The guanine-nucleotide-exchange factor Cdc24p is targeted to the nucleus and polarized growth sites

Abstract

Generation of cellular asymmetry or cell polarity plays a critical role in cell-cycle-regulated morphogenetic processes involving the actin cytoskeleton. The GTPase Cdc42 regulates actin rearrangements and signal transduction pathways in all eukaryotic cells [1], and the temporal and spatial regulation of Cdc42p depends on the activity and targeting of its guanine-nucleotide exchange factor (GEF). Cdc24p, the Saccharomyces cerevisiae GEF for Cdc42p, is found in a particulate fraction and localizes to the plasma membrane [2] [3] at sites of polarized growth [4]. We show that Cdc24p labeled with green fluorescent protein (GFP-Cdc24p) was targeted to pre-bud sites, the tips and sides of enlarging buds, and mating projections in pheromone-treated cells. Unexpectedly, GFP-Cdc24p also localized to the nucleus and GFP-Cdc24p levels diminished before nuclear division followed by its reappearance in divided nuclei and mother-bud necks during cytokinesis. The Cdc24p amino-terminal 283 amino acids were necessary and sufficient for nuclear localization, which depended on the cyclin-dependent-kinase inhibitor Far1p. The Cdc24p carboxy-terminal 289 amino acids were necessary and sufficient for targeting to the pre-bud site, bud, mother-bud neck, and mating projection. Targeting was independent of the Cdc24p-binding proteins Far1p, the GTPase Rsr1p/Bud1p, the scaffold protein Bem1p, and the G(beta) subunit Ste4p. These data are consistent with a temporal and spatial regulation of Cdc24p-dependent activation of Cdc42p during the cell cycle.

Activated Ezrin Promotes Cell Migration through Recruitment of the GEF Dbl to Lipid Rafts and Preferential Downstream Activation of Cdc42

“…This indicates that even the VAV2/Tiam1-promoted increase in Rac1 activity is not sufficient to promote cell spreading highlighting the significance of proper subcellular localization (Arthur et al, 2004). In Saccharomyces cerevisiae, targeting of the Cdc42p-specific GEF Cdc24p to the incipient bud site is essential for the recruitment and activation of Cdc42p, and deletion of the Dbl-homology domain responsible for targeting Cdc24p to the budding site is lethal and unable to complement the growth defects of Cdc24⌬ cells (Ziman and Johnson, 1994;Toenjes et al, 1999;Shimada et al, 2004). This indicates an evolutionarily conserved mechanism for proper localized GTPase activation.…”

Novel Mechanism of the Co-regulation of Nuclear Transport of SmgGDS and Rac1

“…9A). However, the nuclear localization of several GEFs for Rac1 (33)(34)(35) and for other Rho family members (36,37) suggests the interesting possibility that Rac1-GDP converts to Rac1-GTP when the Rac1⅐p120ctn complex arrives at the nuclear pore, where the Rac1⅐p120ctn complex might have access to nuclear GEFs. This possibility is consistent with p120ctn associating with Vav (16), which is a Rac1 GEF that is present in the nucleus (33,34).…”

Guanine Nucleotide Exchange Factor, Tiam1, Directly Binds to c-Myc and Interferes with c-Myc-mediated Apoptosis in Rat-1 Fibroblasts

“…A broad body of work argues convincingly that c-Myc is a transcription factor, which activates and represses many target genes (39) The question may be raised whether Tiam1 can directly associate with c-Myc. Recently it was reported that Cdc24, a GEF for Cdc42 that is one of the Rho family GTPases (40,41), was sequestered in the cell nucleus by the adapter protein Far1. It was then relocated to the cytoplasm by degradation of Far1 by the G 1 cyclin-dependent kinase Cdc28-Cln at the actin cytoskeletal change, and by the importin ␤-family member Msn5, which is required for nuclear export (40,41).…”

“…Recently it was reported that Cdc24, a GEF for Cdc42 that is one of the Rho family GTPases (40,41), was sequestered in the cell nucleus by the adapter protein Far1. It was then relocated to the cytoplasm by degradation of Far1 by the G 1 cyclin-dependent kinase Cdc28-Cln at the actin cytoskeletal change, and by the importin ␤-family member Msn5, which is required for nuclear export (40,41). These reports demonstrated an important process; a GEF for the Rho-family GTPases could be sequestrated in the nucleus and relocated in the cytoplasm by other proteins (41).…”