Glucose uptake is required for glucose-stimulated transcriptional response in Saccharomyces cerevisiae
ABSTRACT: Saccharomyces cerevisiae developed elegant mechanisms to monitor nutrient availability and trigger adaptative responses to nutrient deficiency. Nutrient sensing requires close coordination of cell surface sensors with intracellular mechanisms. This yeast senses the presence of glucose by two modified hexose transporters, Rgt2 and Snf3 (regulating expression of genes encoding hexose transporters) and the G-protein coupled receptor Gpr1 (modulating Protein Kinase A (PKA) activity).. It has been difficult to differentiate between cellular responses mediated by cell surface and intracellular sensors, respectively. Using a strain that is devoid of glucose uptake, we show that the mere presence of glucose does not elicit any glucose-dependent transcriptional responses. This indicates that signals generated by surface sensors are not sufficient to mediate glucose-dependent transcriptional responses. Instead, intracellular glucose or metabolites derived from it are required for transcriptional changes associated with glucose exposure. We used microarrays from biological triplicate samples to measure the global transcriptional response to sudden addition of glucose to yeast cells growing at steady state on ethanol. The experiment was conducted using a strain that is devoid of glucose uptake and compared with an isogenic strain. Overall design: The CEN.PK strain was used in this research. A strain with all known hexose transporters deleted (Null strain) was compared with an isogenic reference. The two strains were grown in a chemostat (D = 0.1 h-1) using ethanol as the carbon source. Transcriptional responses between the strains were measured in biological triplicates at steady state and then pulsed with glucose at time t = 0. Transcriptional response was measured again after t = 20 min to determine changes in gene expression chanes only in response to the presence of glucose.
Project description:Saccharomyces cerevisiae developed elegant mechanisms to monitor nutrient availability and trigger adaptative responses to nutrient deficiency. Nutrient sensing requires close coordination of cell surface sensors with intracellular mechanisms. This yeast senses the presence of glucose by two modified hexose transporters, Rgt2 and Snf3 (regulating expression of genes encoding hexose transporters) and the G-protein coupled receptor Gpr1 (modulating Protein Kinase A (PKA) activity).. It has been difficult to differentiate between cellular responses mediated by cell surface and intracellular sensors, respectively. Using a strain that is devoid of glucose uptake, we show that the mere presence of glucose does not elicit any glucose-dependent transcriptional responses. This indicates that signals generated by surface sensors are not sufficient to mediate glucose-dependent transcriptional responses. Instead, intracellular glucose or metabolites derived from it are required for transcriptional changes associated with glucose exposure. We used microarrays from biological triplicate samples to measure the global transcriptional response to sudden addition of glucose to yeast cells growing at steady state on ethanol. The experiment was conducted using a strain that is devoid of glucose uptake and compared with an isogenic strain. The CEN.PK strain was used in this research. A strain with all known hexose transporters deleted (Null strain) was compared with an isogenic reference. The two strains were grown in a chemostat (D = 0.1 h-1) using ethanol as the carbon source. Transcriptional responses between the strains were measured in biological triplicates at steady state and then pulsed with glucose at time t = 0. Transcriptional response was measured again after t = 20 min to determine changes in gene expression changes only in response to the presence of glucose.
Project description:Hxt1 is a high affinity hexose transporter important for virulence of the phytopathogenic basidiomycete Ustilago maydis on its host plant maize. Hxt1 shows the highest similarities to the glucose sensors Rgt2 and Snf3 from S. cereviciae (42% and 39% identity on amino acid level, respectively). In these sensors, the substitution of a highly conserved arginine to lysine leads to a constitutive active signal, resulting in expression of several glucose induced genes. Introduction of an analogous mutation in Hxt1 leads to loss of transport activity in the resulting Hxt1(R164K) protein. Expression of Hxt1(R164K) in hxt1 deletion strains results in a completely avirulent phenotype. Pathogenic developement of ∆hxt1 hxt1(R164K) strains is blocked immediately after plant penetration. Expression analysis of ∆hxt1 hxt1(R164K) cells 24 hours post inoculation revealed downregulation of a set of genes involved in carbohydrate metabolism indicating a role of Hxt1 in carbohydrate signaling during initiation of the pathogenic stage. To analyze expression changes of SG200 and SG200∆hxt1 and SG200∆hxt1 hxt1(R164K) cells were harvested from the surface of maize leaves 24 hour post inoculation. For each strain three independent replicates were conducted.
Project description:The global transcriptional response of Saccharomyces cerevisiae was investigated in low temperature chemostat cultures grown in carbon or nitrogen limitation. During steady state chemostats, the growth rates and in vivo fluxes were kept constant however the growth-limiting nutrient was significantly higher at 12oC than at 30oC and had significant effects on transcriptional responses. Growth at 12oC resulted in a rearrangement of transporters for the limiting nutrient, where hexose transporters (HXTs) and ammonium permeases (MEPs) were differentially expressed in cultures grown at 30oC in carbon and nitrogen limitations, respectively. In addition, we found repression of genes encoding proteins in reserve carbohydrates metabolism and metabolism of alternative carbon or nitrogen sources other than glucose or ammonia. However, there were also similar responses when the transcriptional response was evaluated regardless of the growth-limiting nutrient. In particular, induction of ribosome biogenesis genes emphasizes the significance of transcription and translational adaptation at low temperature. In contrast, genes encoding proteins during stress response were downregulated. This down-regulation of stress elements better known as environmental stress response (ESR) is in contradiction with previous low temperature transcriptome analyses. During continuous steady state low temperature cultivation, ESR no longer plays an integral role in S. cerevisiae’s response to temperature change. Similarly, trehalose accumulation, consistent with its gene expression, was not indispensable for growth at 12oC. This response, however, does not exclude that ESR may be required for transition phase in low temperature growth when cells are transferred from one temperature to another. Keywords: chemostat temperature 12 degree celsuis 30 degree celsius The global transcriptional response of Saccharomyces cerevisiae was investigated in low temperature chemostat cultures grown in carbon or nitrogen limitation at a dilution rate of 0.03h-1
Project description:Aim: Analyse inhibitory effects of galacturonic acid, an important constituent of plant biomass hydrolysates, on growing and starving cultures of Saccharomyces cerevisiae CEN.PK113-7D. Method & Results: Biomass yields in aerobic and anaerobic glucose-limited chemostat cultures (pH 3.5) were reduced by 25 and 10%, respectively, upon addition of 10 g∙l-1 galacturonic acid. Genes previously reported to show a transcriptional response to other organic acids were overrepresented in a set of galacturonic-acid responsive genes identified by microarray analysis. These results suggested that galacturonic acid causes weak-acid uncoupling of the yeast plasma membrane pH gradient. Consistent with this hypothesis, galacturonate-accelerated loss of viability in starving cell suspensions was strongly pH dependent. Loss of viability was much slower in a strain in which all HXT (hexose transporter) genes were deleted. Moreover, deletion of HXT genes alleviated growth inhibition on ethanol observed at galacturonic acid concentrations of 10 g∙l-1 and above. Conclusions: At low pH, galacturonic acid negatively affects the physiology of S. cerevisiae. Reduced sensitivity of hexose-transporter mutants indicated that one or more HXT transporters are involved in transport of galacturonic acid. Significance and Impact: This study shows that galacturonic acid toxicity should be taken into account in process development for yeast-based fermentative conversion of pectin-rich feedstocks such as sugar beet pulp and citrus peel. Involvement of hexose transporters in galacturonic acid toxicity provides leads for improving tolerance. To investigate the impact of galacturonic acid on S. cerevisiae, a DNA microarray-based transcriptome analysis was performed on aerobic, glucose-limited chemostat cultures grown in the presence and absence of 10 g∙l-1 galacturonic acid at pH3.5.
Project description:Background We previously described the first respiratory Saccharomyces cerevisiae strain, KOY.TM6*P, by integrating the gene encoding a chimeric hexose transporter, Tm6*, into the genome of an hxt null yeast. Subsequently we demonstrated the transferability of this respiratory phenotype in the presence of up to 100 g/L glucose to a yeast strain in which only HXT1-7 had been deleted. In this study, we wanted to examine the basis of the respiratory phenotype of the resultant strain, V5.TM6*P, by comparing its transcriptome with that of its parent, V5, at different glucose concentrations. Results cDNA array analyses revealed that alterations in gene expression that occur when transitioning from a respiro-fermentative (V5) to a respiratory (V5.TM6*P) strain, are very similar to those in cells undergoing a diauxic shift. Highly complete collections of known genes of the TCA cycle, glyoxylate cycle and respiratory chain were identified, consistent with a respiratory metabolism. We also undertook an analysis of transcription factor binding sites in our dataset by examining previously-published biological data for Hap4, Cat8 and Mig1, and using this in combination with verified binding consensus sequences, to identify genes likely to be regulated by one or more of these transcription factors. Of the induced genes of our dataset, 77 % had binding sites for Hap2/3/5 (Hap4 is an activator of this complex), with 72 % having at least two (the latter set being more induced than the former). This is relevant since Hap4 is known to be involved in the transcriptional activation of respiratory genes and other mitochondrial functions. In addition, 13 % of genes were found to have a binding site for Cat8, which together with its complexes with Sip4 have previously been identified as mediating de-repression of a number of genes during the diauxic shift. Finally, 21 % of genes had a binding site for Mig1 which is a transcriptional repressor involved in glucose repression. Unexpectedly, both the up- and down-regulation of many of the genes in our dataset had a clear glucose dependence in the parent V5 strain that was not present in V5.TM6*P. This important result indicates that the relief of glucose repression is already operable at much higher glucose concentrations than is widely accepted and suggests that glucose sensing might occur inside the cell. Conclusions Our dataset gives a remarkably complete view of the involvement of genes in the TCA cycle, glyoxylate cycle and respiratory chain in the expression of the phenotype of V5.TM6*P. Furthermore, 88 % of the transcriptional response of the induced genes in our dataset can be related to the potential activities of just three transcription factors; Hap2/3/5, Cat8 and Mig1. Overall, our data support genetic remodelling in V5.TM6*P consistent with a respiratory metabolism which is insensitive to external glucose concentrations. Overall design: Compare a wild type Saccaromyces cerevisise strain V5 strain (=V), with a mutant strain where glucose transport has been reduced by at least 30% in the strain V5.TM6*P (=T), mutant is devoided of 7 hexose transporters HXT1, HXT2, HXT3, HXT4, HXT5, HXT6, HXT7, the plasma membrane contains a HXT1-HXT7 fusion protein. This construct is a combination of a low and high affinity glucose transporter. The glucose concentration in the culture media of each array is the parameter that can be how the arrays are sorted. Accession Strain Glucose [g/L] GSM298426 V5.TM6*P 36.5 GSM298477 V5.TM6*P 36.5 GSM298478 V5.TM6*P 34.8 GSM298480 V5.TM6*P 34.8 GSM298483 V5.TM6*P 26.3 GSM298484 V5.TM6*P 26.3 GSM298485 V5.TM6*P 25.1 GSM298487 V5.TM6*P 25.1 GSM298489 V5.TM6*P 13.5 GSM298491 V5.TM6*P 13.5 GSM298492 V5.TM6*P 5.6 GSM298494 V5.TM6*P 5.6 GSM298496 V5-wild type 38.4 GSM298497 V5-wild type 38.4 GSM298500 V5-wild type 35 GSM298501 V5-wild type 35 GSM298502 V5-wild type 25.5 GSM298503 V5-wild type 25.5 GSM298504 V5-wild type 24.4 GSM298505 V5-wild type 24.4 GSM298506 V5-wild type 10.5 GSM298508 V5-wild type 10.5 GSM298509 V5-wild type 7.4 GSM298510 V5-wild type 7.4
Project description:Bloodstream form African trypanosomes are thought to rely exclusively upon glycolysis for ATP production. Indeed, the pathway has long been considered a potential therapeutic target to tackle the devastating and neglected tropical diseases caused by these parasites. However, plasma membrane glucose and glycerol transporters are both expressed by trypanosomes and these parasites can infiltrate tissues that contain glycerol.</br> Here, we show that trypanosomes can use glycerol for gluconeogenesis, particularly when deprived of glucose. We demonstrate that Trypanosoma brucei hexose transporters 1 and 2 (THT1 and THT2) are localized to the plasma membrane and that knock down of THT1 expression leads to a growth defect that is more severe when THT2 is also knocked down. These data are consistent with THT1 and THT2 being the primary routes of glucose supply for the production of ATP by glycolysis. However, supplementation of the growth medium with glycerol substantially rescued the growth defect caused by THT1 and THT2 knock down. Metabolomic analyses with heavy-isotope labelled glycerol demonstrated that trypanosomes take up glycerol and use it to synthesize intermediates of gluconeogenesis, including fructose 1,6-bisphosphate and hexose 6-phosphates, which feed the pentose phosphate pathway and surface glycoprotein biosynthesis. We also observed increased flux through the tricarboxylic acid cycle and the succinate shunt. We also detected gluconeogenesis-specific fructose-1,6-bisphosphatase activity, even in wild-type cells grown in the presence of glucose. Thus, contrary to prior thinking, gluconeogenesis can operate in bloodstream form T. brucei. This pathway, using glycerol as a physiological substrate, may be required in mammalian host tissues.
Project description:Interleukin-2 (IL-2) and Janus kinases (JAKs) regulate transcriptional programs and protein synthesis to control the differentiation of effector CD8+ cytotoxic T cells (CTL). Using high-resolution mass spectrometry, we have generated an in-depth characterisation of how IL-2 and JAKs configure the CTL proteome to control CTL function. We found that IL-2-JAK1/3 signaling selectively regulated the abundance of a key subset of proteins influencing the accumulation of critical cytokines and effector molecules in T cells. Moreover, IL-2 controlled the concentration of proteins that support core metabolic processes essential for cellular fitness. One fundamental insight was the dominant role for IL-2 in controlling how effector T cells respond to their microenvironment. IL-2-JAK1/3 signaling pathways thus controlled the abundance of nutrient transporters, nutrient sensors and critical oxygen sensing molecules. The data provide key insights of how IL-2 controls T cell function and highlight signaling mechanisms and transcription factors that link oxygen sensing to transcriptional control of CD8+ T cell differentiation.
Project description:Alkaline pH stress invokes in S. cerevisiae a potent and fast transcriptional response that includes many genes repressed by glucose. Certain mutants in the glucose-sensing and response pathways, such as those lacking the Snf1 kinase, are sensitive to alkalinization. We show that addition of glucose to the medium improves growth of wild type cells at high pH, fully abolish the snf1 alkali-sensitive phenotype and attenuates high pH-induced Snf1 phosphorylation at Thr210. The elm1 mutant, lacking one of the three upstream Snf1 kinases (tos3, elm1 and sak1), is markedly alkali sensitive, whereas the phenotype of the tos3 elm1 sak1 strain is even stronger than that of snf1 cells and it is not fully rescued by glucose supplementation. DNA microarray analysis reveals that about 75% of genes induced at short term by high pH are also induced by glucose scarcity. Snf1 mediates, in full or in part, the activation of a significant subset (38%) of short-term alkali-induced genes, including those coding high-affinity hexose transporters and phosphorylating enzymes. Induction of genes encoding enzymes involved in glycogen (but not trehalose) metabolism is largely dependent of the presence of Snf1. Therefore, the function of Snf1 in adaptation to glucose scarcity appears crucial for alkaline pH tolerance. Incorporation of micromolar amounts of iron and copper to a glucose-supplemented medium result in an additive effect and allows near normal growth at high pH, thus indicating that these three nutrients are key limiting factors for growth in an alkaline environment. Overall design: We identified the changes in the expression profiles caused by alkalinization of the medium (pH8 vs. pH5.5 for 10 min) in several strains: wild type cells (4 chips), snf1 mutant cells (4 chips) We also identified the transcriptomic changes that occur after glucose deprivation (0.05% vs 2% for 15 min) in: wild type cells (2 chips) snf1 mutant cells (2 chips) Total: 12 chips
Project description:This experiment compares the transcriptional profiles of a WT yeast strain grown in either 2% glucose or 3% pyruvate. The goal was to identify genes whose expression is either induced or repressed by glucose (catabolite repression). Keywords: nutrient response Overall design: This experiment used dye-swap replicates.
Project description:This is the model described in: Bacterial adaptation through distributed sensing of metabolic fluxes
Oliver Kotte, Judith B Zaugg and Matthias Heinemann;Mol Sys Biol2010;6:355. doi:10.1038/msb.2010.10;
The recognition of carbon sources and the regulatory adjustments to recognized changes are of particular importance for bacterial survival in fluctuating environments. Despite a thorough knowledge base of Escherichia coli's central metabolism and its regulation, fundamental aspects of the employed sensing and regulatory adjustment mechanisms remain unclear. In this paper, using a differential equation model that couples enzymatic and transcriptional regulation of E. coli's central metabolism, we show that the interplay of known interactions explains in molecular-level detail the system-wide adjustments of metabolic operation between glycolytic and gluconeogenic carbon sources. We show that these adaptations are enabled by an indirect recognition of carbon sources through a mechanism we termed distributed sensing of intracellular metabolic fluxes. This mechanism uses two general motifs to establish flux-signaling metabolites, whose bindings to transcription factors form flux sensors. As these sensors are embedded in global feedback loop architectures, closed-loop self-regulation can emerge within metabolism itself and therefore, metabolic operation may adapt itself autonomously (not requiring upstream sensing and signaling) to fluctuating carbon sources.
In its current form this SBML model is parametrized for the glucose to acetate transition and to simulate the extended diauxic shift as shown in figure 3 and scenario 6 of the attached matlab file. In this scenario the cells first are grown from an OD600 (BM) of 0.03 with a starting glucose concentration of 0.5 g/l for 8.15 h (29340 sec). Then a medium containing 5 g/l acetate is inoculated with these cells to an OD600 of 0.03 and grown for another 19.7 hours (70920 sec). Finally the cells are shifted to a medium containing both glucose and acetate at a concentration of 3 g/l with a starting OD600 of 0.0005.
The shifts where implemented using events triggering at the times determined by the parameters shift1 and shift2 (in hours). To simulate other scenarios the initial conditions need to be changed as described in the supplemental materials (supplement 1)
The original SBML model and the MATLAB file used for the calculations can be down loaded as supplementary materials of the publication from the MSB website. (supplement 2).
The units of the external metabolites are in [g/l], those of the biomass in optical density,OD600, taken as dimensionless, and [micromole/(gramm dry weight)] for all intracellular metabolites. As the latter cannot be implemented in SBML, it was chosen to be micromole only and the units of the parameters are left mostly undefined.