title: Formin-induced actin cables are required for polarized recruitment of the Ste5 scaffold and high level activation of MAPK Fus3.
abstract: Little is known about how a mitogen-activated protein kinase (MAPK) cascade is targeted to specific sites at the plasma membrane during receptor stimulation. In budding yeast, the Ste5 scaffold is recruited to a receptor-coupled G protein during mating pheromone stimulation, allowing the tethered MAPK cascade to be activated by Ste20, a Cdc42-anchored kinase. Here we show that stable recruitment of Ste5 at cortical sites requires the formin Bni1, Bni1-induced actin cables, Rho1 and Myo2. Rho1 directs recruitment of Bni1 via the Rho-binding domain, and Bni1 mediates localization of Ste5 through actin cables and Myo2, which co-immunoprecipitates with Ste5 during receptor stimulation. Bni1 is also required for polarized recruitment and full activation of MAPK Fus3, which must bind Ste5 to be activated, and polarized recruitment of Cdc24, the guanine exchange factor that binds Ste5 and promotes its recruitment to the G protein. In contrast, Bni1 is not important for activation of MAPK Kss1, which can be activated while not bound to Ste5 and does not accumulate at cortical sites. These findings reveal that Bni1 mediates the formation of a Ste5 scaffold/Fus3 MAPK signaling complex at polarized sites, and suggests that a pool of Ste5 may translocate along formin-induced actin cables to the cell cortex.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, MA 02115, USA.
authors.forename: Maosong
authors.initials: M
authors.lastname: Qi
authors.forename: Elaine A
authors.initials: EA
authors.lastname: Elion
mesh_terms: D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D016764:Cell Polarity; D008840:Microfilament Proteins / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D024701:Myosin Type V / Q000378:metabolism; D010675:Pheromones / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C105191:Bni1 protein, S cerevisiae; D019086:Bridged Bicyclo Compounds, Heterocyclic; C077512:MYO2 protein, S cerevisiae; D008840:Microfilament Proteins; D010675:Pheromones; C080321:STE5 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D013844:Thiazoles; D053778:Thiazolidines; C075580:FUS3 protein, S cerevisiae; C541984:KSS1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D024701:Myosin Type V; D018995:Myosin Heavy Chains; C037067:latrunculin A