Mediator tail subunits can form amyloid-like aggregates<i>in vivo</i>and affect stress response in yeast

Zhu, Xuefeng; Chen, Lihua; Carlsten, Jonas; Liu, Qian; Liu, Beidong; Gustafsson, Claes M.

doi:10.1093/nar/gkv629

Cited by 22 publications

(28 citation statements)

References 43 publications

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“…Additionally, we tested the phenotypes of the med15BΔ and HTUΔ/CgMED15B strains under different biological stimuli and found that Med15B was essential for cell tolerance under oxidative and osmotic stress conditions (data not shown). These data are consistent with Med15 from S. cerevisiae having a critical role in the stress response (20,21,32). Our results indicated that Med15B has a vital modulatory role in pH homeostasis in C. glabrata, so it will be important to examine this function in other eukaryotes.…”

Section: Discussionsupporting

confidence: 89%

“…The tail module subunits Med2, Med3, and Med15 can form a subcomplex and are involved in a heat shock response through recruitment by activated heat shock transcription factor 1 (Hsf1) to its target genes (19). By changing the Mediator subunit composition, the tail subcomplex affects the response to oxidative stress (20). The tail module subunits are also required for mitogen-activated protein kinase (MAPK) Hog1-mediated gene expression, which is essential for proper cell adaptation to osmotic stress (21).…”

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confidence: 99%

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Med15B Regulates Acid Stress Response and Tolerance in Candida glabrata by Altering Membrane Lipid Composition

Liu

et al. 2017

Appl Environ Microbiol

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Candida glabrata is a promising producer of organic acids. To elucidate the physiological function of the Mediator tail subunit Med15B in the response to low-pH stress, we constructed a deletion strain, C. glabrata med15BΔ, and an overexpression strain, C. glabrata HTUΔ/CgMED15B. Deletion of MED15B caused biomass production, glucose consumption rate, and cell viability to decrease by 28.3%, 31.7%, and 26.5%, respectively, compared with those of the parent (HTUΔ) strain at pH 2.0. Expression of lipid metabolism-related genes was significantly downregulated in the med15BΔ strain, whereas key genes of ergosterol biosynthesis showed abnormal upregulation. This caused the proportion of C 18:1 fatty acids, the ratio of unsaturated to saturated fatty acids (UFA/SFA), and the total phospholipid content to decrease by 11.6%, 27.4%, and 37.6%, respectively. Cells failed to synthesize fecosterol and ergosterol, leading to the accumulation and a 60.3-fold increase in the concentration of zymosterol. Additionally, cells showed reductions of 69.2%, 11.6%, and 21.8% in membrane integrity, fluidity, and H ϩ -ATPase activity, respectively. In contrast, overexpression of Med15B increased the C 18:1 levels, total phospholipids, ergosterol content, and UFA/SFA by 18.6%, 143.5%, 94.5%, and 18.7%, respectively. Membrane integrity, fluidity, and H ϩ -ATPase activity also increased by 30.2%, 6.9%, and 51.8%, respectively. Furthermore, in the absence of pH buffering, dry weight of cells and pyruvate concentrations were 29.3% and 61.2% higher, respectively, than those of the parent strain. These results indicated that in C. glabrata, Med15B regulates tolerance toward low pH via transcriptional regulation of acid stress response genes and alteration in lipid composition. IMPORTANCE This study explored the role of the Mediator tail subunit Med15B in the metabolism of Candida glabrata under acidic conditions. Overexpression of MED15B enhanced yeast tolerance to low pH and improved biomass production, cell viability, and pyruvate yield. Membrane lipid composition data indicated that Med15B might play a critical role in membrane integrity, fluidity, and H ϩ -ATPase activity homeostasis at low pH. Thus, controlling membrane composition may serve to increase C. glabrata productivity at low pH.KEYWORDS Candida glabrata, Mediator subunit Med15B, low-pH stress, transcriptomics, membrane lipid T he Mediator coactivator complex is required for transcription initiation in eukaryotes (1, 2). It is recruited by transcription activators and conveys regulatory information from gene-specific regulators to promoters (3, 4). Mediator can influence almost all stages of transcription and coordinated processes such as chromatin remodeling, transcription elongation, and posttranslational modifications (5, 6). Mediator is a multisubunit assembly comprising four modules: head, middle, tail, and cyclin-dependent kinase 8 (CDK8) (7). The head and middle modules are highly

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Section: Discussionsupporting

confidence: 89%

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confidence: 99%

Med15B Regulates Acid Stress Response and Tolerance in Candida glabrata by Altering Membrane Lipid Composition

Liu

et al. 2017

Appl Environ Microbiol

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“…Med15 makes multiple contacts with Gcn4 including polymorphic polyQ repeats and KIX domain (Jedidi et al 2010). Overexpression of Med15 causes protein aggregation, presumably via the polyQ and polyQA regions of this region alone aggregates in response to hydrogen peroxide (Zhu et al 2015). Overexpression of the first polyQ and polyQA of Med15 reduces cell growth in unstressed cells and salt exposed yeast but rescues growth in the presence of rapamycin (8).…”

Section: Introductionmentioning

confidence: 99%

“…Overexpression of Med15 causes protein aggregation, presumably via the polyQ and polyQA regions of this region alone aggregates in response to hydrogen peroxide (Zhu et al 2015). Overexpression of the first polyQ and polyQA of Med15 reduces cell growth in unstressed cells and salt exposed yeast but rescues growth in the presence of rapamycin (8). Full-length Med15 also forms cytosolic foci in yeast exposed to hydrogen peroxide (8).…”

Section: Introductionmentioning

confidence: 99%

“…Overexpression of the first polyQ and polyQA of Med15 reduces cell growth in unstressed cells and salt exposed yeast but rescues growth in the presence of rapamycin (8). Full-length Med15 also forms cytosolic foci in yeast exposed to hydrogen peroxide (8). The pathogenic effects of polyQ proteins were uncovered when the causative mutation for Huntington's disease was discovered (9).…”

Section: Introductionmentioning

confidence: 99%

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The polymorphic PolyQ tail protein of the Mediator Complex, Med15, regulates variable response to stress

Gallagher

Nassif

Pupo

2019

Preprint

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The Mediator is a multi-protein complex composed of subunits called head, body, tail, and CDK that is conserved from yeast to humans and plays a central role in transcription. However, not all the components are required for basal transcription. Components of the tail are not essential but to varying degrees are required for growth in different stresses. While some stresses are familiar such as heat, desiccation, and starvation, others are exotic, yet yeast can elicit a successful stress response. MCHM is a hydrotrope that induces growth arrest in yeast. By exploiting genetic variation, specifically in Med15, between yeast strains, we found that a naturally occurring Med15 allele with polyQ (polyglutamine) expansion conferred MCHM sensitivity. Expansion in polyQ repeat can induce protein aggregation and in humans can cause neurodegenerative diseases. In yeast, the MCHM sensitivity was not from a loss of function as the reciprocal hemizygous hybrids were all sensitive and the homozygous null mutant was less sensitive than the hemizygous hybrids. This suggests that there is an incompatibility between Mediator components from genetic divergent yeast strains. Transcriptomics from yeast expressing the incompatible Med15 (longer polyQ repeats in the strain with fewer repeats) changed gene expression in diverse pathways. Med15 protein existed in multiple isoforms, mostly from likely post-translational modifications and different alleles have different patterns of isoforms. Stability of both alleles of Med15 was dependent on Ydj1, a J-type chaperone. The protein level of the incompatible Med15 allele was lower than the compatible allele and was turned over faster. Med15 is tethered to the rest of the Mediator complex via Med2 and 3. Deletion of either Med2 or Med3 changed the Med15 isoform patterns in a similar manner. Whereas deletion of Med5, a distal component of the Mediator tail, did not change the pattern. The med2 and med3 mutants were similarly sensitive to MCHM while med5 mutants were not. Differences in the phenotype of yeast carrying different Med15 alleles extend to other stresses. The incompatible allele of Med15 improved growth of yeast to chemicals that produce free radicals and the compatible allele of Med15 improved growth to reducing agents, caffeine, and hydroxyurea. Med15 directly interacts with Gcn4 and other TFs and in vitro form phaseseparated droplets. This variation may reflect the positive and negative role that Med15 has in transcription. Genetic variation in transcriptional regulators can magnify differences in response to environmental changes, in contrast, genetic variation in a metabolic enzyme. These polymorphic control genes are master variators.

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A Pliable Mediator Acts as a Functional Rather Than an Architectural Bridge between Promoters and Enhancers

Khattabi

Zhao

Kalchschmidt

et al. 2019

Cell

225

229

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Mediator tail subunits can form amyloid-like aggregatesin vivoand affect stress response in yeast

Cited by 22 publications

References 43 publications

Med15B Regulates Acid Stress Response and Tolerance in Candida glabrata by Altering Membrane Lipid Composition

Med15B Regulates Acid Stress Response and Tolerance in Candida glabrata by Altering Membrane Lipid Composition

The polymorphic PolyQ tail protein of the Mediator Complex, Med15, regulates variable response to stress

A Pliable Mediator Acts as a Functional Rather Than an Architectural Bridge between Promoters and Enhancers

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