Related Experiment Videos
A novel functional link between MAP kinase cascades and the Ras/cAMP pathway that regulates survival
Vera A Cherkasova1, Ryan McCully, Yunmei Wang
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
Abstract:
In mammalian cells, Ras regulates multiple effectors, including activators of mitogen-activated protein kinase (MAPK) cascades, phosphatidylinositol-3-kinase, and guanine nucleotide exchange factors (GEFs) for RalGTPases. In S. cerevisiae, Ras regulates the Kss1 MAPK cascade that promotes filamentous growth and cell integrity, but its major function is to activate adenylyl cyclase and control proliferation and survival ([; see Figure S1 in the Supplemental Data available with this article online). Previous work hints that the mating Fus3/Kss1 MAPK cascade cross-regulates the Ras/cAMP pathway during growth and mating, but direct evidence is lacking. Here, we report that Kss1 and Fus3 act upstream of the Ras/cAMP pathway to regulate survival. Loss of Fus3 increases cAMP and causes poor long-term survival and resistance to stress. These effects are dependent on Kss1 and Ras2. Activation of Kss1 by a hyperactive Ste11 MAPKKK also increases cAMP, but mating receptor/scaffold activation has little effect and may therefore insulate the MAPKs from cross-regulation. Catalytically inactive Fus3 represses cAMP by blocking accumulation of active Kss1 and by another function also shared by Kss1. The conserved RasGEF Cdc25 is a likely control point, because Kss1 and Fus3 complexes associate with and phosphorylate Cdc25. Cross-regulation of Cdc25 may be a general way that MAPKs control Ras signaling networks.
Insights
In yeast, mating MAP kinases Fus3 and Kss1 regulate survival by controlling the Ras/cAMP pathway. Loss of Fus3 elevates cAMP, impairing survival and stress resistance, highlighting MAPK control over Ras signaling.
Area of Science:
- Cellular signaling pathways
- Yeast genetics and molecular biology
Background:
- Ras signaling controls proliferation and survival in yeast.
- Mitogen-activated protein kinase (MAPK) cascades, including Fus3 and Kss1, are involved in growth and mating.
- Cross-regulation between MAPK pathways and the Ras/cAMP pathway is suspected but lacks direct evidence.
Purpose of the Study:
- To investigate the direct role of Fus3 and Kss1 MAP kinases in regulating the Ras/cAMP pathway.
- To elucidate the mechanism by which MAPKs control Ras signaling and cellular survival.
Main Methods:
- Genetic analysis of yeast mutants (S. cerevisiae).
- Measurement of cyclic AMP (cAMP) levels.
- Analysis of protein interactions and phosphorylation.
- Assessment of cell survival and stress resistance.
Main Results:
- Loss of Fus3 kinase activity leads to increased cAMP levels and reduced long-term survival and stress resistance.
- These effects are dependent on Kss1 and Ras2, indicating pathway integration.
- Activation of Kss1 increases cAMP, while mating receptor activation has minimal impact.
- Fus3 and Kss1 physically associate with and phosphorylate Cdc25, a Ras guanine nucleotide exchange factor (GEF).
Conclusions:
- Fus3 and Kss1 MAP kinases act upstream of the Ras/cAMP pathway to regulate survival in yeast.
- MAPK-mediated phosphorylation of Cdc25 is a key mechanism for controlling Ras signaling networks.
- This cross-regulation provides a link between mating pathways and cell survival/proliferation.