Vps factors are required for efficient transcription elongation in budding yeast

Enhanced β-carotene production by overexpressing the DID2 gene, a subunit of ESCRT complex, in engineered Yarrowia lipolytica

OBJECTIVE

β-Carotene has been widely used in the food and feed industry and has significant commercial value. This study aimed to increase the β-carotene production in engineered Yarrowia lipolytica by optimizing the host metabolic network. The DID2 gene, a subunit of the endosomal sorting complex required for transport (ESCRT), was integrated into a β-carotene producing strain.

RESULTS

The β-carotene production was increased by 260%, and the biomass increased by 10% for engineered Y. lipolytica. Meanwhile, DID2 elevated the mRNA level and protein level of the genes in the β-carotene synthesis pathway, then increased precursors (FPP, Lycopene) utilization. DID2 also increased the mRNA level of the genes in the glucose pathway, pentose phosphate pathway, and tricarboxylic acid cycle and promoted glucose utilization and cofactors consumption.

CONCLUSION

The ESCRT protein complex subunit, DID2, improved β-carotene production in engineered Y. lipolytica and beneficial to glucose utilization and cofactors consumption. This study provided new finding of the DID2 gene's function and it mostly could be used for many other natural product productions.

Several New Putative Bacterial ADP-Ribosyltransferase Toxins Are Revealed from In Silico Data Mining, Including the Novel Toxin Vorin, Encoded by the Fire Blight Pathogen Erwinia amylovora

Mono-ADP-ribosyltransferase (mART) toxins are secreted by several pathogenic bacteria that disrupt vital host cell processes in deadly diseases like cholera and whooping cough. In the last two decades, the discovery of mART toxins has helped uncover the mechanisms of disease employed by pathogens impacting agriculture, aquaculture, and human health. Due to the current abundance of mARTs in bacterial genomes, and an unprecedented availability of genomic sequence data, mART toxins are amenable to discovery using an in silico strategy involving a series of sequence pattern filters and structural predictions. In this work, a bioinformatics approach was used to discover six bacterial mART sequences, one of which was a functional mART toxin encoded by the plant pathogen, Erwinia amylovora, called Vorin. Using a yeast growth-deficiency assay, we show that wild-type Vorin inhibited yeast cell growth, while catalytic variants reversed the growth-defective phenotype. Quantitative mass spectrometry analysis revealed that Vorin may cause eukaryotic host cell death by suppressing the initiation of autophagic processes. The genomic neighbourhood of Vorin indicated that it is a Type-VI-secreted effector, and co-expression experiments showed that Vorin is neutralized by binding of a cognate immunity protein, VorinI. We demonstrate that Vorin may also act as an antibacterial effector, since bacterial expression of Vorin was not achieved in the absence of VorinI. Vorin is the newest member of the mART family; further characterization of the Vorin/VorinI complex may help refine inhibitor design for mART toxins from other deadly pathogens.

Polo kinase recruitment via the constitutive centromere-associated network at the kinetochore elevates centromeric RNA

The kinetochore, a multi-protein complex assembled on centromeres, is essential to segregate chromosomes during cell division. Deficiencies in kinetochore function can lead to chromosomal instability and aneuploidy-a hallmark of cancer cells. Kinetochore function is controlled by recruitment of regulatory proteins, many of which have been documented, however their function often remains uncharacterized and many are yet to be identified. To identify candidates of kinetochore regulation we used a proteome-wide protein association strategy in budding yeast and detected many proteins that are involved in post-translational modifications such as kinases, phosphatases and histone modifiers. We focused on the Polo-like kinase, Cdc5, and interrogated which cellular components were sensitive to constitutive Cdc5 localization. The kinetochore is particularly sensitive to constitutive Cdc5 kinase activity. Targeting Cdc5 to different kinetochore subcomplexes produced diverse phenotypes, consistent with multiple distinct functions at the kinetochore. We show that targeting Cdc5 to the inner kinetochore, the constitutive centromere-associated network (CCAN), increases the levels of centromeric RNA via an SPT4 dependent mechanism.

Modulation of acetate utilization in Komagataella phaffii by metabolic engineering of tolerance and metabolism

BACKGROUND

Acetate, an economical industrial chemical, which is also the precursor of acetyl-CoA, could serve as an alternative substrate for biomanufacturing. This nontraditional substrate can be widely produced from syngas via hydrolysis or pyrolysis of the cellulosic biomass, chemical or microbial catalysis, anaerobic fermentation in treated wastewater, etc. However, the toxicity of acetate to microorganisms has held back its utilization, especially for the eukaryotes that are good hosts for production of complicated pharmaceuticals or chemicals. This study seeks to improve acetate utilization in a widely used yeast host, Komagataella phaffii (previously Pichia pastoris), by metabolic engineering of acetate tolerance, transport, and metabolism.

RESULTS

A kinase-deficient library of K. phaffii was firstly used to screen acetate-resistant kinases. The HRK1 knockout strain was sensitive to acetate and overexpression of this gene improved acetate tolerance and cell growth of the strain. Also, overexpression of HRK1 caused a 55% productivity improvement of acetyl-CoA-dependent 6-methylsalicylic acid (6-MSA). However, activation of Hrk1 on membrane H(+)-ATPase Pma1 seemed not to work in the engineered strain. Acetate transporter gene ScFPS1* was further overexpressed, despite of not improving 6-MSA biosynthesis. To enhance acetate metabolism, acetyl-CoA synthesizing related genes, yeast PpACS1, ScACS1*, and E. coli ackA/pta were overexpressed separately. Introduction of PpACS1 and ScACS1* each increased biosynthesis of 6-MSA by approximately 20% on 20 mM acetate. Finally, co-overexpression of HRK1 and ScACS1* improved 6-MSA productivity by 51% on 20 mM acetate, despite that a low expression level of HRK1 happened when genes were expressed under the same promoter.

CONCLUSIONS

HRK1 screened by K. phaffii kinase-deficient library played an important role in acetate tolerance and was proved to profit the biosynthesis of acetyl-CoA-derived chemicals. It could be a potential target for metabolic engineering of acetate utilization in other eukaryotic hosts as well. A combined strategy of introducing genes for acetate tolerance and metabolism further improved biosynthesis of acetyl-CoA derived reporter compound in K. phaffii. This makes it a good choice for acetyl-CoA-derived chemicals with acetate as substrate or precursor in K. phaffii, which would also extend the use of this chassis host.

Harnessing Macrophages for Controlled-Release Drug Delivery: Lessons From Microbes

With the effectiveness of therapeutic agents ever decreasing and the increased incidence of multi-drug resistant pathogens, there is a clear need for administration of more potent, potentially more toxic, drugs. Alternatively, biopharmaceuticals may hold potential but require specialized protection from premature in vivo degradation. Thus, a paralleled need for specialized drug delivery systems has arisen. Although cell-mediated drug delivery is not a completely novel concept, the few applications described to date are not yet ready for in vivo application, for various reasons such as drug-induced carrier cell death, limited control over the site and timing of drug release and/or drug degradation by the host immune system. Here, we present our hypothesis for a new drug delivery system, which aims to negate these limitations. We propose transport of nanoparticle-encapsulated drugs inside autologous macrophages polarized to M1 phenotype for high mobility and treated to induce transient phagosome maturation arrest. In addition, we propose a significant shift of existing paradigms in the study of host-microbe interactions, in order to study microbial host immune evasion and dissemination patterns for their therapeutic utilization in the context of drug delivery. We describe a system in which microbial strategies may be adopted to facilitate absolute control over drug delivery, and without sacrificing the host carrier cells. We provide a comprehensive summary of the lessons we can learn from microbes in the context of drug delivery and discuss their feasibility for in vivo therapeutic application. We then describe our proposed "synthetic microbe drug delivery system" in detail. In our opinion, this multidisciplinary approach may hold the solution to effective, controlled drug delivery.

Wide-ranging and unexpected consequences of altered Pol II catalytic activity in vivo

Here we employ a set of RNA Polymerase II (Pol II) activity mutants to determine the consequences of increased or decreased Pol II catalysis on gene expression in Saccharomyces cerevisiae. We find that alteration of Pol II catalytic rate, either fast or slow, leads to decreased Pol II occupancy and apparent reduction in elongation rate in vivo. However, we also find that determination of elongation rate in vivo by chromatin immunoprecipitation can be confounded by the kinetics and conditions of transcriptional shutoff in the assay. We identify promoter and template-specific effects on severity of gene expression defects for both fast and slow Pol II mutants. We show that mRNA half-lives for a reporter gene are increased in both fast and slow Pol II mutant strains and the magnitude of half-life changes correlate both with mutants' growth and reporter expression defects. Finally, we tested a model that altered Pol II activity sensitizes cells to nucleotide depletion. In contrast to model predictions, mutated Pol II retains normal sensitivity to altered nucleotide levels. Our experiments establish a framework for understanding the diversity of transcription defects derived from altered Pol II activity mutants, essential for their use as probes of transcription mechanisms.

The class III phosphatidylinositol 3-kinase Vps34 in Saccharomyces cerevisiae

The class III phosphatidylinositol 3-kinase Vps34 (vacuolar protein sorting 34) catalyzes for the formation of the signaling lipid phosphatidylinositol-3-phopsphate, which is a central factor in the regulation of autophagy, endocytic trafficking and vesicular transport. In this article, we discuss the functional role of the lipid kinase Vps34 in Saccharomyces cerevisiae.

Genome-wide bisulfite sensitivity profiling of yeast suggests bisulfite inhibits transcription

Bisulfite, in the form of sodium bisulfite or metabisulfite, is used commercially as a food preservative. Bisulfite is used in the laboratory as a single-stranded DNA mutagen in epigenomic analyses of DNA methylation. Recently it has also been used on whole yeast cells to induce mutations in exposed single-stranded regions in vivo. To understand the effects of bisulfite on live cells we conducted a genome-wide screen for bisulfite sensitive mutants in yeast. Screening the deletion mutant array, and collections of essential gene mutants we define a genetic network of bisulfite sensitive mutants. Validation of screen hits revealed hyper-sensitivity of transcription and RNA processing mutants, rather than DNA repair pathways and follow-up analyses support a role in perturbation of RNA transactions. We propose a model in which bisulfite-modified nucleotides may interfere with transcription or RNA metabolism when used in vivo.

New integrative modules for multicolor-protein labeling and live-cell imaging in Saccharomyces cerevisiae

Live-imaging analysis is performed in many laboratories all over the world. Various tools have been developed to enable protein labeling either in plasmid or genomic context in live yeast cells. Here, we introduce a set of nine integrative modules for the C-terminal gene tagging that combines three fluorescent proteins (FPs)-ymTagBFP, mCherry and yTagRFP-T with three dominant selection markers: geneticin, nourseothricin and hygromycin. In addition, the construction of two episomal modules for Saccharomyces cerevisiae with photostable yTagRFP-T is also referred to. Our cassettes with orange, red and blue FPs can be combined with other fluorescent probes like green fluorescent protein to prepare double- or triple-labeled strains for multicolor live-cell imaging. Primers for PCR amplification of the cassettes were designed in such a way as to be fully compatible with the existing PCR toolbox representing over 50 various integrative modules and also with deletion cassettes either for single or repeated usage to enable a cost-effective and an easy exchange of tags. New modules can also be used for biochemical analysis since antibodies are available for all three fluorescent probes.

Evidence for a Nonendosomal Function of the Saccharomyces cerevisiae ESCRT-III-Like Protein Chm7

Endosomal sorting complex required for transport (ESCRT) proteins are involved in a number of cellular processes, such as endosomal protein sorting, HIV budding, cytokinesis, plasma membrane repair, and resealing of the nuclear envelope during mitosis. Here we explored the function of a noncanonical member of the ESCRT-III protein family, the Saccharomyces cerevisiae ortholog of human CHMP7. Very little is known about this protein. In silico analysis predicted that Chm7 (yeast ORF YJL049w) is a fusion of an ESCRT-II and ESCRT-III-like domain, which would suggest a role in endosomal protein sorting. However, our data argue against a role of Chm7 in endosomal protein sorting. The turnover of the endocytic cargo protein Ste6 and the vacuolar protein sorting of carboxypeptidase S (CPS) were not affected by CHM7 deletion, and Chm7 also responded very differently to a loss in Vps4 function compared to a canonical ESCRT-III protein. Our data indicate that the Chm7 function could be connected to the endoplasmic reticulum (ER). In line with a function at the ER, we observed a strong negative genetic interaction between the deletion of a gene function (APQ12) implicated in nuclear pore complex assembly and messenger RNA (mRNA) export and the CHM7 deletion. The patterns of genetic interactions between the APQ12 deletion and deletions of ESCRT-III genes, two-hybrid interactions, and the specific localization of mCherry fusion proteins are consistent with the notion that Chm7 performs a novel function at the ER as part of an alternative ESCRT-III complex.

The Dual Role of an ESCRT-0 Component HGS in HBV Transcription and Naked Capsid Secretion

The Endosomal Sorting Complex Required for Transport (ESCRT) is an important cellular machinery for the sorting and trafficking of ubiquitinated cargos. It is also known that ESCRT is required for the egress of a number of viruses. To investigate the relationship between ESCRT and hepatitis B virus (HBV), we conducted an siRNA screening of ESCRT components for their potential effect on HBV replication and virion release. We identified a number of ESCRT factors required for HBV replication, and focused our study here on HGS (HRS, hepatocyte growth factor-regulated tyrosine kinase substrate) in the ESCRT-0 complex. Aberrant levels of HGS suppressed HBV transcription, replication and virion secretion. Hydrodynamic delivery of HGS in a mouse model significantly suppressed viral replication in the liver and virion secretion in the serum. Surprisingly, overexpression of HGS stimulated the release of HBV naked capsids, irrespective of their viral RNA, DNA, or empty contents. Mutant core protein (HBc 1-147) containing no arginine-rich domain (ARD) failed to secrete empty virions with or without HGS. In contrast, empty naked capsids of HBc 1-147 could still be promoted for secretion by HGS. HGS exerted a strong positive effect on the secretion of naked capsids, at the expense of a reduced level of virions. The association between HGS and HBc appears to be ubiquitin-independent. Furthermore, HBc is preferentially co-localized with HGS near the cell periphery, instead of near the punctate endosomes in the cytoplasm. In summary, our work demonstrated the importance of an optimum level of HGS in HBV propagation. In addition to an effect on HBV transcription, HGS can diminish the pool size of intracellular nucleocapsids with ongoing genome maturation, probably in part by promoting the secretion of naked capsids. The secretion routes of HBV virions and naked capsids can be clearly distinguished based on the pleiotropic effect of HGS involved in the ESCRT-0 complex.

Accumulation of a threonine biosynthetic intermediate attenuates general amino acid control by accelerating degradation of Gcn4 via Pho85 and Cdk8

Gcn4 is a master transcriptional regulator of amino acid and vitamin biosynthetic enzymes subject to the general amino acid control (GAAC), whose expression is upregulated in response to amino acid starvation in Saccharomyces cerevisiae. We found that accumulation of the threonine pathway intermediate β-aspartate semialdehyde (ASA), substrate of homoserine dehydrogenase (Hom6), attenuates the GAAC transcriptional response by accelerating degradation of Gcn4, already an exceedingly unstable protein, in cells starved for isoleucine and valine. The reduction in Gcn4 abundance on ASA accumulation requires Cdk8/Srb10 and Pho85, cyclin-dependent kinases (CDKs) known to mediate rapid turnover of Gcn4 by the proteasome via phosphorylation of the Gcn4 activation domain under nonstarvation conditions. Interestingly, rescue of Gcn4 abundance in hom6 cells by elimination of SRB10 is not accompanied by recovery of transcriptional activation, while equivalent rescue of UAS-bound Gcn4 in hom6 pho85 cells restores greater than wild-type activation of Gcn4 target genes. These and other findings suggest that the two CDKs target different populations of Gcn4 on ASA accumulation, with Srb10 clearing mostly inactive Gcn4 molecules at the promoter that are enriched for sumoylation of the activation domain, and Pho85 clearing molecules unbound to the UAS that include both fully functional and inactive Gcn4 species.

Transcriptional activator Gcn4 maintains amino acid homeostasis in budding yeast by inducing multiple amino acid biosynthetic pathways in response to starvation for any amino acid—the general amino acid control. Gcn4 abundance is tightly regulated by the interplay between an intricate translational control mechanism, which induces Gcn4 synthesis in starved cells, and a pathway of phosphorylation and ubiquitylation that mediates its rapid degradation by the proteasome. Here, we discovered that accumulation of a threonine biosynthetic pathway intermediate, β-aspartate semialdehyde (ASA), in hom6Δ mutant cells impairs general amino acid control in cells starved for isoleucine and valine by accelerating the already rapid degradation of Gcn4, in a manner requiring its phosphorylation by cyclin-dependent kinases Cdk8/Srb10 and Pho85. Interestingly, our results unveil a division of labor between these two kinases wherein Srb10 primarily targets inactive Gcn4 molecules—presumably damaged under conditions of ASA excess—while Pho85 clears a greater proportion of functional Gcn4 species from the cell. The ability of ASA to inhibit transcriptional induction of threonine pathway enzymes by Gcn4, dampening ASA accumulation and its toxic effects on cell physiology, should be adaptive in the wild when yeast encounters natural antibiotics that target Hom6 enzymatic activity.

Autophagy suppression by appendicitis and appendectomy protects against colitis

BACKGROUND

When done at a young age, appendicitis followed by appendectomy (AA) offers protection against ulcerative colitis development in later life. We developed the first ever murine AA model. Using this model, we showed earlier that previous AA ameliorated colitis. We aimed to determine whether autophagy genes contribute to the anti-colitis protection conferred by AA, and if so, to delineate the autophagy-linked genes involved in this.

METHODS

Mice with 2 laparotomies each served as controls (sham-sham). Distal colons were harvested (4 AA-group colons, 4 sham-sham group colons), and RNA extracted from each. The RNA was taken through microarray analysis or reverse transcription-polymerase chain reaction validation. Gene set enrichment analysis software was used to analyze the microarray data.

RESULTS

Out of 28 key autophagy-related genes investigated (VPS15, VPS34, FIP200, ATG03, ATG04A, ATG04B, ATG05, ATG07, ATG10, ATG12, ATG13b, ATG14, ATG16L1, BECN1, GABARAPL1, IRGM1, IRGM2, LAMP2, LC3A, LC3B, RAB7A, UVRAG, NOD2, XBP1, LRRK2, ULK1, ULK2, PTPN2), 7 have genetic associations with inflammatory bowel diseases (ATG16L1, IRGM1, NOD2, XBP1, LRRK2, ULK1, PTPN2). There was slight upregulation of IRGM1, FIP200, and ATG04A (P < 0.05), but no variations with the other 25 genes. In contrast, gene set enrichment analysis revealed that AA downregulated 74 gene sets (associated with 28 autophagy genes) while upregulating only 5 (false discovery rate <5%; P < 0.001) gene sets. Additionally, 22 gene sets associated with the 7 autophagy + inflammatory bowel disease-associated genes were downregulated by AA, whereas only 3 were upregulated. The genes with maximum AA-induced gene set suppression were VPS15, LAMP2, LC3A, XBP1, and ULK1.

CONCLUSIONS

AA induces profound autophagy suppression in the distal colon. The AA-induced upregulation of individual genes (IRGM1, FIP200, ATG04A) could be a reflection of complex compensatory changes or the initial abnormality that led to the pronounced autophagy suppression. Autophagy suppression by AA may induce lesser antigen processing, leading to lesser cross-reactive immunity between microbes and self-antigens, and subsequent amelioration of colitis.

Destination: inner nuclear membrane

The inner nuclear membrane (INM) of eukaryotic cells is enriched in proteins that are required for nuclear structure, chromosome organization, DNA repair, and transcriptional control. Mislocalization of INM proteins is observed in a wide spectrum of human diseases; however, the mechanism by which INM proteins reach their final destination is poorly understood. In this review we discuss how investigating INM composition, dissecting targeting pathways of conserved INM proteins in multiple systems and analyzing the nuclear transport of viruses and signaling complexes have broadened our knowledge of INM transport to include both nuclear pore complex-dependent and -independent pathways. The study of these INM targeting pathways is important to understanding nuclear organization and in both normal and diseased cells.

New roles for old characters: an educational primer for use with "Vps factors are required for efficient transcription elongation in budding yeast"

An article from Alan Hinnebusch's laboratory in the March 2013 issue of GENETICS establishes an exciting new link between proteins with well-established roles in the endomembrane system and the process of transcription elongation. This Primer article provides tools needed for students to fully appreciate, analyze, and critically evaluate the experiments and interpretations of Gaur et al. (2013). The primer includes detailed descriptions of techniques used in the study, such as the chromatin immunoprecipitation assay and assays for transcription elongation, and it provides a framework to facilitate an understanding of how a combination of genetic, biochemical, and cell microscopy experimental approaches were used by the authors to converge on a single major conclusion. Suggestions for using this Primer article in an undergraduate or graduate-level course in conjunction with the original article to promote student learning are also presented.