Rpb9-deficient cells are defective in DNA damage response and require histone H3 acetylation for survival

Identification of host proteins interacting with the E protein of porcine epidemic diarrhea virus

Introduction

Porcine epidemic diarrhea (PED) is an acute, highly contagious, and high-mortality enterophilic infectious disease caused by the porcine epidemic diarrhea virus (PEDV). PEDV is globally endemic and causes substantial economic losses in the swine industry. The PEDV E protein is the smallest structural protein with high expression levels that interacts with the M protein and participates in virus assembly. However, how the host proteins interact with E proteins in PEDV replication remains unknown.

Methods

We identified host proteins that interact with the PEDV E protein using a combination of PEDV E protein-labeled antibody co-immunoprecipitation and tandem liquid-chromatography mass-spectroscopy (LC-MS/MS).

Results

Bioinformatical analysis showed that in eukaryotes, ribosome biogenesis, RNA transport, and amino acid biosynthesis represent the three main pathways that are associated with the E protein. The interaction between the E protein and isocitrate dehydrogenase [NAD] β-subunit (NAD-IDH-β), DNA-directed RNA polymerase II subunit RPB9, and mRNA-associated protein MRNP 41 was validated using co-immunoprecipitation and confocal assays. NAD-IDH-β overexpression significantly inhibited viral replication.

Discussion

The antiviral effect of NAD-IDH-β suggesting that the E protein may regulate host metabolism by interacting with NAD-IDH-β, thereby reducing the available energy for viral replication. Elucidating the interaction between the PEDV E protein and host proteins may clarify its role in viral replication. These results provide a theoretical basis for the study of PEDV infection mechanism and antiviral targets.

Interactions between Fkh1 monomers stabilize its binding to DNA replication origins

Eukaryotic DNA replication is initiated from multiple genomic origins, which can be broadly categorized as firing early or late in the S phase. Several factors can influence the temporal usage of origins to determine the timing of their firing. In budding yeast, the Forkhead family proteins Fkh1 and Fkh2 bind to a subset of replication origins and activate them at the beginning of the S phase. In these origins, the Fkh1/2 binding sites are arranged in a strict configuration, suggesting that Forkhead factors must bind the origins in a specific manner. To explore these binding mechanisms in more detail, we mapped the domains of Fkh1 that were required for its role in DNA replication regulation. We found that a short region of Fkh1 near its DNA binding domain was essential for the protein to bind and activate replication origins. Analysis of purified Fkh1 proteins revealed that this region mediates dimerization of Fkh1, suggesting that intramolecular contacts of Fkh1 are required for efficient binding and regulation of DNA replication origins. We also show that the Sld3-Sld7-Cdc45 complex is recruited to Forkhead-regulated origins already in the G1 phase and that Fkh1 is constantly required to keep these factors bound on origins before the onset of the S phase. Together, our results suggest that dimerization-mediated stabilization of DNA binding by Fkh1 is crucial for its ability to activate DNA replication origins.

Polymerases and DNA Repair in Neurons: Implications in Neuronal Survival and Neurodegenerative Diseases

Most of the neurodegenerative diseases and aging are associated with reactive oxygen species (ROS) or other intracellular damaging agents that challenge the genome integrity of the neurons. As most of the mature neurons stay in G0/G1 phase, replication-uncoupled DNA repair pathways including BER, NER, SSBR, and NHEJ, are pivotal, efficient, and economic mechanisms to maintain genomic stability without reactivating cell cycle. In these progresses, polymerases are prominent, not only because they are responsible for both sensing and repairing damages, but also for their more diversified roles depending on the cell cycle phase and damage types. In this review, we summarized recent knowledge on the structural and biochemical properties of distinct polymerases, including DNA and RNA polymerases, which are known to be expressed and active in nervous system; the biological relevance of these polymerases and their interactors with neuronal degeneration would be most graphically illustrated by the neurological abnormalities observed in patients with hereditary diseases associated with defects in DNA repair; furthermore, the vicious cycle of the trinucleotide repeat (TNR) and impaired DNA repair pathway is also discussed. Unraveling the mechanisms and contextual basis of the role of the polymerases in DNA damage response and repair will promote our understanding about how long-lived postmitotic cells cope with DNA lesions, and why disrupted DNA repair contributes to disease origin, despite the diversity of mutations in genes. This knowledge may lead to new insight into the development of targeted intervention for neurodegenerative diseases.

Absence of the Rpb9 subunit of RNA polymerase II reduces the chronological life span in fission yeast

Fission yeast RNA polymerase II consists of 12 subunits, Rpb1-Rpb12. Among these subunits, Rpb9 is the only subunit whose absence does not cause lethality under optimum growth conditions in fission yeast. However, an rpb9 null fission yeast mutant exhibits a slow-growth phenotype under optimum growth conditions and a defect in survival under environmental and genotoxic stress conditions. To further gain an understanding of its physiological roles, in the present study we have elucidated the role of the Rpb9 subunit in chronological aging using fission yeast as the model organism. Our results provide evidence that the absence of Rpb9 reduces the chronological life span in fission yeast. Our data further shows that lack of Rpb9 in fission yeast causes oxidative stress sensitivity and accumulation of reactive oxygen species during the stationary phase. Our domain mapping experiments have demonstrated that the Rpb9 region encompassing its amino-terminal zinc finger domain and the central linker region is important for the role of Rpb9 in chronological aging. Finally, we also show that expression of the budding yeast or human Rpb9 ortholog can functionally complement the reduced chronological life span phenotype of the fission yeast rpb9 deletion mutant. Taken together, our study has identified a new role of the Rpb9 subunit in chronological aging.

Purine Auxotrophic Starvation Evokes Phenotype Similar to Stationary Phase Cells in Budding Yeast

Purine auxotrophy is an abundant trait among eukaryotic parasites and a typical marker for many budding yeast strains. Supplementation with an additional purine source (such as adenine) is necessary to cultivate these strains. If not supplied in adequate amounts, purine starvation sets in. We explored purine starvation effects in a model organism, a budding yeast Saccharomyces cerevisiae ade8 knockout, at the level of cellular morphology, central carbon metabolism, and global transcriptome. We observed that purine-starved cells stopped their cycle in G1/G0 state and accumulated trehalose, and the intracellular concentration of AXP decreased, but adenylate charge remained stable. Cells became tolerant to severe environmental stresses. Intracellular RNA concentration decreased, and massive downregulation of ribosomal biosynthesis genes occurred. We proved that the expression of new proteins during purine starvation is critical for cells to attain stress tolerance phenotype Msn2/4p targets are upregulated in purine-starved cells when compared to cells cultivated in purine-rich media. The overall transcriptomic response to purine starvation resembles that of stationary phase cells. Our results demonstrate that the induction of a strong stress resistance phenotype in budding yeast can be caused not only by natural starvation, but also starvation for metabolic intermediates, such as purines.

Comprehensive Bioinformatics Analysis Identifies POLR2I as a Key Gene in the Pathogenesis of Hypertensive Nephropathy

Hypertensive nephropathy (HN), mainly caused by chronic hypertension, is one of the major causes of end-stage renal disease. However, the pathogenesis of HN remains unclarified, and there is an urgent need for improved treatments. Gene expression profiles for HN and normal tissue were obtained from the Gene Expression Omnibus database. A total of 229 differentially co-expressed genes were identified by weighted gene co-expression network analysis and differential gene expression analysis. These genes were used to construct protein–protein interaction networks to search for hub genes. Following validation in an independent external dataset and in a clinical database, POLR2I, one of the hub genes, was identified as a key gene related to the pathogenesis of HN. The expression level of POLR2I is upregulated in HN, and the up-regulation of POLR2I is positively correlated with renal function in HN. Finally, we verified the protein levels of POLR2I in vivo to confirm the accuracy of our analysis. In conclusion, our study identified POLR2I as a key gene related to the pathogenesis of HN, providing new insights into the molecular mechanisms underlying HN.

Deletion of the non-essential Rpb9 subunit of RNA polymerase II results in pleiotropic phenotypes in Schizosaccharomyces pombe

Schizosaccharomyces pombe RNA polymerase II comprises twelve different subunits. Its Rpb9 subunit comprises 113 amino acids, and is the only non-essential subunit of S. pombe RNA polymerase II. However, its functions have not been studied in S. pombe. The results presented in this study demonstrate that Rpb9 is involved in regulating growth under optimum and certain stress conditions in S. pombe. To further address the role (s) of various domains of this subunit in regulating these phenotypes, deletion mutant analysis was done. We observed that the region spanning 1-74 amino acids, encompassing the amino-terminal zinc finger domain and the linker region of Rpb9 was able to rescue the phenotypes associated with rpb9⁺deletion. We also demonstrate that the functions of this subunit are only partially conserved among yeast and humans. Our computational biology approaches provide a structural basis for the differential role of various Rpb9 domains in S. pombe. Furthermore, using these tools we show that there has been a co-evolution of the interaction residues between the Rpb9 subunit and the two largest subunits of RNA polymerase II, allowing for a more stringent organism-specific packing. Taken together, our results have provided functional and structural insights into the Rpb9 subunit of S. pombe.

Damage-induced chromatome dynamics link Ubiquitin ligase and proteasome recruitment to histone loss and efficient DNA repair

Eukaryotic cells package their genomes around histone octamers. In response to DNA damage, checkpoint activation in yeast induces core histone degradation resulting in 20%-40% reduction in nucleosome occupancy. To gain insight into this process, we developed a new approach to analyze the chromatin-associated proteome comprehensively before and after damage. This revealed extensive changes in protein composition after Zeocin-induced damage. First, core histones and the H1 homolog Hho1 were partially lost from chromatin along with replication, transcription, and chromatin remodeling machineries, while ubiquitin ligases and the proteasome were recruited. We found that the checkpoint- and INO80C-dependent recruitment of five ubiquitin-conjugating factors (Rad6, Bre1, Pep5, Ufd4, and Rsp5) contributes to core and linker histone depletion, reducing chromatin compaction and enhancing DNA locus mobility. Importantly, loss of Rad6/Bre1, Ufd4/TRIP12, and Pep5/VPS11 compromise DNA strand invasion kinetics during homology-driven repair. Thus we provide a comprehensive overview of a functionally relevant genome-wide chromatin response to DNA damage.

Taf14 is required for the stabilization of transcription pre-initiation complex in Saccharomyces cerevisiae

Background

The YEATS domain is a highly conserved protein structure that interacts with acetylated and crotonylated lysine residues in N-terminal tails of histones. The budding yeast genome encodes three YEATS domain proteins (Taf14, Yaf9, and Sas5) that are all the subunits of different complexes involved in histone acetylation, gene transcription, and chromatin remodeling. As the strains deficient in all these three genes are inviable, it has been proposed that the YEATS domain is essential in yeast. In this study we investigate in more detail the requirement of YEATS domain proteins for yeast survival and the possible roles of Taf14 YEATS domain in the regulation of gene transcription.

Results

We found that YEATS domains are not essential for the survival of Saccharomyces cerevisiae cells. Although the full deletion of all YEATS proteins is lethal in yeast, we show that the viability of cells can be restored by the expression of the YEATS-less version of Taf14 protein. We also explore the in vivo functions of Taf14 protein and show that the primary role of its YEATS domain is to stabilize the transcription pre-initiation complex (PIC). Our results indicate that Taf14-mediated interactions become crucial for PIC formation in rpb9Δ cells, where the recruitment of TFIIF to the PIC is hampered. Although H3 K9 residue has been identified as the interaction site of the Taf14 YEATS domain in vitro, we found that it is not the only interaction target in vivo.

Conclusions

Lethality of YEATS-deficient cells can be rescued by the expression of truncated Taf14 protein lacking the entire YEATS domain, indicating that the YEATS domains are not required for cell survival. The YEATS domain of Taf14 participates in PIC stabilization and acetylated/crotonylated H3K9 is not the critical target of the Taf14 YEATS domain in vivo.