Hog1 Stress-activated Protein Kinase Research Articles

Functional tug of war between kinases, phosphatases, and the Gcn5 acetyltransferase in chromatin and cell cycle checkpoint controls.

Covalent modifications of chromatin regulate genomic structure and accessibility in diverse biological processes such as transcriptional regulation, cell cycle progression, and DNA damage repair. Many histone modifications have been characterized, yet understanding the interactions between these and their combinatorial effects remains an active area of investigation, including dissecting functional interactions between enzymes mediating these modifications. In budding yeast, the histone acetyltransferase Gcn5 interacts with Rts1, a regulatory subunit of protein phosphatase 2A (PP2A). Implicated in the interaction is the potential for the dynamic phosphorylation of conserved residues on histone H2B and the Cse4 centromere-specific histone H3 variant. To probe these dynamics, we sought to identify kinases which contribute to the phosphorylated state. In a directed screen beginning with in silico analysis of the 127 members of yeast kinome, we have now identified 16 kinases with genetic interactions with GCN5 and specifically found distinct roles for the Hog1 stress-activated protein kinase. Deletion of HOG1 (hog1Δ) rescues gcn5Δ sensitivity to the microtubule poison nocodazole and the lethality of the gcn5Δ rts1Δ double mutant. The Hog1-Gcn5 interaction requires the conserved H2B-T91 residue, which is phosphorylated in vertebrate species. Furthermore, deletion of HOG1 decreases aneuploidy and apoptotic populations in gcn5Δ cells. Together, these results introduce Hog1 as a kinase that functionally opposes Gcn5 and Rts1 in the context of the spindle assembly checkpoint and suggest further kinases may also influence GCN5's functions.

The regulatory mechanism of the yeast osmoresponse under different glucose concentrations

Cells constantly respond to environmental changes by modulating gene expression programs. These responses may demand substantial costs and, thus, affect cell growth. Understanding the regulation of these processes represents a key question in biology and biotechnology. Here, we studied the responses to osmotic stress in glucose-limited environments. By analyzing seventeen osmotic stress-induced genes and stress-activated protein kinase Hog1, we found that cells exhibited stronger osmotic gene expression response and larger integral of Hog1 nuclear localization during adaptation to osmotic stress under glucose-limited conditions than under glucose-rich conditions. We proposed and verified that in glucose-limited environment, glycolysis intermediates (representing "reserve flux") were limited, which required cells to express more glycerol-production enzymes for stress adaptation. Consequently, the regulatory mechanism of osmoresponse was derived in the presence and absence of such reserve flux. Further experiments suggested that this reserve flux-dependent stress-defense strategy may be a general principle under nutrient-limited environments.

The HOG pathway and the regulation of osmoadaptive responses in yeast.

Cells coordinate intracellular activities in response to changes in the extracellular environment to maximize their probability of survival and proliferation. Eukaryotic cells need to adapt to constant changes in the osmolarity of their environment. In yeast, the high-osmolarity glycerol (HOG) pathway is responsible for the response to high osmolarity. Activation of the Hog1 stress-activated protein kinase (SAPK) induces a complex program required for cellular adaptation that includes temporary arrest of cell cycle progression, adjustment of transcription and translation patterns, and the regulation of metabolism, including the synthesis and retention of the compatible osmolyte glycerol. Hog1 is a member of the family of p38 SAPKs, which are present across eukaryotes. Many of the properties of the HOG pathway and downstream-regulated proteins are conserved from yeast to mammals. This review addresses the global view of this signaling pathway in yeast, as well as the contribution of Dr Hohmann's group to its understanding.

Anticipatory Stress Responses and Immune Evasion in Fungal Pathogens.

In certain niches, microbes encounter environmental challenges that are temporally linked. In such cases, microbial fitness is enhanced by the evolution of anticipatory responses where the initial challenge simultaneously activates pre-emptive protection against the second impending challenge. The accumulation of anticipatory responses in domesticated yeasts, which have been termed 'adaptive prediction', has led to the emergence of 'core stress responses' that provide stress cross-protection. Protective anticipatory responses also seem to be common in fungal pathogens of humans. These responses reflect the selective pressures that these fungi have faced relatively recently in their evolutionary history. Consequently, some pathogens have evolved 'core environmental responses' which exploit host signals to trigger immune evasion strategies that protect them against imminent immune attack.

Hog1 activation delays mitotic exit via phosphorylation of Net1

Adaptation to environmental changes is crucial for cell fitness. In Saccharomyces cerevisiae, variations in external osmolarity trigger the activation of the stress-activated protein kinase Hog1 (high-osmolarity glycerol 1), which regulates gene expression, metabolism, and cell-cycle progression. The activation of this kinase leads to the regulation of G1, S, and G2 phases of the cell cycle to prevent genome instability and promote cell survival. Here we show that Hog1 delays mitotic exit when cells are stressed during metaphase. Hog1 phosphorylates the nucleolar protein Net1, altering its affinity for the phosphatase Cdc14, whose activity is essential for mitotic exit and completion of the cell cycle. The untimely release of Cdc14 from the nucleolus upon activation of Hog1 is linked to a defect in ribosomal DNA (rDNA) and telomere segregation, and it ultimately delays cell division. A mutant of Net1 that cannot be phosphorylated by Hog1 displays reduced viability upon osmostress. Thus, Hog1 contributes to maximizing cell survival upon stress by regulating mitotic exit.

Thiol-based direct threat sensing by the stress-activated protein kinase Hog1.

The yeast stress-activated protein kinase Hog1 is best known for its role in mediating the response to osmotic stress, but it is also activated by various mechanistically distinct environmental stressors, including heat shock, endoplasmic reticulum stress, and arsenic. In the osmotic stress response, the signal is sensed upstream and relayed to Hog1 through a kinase cascade. Here, we identified a mode of Hog1 function whereby Hog1 senses arsenic through a direct physical interaction that requires three conserved cysteine residues located adjacent to the catalytic loop. These residues were essential for Hog1-mediated protection against arsenic, were dispensable for the response to osmotic stress, and promoted the nuclear localization of Hog1 upon exposure of cells to arsenic. Hog1 promoted arsenic detoxification by stimulating phosphorylation of the transcription factor Yap8, promoting Yap8 nuclear localization, and stimulating the transcription of the only known Yap8 targets, ARR2 and ARR3, both of which encode proteins that promote arsenic efflux. The related human kinases ERK1 and ERK2 also bound to arsenic in vitro, suggesting that this may be a conserved feature of some members of the mitogen-activated protein kinase (MAPK) family. These data provide a mechanistic basis for understanding how stress-activated kinases can sense distinct threats and perform highly specific adaptive responses.

Hog1 signalling in the emerging multidrug resistant fungal pathogen Candida auris

The emerging fungal pathogen Candida auris is responsible for recent global outbreaks caused by genetically divergent clades that, alarmingly, display multi-drug resistance to currently available antifungals. Although not much is known about the pathobiology of this emerging pathogen, we recently found that the Hog1 stress-activated protein kinase (SAPK) in C. auris promotes stress resistance and virulence. SAPKs are evolutionary conserved pathways employed by fungi to promote survival in hostile environments. The aim of this project is to characterise the upstream signalling proteins that relay stress signals to C. auris Hog1. In all eukaryotes, SAPK pathways are comprised of three tiers of kinases with upstream MAPKKK and MAPKKs relaying signals to the terminal SAPK. However, unique to fungi and plants, is an upstream two-component related signalling cascade that transmits signals to the SAPK module, comprising of a histidine kinase, a phosphorelay protein and a response regulator. In C. auris, the proteins that regulate Hog1 activation are unknown. However, bioinformatics analyses of the C. auris genome has allowed for the identification of putative homologues of key Hog1 regulatory proteins including the Pbs2 MAPKK, the Ssk2 MAPKKK, the Ssk1 response regulator, the Ypd1 phosphorelay protein and the Sln1 and Nik1 histidine kinases. Mutational analyses is currently underway to dissect the role of these proteins in Hog1 regulation. Understanding how the Hog1 SAPK is regulated in C. auris may facilitate the identification of fungal specific anti-fungal targets that can be exploited to tackle the threat of this emerging drug resistant pathogen.

Nut1/Hos1 and Sas2/Rpd3 control the H3 acetylation of two different sets of osmotic stress-induced genes

ABSTRACTEpigenetic information is able to interact with the cellular environment and could be especially useful for reprograming gene expression in response to a physiological perturbation. In fact the genes induced or repressed by osmotic stress undergo significant changes in terms of the levels of various histone modifications, especially in the acetylation levels of histone H3. Exposing yeast to high osmolarity results in the activation of stress-activated protein kinase Hog1, which plays a central role in gene expression control. We evaluated the connection between the presence of Hog1 and changes in histone H3 acetylation in stress-regulated genes. We found a parallel increase in the acetylation of lysines 9 and 14 of H3 in induced genes during stress, which was largely dependent on Hog1 at the genome-wide level. Conversely, we observed that acetylation decreased in repressed genes and was not dependent on Hog1. However, lack of Hog1 sometimes produced different, and even opposite, effects on the induction and acetylation of H3 of each gene. We also found that the acetylation state of lysine 9 of H3 was altered in the strains deficient in Nut1 HAT and Hos1 HDAC in the genes up-regulated during osmotic stress in an Msn2/Msn4-independent manner, while lysine 9 acetylation of H3 varied in the strains deficient in Sas2 HAT and Rpd3 HDAC for the Msn2/Msn4-dependent induced genes. The results presented here show new, unexpected participants in gene regulation processes in response to environmental perturbations.

Stress-Activated Protein Kinases in Human Fungal Pathogens

The ability of fungal pathogens to survive hostile environments within the host depends on rapid and robust stress responses. Stress-activated protein kinase (SAPK) pathways are conserved MAPK signaling modules that promote stress adaptation in all eukaryotic cells, including pathogenic fungi. Activation of the SAPK occurs via the dual phosphorylation of conserved threonine and tyrosine residues within a TGY motif located in the catalytic domain. This induces the activation and nuclear accumulation of the kinase and the phosphorylation of diverse substrates, thus eliciting appropriate cellular responses. The Hog1 SAPK has been extensively characterized in the model yeast Saccharomyces cerevisiae. Here, we use this a platform from which to compare SAPK signaling mechanisms in three major fungal pathogens of humans, Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. Despite the conservation of SAPK pathways within these pathogenic fungi, evidence is emerging that their role and regulation has significantly diverged. However, consistent with stress adaptation being a common virulence trait, SAPK pathways are important pathogenicity determinants in all these major human pathogens. Thus, the development of drugs which target fungal SAPKs has the exciting potential to generate broad-acting antifungal treatments.

Methylated metabolite of arsenite blocks glycerol production in yeast by inhibition of glycerol-3-phosphate dehydrogenase.

The yeast high-osmolarity glycerol (HOG) stress-activated protein kinase Hog1 is activated in response to hyperosmotic stress, inducing the production and retention of glycerol to restore osmotic balance. Hog1 promotes retention of glycerol through closure of the plasma-membrane glycerol channel Fps1. Treatment of yeast with the toxic trivalent metalloid arsenite (As(III)) also activates Hog1 as part of a protective response in which Hog1 closes Fps1, the main entry port for As(III). In this study, we investigated how cells treated with As(III) avoid creating a new stress caused by the accumulation of glycerol in the absence of hyperosmotic stress conditions. We found that As(III) treatment did not induce glycerol accumulation and, in fact, blocked the accumulation of glycerol induced by constitutive Hog1 activity. We demonstrated that As(III) blocks glycerol production indirectly after its metabolic activation to methylarsenite (MAs(III)), which is a potent inhibitor of glycerol-3-phosphate dehydrogenase. Finally, we used a biotinylated arsenic probe to establish that Cys306 of yeast Gpd1, a highly conserved residue within the active site, is the key target of MAs(III). Conservative mutations at this residue greatly diminished Gpd1 activity. This study offers insight into mechanisms by which SAPK outputs are tailored to specific stressors.

Hog1 Regulates Stress Tolerance and Virulence in the Emerging Fungal Pathogen Candida auris.

Candida auris has recently emerged as an important, multidrug-resistant fungal pathogen of humans. Comparative studies indicate that despite high levels of genetic divergence, C. auris is as virulent as the most pathogenic member of the genus, Candida albicans However, key virulence attributes of C. albicans, such as morphogenetic switching, are not utilized by C. auris, indicating that this emerging pathogen employs alternative strategies to infect and colonize the host. An important trait required for the pathogenicity of many fungal pathogens is the ability to adapt to host-imposed stresses encountered during infection. Here, we investigated the relative resistance of C. auris and other pathogenic Candida species to physiologically relevant stresses and explored the role of the evolutionarily conserved Hog1 stress-activated protein kinase (SAPK) in promoting stress resistance and virulence. In comparison to C. albicans, C. auris is relatively resistant to hydrogen peroxide, cationic stress, and cell-wall-damaging agents. However, in contrast to other Candida species examined, C. auris was unable to grow in an anaerobic environment and was acutely sensitive to organic oxidative-stress-inducing agents. An analysis of C. aurishog1Δ cells revealed multiple roles for this SAPK in stress resistance, cell morphology, aggregation, and virulence. These data demonstrate that C. auris has a unique stress resistance profile compared to those of other pathogenic Candida species and that the Hog1 SAPK has pleiotropic roles that promote the virulence of this emerging pathogen.IMPORTANCE The rapid global emergence and resistance of Candidaauris to current antifungal drugs highlight the importance of understanding the virulence traits exploited by this human fungal pathogen to cause disease. Here, we characterize the stress resistance profile of C. auris and the role of the Hog1 stress-activated protein kinase (SAPK) in stress resistance and virulence. Our findings that C. auris is acutely sensitive to certain stresses may facilitate control measures to prevent persistent colonization in hospital settings. Furthermore, our observation that the Hog1 SAPK promotes C. auris virulence akin to that reported for many other pathogenic fungi indicates that antifungals targeting Hog1 signaling would be broad acting and effective, even on emerging drug-resistant pathogens.

Regulation of transcription elongation in response to osmostress.

Cells trigger massive changes in gene expression upon environmental fluctuations. The Hog1 stress-activated protein kinase (SAPK) is an important regulator of the transcriptional activation program that maximizes cell fitness when yeast cells are exposed to osmostress. Besides being associated with transcription factors bound at target promoters to stimulate transcriptional initiation, activated Hog1 behaves as a transcriptional elongation factor that is selective for stress-responsive genes. Here, we provide insights into how this signaling kinase functions in transcription elongation. Hog1 phosphorylates the Spt4 elongation factor at Thr42 and Ser43 and such phosphorylations are essential for the overall transcriptional response upon osmostress. The phosphorylation of Spt4 by Hog1 regulates RNA polymerase II processivity at stress-responsive genes, which is critical for cell survival under high osmostress conditions. Thus, the direct regulation of Spt4 upon environmental insults serves to stimulate RNA Pol II elongation efficiency.

Stress-induced nuclear accumulation is dispensable for Hog1-dependent gene expression and virulence in a fungal pathogen

Stress-activated protein kinase (SAPK) pathways are evolutionarily conserved eukaryotic signalling modules that are essential for the virulence of human pathogenic fungi. The Hog1 SAPK in Candida albicans is robustly phosphorylated in response to a number of host-imposed stresses, and is essential for virulence. The current dogma is that stress-induced phosphorylation activates the SAPK, and promotes its nuclear accumulation that is necessary for the expression of SAPK-dependent stress-protective genes. Here we challenge this dogma. C. albicans strains were constructed in which Hog1 was either tethered to the plasma membrane or constitutively nuclear. Strikingly, tethering Hog1 to the plasma membrane did not abrogate stress resistance or stress-induced gene expression. Furthermore, preventing the nuclear accumulation of Hog1 had no impact on C. albicans virulence in two distinct models of systemic infection. However, tethering Hog1 to the plasma membrane did impact on signal fidelity, and on the magnitude and kinetics of the stress-induced phosphorylation of this SAPK. Taken together, these findings challenge the dogma that nuclear accumulation of SAPKs is a pre-requisite for SAPK-dependent gene expression, and reveal that stress-induced nuclear accumulation of Hog1 is dispensable for the virulence of a major human fungal pathogen.

Blocking two-component signalling enhances Candida albicans virulence and reveals adaptive mechanisms that counteract sustained SAPK activation.

The Ypd1 phosphorelay protein is a central constituent of fungal two-component signal transduction pathways. Inhibition of Ypd1 in Saccharomyces cerevisiae and Cryptococcus neoformans is lethal due to the sustained activation of the ‘p38-related’ Hog1 stress-activated protein kinase (SAPK). As two-component signalling proteins are not found in animals, Ypd1 is considered to be a prime antifungal target. However, a major fungal pathogen of humans, Candida albicans, can survive the concomitant sustained activation of Hog1 that occurs in cells lacking YPD1. Here we show that the sustained activation of Hog1 upon Ypd1 loss is mediated through the Ssk1 response regulator. Moreover, we present evidence that C. albicans survives SAPK activation in the short-term, following Ypd1 loss, by triggering the induction of protein tyrosine phosphatase-encoding genes which prevent the accumulation of lethal levels of phosphorylated Hog1. In addition, our studies reveal an unpredicted, reversible, mechanism that acts to substantially reduce the levels of phosphorylated Hog1 in ypd1Δ cells following long-term sustained SAPK activation. Indeed, over time, ypd1Δ cells become phenotypically indistinguishable from wild-type cells. Importantly, we also find that drug-induced down-regulation of YPD1 expression actually enhances the virulence of C. albicans in two distinct animal infection models. Investigating the underlying causes of this increased virulence, revealed that drug-mediated repression of YPD1 expression promotes hyphal growth both within murine kidneys, and following phagocytosis, thus increasing the efficacy by which C. albicans kills macrophages. Taken together, these findings challenge the targeting of Ypd1 proteins as a general antifungal strategy and reveal novel cellular adaptation mechanisms to sustained SAPK activation.

New Genes Involved in Osmotic Stress Tolerance in Saccharomyces cerevisiae.

Adaptation to changes in osmolarity is fundamental for the survival of living cells, and has implications in food and industrial biotechnology. It has been extensively studied in the yeast Saccharomyces cerevisiae, where the Hog1 stress activated protein kinase was discovered about 20 years ago. Hog1 is the core of the intracellular signaling pathway that governs the adaptive response to osmotic stress in this species. The main endpoint of this program is synthesis and intracellular retention of glycerol, as a compatible osmolyte. Despite many details of the signaling pathways and yeast responses to osmotic challenges have already been described, genome-wide approaches are contributing to refine our knowledge of yeast adaptation to hypertonic media. In this work, we used a quantitative fitness analysis approach in order to deepen our understanding of the interplay between yeast cells and the osmotic environment. Genetic requirements for proper growth under osmotic stress showed both common and specific features when hypertonic conditions were induced by either glucose or sorbitol. Tolerance to high-glucose content requires mitochondrial function, while defective protein targeting to peroxisome, GID-complex function (involved in negative regulation of gluconeogenesis), or chromatin dynamics, result in poor survival to sorbitol-induced osmotic stress. On the other side, the competitive disadvantage of yeast strains defective in the endomembrane system is relieved by hypertonic conditions. This finding points to the Golgi-endosome system as one of the main cell components negatively affected by hyperosmolarity. Most of the biological processes highlighted in this analysis had not been previously related to osmotic stress but are probably relevant in an ecological and evolutionary context.

Correction for Liang et al., A Novel Function for Hog1 Stress-Activated Protein Kinase in Controlling White-Opaque Switching and Mating in Candida albicans.

This author correction was added to the December 2015 issue of Eukaryotic Cell. As of January 2016, research on eukaryotic microbes is published by ASM’s multidisciplinary, open-access journal mSphere®. Volume 13, no. 12, p. [1557–1566][1], 2014, . Page

Hog1 targets Whi5 and Msa1 transcription factors to downregulate cyclin expression upon stress.

Yeast cells have developed complex mechanisms to cope with extracellular insults. An increase in external osmolarity leads to activation of the stress-activated protein kinase Hog1, which is the main regulator of adaptive responses, such as gene expression and cell cycle progression, that are essential for cellular survival. Upon osmostress, the G1-to-S transition is regulated by Hog1 through stabilization of the cyclin-dependent kinase inhibitor Sic1 and the downregulation of G1 cyclin expression by an unclear mechanism. Here, we show that Hog1 interacts with and phosphorylates components of the core cell cycle transcriptional machinery such as Whi5 and the coregulator Msa1. Phosphorylation of these two transcriptional regulators by Hog1 is essential for inhibition of G1 cyclin expression, for control of cell morphogenesis, and for maximal cell survival upon stress. The control of both Whi5 and Msa1 by Hog1 also revealed the necessity for proper coordination of budding and DNA replication. Thus, Hog1 regulates G1 cyclin transcription upon osmostress to ensure coherent passage through Start.

A novel function for Hog1 stress-activated protein kinase in controlling white-opaque switching and mating in Candida albicans.

Candida albicans is a commensal in heathy people but has the potential to become an opportunistic pathogen and is responsible for half of all clinical infections in immunocompromised patients. Central to understanding C. albicans behavior is the white-opaque phenotypic switch, in which cells can undergo an epigenetic transition between the white state and the opaque state. The phenotypic switch regulates multiple properties, including biofilm formation, virulence, mating, and fungus-host interactions. Switching between the white and opaque states is associated with many external stimuli, such as oxidative stress, pH, and N-acetylglucosamine, and is directly regulated by the Wor1 transcriptional circuit. The Hog1 stress-activated protein kinase (SAPK) pathway is recognized as the main pathway for adapting to environmental stress in C. albicans. In this work, we first show that loss of the HOG1 gene in A: / A: and α/α cells, but not A: /α cells, results in 100% white-to-opaque switching when cells are grown on synthetic medium, indicating that switching is repressed by the A1: /α2 heterodimer that represses WOR1 gene expression. Indeed, switching in the hog1Δ strain was dependent on the presence of WOR1, as a hog1Δ wor1Δ strain did not show switching to the opaque state. Deletion of PBS2 and SSK2 also resulted in C. albicans cells switching from white to opaque with 100% efficiency, indicating that the entire Hog1 SAPK pathway is involved in regulating this unique phenotypic transition. Interestingly, all Hog1 pathway mutants also caused defects in shmoo formation and mating efficiencies. Overall, this work reveals a novel role for the Hog1 SAPK pathway in regulating white-opaque switching and sexual behavior in C. albicans.

Mechanisms underlying the exquisite sensitivity of Candida albicans to combinatorial cationic and oxidative stress that enhances the potent fungicidal activity of phagocytes.

ABSTRACTImmune cells exploit reactive oxygen species (ROS) and cationic fluxes to kill microbial pathogens, such as the fungus Candida albicans. Yet, C. albicans is resistant to these stresses in vitro. Therefore, what accounts for the potent antifungal activity of neutrophils? We show that simultaneous exposure to oxidative and cationic stresses is much more potent than the individual stresses themselves and that this combinatorial stress kills C. albicans synergistically in vitro. We also show that the high fungicidal activity of human neutrophils is dependent on the combinatorial effects of the oxidative burst and cationic fluxes, as their pharmacological attenuation with apocynin or glibenclamide reduced phagocytic potency to a similar extent. The mechanistic basis for the extreme potency of combinatorial cationic plus oxidative stress—a phenomenon we term stress pathway interference—lies with the inhibition of hydrogen peroxide detoxification by the cations. In C. albicans this causes the intracellular accumulation of ROS, the inhibition of Cap1 (a transcriptional activator that normally drives the transcriptional response to oxidative stress), and altered readouts of the stress-activated protein kinase Hog1. This leads to a loss of oxidative and cationic stress transcriptional outputs, a precipitous collapse in stress adaptation, and cell death. This stress pathway interference can be suppressed by ectopic catalase (Cat1) expression, which inhibits the intracellular accumulation of ROS and the synergistic killing of C. albicans cells by combinatorial cationic plus oxidative stress. Stress pathway interference represents a powerful fungicidal mechanism employed by the host that suggests novel approaches to potentiate antifungal therapy.

The Hog1 Stress-activated Protein Kinase Targets Nucleoporins to Control mRNA Export upon Stress

The control of mRNA biogenesis is exerted at several steps. In response to extracellular stimuli, stress-activated protein kinases (SAPK) modulate gene expression to maximize cell survival. In yeast, the Hog1 SAPK plays a key role in reprogramming the gene expression pattern required for cell survival upon osmostress by acting during transcriptional initiation and elongation. Here, we genetically show that an intact nuclear pore complex is important for cell survival and maximal expression of stress-responsive genes. The Hog1 SAPK associates with nuclear pore complex components and directly phosphorylates the Nup1, Nup2, and Nup60 components of the inner nuclear basket. Mutation of those factors resulted in a deficient export of stress-responsive genes upon stress. Association of Nup1, Nup2, and Nup60 to stress-responsive promoters occurs upon stress depending on Hog1 activity. Accordingly, STL1 gene territory is maintained at the nuclear periphery upon osmostress in a Hog1-dependent manner. Cells containing non-phosphorylatable mutants in Nup1 or Nup2 display reduced expression of stress-responsive genes. Together, proper mRNA biogenesis of stress-responsive genes requires of the coordinate action of synthesis and export machineries by the Hog1 SAPK.