Response to hyperosmotic stress

An appropriate response and adaptation to hyperosmolarity, i.e., an external osmolarity that is higher than the physiological range, can be a matter of life or death for all cells. It is especially important for free-living organisms such as the yeast Saccharomyces cerevisiae. When exposed to hyperosmotic stress, the yeast initiates a complex adaptive program that includes temporary arrest of cell-cycle progression, adjustment of transcription and translation patterns, and the synthesis and retention of the compatible osmolyte glycerol. These adaptive responses are mostly governed by the high osmolarity glycerol (HOG) pathway, which is composed of membrane-associated osmosensors, an intracellular signaling pathway whose core is the Hog1 MAP kinase (MAPK) cascade, and cytoplasmic and nuclear effector functions. The entire pathway is conserved in diverse fungal species, while the Hog1 MAPK cascade is conserved even in higher eukaryotes including humans. This conservation is illustrated by the fact that the mammalian stress-responsive p38 MAPK can rescue the osmosensitivity of hog1Δ mutations in response to hyperosmotic challenge. As the HOG pathway is one of the best-understood eukaryotic signal transduction pathways, it is useful not only as a model for analysis of osmostress responses, but also as a model for mathematical analysis of signal transduction pathways. In this review, we have summarized the current understanding of both the upstream signaling mechanism and the downstream adaptive responses to hyperosmotic stress in yeast.The laboratory of H.S. is supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The laboratory of F.P. is supported by grants from the Ministerio de Economia y Competitividad (Spanish Government), the Consolider Ingenio 2010 Programme, and a FP7 UNICELLSYS grant. F.P. is also supported by the Fundación Marcelino Botín and by the Acadèmia program from Institució Catalana de Recerca i Estudis Avançats (Generalitat de Catalunya)

Response to hyperosmotic stress

An appropriate response and adaptation to hyperosmolarity, i.e., an external osmolarity that is higher than the physiological range, can be a matter of life or death for all cells. It is especially important for free-living organisms such as the yeast Saccharomyces cerevisiae. When exposed to hyperosmotic stress, the yeast initiates a complex adaptive program that includes temporary arrest of cell-cycle progression, adjustment of transcription and translation patterns, and the synthesis and retention of the compatible osmolyte glycerol. These adaptive responses are mostly governed by the high osmolarity glycerol (HOG) pathway, which is composed of membrane-associated osmosensors, an intracellular signaling pathway whose core is the Hog1 MAP kinase (MAPK) cascade, and cytoplasmic and nuclear effector functions. The entire pathway is conserved in diverse fungal species, while the Hog1 MAPK cascade is conserved even in higher eukaryotes including humans. This conservation is illustrated by the fact that the mammalian stress-responsive p38 MAPK can rescue the osmosensitivity of hog1Δ mutations in response to hyperosmotic challenge. As the HOG pathway is one of the best-understood eukaryotic signal transduction pathways, it is useful not only as a model for analysis of osmostress responses, but also as a model for mathematical analysis of signal transduction pathways. In this review, we have summarized the current understanding of both the upstream signaling mechanism and the downstream adaptive responses to hyperosmotic stress in yeast.The laboratory of H.S. is supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. The laboratory of F.P. is supported by grants from the Ministerio de Economia y Competitividad (Spanish Government), the Consolider Ingenio 2010 Programme, and a FP7 UNICELLSYS grant. F.P. is also supported by the Fundación Marcelino Botín and by the Acadèmia program from Institució Catalana de Recerca i Estudis Avançats (Generalitat de Catalunya)

Osmostress-induced gene expression--a model to understand how stress-activated protein kinases (SAPKs) regulate transcription

Adaptation is essential for maximizing cell survival and for cell fitness in response to sudden changes in the environment. Several aspects of cell physiology change during adaptation. Major changes in gene expression are associated with cell exposure to environmental changes, and several aspects of mRNA biogenesis appear to be targeted by signaling pathways upon stress. Exhaustive reviews have been written regarding adaptation to stress and regulation of gene expression. In this review, using osmostress in yeast as a prototypical case study, we highlight those aspects of regulation of gene induction that are general to various environmental stresses as well as mechanistic aspects that are potentially conserved from yeast to mammals.The laboratory of F.P. and E.N. is supported by grants from the Spanish Ministry of Economy and Competitiveness (BFU2012-33503 and FEDER, BFU2014-52125-REDT and BFU2014-51672-REDC to F.P. and BFU2014-52333-P to E.N.), the Catalan Government (2014 SGR 599) and an ERC Advanced Grant (number 294294) from the EU seventh framework program (SYNCOM) to F.P. This project is supported by the Fundación Botín and by Banco Santander through its Santander Universities Global Division to F.P. F.P. and E.N. are recipients of an ICREA Acadèmia (Generalitat de Catalunya)

Sir2 plays a key role in cell fate determination upon SAPK activation

Although the benefit of sirtuin activation in age-related diseases is well-characterized, the benefit of sirtuin activation in acute diseases has been elusive. Here we discuss that, at least in yeast, Sir2 activation prevents programmed cell death induced by the sustained activation of the stress activated protein kinase (SAPK) Hog1, the yeast homologue of the p38 SAPK. Sir2 prevents ROS formation and maximize cell survival upon SAPK activation. The conserved function of Sir2 in age-related diseases and the conserved role of SAPKs open the possibility of a novel role for sirtuins in cell fate determination in eukaryotic cells.We thank to EdeN for constant support. The laboratory of FP and EdeN is supported by grants from the Ministerio de Ciéncia y Innovación, the Consolider Ingenio 2010 programme and FP7 UNICELLSYS grant to F.P, EdeN. F.P. is also supported by the Fundación Marcelino Botín (FMB) and ICREA Acadèmia (Generalitat de Catalunya

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.The laboratories of FP and EdN are supported by grants from the Ministry of Science, Innovation and Universities (PGC2018-094136-B-I00 to FP; BFU2017-85152-P and FEDER to EdN) and the Government of Catalonia (2017 SGR 799). We gratefully acknowledge institutional funding from the Ministry of Science, Innovation and Universities through the Centres of Excellence Severo Ochoa Award, and from the CERCA Programme of the Government of Catalonia and the Unidad de Excelencia María de Maeztu, funded by the AEI (CEX2018-000792-M). FP and EdN are recipients of ICREA Acadèmia awards (Government of Catalonia)

Osmostress-induced gene expression--a model to understand how stress-activated protein kinases (SAPKs) regulate transcription

Adaptation is essential for maximizing cell survival and for cell fitness in response to sudden changes in the environment. Several aspects of cell physiology change during adaptation. Major changes in gene expression are associated with cell exposure to environmental changes, and several aspects of mRNA biogenesis appear to be targeted by signaling pathways upon stress. Exhaustive reviews have been written regarding adaptation to stress and regulation of gene expression. In this review, using osmostress in yeast as a prototypical case study, we highlight those aspects of regulation of gene induction that are general to various environmental stresses as well as mechanistic aspects that are potentially conserved from yeast to mammals.The laboratory of F.P. and E.N. is supported by grants from the Spanish Ministry of Economy and Competitiveness (BFU2012-33503 and FEDER, BFU2014-52125-REDT and BFU2014-51672-REDC to F.P. and BFU2014-52333-P to E.N.), the Catalan Government (2014 SGR 599) and an ERC Advanced Grant (number 294294) from the EU seventh framework program (SYNCOM) to F.P. This project is supported by the Fundación Botín and by Banco Santander through its Santander Universities Global Division to F.P. F.P. and E.N. are recipients of an ICREA Acadèmia (Generalitat de Catalunya)

Dealing with transcriptional outbursts during S phase to protect genomic integrity

Transcription during S phase needs to be spatially and temporally regulated to prevent collisions between the transcription and replication machineries. Cells have evolved a number of mechanisms to make both processes compatible under normal growth conditions. When conflict management fails, the head-on encounter between RNA and DNA polymerases results in genomic instability unless conflict resolution mechanisms are activated. Nevertheless, there are specific situations in which cells need to dramatically change their transcriptional landscape to adapt to environmental challenges. Signal transduction pathways, such as stress-activated protein kinases (SAPKs), serve to regulate gene expression in response to environmental insults. Prototypical members of SAPKs are the yeast Hog1 and mammalian p38. In response to stress, p38/Hog1 SAPKs control transcription and also regulate cell cycle progression. When yeast cells are stressed during S phase, Hog1 promotes gene induction and, remarkably, also delays replication by directly affecting early origin firing and fork progression. Therefore, by delaying replication, Hog1 plays a key role in preventing conflicts between RNA and DNA polymerases. In this review, we focus on the genomic determinants and mechanisms that make compatible transcription with replication during S phase to prevent genomic instability, especially in response to environmental changes.The laboratory of F.P. and E.N. is supported by grants from the Spanish Government (BFU2012-33503 and FEDER to F.P.; BFU2011-26722 to E.N.), the Consolider Ingenio 2010 program CSD2007-0015 and the Fundación Marcelino Botín to F.P. F.P. and E.N. are recipients of an Institució Catalana de Recerca i Estudis Avançats Acadèmia (Generalitat de Catalunya)

Untargeted metabolomics unravels functionalities of phosphorylation sites in Saccharomyces cerevisiae

Background: Coordinated through a complex network of kinases and phosphatases, protein phosphorylation regulates essentially all cellular processes in eukaryotes. Recent advances in proteomics enable detection of thousands of phosphorylation sites (phosphosites) in single experiments. However, functionality of the vast majority of these sites remains unclear and we lack suitable approaches to evaluate functional relevance at a pace that matches their detection. Results: Here, we assess functionality of 26 phosphosites by introducing phosphodeletion and phosphomimic mutations in 25 metabolic enzymes and regulators from the TOR and HOG signaling pathway in Saccharomyces cerevisiae by phenotypic analysis and untargeted metabolomics. We show that metabolomics largely outperforms growth analysis and recovers 10 out of the 13 previously characterized phosphosites and suggests functionality for several novel sites, including S79 on the TOR regulatory protein Tip41. We analyze metabolic profiles to identify consequences underlying regulatory phosphorylation events and detecting glycerol metabolism to have a so far unknown influence on arginine metabolism via phosphoregulation of the glycerol dehydrogenases. Further, we also find S508 in the MAPKK Pbs2 as a potential link for cross-talking between HOG signaling and the cell wall integrity pathway. Conclusions: We demonstrate that metabolic profiles can be exploited for gaining insight into regulatory consequences and biological roles of phosphosites. Altogether, untargeted metabolomics is a fast, sensitive and informative approach appropriate for future large-scale functional analyses of phosphosites.This work was funded through the SystemsX.ch project SignalX, evaluated by the Swiss National Science Foundation to US and ZRN and grants from the Spanish Ministry of Economy and Competitiveness (BFU2015-64437-P and FEDER), the Catalan Government (2014 SGR 599) and Fundación Botín, by Banco Santander through its Santander Universities Global Division to FP. FP is recipients of an ICREA Acadèmia (Generalitat de Catalunya). GS was supported by an Advanced Postdoc.Mobility fellowship (P300P3_147895) by the Swiss National Science Foundation

Understanding retinoblastoma post-translational regulation for the design of targeted cancer therapies

The retinoblastoma protein (Rb1) is a prototypical tumor suppressor protein whose role was described more than 40 years ago. Together with p107 (also known as RBL1) and p130 (also known as RBL2), the Rb1 belongs to a family of structurally and functionally similar proteins that inhibits cell cycle progression. Given the central role of Rb1 in regulating proliferation, its expression or function is altered in most types of cancer. One of the mechanisms underlying Rb-mediated cell cycle inhibition is the binding and repression of E2F transcription factors, and these processes are dependent on Rb1 phosphorylation status. However, recent work shows that Rb1 is a convergent point of many pathways and thus the regulation of its function through post-translational modifications is more complex than initially expected. Moreover, depending on the context, downstream signaling can be both E2F-dependent and -independent. This review seeks to summarize the most recent research on Rb1 function and regulation and discuss potential avenues for the design of novel cancer therapies.This project received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie PROBIST grant agreement No. 754510 (postdoctoral fellowship to R.J.) and from BIST Living Allowance Fellowship to A.T.-S. This work was supported by grants from the Spanish Ministry of Economy and Competitiveness [BFU2017-85152-P and FEDER to E.d.N. and PGC2018-094136-B-I00 and FEDER to F.P.], the AECC Foundation [PROYE18010POSA to F.P.] and the Government of Catalonia [2017 SGR 799 to E.d.N. and F.P.]. E.d.N. and F.P. are recipients of ICREA Acadèmia awards (Government of Catalonia). We gratefully acknowledge institutional funding from the Ministry of Science, Innovation and Universities through the Centres of Excellence Severo Ochoa Award, and from the CERCA Programme of the Government of Catalonia and the Unidad de Excelencia María de Maeztu, funded by the AEI (CEX2018-000792-M)