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Synergistic activation by Ras and 14-3-3 protein of a mitogen-activated protein kinase kinase kinase named
K Shimizu1, S Kuroda, B Yamamori
1Department of Molecular Biology and Biochemistry, Osaka University Medical School, Japan.
Abstract:
We have identified, in Xenopus oocyte cytosol, a protein kinase named REKS (Ras-dependent extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase kinase (MEK) stimulator), which phosphorylates and activates recombinant ERK2 through recombinant MEK in a recombinant GTP gamma S (guanosine 5'-(3-O-thio)triphosphate)-Ras-dependent manner. We show here that this REKS activity is synergistically enhanced by a combination of mammalian recombinant GTP gamma S-KiRas and 14-3-3 protein purified from rat brain. 14-3-3 protein is known to activate tyrosine and tryptophan hydroxylases, to modulate the protein kinase C activity, to stimulate secretion, and to show phospholipase A2 activity per se. 14-3-3 protein did not affect the MEK activity. 14-3-3 protein neither interacted with Ki-Ras nor affected the neurofibromin activity to stimulate the GTPase activity of Ki-Ras under the conditions where the recombinant N-terminal fragment of c-Raf-1 inhibited it. These results suggest that 14-3-3 protein has an additional function in the regulation of the Ras-MEK-ERK cascade pathway through the activation of REKS.
Insights
Researchers discovered REKS, a protein kinase that activates the Ras-MEK-ERK pathway. Its activity is enhanced by 14-3-3 protein, suggesting a new regulatory role in this crucial signaling cascade.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- The Ras-MEK-ERK pathway is a critical signaling cascade involved in cell proliferation and differentiation.
- Understanding the regulation of this pathway is essential for comprehending various cellular processes and diseases.
Purpose of the Study:
- To identify and characterize novel regulators of the Ras-MEK-ERK pathway.
- To investigate the role of REKS and 14-3-3 protein in modulating this signaling cascade.
Main Methods:
- Protein kinase assays using recombinant proteins in Xenopus oocyte cytosol.
- Analysis of protein-protein interactions and enzyme activities.
- GTPase activity assays.
Main Results:
- Identified REKS (Ras-dependent ERK/MEK stimulator), a protein kinase that activates ERK2 via MEK in a Ras-dependent manner.
- Demonstrated synergistic enhancement of REKS activity by GTPγS-Ki-Ras and 14-3-3 protein.
- Showed that 14-3-3 protein does not directly affect MEK activity or Ki-Ras/neurofibromin interaction.
Conclusions:
- 14-3-3 protein plays a novel regulatory role in the Ras-MEK-ERK pathway by activating REKS.
- This finding expands our understanding of the complex regulatory mechanisms governing cell signaling.