The Rho GDI Rdi1 regulates Rho GTPases by distinct mechanisms

Institute of Biochemistry, Christian Albrecht University, 24098 Kiel, Germany.
Molecular biology of the cell (Impact Factor: 4.47). 08/2008; 19(7):2885-96. DOI: 10.1091/mbc.E07-11-1152
Source: PubMed


The small guanosine triphosphate (GTP)-binding proteins of the Rho family are implicated in various cell functions, including establishment and maintenance of cell polarity. Activity of Rho guanosine triphosphatases (GTPases) is not only regulated by guanine nucleotide exchange factors and GTPase-activating proteins but also by guanine nucleotide dissociation inhibitors (GDIs). These proteins have the ability to extract Rho proteins from membranes and keep them in an inactive cytosolic complex. Here, we show that Rdi1, the sole Rho GDI of the yeast Saccharomyces cerevisiae, contributes to pseudohyphal growth and mitotic exit. Rdi1 interacts only with Cdc42, Rho1, and Rho4, and it regulates these Rho GTPases by distinct mechanisms. Binding between Rdi1 and Cdc42 as well as Rho1 is modulated by the Cdc42 effector and p21-activated kinase Cla4. After membrane extraction mediated by Rdi1, Rho4 is degraded by a novel mechanism, which includes the glycogen synthase kinase 3beta homologue Ygk3, vacuolar proteases, and the proteasome. Together, these results indicate that Rdi1 uses distinct modes of regulation for different Rho GTPases.

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Available from: Christopher Tiedje
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    • "If not through the Bem1 feedback loop, how then does Cdc42 polarize without actin? In addition to the membrane-bound pool, which is targeted by actin, Cdc42 exists in the cytosol in a soluble pool as the Rdi1-bound complex (Koch et al., 1997; Tiedje et al., 2008; Slaughter et al., 2009). Consistent with a new study published recently (Freisinger et al., 2013), rdi1 cells fail to polarize Cdc42 in the presence of LatA after release from pheromone G1 arrest (Fig. 6, A and B), suggesting that targeting from the Rdi1-bound cytosolic pool is not only required for maintaining but also for establishing Cdc42 protein polarization when actin is disrupted. "
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    ABSTRACT: The ability to break symmetry and polarize through self-organization is a fundamental feature of cellular systems. A prevailing theory in yeast posits that symmetry breaking occurs via a positive feedback loop, wherein the adaptor protein Bem1 promotes local activation and accumulation of Cdc42 by directly tethering Cdc42(GTP) with its guanine nucleotide exchange factor (GEF) Cdc24. In this paper, we find that neither Bem1 nor the ability of Bem1 to bind Cdc42(GTP) is required for cell polarization. Instead, Bem1 functions primarily by boosting GEF activity, a role critical for polarization without actin filaments. In the absence of actin-based transport, polarization of Cdc42 is accomplished through Rdi1, the Cdc42 guanine nucleotide dissociation inhibitor. A mathematical model is constructed describing cell polarization as a product of distinct pathways controlling Cdc42 activation and protein localization. The model predicts a nonmonotonic dependence of cell polarization on the concentration of Rdi1 relative to that of Cdc42.
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    • "Rho4 is the only GTPase that binds to the GBD of Bnr1 (Imamura et al. 1997), but this binding is not required for Bnr1 activation in vivo (Dong et al. 2003). In addition, Bnr1 localizes to the mother-bud neck in a septin-dependent manner from bud emergence to the onset of cytokinesis (Pruyne et al. 2004); whereas Rho4 localizes to the sites of polarized growth (Tiedje et al. 2008). Thus, Rho4 is unlikely to activate Bnr1 directly. "
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    ABSTRACT: Asymmetric cell division, which includes cell polarization and cytokinesis, is essential for generating cell diversity during development. The budding yeast Saccharomyces cerevisiae reproduces by asymmetric cell division, and has thus served as an attractive model for unraveling the general principles of eukaryotic cell polarization and cytokinesis. Polarity development requires G-protein signaling, cytoskeletal polarization, and exocytosis, whereas cytokinesis requires concerted actions of a contractile actomyosin ring and targeted membrane deposition. In this chapter, we discuss the mechanics and spatial control of polarity development and cytokinesis, emphasizing the key concepts, mechanisms, and emerging questions in the field.
    Full-text · Article · Jun 2012 · Genetics
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    • "As rdi1D mutants are viable (Masuda et al. 1994), and still manage to concentrate Cdc42p at the polarization site (Slaughter et al. 2009; Boulter et al. 2010), there must also be a GDI-independent route for concentrating Cdc42p. Some studies reported the presence of Cdc42p in cytoplasmic fractions even in rdi1D mutant cells (Koch et al. 1997; Tiedje et al. 2008), suggesting that there are other mechanisms that can extract prenylated Cdc42p from membranes. If such (currently undescribed) mechanisms were selective for GDP-Cdc42p, then (like the GDI) they too would promote Cdc42p concentration at the polarization site. "
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    ABSTRACT: Studies of the processes leading to the construction of a bud and its separation from the mother cell in Saccharomyces cerevisiae have provided foundational paradigms for the mechanisms of polarity establishment, cytoskeletal organization, and cytokinesis. Here we review our current understanding of how these morphogenetic events occur and how they are controlled by the cell-cycle-regulatory cyclin-CDK system. In addition, defects in morphogenesis provide signals that feed back on the cyclin-CDK system, and we review what is known regarding regulation of cell-cycle progression in response to such defects, primarily acting through the kinase Swe1p. The bidirectional communication between morphogenesis and the cell cycle is crucial for successful proliferation, and its study has illuminated many elegant and often unexpected regulatory mechanisms. Despite considerable progress, however, many of the most puzzling mysteries in this field remain to be resolved.
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