Formin-dependent actin assembly is regulated by distinct modes of Rho signaling in yeast.
Formins are actin filament nucleators regulated by Rho-GTPases. In budding yeast, the formins Bni1p and Bnr1p direct the assembly of actin cables, which guide polarized secretion and growth. From the six yeast Rho proteins (Cdc42p and Rho1-5p), we have determined that four participate in the regulation of formin activity. We show that the essential function of Rho3p and Rho4p is to activate the formins Bni1p and Bnr1p, and that activated alleles of either formin are able to bypass the requirement for these Rho proteins. Through a separate signaling pathway, Rho1p is necessary for formin activation at elevated temperatures, acting through protein kinase C (Pkc1p), the major effector for Rho1p signaling to the actin cytoskeleton. Although Pkc1p also activates a MAPK pathway, this pathway does not function in formin activation. Formin-dependent cable assembly does not require Cdc42p, but in the absence of Cdc42p function, cable assembly is not properly organized during initiation of bud growth. These results show that formin function is under the control of three distinct, essential Rho signaling pathways.
Dong
Yuqing
Y
Department of Molecular Biology and Genetics, Cornell University, 353 Biotechnology Building, Ithaca, NY 14853, USA.
Pruyne
David
D
Bretscher
Anthony
A
D008841:Actin Cytoskeleton / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins; D019204:GTP-Binding Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013696:Temperature; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
C106463:BNR1 protein, S cerevisiae; C105191:Bni1 protein, S cerevisiae; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D008840:Microfilament Proteins; D029701:Saccharomyces cerevisiae Proteins; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; C051302:RHO1 protein, S cerevisiae; C074647:RHO3 protein, S cerevisiae; C074648:RHO4 protein, S cerevisiae; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020741:rho GTP-Binding Proteins