Jekyll and Hyde in the Microbial World

2006

Eukaryot Cell

Self Cite

When confronted with a marked increase in external osmolarity, budding yeast (Saccharomyces cerevisiae) cells utilize a conserved mitogen-activated protein kinase (MAPK) signaling cascade (the high-osmolarity glycerol or HOG pathway) to elicit cellular responses necessary to permit continued growth. One input that stimulates the HOG pathway requires the integral membrane protein and putative osmosensor Sho1, which recruits and enables activation of the MAPK kinase kinase Ste11. In mutants that lack the downstream MAPK kinase (pbs2⌬) or the MAPK (hog1⌬) of the HOG pathway, Ste11 activated by hyperosmotic stress is able to inappropriately stimulate the pheromone response pathway. This loss of signaling specificity is known as cross talk. To determine whether it is the Hog1 polypeptide per se or its kinase activity that is necessary to prevent cross talk, we constructed a fully functional analog-sensitive allele of HOG1 to permit acute inhibition of this enzyme without other detectable perturbations of the cell. We found that the catalytic activity of Hog1 is required continuously to prevent cross talk between the HOG pathway and both the pheromone response and invasive growth pathways. Moreover, contrary to previous reports, we found that the kinase activity of Hog1 is necessary for its stress-induced nuclear import. Finally, our results demonstrate a role for active Hog1 in maintaining signaling specificity under conditions of persistently high external osmolarity.

mentioning

confidence: 99%

mentioning

confidence: 99%

Analysis of Mitogen-Activated Protein Kinase Signaling Specificity in Response to Hyperosmotic Stress: Use of an Analog-Sensitive HOG1 Allele

Westfall

2006

Eukaryot Cell

Self Cite

“…Budding yeast (Saccharomyces cerevisiae) uses MAPK modules to adapt rapidly to environmental changes, such as nutrient limitation (filamentous growth signaling) (84), hyperosmotic stress (high-osmolarity glycerol [HOG] signaling) (91), cell wall damage (Pkc1-dependent signaling) (20), presence of mating-inducing peptides (pheromone signaling) (90), and conditions that evoke meiosis in diploid cells (sporulation) (6,89). Nutrient deprivation triggers a developmental transition from yeast-form (round) cells to cells capable of invasive or pseudohyphal growth (23,63).…”

mentioning

confidence: 99%

The RA Domain of Ste50 Adaptor Protein Is Required for Delivery of Ste11 to the Plasma Membrane in the Filamentous Growth Signaling Pathway of the Yeast Saccharomyces cerevisiae

Truckses

Bloomekatz

Molecular and Cellular Biology

2006

Self Cite

In Saccharomyces cerevisiae, pheromone response requires Ste5 scaffold protein, which ensures efficient G-protein-dependent recruitment of mitogen-activated protein kinase (MAPK) cascade components Ste11 (MAPK kinase kinase), Ste7 (MAPK kinase), and Fus3 (MAPK) to the plasma membrane for activation by Ste20 protein kinase. Ste20, which phosphorylates Ste11 to initiate signaling, is activated by binding to Cdc42 GTPase (membrane anchored via its C-terminal geranylgeranylation). Less clear is how activated and membrane-localized Ste20 contacts Ste11 to trigger invasive growth signaling, which also requires Ste7 and the MAPK Kss1, but not Ste5. Ste50 protein associates constitutively via an N-terminal sterile-alpha motif domain with Ste11, and this interaction is required for optimal invasive growth and hyperosmotic stress (highosmolarity glycerol [HOG]) signaling but has a lesser role in pheromone response. We show that a conserved C-terminal, so-called "Ras association" (RA) domain in Ste50 is also essential for invasive growth and HOG signaling in vivo. In vitro the Ste50 RA domain is not able to associate with Ras2, but it does associate with Cdc42 and binds to a different face than does Ste20. RA domain function can be replaced by the nine C-terminal, plasma membrane-targeting residues (KKSKKCAIL) of Cdc42, and membrane-targeted Ste50 also suppresses the signaling deficiency of cdc42 alleles specifically defective in invasive growth. Thus, Ste50 serves as an adaptor to tether Ste11 to the plasma membrane and can do so via association with Cdc42, thereby permitting the encounter of Ste11 with activated Ste20.

“…Pseudohyphal growth under nitrogen source limitation and invasive 1 growth under carbon source limitation involve many of the molecular factors and signaling pathways (for an overview of these pathway components, please refer to the schematic summary of the results of this study shown in Figure 7). In particular, pseudohyphal growth and invasive growth require two classical signaling modalities: (i) a mitogen-activated protein kinase (MAPK) cascade and (ii) 39, 59-cyclic adenosine monophosphate (cAMP) and cAMP-dependent protein kinase A (PKA) (Lengeler et al 2000;Pan et al 2000;Truckses et al 2004). The MAPK cascade that promotes FG consists of Ste20 (PAK/MAPKKKK), Ste11 (MAPKKK), Ste7 (MAPKK), and Kss1 (MAPK).…”

mentioning

confidence: 99%

“…External nutrient supply affects the division pattern, adhesivity, and morphology of cells and the colonies of the budding yeast Saccharomyces cerevisiae (Gancedo 2001;Gagiano et al 2002;Palecek et al 2002;Schneper et al 2004;Truckses et al 2004;Verstrepen and Klis 2006;Chen and Thorner 2007;Granek and Magwene 2010). During conditions of nutrient sufficiency, cells are ovoid, and haploid cells bud to form daughter cells at the cell pole corresponding to their own birth site (an ''axial'' budding pattern), whereas diploid cells bud alternately from their birth end and from the opposite cell pole (a ''bipolar'' budding pattern).…”

mentioning

confidence: 99%

Systematic Epistasis Analysis of the Contributions of Protein Kinase A- and Mitogen-Activated Protein Kinase-Dependent Signaling to Nutrient Limitation-Evoked Responses in the Yeast Saccharomyces cerevisiae

Chen¹,

2010

Genetics

Self Cite

Cellular responses to environmental stimuli require conserved signal transduction pathways. In budding yeast (Saccharomyces cerevisiae), nutrient limitation induces morphological changes that depend on the protein kinase A (PKA) pathway and the Kss1 mitogen-activated protein kinase (MAPK) pathway. It was unclear to what extent and at what level there is synergy between these two distinct signaling modalities. We took a systematic genetic approach to clarify the relationship between these inputs. We performed comprehensive epistasis analysis of mutants lacking different combinations of all relevant pathway components. We found that these two pathways contribute additively to nutrient limitationinduced haploid invasive growth. Moreover, full derepression of either pathway rendered it individually sufficient for invasive growth and thus, normally, both are required only because neither is maximally active. Furthermore, in haploids, the MAPK pathway contributes more strongly than the PKA pathway to cell elongation and adhesion, whereas nutrient limitation-induced unipolar budding is independent of both pathways. In contrast, in diploids, upon nutrient limitation the MAPK pathway regulates cell elongation, the PKA pathway regulates unipolar budding, and both regulate cell adhesion. Thus, although there are similarities between haploids and diploids, cell type-specific differences clearly alter the balance of the signaling inputs required to elicit the various nutrient limitation-evoked cellular behaviors.