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Raf-1 and p21v-ras cooperate in the activation of mitogen-activated protein kinase
N G Williams1, H Paradis, S Agarwal
1Dana-Farber Cancer Institute, Boston, MA.
Abstract:
Mitogen-activated protein (MAP) kinases Raf-1, pp60src, and p21ras all play important roles in the transfer of signals from the cell surface to the nucleus. We have used the baculovirus/Sf9 insect cell system to elucidate the regulatory relationships between pp60v-src, p21v-ras, MAP kinase (p44erk1/mapk), and Raf-1. In Sf9 cells, p44erk1/mapk is activated by coexpression with either v-Raf or a constitutively activated form of Raf-1 (Raf22W). In contrast, p44erk1/mapk is activated to only a limited extent by coexpression with either Raf-1 or p21v-ras alone. This activation of p44erk1/mapk is greatly enhanced by coexpression with both p21v-ras and Raf-1. Since we have previously shown that p21v-ras stimulates Raf-1 activity, the activation of p44erk1/mapk by p21v-ras may occur exclusively via a Raf-1-dependent pathway. However, a dominant-inhibitory mutant of Raf-1 (Raf301) does not block the activation of p44erk1/mapk by p21-v-ras. Further, pp60v-src, which activates Raf-1 at least as effectively as p21v-ras, fails to enhance p44erk1/mapk activity greatly when coexpressed with Raf-1. These data suggest that activation of p44erk1/mapk by p21v-ras may occur via both Raf-1-dependent and Raf-1-independent pathways.
Insights
Mitogen-activated protein kinases (MAPK) are crucial for cell signaling. This study reveals that p21ras activates MAPK through both Raf-1-dependent and independent pathways, clarifying complex cell communication mechanisms.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Signal transduction
Background:
- Mitogen-activated protein (MAP) kinases (MAPK) are key regulators of intracellular signal transduction.
- Raf-1, pp60src, and p21ras are critical components in transmitting signals from the cell surface to the nucleus.
- Understanding the interplay between these proteins is essential for deciphering cellular responses.
Purpose of the Study:
- To investigate the regulatory relationships between pp60v-src, p21v-ras, MAP kinase (p44erk1/mapk), and Raf-1.
- To elucidate the specific pathways involved in MAP kinase activation by p21ras and Raf-1.
- To determine if p21ras-mediated MAP kinase activation is solely dependent on Raf-1.
Main Methods:
- Utilized the baculovirus/Sf9 insect cell expression system.
- Coexpressed various combinations of Raf-1, constitutively active Raf-1 (Raf22W), dominant-inhibitory Raf-1 (Raf301), pp60v-src, p21v-ras, and MAP kinase (p44erk1/mapk).
- Assessed the activation status of p44erk1/mapk under different coexpression conditions.
Main Results:
- p44erk1/mapk was activated by coexpression with v-Raf or Raf22W.
- Coexpression with p21v-ras and Raf-1 synergistically enhanced p44erk1/mapk activation compared to individual components.
- A dominant-inhibitory Raf-1 mutant did not fully block p44erk1/mapk activation by p21v-ras, and pp60v-src did not significantly enhance p44erk1/mapk activity when coexpressed with Raf-1.
- These findings suggest p21ras activates p44erk1/mapk via both Raf-1-dependent and independent routes.
Conclusions:
- p21ras-mediated activation of MAP kinase (p44erk1/mapk) involves both Raf-1-dependent and Raf-1-independent signaling pathways.
- The interaction between p21ras, Raf-1, and MAP kinase is complex and not exclusively linear.
- This study provides critical insights into the intricate network of intracellular signal transduction pathways.