Cdc42p-Interacting Protein Bem4p Regulates the Filamentous-Growth Mitogen-Activated Protein Kinase Pathway

Abstract

The ubiquitous Rho (Ras homology) GTPase Cdc42p can function in different settings to regulate cell polarity and cellular signaling. How Cdc42p and other proteins are directed to function in a particular context remains unclear. We show that the Cdc42p-interacting protein Bem4p regulates the mitogen-activated protein kinase (MAPK) pathway that controls filamentous growth in Saccharomyces cerevisiae. Bem4p controlled the filamentous-growth pathway but not other MAPK pathways (mating or high-osmolarity glycerol response [HOG]) that also require Cdc42p and other shared components. Bem4p associated with the plasma membrane (PM) protein, Sho1p, to regulate MAPK activity and cell polarization under nutrient-limiting conditions that favor filamentous growth. Bem4p also interacted with the major activator of Cdc42p, the guanine nucleotide exchange factor (GEF) Cdc24p, which we show also regulates the filamentous-growth pathway. Bem4p interacted with the pleckstrin homology (PH) domain of Cdc24p, which functions in an autoinhibitory capacity, and was required, along with other pathway regulators, to maintain Cdc24p at polarized sites during filamentous growth. Bem4p also interacted with the MAPK kinase kinase (MAPKKK) Ste11p. Thus, Bem4p is a new regulator of the filamentous-growth MAPK pathway and binds to general proteins, like Cdc42p and Ste11p, to promote a pathway-specific response.

Spatial landmarks regulate a Cdc42-dependent MAPK pathway to control differentiation and the response to positional compromise

“…S1A) (44), FLO11 (see below), and FUS1-HIS3 (SI Appendix, Fig. S1B), which in P 1278b cells lacking an intact mating pathway (ste4) shows dependency on fMAPK regulators (21,34).…”

“…Rsr1p is an established regulator of bud-site selection that functions through Cdc42p (7,10,48). Rsr1p was also uncovered in a screen for Cdc42p-interacting proteins that impact fMAPK activity (34). To determine whether Rsr1p regulates the fMAPK pathway, the rsr1Δ mutant was examined in a strain background that undergoes filamentous/invasive growth ( P 1278b) (14,49), a fungal behavioral response that is controlled by the fMAPK pathway.…”

“…The transmembrane regulators connect (in some manner) to a cytosolic scaffold-type adaptor, Bem4p, that also regulates the fMAPK pathway (34)(35)(36). Msb2p and Bem4p associate with Cdc42p (21,34) to promote its function in the fMAPK pathway (37,38). Like many Rho GTPases (39)(40)(41)(42), Cdc42p has multiple roles in regulating cell polarity and signaling.…”

“…At the plasma membrane (PM), Msb2p functions with transmembrane proteins Sho1p (21,24,25) and Opy2p (26)(27)(28)(29)(30)(31)(32)(33). The transmembrane regulators connect (in some manner) to a cytosolic scaffold-type adaptor, Bem4p, that also regulates the fMAPK pathway (34)(35)(36). Msb2p and Bem4p associate with Cdc42p (21,34) to promote its function in the fMAPK pathway (37,38).…”

Role of Phosphatidylinositol Phosphate Signaling in the Regulation of the Filamentous-Growth Mitogen-Activated Protein Kinase Pathway

“…Msb2p, the tetraspan adaptor Sho1p (31,(34)(35)(36), and the cytosolic adaptor protein Bem4p (37) together regulate the Rho-type GTPase Cdc42p and effector p21-activated kinase Ste20p (38,39) in the filamentous-growth MAPK pathway. Ste20p activates the MAPK cascade by phosphorylating the MAPKKK Ste11p.…”