The Rho1p Exchange Factor Rgf1p Signals Upstream from the Pmk1 Mitogen-activated Protein Kinase Pathway in Fission Yeast

Garcia, Patrícia Salomão; Tajadura, Virginia; Sánchez, Yolanda

doi:10.1091/mbc.e08-07-0673

Cited by 39 publications

(96 citation statements)

References 54 publications

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“…Indeed, we describe here that rho1-596 cells, with low Rho1 activity, showed increased basal Pmk1 phosphorylation as compared to the wild-type cells. This feature seems contradictory to previous results showing that overexpression of the constitutively active rho1G15V allele increased Pmk1 phosphorylation (García et al 2009) and that Rgf1, described as specific Rho1 GEF, also can trigger activation of the cascade (García et al 2009). However, all these observations can be explained considering that the Pmk1 pathway is activated both by hypertonic and hypotonic stresses, which are expected in gain-of-function or loss-of-function Rho1 alleles, respectively (Barba et al 2008).…”

Section: Discussioncontrasting

confidence: 96%

Negative Functional Interaction Between Cell Integrity MAPK Pathway and Rho1 GTPase in Fission Yeast

et al. 2013

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Rho1 GTPase is the main activator of cell wall glucan biosynthesis and regulates actin cytoskeleton in fungi, including Schizosaccharomyces pombe. We have obtained a fission yeast thermosensitive mutant strain carrying the rho1-596 allele, which displays reduced Rho1 GTPase activity. This strain has severe cell wall defects and a thermosensitive growth, which is partially suppressed by osmotic stabilization. In a global screening for rho1-596 multicopy suppresors the pmp1 + gene was identified. Pmp1 is a dual specificity phosphatase that negatively regulates the Pmk1 mitogen-activated protein kinase (MAPK) cell integrity pathway. Accordingly, elimination of Pmk1 MAPK partially rescued rho1-596 thermosensitivity, corroborating the unexpected antagonistic functional relationship of these genes. We found that rho1-596 cells displayed increased basal activation of the cell integrity MAPK pathway and therefore were hypersensitive to MgCl 2 and FK506. Moreover, the absence of calcineurin was lethal for rho1-596. We found a higher level of calcineurin activity in rho1-596 than in wild-type cells, and overexpression of constitutively active calcineurin partially rescued rho1-596 thermosensitivity. All together our results suggest that loss of Rho1 function causes an increase in the cell integrity MAPK activity, which is detrimental to the cells and turns calcineurin activity essential. RHO GTPases are conserved proteins that regulate the actin cytoskeleton organization in all eukaryots (Heasman and Ridley 2008). Additionally, in yeast and other fungi, these GTPases provide the coordinated regulation of cell wall biosynthesis and actin organization, which is required to maintain cell integrity and polarized growth (Levin 2005;Park and Bi 2007;Perez and Cansado 2010). The Schizosaccharomyces pombe genome contains six genes coding Rho GTPases. Among them, rho1 + is essential (Arellano et al. 1996). Rho1 function is mediated by its interaction with at least three different targets: the b(1,3)-glucan synthase (Arellano et al. 1996), which is responsible for the synthesis of the major cell wall component, and the kinases Pck1 and Pck2 Sayers et al. 2000). Through both kinases, Rho1 also regulates the cell wall synthesis. Rho2 also interacts with Pck2 and, therefore, both GTPases regulate the a-D-glucan synthesis through Pck2 (Katayama et al. 1999;Calonge et al. 2000). Lack of Rho1 is lethal, and this phenotype is not suppressed by osmotic stabilization (Arellano et al. 1997), suggesting that defective biosynthesis of the cell wall is not the unique cause of death. On the contrary, Rho2-less cells are viable, although they become slightly rounded and more sensitive to treatment with glucanases (Hirata et al. 1998). Rho2 and Pck2 participate in the activation of the cell integrity mitogen-activated protein kinase (MAPK) signaling pathway (Ma et al. 2006). This signaling cascade responds to different extracellular stress stimuli such as hyper-or hypotonic conditions, oxidative stress, cell wall damaging compounds, and g...

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Section: Discussioncontrasting

confidence: 96%

Negative Functional Interaction Between Cell Integrity MAPK Pathway and Rho1 GTPase in Fission Yeast

et al. 2013

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“…However, Spn1 appeared to localize normally when either Rgf1 or Rgf3 was overexpressed ( Figure 4F). In addition, the mild vegetative phenotypes of rgf1D and rgf2D mutants (Morrell-Falvey et al 2005;Mutoh et al 2005;García et al 2006García et al , 2009bour unpublished data) suggest that septin function is not perturbed by a lack of Rgf1 or Rgf2, and septins also appeared to localize normally in an rgf3-s44 mutant strain ( Figure 3B). …”

Section: Resultsmentioning

confidence: 90%

“…These synthases are regulated by the Rho GTPases Rho1 and Rho2 and the protein kinase C isoforms Pck1 and Pck2 (Arellano et al 1996(Arellano et al , 1997Nakano et al 1997;Hirata et al 1998;Calonge et al 2000;Sayers et al 2000;Ma et al 2006;Barba et al 2008;García et al 2009b). The Rho GTPases themselves appear to be regulated by both GTPase-activating proteins (GAPs) and guanine-nucleotide-exchange factors (GEFs) (Nakano et al 2001;Calonge et al 2003;Iwaki et al 2003;Tajadura et al 2004;Morrell-Falvey et al 2005;Mutoh et al 2005;García et al 2006García et al , 2009a.…”

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confidence: 99%

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

Wang

et al. 2010

Genetics

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A major question about cytokinesis concerns the role of the septin proteins, which localize to the division site in all animal and fungal cells but are essential for cytokinesis only in some cell types. For example, in Schizosaccharomyces pombe, four septins localize to the division site, but deletion of the four genes produces only a modest delay in cell separation. To ask if the S. pombe septins function redundantly in cytokinesis, we conducted a synthetic-lethal screen in a septin-deficient strain and identified seven mutations. One mutation affects Cdc4, a myosin light chain that is an essential component of the cytokinetic actomyosin ring. Five others cause frequent cell lysis during cell separation and map to two loci. These mutations and their dosage suppressors define a signaling pathway (including Rho1 and a novel arrestin) for repairing cell-wall damage. The seventh mutation affects the poorly understood RNAbinding protein Scw1 and severely delays cell separation when combined either with a septin mutation or with a mutation affecting the septin-interacting, anillin-like protein Mid2, suggesting that Scw1 functions in a pathway parallel to that of the septins. Taken together, our results suggest that the S. pombe septins participate redundantly in one or more pathways that cooperate with the actomyosin ring during cytokinesis and that a septin defect causes septum defects that can be repaired effectively only when the cellintegrity pathway is intact.

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“…Sporulation phenotype of wild type (YS260), bgs2D (MS228), rgf2D (PG9), and rgf2Dbgs2D (NG188) homothallic haploid strains highly conserved region of the DH domain and is where many mutations that decrease nucleotide exchange activity map (Liu et al 1998;Soisson et al 1998). We have previously shown that a similar mutation in Rgf1p (rgf1-PTTRD mutant) produces a loss-of-function phenotype (García et al 2006a(García et al , 2009). As expected, overexpression of the rgf2-PTTRD mutant in a pREP3X vector produced viable cells and no multiseptated phenotype was seen, even at very long times of derepresion in the absence of thiamine ( Figure 4A).…”

Section: Rgf2p Contains a Putative Dbl Homology Domain (Dh)mentioning

confidence: 99%

“…Thus, it is probable that Rgf3p stimulates Rho1p-mediated activation of a type of GS activity that is crucial for proper septum function (Tajaduraet al 2004). Rgf1p is not essential for viability, but it does play an important role in regulating the growth pattern of fission yeast cells and signals upstream from the Pmk1 mitogenactivated protein kinase pathway (García et al 2006a(García et al , 2009. Rgf1p localizes to the cell tips in interphase cells and to the division septum in mitotic cells, and it activates the b-GS complex containing the catalytic subunit Bgs4p (Morrell-Falvey et al 2005;Mutoh et al 2005;García et al 2006a).…”

mentioning

confidence: 99%

Fission Yeast Rgf2p Is a Rho1p Guanine Nucleotide Exchange Factor Required for Spore Wall Maturation and for the Maintenance of Cell Integrity in the Absence of Rgf1p

Garcia

García²,

Marcos

et al. 2009

Genetics

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Schizosaccharomyces pombe Rho1p is essential, directly activates b-1,3-glucan synthase, and participates in the regulation of morphogenesis. In S. pombe, Rho1p is activated by at least three guanine nucleotide exchange factors (GEFs): Rgf1p, Rgf2p, and Rgf3p. In this study we show that Rgf2p is a Rho1p GEF required for sporulation. The rgf2 1 deletion did not affect forespore membrane formation and the nuclei were encapsulated properly. However, the mutant ascospores appeared dark and immature. The rgf2D zygotes were not able to release the ascospores spontaneously, and the germination efficiency was greatly reduced compared to wild-type (wt) spores. This phenotype resembles that of the mutants in bgs2 1 , which encodes a sporulation-specific glucan synthase subunit. In fact, glucan synthase activity was diminished in sporulating rgf2D diploids. Rgf2p also plays a role in b-glucan biosynthesis during vegetative growth. Overexpression of rgf2 1 specifically increased GTP-bound Rho1p, caused changes in cell morphology, and elicited an increase in b-1,3-glucan synthase activity. Moreover, the simultaneous disruption of rgf1 1 and rgf2 1 was lethal and both Rgf1p and Rgf2p were able to partially substitute for each other. Our results suggest that Rgf1p and Rgf2p are alternative GEFs with an essential overlapping function in Rho1p activation during vegetative growth.

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The Rho1p Exchange Factor Rgf1p Signals Upstream from the Pmk1 Mitogen-activated Protein Kinase Pathway in Fission Yeast

Cited by 39 publications

References 54 publications

Negative Functional Interaction Between Cell Integrity MAPK Pathway and Rho1 GTPase in Fission Yeast

Negative Functional Interaction Between Cell Integrity MAPK Pathway and Rho1 GTPase in Fission Yeast

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

Fission Yeast Rgf2p Is a Rho1p Guanine Nucleotide Exchange Factor Required for Spore Wall Maturation and for the Maintenance of Cell Integrity in the Absence of Rgf1p

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