A Novel Functional Link Between MAP Kinase Cascades and the Ras/cAMP Pathway That Regulates Survival

Curr Biol. 2003 Jul 15;13(14):1220-6. doi: 10.1016/s0960-9822(03)00490-1.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cell Cycle Proteins / physiology
  • Cyclic AMP / physiology*
  • Fungal Proteins / physiology
  • Genes, ras / physiology*
  • MAP Kinase Kinase Kinases / physiology
  • MAP Kinase Signaling System / physiology*
  • Mitogen-Activated Protein Kinases / genetics
  • Mitogen-Activated Protein Kinases / physiology
  • Precipitin Tests
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / physiology
  • Signal Transduction*
  • ras-GRF1 / physiology


  • Cell Cycle Proteins
  • Fungal Proteins
  • Saccharomyces cerevisiae Proteins
  • ras-GRF1
  • Cyclic AMP
  • FUS3 protein, S cerevisiae
  • KSS1 protein, S cerevisiae
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase Kinases
  • Ste11 protein, S cerevisiae