Dual role for membrane localization in yeast MAP kinase cascade activation and its contribution to signaling fidelity.
Distinct MAP kinase pathways in yeast share several signaling components , including the PAK Ste20 and the MAPKKK Ste11, yet signaling is specific. Mating pheromones trigger an initial step in which Ste20 activates Ste11 , and this requires plasma membrane recruitment of the MAP kinase cascade scaffold protein, Ste5 . Here, we demonstrate an additional role for Ste5 membrane localization. Once Ste11 is activated, signaling through the mating pathway remains minimal but is substantially amplified when Ste5 is recruited to the membrane either by the Gbetagamma dimer or by direct membrane targeting, even to internal membranes. Ste11 signaling is also amplified by Ste5 oligomerization and by a hyperactivating mutation in the Ste7 binding region of Ste5. We suggest a model in which membrane recruitment of Ste5 concentrates its binding partners and thereby amplifies signaling through the kinase cascade. We find similar behavior in the osmotically responsive HOG pathway. Remarkably, while both pheromone and hyperosmotic stimuli amplify signaling from constitutively active Ste11, the resulting signaling output remains pathway specific. These findings suggest a common mode of regulation in which pathway stimuli both initiate and amplify MAP kinase cascade signaling. The regulation of rate-limiting steps that lie after a branchpoint from shared components helps ensure signaling specificity.
Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
Rachel E
RE
Lamson
Satoe
S
Takahashi
Matthew J
MJ
Winters
Peter M
PM
Pryciak
D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis / Q000737:chemistry / Q000502:physiology*; D002462:Cell Membrane / Q000201:enzymology* / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; C080321:STE5 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins