Ras1 acts through duplicated Cdc42 and Rac proteins to regulate morphogenesis and pathogenesis in the human fungal pathogen Cryptococcus neoformans

• Published in: PLoS genetics Vol. 9; no. 8; p. e1003687
• Main Authors: Ballou, Elizabeth Ripley, Kozubowski, Lukasz, Nichols, Connie B, Alspaugh, J Andrew
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01-08-2013; Public Library of Science (PLoS)
• Subjects: Biology; cdc42 GTP-Binding Protein - genetics; cdc42 GTP-Binding Protein - metabolism; Cell cycle; Cell growth; Cryptococcus; Cryptococcus neoformans - genetics; Cryptococcus neoformans - pathogenicity; Cytokinesis - genetics; Fungal Proteins - genetics; Fungal Proteins - metabolism; Fungi; Gene Expression Regulation, Fungal; Genetic aspects; Humans; Kinases; Medicine; Microbial genetics; Morphogenesis; Morphogenesis - genetics; Mutation; Physiological aspects; Physiology, Pathological; rac GTP-Binding Proteins - genetics; rac GTP-Binding Proteins - metabolism; Signal Transduction; Yeast; United States
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1003687

Proliferation and morphogenesis in eukaryotic cells depend on the concerted activity of Rho-type GTPases, including Ras, Cdc42, and Rac. The sexually dimorphic fungus Cryptococcus neoformans, which encodes paralogous, non-essential copies of all three, provides a unique model in which to examine the interactions of these conserved proteins. Previously, we demonstrated that RAS1 mediates C. neoformans virulence by acting as a central regulator of both thermotolerance and mating. We report here that ras1Δ mutants accumulate defects in polarized growth, cytokinesis, and cell cycle progression. We demonstrate that the ras1Δ defects in thermotolerance and mating can be largely explained by the compromised activity of four downstream Rho-GTPases: the Cdc42 paralogs, Cdc42 and Cdc420; and the Rac paralogs, Rac1 and Rac2. Further, we demonstrate that the separate GTPase classes play distinct Ras-dependent roles in C. neoformans morphogenesis and pathogenesis. Cdc42 paralogs primarily control septin localization and cytokinesis, while Rac paralogs play a primary role in polarized cell growth. Together, these duplicate, related signaling proteins provide a robust system to allow microbial proliferation in the presence of host-derived cell stresses.