The citron homology domain as a scaffold for Rho1 signaling

Aspergillus fumigatus is a human opportunistic pathogen showing emerging resistance against a limited repertoire of antifungal agents available. The GTPase Rho1 has been identified as an important regulator of the cell wall integrity signaling pathway that regulates the composition of the cell wall, a structure that is unique to fungi and serves as a target for antifungal compounds. Rom2, the guanine nucleotide exchange factor to Rho1, contains a C-terminal citron homology (CNH) domain of unknown function that is found in many other eukaryotic genes. Here, we show that the Rom2 CNH domain interacts directly with Rho1 to modulate β-glucan and chitin synthesis. We report the structure of the Rom2 CNH domain, revealing that it adopts a seven-bladed β-propeller fold containing three unusual loops. A model of the Rho1–Rom2 CNH complex suggests that the Rom2 CNH domain interacts with the Rho1 Switch II motif. This work uncovers the role of the Rom2 CNH domain as a scaffold for Rho1 signaling in fungal cell wall biosynthesis.

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Induction of cell retraction by the combined actions of Abl–CrkII and Rho–ROCK1 signaling

The Journal of Cell Biology ◽

10.1083/jcb.200801192 ◽

2008 ◽

Vol 183 (4) ◽

pp. 711-723 ◽

Cited By ~ 30

Author(s):

XiaoDong Huang ◽

Diana Wu ◽

Hua Jin ◽

Dwayne Stupack ◽

Jean Y.J. Wang

Keyword(s):

Nucleotide Exchange ◽

Downstream Target ◽

Abl Tyrosine Kinase ◽

Guanine Nucleotide Exchange ◽

Cell Matrix ◽

Nucleotide Exchange Factor ◽

Wide Range ◽

Important Regulator ◽

Guanosine Triphosphatase ◽

Cell Retraction

Dynamic modulation of cell adhesion is integral to a wide range of biological processes. The small guanosine triphosphatase (GTPase) Rap1 is an important regulator of cell–cell and cell–matrix adhesions. We show here that induced expression of activated Abl tyrosine kinase reduces Rap1-GTP levels through phosphorylation of Tyr221 of CrkII, which disrupts interaction of CrkII with C3G, a guanine nucleotide exchange factor for Rap1. Abl-dependent down-regulation of Rap1-GTP causes cell rounding and detachment only when the Rho–ROCK1 pathway is also activated, for example, by lysophosphatidic acid (LPA). During ephrin-A1–induced retraction of PC3 prostate cancer cells, we show that endogenous Abl is activated and disrupts the CrkII–C3G complex to reduce Rap1-GTP. Interestingly, ephrin-A1–induced PC3 cell retraction also requires LPA, which stimulates Rho to a much higher level than that is activated by ephrin-A1. Our results establish Rap1 as another downstream target of the Abl–CrkII signaling module and show that Abl–CrkII collaborates with Rho–ROCK1 to stimulate cell retraction.

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Role of the Guanine Nucleotide Exchange Factor Rom2 in Cell Wall Integrity Maintenance of Aspergillus fumigatus

Eukaryotic Cell ◽

10.1128/ec.00246-12 ◽

2012 ◽

Vol 12 (2) ◽

pp. 288-298 ◽

Cited By ~ 21

Author(s):

Sweta Samantaray ◽

Michael Neubauer ◽

Christoph Helmschrott ◽

Johannes Wagener

Keyword(s):

Cell Wall ◽

Aspergillus Fumigatus ◽

Guanine Nucleotide Exchange Factor ◽

Cell Wall Integrity ◽

Guanine Nucleotide ◽

Nucleotide Exchange ◽

Content Type ◽

Guanine Nucleotide Exchange ◽

Stress Sensors ◽

Nucleotide Exchange Factor

ABSTRACTAspergillus fumigatusis a mold and the causal agent of invasive aspergillosis, a systemic disease with high lethality. Recently, we identified and functionally characterized three stress sensors implicated in the cell wall integrity (CWI) signaling of this pathogen, namely, Wsc1, Wsc3, and MidA. Here, we functionally characterize Rom2, a guanine nucleotide exchange factor with essential function for the cell wall integrity ofA. fumigatus. A conditionalrom2mutant has severe growth defects under repressive conditions and incorporates all phenotypes of the three cell wall integrity sensor mutants, e.g., the echinocandin sensitivity of the Δwsc1mutant and the Congo red, calcofluor white, and heat sensitivity of the ΔmidAmutant. Rom2 interacts with Rho1 and shows a similar intracellular distribution focused at the hyphal tips. Our results place Rom2 between the cell surface stress sensors Wsc1, Wsc3, MidA, and Rho1 and their downstream effector mitogen-activated protein (MAP) kinase module Bck1-Mkk2-MpkA.

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Wsc1 and Mid2 Are Cell Surface Sensors for Cell Wall Integrity Signaling That Act through Rom2, a Guanine Nucleotide Exchange Factor for Rho1

Molecular and Cellular Biology ◽

10.1128/mcb.21.1.271-280.2001 ◽

2001 ◽

Vol 21 (1) ◽

pp. 271-280 ◽

Cited By ~ 199

Author(s):

Bevin Philip ◽

David E. Levin

Keyword(s):

Cell Wall ◽

Protein Kinase ◽

Cell Surface ◽

G Protein ◽

Guanine Nucleotide Exchange Factor ◽

Cell Wall Integrity ◽

Guanine Nucleotide ◽

Nucleotide Exchange ◽

Guanine Nucleotide Exchange ◽

Nucleotide Exchange Factor

ABSTRACT Wsc1 and Mid2 are highly O-glycosylated cell surface proteins that reside in the plasma membrane of Saccharomyces cerevisiae. They have been proposed to function as mechanosensors of cell wall stress induced by wall remodeling during vegetative growth and pheromone-induced morphogenesis. These proteins are required for activation of the cell wall integrity signaling pathway that consists of the small G-protein Rho1, protein kinase C (Pkc1), and a mitogen-activated protein kinase cascade. We show here by two-hybrid experiments that the C-terminal cytoplasmic domains of Wsc1 and Mid2 interact with Rom2, a guanine nucleotide exchange factor (GEF) for Rho1. At least with regard to Wsc1, this interaction is mediated by the Rom2 N-terminal domain. This domain is distinct from the Rho1-interacting domain, suggesting that the GEF can interact simultaneously with a sensor and with Rho1. We also demonstrate that extracts from wsc1 and mid2 mutants are deficient in the ability to catalyze GTP loading of Rho1 in vitro, providing evidence that the function of the sensor-Rom2 interaction is to stimulate nucleotide exchange toward this G-protein. In a related line of investigation, we identified the PMT2 gene in a genetic screen for mutations that confer an additive cell lysis defect with a wsc1 null allele. Pmt2 is a member of a six-protein family in yeast that catalyzes the first step in O mannosylation of target proteins. We demonstrate that Mid2 is not mannosylated in apmt2 mutant and that this modification is important for signaling by Mid2.

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