Two CDC42 paralogues modulate Cryptococcus neoformans thermotolerance and morphogenesis under host physiological conditions

Department of Medicine, Duke University School of Medicine, Durham, NC 27710, USA.
Molecular Microbiology (Impact Factor: 4.42). 12/2009; 75(3):763-80. DOI: 10.1111/j.1365-2958.2009.07019.x
Source: PubMed


The precise regulation of morphogenesis is a key mechanism by which cells respond to a variety of stresses, including those encountered by microbial pathogens in the host. The polarity protein Cdc42 regulates cellular morphogenesis throughout eukaryotes, and we explore the role of Cdc42 proteins in the host survival of the human fungal pathogen Cryptococcus neoformans. Uniquely, C. neoformans has two functional Cdc42 paralogues, Cdc42 and Cdc420. Here we investigate the contribution of each paralogue to resistance to host stress. In contrast to non-pathogenic model organisms, C. neoformans Cdc42 proteins are not required for viability under non-stress conditions but are required for resistance to high temperature. The paralogues play differential roles in actin and septin organization and act downstream of C. neoformans Ras1 to regulate its morphogenesis sub-pathway, but not its effects on mating. Cdc42, and not Cdc420, is upregulated in response to temperature stress and is required for virulence in a murine model of cryptococcosis. The C. neoformans Cdc42 proteins likely perform complementary functions with other Rho-like GTPases to control cell polarity, septin organization and hyphal transitions that allow survival in the environment and in the host.

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Available from: Elizabeth R Ballou
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    • "Although pak1D mutants are most phenotypically similar to the rac1D and rac2D mutants, and ste20D mutants are most similar to cdc42D mutants, yeast two hybrid studies have demonstrated potential interactions between Pak1 and Cdc420, as well as between Rac1 and Ste20 (Vallim et al., 2005; Wang et al., 2002). Additionally, the hyphal defects of pak1Da  pak1Da bilateral crosses, including failed spore production and defects in clamp-cell fusion, are more typical of cdc42D mutant mating defects than those observed in racD mutants crosses (Ballou et al., 2010; Nichols et al., 2004). It is possible that there is some degree of co-activation of downstream effectors by the related Rac and Cdc42 proteins. "
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    ABSTRACT: A genome wide analysis of the human fungal pathogen Cryptococcus neoformans var. grubii has revealed a number of duplications of highly conserved genes involved in morphogenesis. Previously, we reported that duplicate Cdc42 paralogs provide C. neoformans with niche-specific responses to environmental stresses: Cdc42 is required for thermotolerance, while Cdc420 supports the formation of titan cells. The related Rho-GTPase Rac1 has been shown in C. neoformans var. neoformans to play a major role in filamentation and to share Cdc42/Cdc420 binding partners. Here we report the characterization of a second Rac paralog in C. neoformans, Rac2, and describe its overlapping function with the previously described CnRac, Rac1. Further, we demonstrate that the Rac paralogs play a primary role in polarized growth via the organization of reactive oxygen species and play only a minor role in the organization of actin. Finally, we provide preliminary evidence that pharmacological inhibitors of Rac activity and actin stability have synergistic activity.
    Full-text · Article · Jun 2013 · Fungal Genetics and Biology
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    • "Xue et al. (2008) speculated that hyperactive PKA signaling (via Crg2 or dominant active Gpa1) and inhibition of PKA signaling (via reduced cyclase activation in can2Δ mutants) impair the production of long spore chains. Spore chain production is also affected in mutants lacking Cdc42 homologues (Ballou et al., 2009); these defects may be associated with the inability to assemble septins at sites of polarized growth, given that cdc42Δ mutants exhibit defects in septin organization and septin mutants fail to sporulate properly (Ballou et al., 2009; Kozubowski & Heitman, 2010). "
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    ABSTRACT: The ability of fungi to transition between unicellular and multicellular growth has a profound impact on our health and the economy. Many important fungal pathogens of humans, animals, and plants are dimorphic, and the ability to switch between morphological states has been associated with their virulence. Cryptococcus neoformans is a human fungal pathogen that causes life-threatening meningoencephalitis in immunocompromised and, in some cases, immunocompetent hosts. Cryptococcus neoformans grows vegetatively as a budding yeast and switches to hyphal growth during the sexual cycle, which is important in the study of cryptococcal pathogenicity because spores resulting from sexual development are infectious propagules and can colonize the lungs of a host. In addition, sexual reproduction contributes to the genotypic variability of Cryptococcus species, which may lead to increased fitness and virulence. Despite significant advances in our understanding of the mechanisms behind the development of C. neoformans, our knowledge is still incomplete. Recent studies have led to the emergence of many intriguing questions and hypotheses. In this review, we describe and discuss the most interesting aspects of C. neoformans development and address their impact on pathogenicity.
    Preview · Article · Jun 2011 · FEMS microbiology reviews
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    • "marneffei; Boyce et al., 2001). In the basidiomycetes Ustilago maydis and Cryptococcus neoformans, Rac1 is required for the formation of polarized hyphae, while Cdc42 regulates septum formation (Vallim et al., 2005; Mahlert et al., 2006; Ballou et al., 2010). Do any patterns emerge from the characterization of Cdc42 and Rac1 homologues in filamentous fungi? "
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    ABSTRACT: Cdc42/Rho GTPases are universally important regulators of cellular morphogenesis. Whereas their functions are well characterized in budding yeast, they are only beginning to be understood in filamentous fungi. The recent systematic analysis of Cdc42, Rac1 and Rho function in Aspergillus niger provides the first global perspective on their respective roles in hyphal morphogenesis. Surprisingly, the partitioning of these roles between Cdc42 and Rac1 seems to vary even among related fungi. These observations highlight the variable use of a common signalling module in filamentous fungi.
    Preview · Article · Mar 2011 · Molecular Microbiology
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