Pob1 Participates in the Cdc42 Regulation of Fission Yeast Actin Cytoskeleton

Abstract

Rho GTPases regulate the actin cytoskeleton in all eukaryotes. Fission yeast Cdc42 is involved in actin cable assembly and formin For3 regulation. We isolated cdc42-879 as a thermosensitive strain with actin cable and For3 localization defects. In a multicopy suppressor screening, we identified pob1 ؉ as suppressor of cdc42-879 thermosensitivity. Pob1 overexpression also partially restores actin cables and localization of For3 in the mutant strain. Pob1 interacts with Cdc42 and this GTPase regulates Pob1 localization and/or stability. The C-terminal pleckstrin homology (PH) domain of Pob1 is required for Cdc42 binding. Pob1 also binds to For3 through its N-terminal sterile alpha motif (SAM) domain and contributes to the formin localization at the cell tips. The previously described pob1-664 mutant strain (Mol. Biol. Cell. 10, 2745-2757, 1999), which carries a mutation in the PH domain, as well as pob1 mutant strains in which Pob1 lacks the N-terminal region (pob1⌬N) or the SAM domain (pob1⌬SAM), have cytoskeletal defects similar to that of cdc42-879 cells. Expression of constitutively active For3DAD* partially restores actin organization in cdc42-879, pob1-664, pob1⌬N, and pob1⌬SAM. Therefore, we propose that Pob1 is required for For3 localization to the tips and facilitates Cdc42-mediated relief of For3 autoinhibition to stimulate actin cable formation.

Oscillatory AAA + ATPase Knk1 constitutes a novel morphogenetic pathway in fission yeast

“…S5 F-H), similar to oscillations seen in sla2Δ. CRIB-GFP dynamics could not be determined in this mutant, because levels were dramatically decreased (30). However, the detection of Knk1 oscillation despite a reduction of active Cdc42 in cell tips strongly suggests that Knk1 oscillations are not driven by Cdc42 dynamics.…”

Cooperation Between the Septins and the Actomyosin Ring and Role of a Cell-Integrity Pathway During Cell Division in Fission Yeast

“…Our attempts to clone the corresponding genes led to the isolation of numerous dosage suppressors (Table 4), in addition to the gene (rgf3) that actually contains the s44 mutation. Given what is known about the functions of Rho1, the Rho-GEFs, Pck2, and Pob1 in S. pombe (see Introduction; Toya et al 1999;Rincó n et al 2009) and about the well-studied cell-wall-integrity pathway in S. cerevisiae (Levin 2005), it seems clear that the seven genes identified as dosage suppressors all represent components of a similar pathway in S. pombe, as also described, in part, in several other recent studies (Madrid et al 2006(Madrid et al , 2007Barba et al 2008; and references cited therein). In this model, Wsc1 is a sensor of cell-wall damage that works through one or more of the Rho-GEFs Rgf1, Rgf2, and Rgf3 to activate Rho1.…”

Expression and Clinical Significance of REPS2 in Human Esophageal Squamous Cell Carcinoma

“…It is also found that downregulation of REPS2 is accompanied by upregulation of NF-kB activity during progression of prostate cancer from androgen-dependent to androgen-independent growth, and that NF-kB may promote cell proliferation through interacting with the EH domain of REPS2 (Penninkhof et al, 2004). In addition, REPS2 may function to keep RalBP1 cytosolic where it displays a GAP activity towards Rac1 and Cdc42 to signal cell survival so that overexpression of REPS2 may lead to a strong inhibition of Rac1 and Cdc42 signalling, which may consequently result in the attendant induction of apoptosis (Jullien-Flores et al, 1995;Joneson et al, 1999;Rincon et al, 2009). Above molecular mechanisms may provide the theoretical basis of REPS2 for participating in the the progression of ESCC, but that need further research to testify in future clinical practice.…”

“…We have already mentioned the overexpression of REPS2 may lead to a strong inhibition of Rac1 and Cdc42 signalling that is required for the actin cytoskeleton organization and cell morphogenesis. Rac1 and Cdc42, two members of the Rho family of small GTPases, are all involved in cell transformation, survival, proliferation, invasion and metastasis of human cancer cells (Rincon et al, 2009;Bashir et al, 2010;Feng et al, 2012). Overexpression of Rac1 and Cdc42 have been reported in several types of human cancer including esophageal cancer (Bashir et al, 2010;Feng et al, 2012).…”