assays were utilized to assess extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activities.
Main Results:
- A Ras-GRF1 mutant lacking PH1 and IQ domains retained the ability to activate the c-fos promoter in response to LPA.
- This Ras-GRF1 mutant did not enhance ERK activity, suggesting an alternative mechanism for gene transcription induction.
- An isolated DH-PH2 module of Ras-GRF1 was sufficient to activate both c-Jun N-terminal kinase (JNK) and the c-fos promoter upon LPA stimulation.
- These findings indicate an ERK-independent pathway for gene regulation mediated by the DH-PH2 module.
Conclusions:
- Ras-GRF1 functions as a bifunctional molecule, regulating gene transcription through both ERK-dependent and ERK-independent pathways.
- The DH-PH2 module plays a crucial role in mediating LPA-induced gene transcription via an ERK-independent mechanism, potentially involving JNK activation.
- These results offer new insights into the complex signaling network regulated by Ras-GRF1 and its distinct functional domains.