Functions for Cdc42p BEM Adaptors in Regulating a Differentiation-Type MAP Kinase Pathway

Abstract

Impact Sentence: Rho GTPase adaptors play unique and sequential roles in the 27 regulation of MAPK pathways. 28 29 Cdc42p Adaptors Regulate a MAPK Pathway Basu et al. 2 HIGHLIGHTS 30• Comparing Cdc42p-dependent MAPK pathways showed that the fMAPK 31 pathway had slow activation kinetics compared to the mating and HOG 32 pathways. 33 34• A collection of cdc42 alleles was tested for MAPK pathway functions. 35 § Cdc42p E100A , previously characterized as being specifically defective for fMAPK 36 signaling, showed reduced interaction with the fMAPK pathway adaptor Bem4p. 37 § Corresponding residues in Bem4p were identified that were required for 38 interaction with Cdc42p and fMAPK signaling. 39 40 • The polarity adaptor Bem1p regulated the fMAPK pathway. 41 § Bem1p regulated the fMAPK pathway by recruiting Ste20p to the plasma 42 membrane, cycling between an open and closed conformation, and interacting 43 with the Cdc42p GEF, Cdc24p. 44 45 • Different domains of Bem1p had different roles in regulating effector pathways. 46 § Bem1p may function as a multi-functional adaptor in some pathways and an inert 47 48 49• Bem4p and Bem1p regulated the fMAPK pathway in an ordered sequence. 50 § The data support a model where Bem4p recruits Cdc24p to GDP-Cdc42p, and 51 Bem1p directs GTP-Cdc42p to Ste20p at the plasma membrane. 52 § The bud-site GTPase Rsr1p regulates Cdc24p in the fMAPK pathway but does 53 not initiate signaling. 54 55 Cdc42p Adaptors Regulate a MAPK Pathway Basu et al. 3 ABSTRACT 56 Rho GTPases regulate cell polarity and signal transduction pathways to control 57 morphogenetic responses in different settings. In yeast, the Rho GTPase Cdc42p 58 regulates cell polarity, and through the p21-activated kinase Ste20p, Cdc42p also 59 regulates mitogen-activated protein kinase (MAPK) pathways (mating, filamentous 60 growth or fMAPK, and HOG). Although much is known about how Cdc42p regulates 61 cell polarity and the mating pathway, how Cdc42p regulates the fMAPK pathway is not 62 clear. To address this question, Cdc42p-dependent MAPK pathways were compared in 63 the filamentous (∑1278b) strain background. Each MAPK pathway showed a unique 64 activation profile, with the fMAPK pathway exhibiting slow activation kinetics compared 65 to the mating and HOG pathways. A previously characterized version of Cdc42p, 66Cdc42p E100A , that is specifically defective for fMAPK pathway signaling, was defective 67 for interaction with Bem4p, the pathway-specific adaptor for the fMAPK pathway. 68Corresponding residues in Bem4p were identified that were required for interaction with 69 Cdc42p and fMAPK pathway signaling. The polarity adaptor Bem1p also regulated the 70 fMAPK pathway. In the fMAPK pathway, Bem1p recruited Ste20p to the plasma 71 membrane, cycled between an open and closed conformation, and interacted with the 72 GEF for Cdc42, Cdc24p. Bem1p also regulated effector pathways in different ways, 73 behaving as a multi-functional adaptor in some pathways and an inert scaffold in others. 74Genetic suppression ...