Poly(A)(+) mRNA-binding protein Tudor-SN regulates stress granules aggregation dynamics

Composition and function of stress granules and P-bodies in plants

Stress Granules (SGs) and Processing-bodies (P-bodies) are biomolecular condensates formed in the cell with the highly conserved purpose of maintaining balance between storage, translation, and degradation of mRNA. This balance is particularly important when cells are exposed to different environmental conditions and adjustments have to be made in order for plants to respond to and tolerate stressful conditions. While P-bodies are constitutively present in the cell, SG formation is a stress-induced event. Typically thought of as protein-RNA aggregates, SGs and P-bodies are formed by a process called liquid-liquid phase separation (LLPS), and both their function and composition are very dynamic. Both foci are known to contain proteins involved in translation, protein folding, and ATPase activity, alluding to their roles in regulating mRNA and protein expression levels. From an RNA perspective, SGs and P-bodies primarily consist of mRNAs, though long non-coding RNAs (lncRNAs) have also been observed, and more focus is now being placed on the specific RNAs associated with these aggregates. Recently, metabolites such as nucleotides and amino acids have been reported in purified plant SGs with implications for the energetic dynamics of these condensates. Thus, even though the field of plant SGs and P-bodies is relatively nascent, significant progress has been made in understanding their composition and biological role in stress responses. In this review, we discuss the most recent discoveries centered around SG and P-body function and composition in plants.

Bidirectional Functional Effects of Staphylococcus on Carcinogenesis

As a Gram-positive cocci existing in nature, Staphylococcus has a variety of species, such as Staphylococcus aureus and Staphylococcus epidermidis, etc. Growing evidence reveals that Staphylococcus is closely related to the occurrence and development of various cancers. On the one hand, cancer patients are more likely to suffer from bacterial infection and antibiotic-resistant strain infection compared to healthy controls. On the other hand, there exists an association between staphylococcal infection and carcinogenesis. Staphylococcus often plays a pathogenic role and evades the host immune system through surface adhesion molecules, α-hemolysin, PVL (Panton-Valentine leukocidin), SEs (staphylococcal enterotoxins), SpA (staphylococcal protein A), TSST-1 (Toxic shock syndrom toxin-1) and other factors. Staphylococcal nucleases (SNases) are extracellular nucleases that serve as genomic markers for Staphylococcus aureus. Interestingly, a human homologue of SNases, SND1 (staphylococcal nuclease and Tudor domain-containing 1), has been recognized as an oncoprotein. This review is the first to summarize the reported basic and clinical evidence on staphylococci and neoplasms. Investigations on the correlation between Staphylococcus and the occurrence, development, diagnosis and treatment of breast, skin, oral, colon and other cancers, are made from the perspectives of various virulence factors and SND1.

SND1 Promotes Radioresistance in Cervical Cancer Cells by Targeting the DNA Damage Response

Background: Radiotherapy is one of the most effective therapeutic strategies for cervical cancer patients, although radioresistance-mediated residual and recurrent tumors are the main cause of treatment failure. However, the mechanism of tumor radioresistance is still elusive. DNA damage response pathways are key determinants of radioresistance. The purpose of this study was to investigate the role and mechanism of SND1 in radioresistance of cervical cancer. Methods: A stable HeLa cell line with SND1 knockout (HeLa-KO) was generated through a modified CRISPR/Cas9 double-nicking gene editing system. The stable CaSki cell lines with SND1 knockdown (CaSki-Ctrl, CaSki-SND1-sh-1, CaSki-SND1-sh-2) were constructed through lentivirus transfection with the pSil-SND1-sh-1 and pSil-SND1-sh-2 plasmids. Results: It was observed that SND1 deficiency significantly increased the radiosensitivity of cervical cancer cells. It was also found that silencing SND1 promotes radiation-induced apoptosis. Significantly, the cells with a loss of SND1 function exhibited inefficient ataxia telangiectasia mutated pathway activation, subsequently impairing DNA repair and G2/M checkpoint arrest. In addition, threonine 103 is an important phosphorylation site of SND1 under DNA damaging stress. Conclusion: Collectively, the results of this study reveal a potent radiosensitizing effect of silencing SND1 or T103 mutation on cervical cancer cells, providing novel insights into potential therapeutic strategies for cervical cancer treatment.

Monitoring Virus-Induced Stress Granule Dynamics Using Long-Term Live-Cell Imaging

The integrated stress response is a highly regulated signaling cascade that allows cells to react to a variety of external and internal stimuli. Activation of different stress-responsive kinases leads to the phosphorylation of their common downstream target, the eukaryotic translation initiation factor 2 alpha (eIF2α), which is a critical component of functional translation preinitiation complexes. As a consequence, stalled ribonucleoprotein complexes accumulate in the cytoplasm and condense into microscopically visible cytoplasmic stress granules (SGs). Over the past years, numerous microscopy approaches have been developed to study the spatiotemporal control of SG formation in response to a variety of stressors. Here, we apply long-term live-cell microscopy to monitor the dynamic cellular stress response triggered by infection with chronic hepatitis C virus (HCV) at single-cell level and study the behavior of infected cells that repeatedly switch between a stressed and unstressed state. We describe in detail the engineering of fluorescent SG-reporter cells expressing enhanced yellow fluorescent protein (YFP)-tagged T cell internal antigen 1 (TIA-1) using lentiviral delivery, as well as the production of mCherry-tagged HCV trans-complemented particles, which allow live tracking of SG assembly and disassembly, SG number and size in single infected cells over time.

The TSN1 Binding Protein RH31 Is a Component of Stress Granules and Participates in Regulation of Salt-Stress Tolerance in Arabidopsis

Tudor staphylococcal nucleases (TSNs) are evolutionarily conserved RNA binding proteins, which include redundant TSN1 and TSN2 in Arabidopsis. It has been showed TSNs are the components of stress granules (SGs) and regulate plant growth under salt stress. In this study, we find a binding protein of TSN1, RH31, which is a DEAD-box RNA helicase (RH). Subcellular localization studies show that RH31 is mainly located in the nucleus, but under salinity, it translocates to the cytoplasm where it accumulates in cytoplasmic granules. After cycloheximide (CHX) treatment which can block the formation of SGs by interfering with mRNP homeostasis, these cytoplasmic granules disappeared. More importantly, RH31 co-localizes with SGs marker protein RBP47. RH31 deletion results in salt-hypersensitive phenotype, while RH31 overexpression causes more resistant to salt stress. In summary, we demonstrate that RH31, the TSN1 binding protein, is a component of plant SGs and participates in regulation of salt-stress tolerance in Arabidopsis.

Impact of hepatocyte-specific deletion of staphylococcal nuclease and tudor domain containing 1 (SND1) on liver insulin resistance and acute liver failure of mice

Although our previous research shows an ameliorated high-fat diet (HFD)-induced hepatic steatosis and insulin resistance in global SND1 transgenic mice, the involvement of SND1 loss-of-function in hepatic metabolism remains elusive. Herein, we aim to explore the potential impact of hepatocyte-specific SND1 deletion on insulin-resistant mice. As SND1 is reported to be linked to inflammatory response, the pathobiological feature of acute liver failure (ALF) is also investigated. Hence, we construct the conditional liver knockout (LKO) mice of SND1 for the first time. Under the condition of HFD, the absence of hepatic SND1 affects the weight of white adipose tissue, but not the gross morphology, body weight, cholesterol level, liver weight, and hepatic steatosis of mice. Furthermore, we fail to observe significant differences in either HFD-induced insulin resistance or lipopolysaccharide/D-galactosamine-induced (LPS/D-GaIN) ALF between LKO and wild type (WT) mice in terms of inflammation and tissue damage. Compared with negative controls, there is no differential SND1 expression in various species of sample with insulin resistance or ALF, based on several gene expression omnibus datasets, including GSE23343, GSE160646, GSE120243, GSE48794, GSE13271, GSE151268, GSE62026, GSE120652, and GSE38941. Enrichment result of SND1-binding partners or related genes indicates a sequence of issues related to RNA or lipid metabolism, but not glucose homeostasis or hepatic failure. Overall, hepatic SND1 is insufficient to alter the phenotypes of hepatic insulin resistance and acute liver failure in mice. The SND1 in various organs is likely to cooperate in regulating glucose homeostasis by affecting the expression of lipid metabolism-related RNA transcripts during stress.

Tudor staphylococcal nuclease is a docking platform for stress granule components and is essential for SnRK1 activation in Arabidopsis

Tudor staphylococcal nuclease (TSN; also known as Tudor-SN, p100, or SND1) is a multifunctional, evolutionarily conserved regulator of gene expression, exhibiting cytoprotective activity in animals and plants and oncogenic activity in mammals. During stress, TSN stably associates with stress granules (SGs), in a poorly understood process. Here, we show that in the model plant Arabidopsis thaliana, TSN is an intrinsically disordered protein (IDP) acting as a scaffold for a large pool of other IDPs, enriched for conserved stress granule components as well as novel or plant-specific SG-localized proteins. While approximately 30% of TSN interactors are recruited to stress granules de novo upon stress perception, 70% form a protein-protein interaction network present before the onset of stress. Finally, we demonstrate that TSN and stress granule formation promote heat-induced activation of the evolutionarily conserved energy-sensing SNF1-related protein kinase 1 (SnRK1), the plant orthologue of mammalian AMP-activated protein kinase (AMPK). Our results establish TSN as a docking platform for stress granule proteins, with an important role in stress signalling.

Arabidopsis thaliana G3BP Ortholog Rescues Mammalian Stress Granule Phenotype across Kingdoms

Stress granules (SGs) are dynamic RNA–protein complexes localized in the cytoplasm that rapidly form under stress conditions and disperse when normal conditions are restored. The formation of SGs depends on the Ras-GAP SH3 domain-binding protein (G3BP). Formations, interactions and functions of plant and human SGs are strikingly similar, suggesting a conserved mechanism. However, functional analyses of plant G3BPs are missing. Thus, members of the Arabidopsis thaliana G3BP (AtG3BP) protein family were investigated in a complementation assay in a human G3BP knock-out cell line. It was shown that two out of seven AtG3BPs were able to complement the function of their human homolog. GFP-AtG3BP fusion proteins co-localized with human SG marker proteins Caprin-1 and eIF4G1 and restored SG formation in G3BP double KO cells. Interaction between AtG3BP-1 and -7 and known human G3BP interaction partners such as Caprin-1 and USP10 was also demonstrated by co-immunoprecipitation. In addition, an RG/RGG domain exchange from Arabidopsis G3BP into the human G3BP background showed the ability for complementation. In summary, our results support a conserved mechanism of SG function over the kingdoms, which will help to further elucidate the biological function of the Arabidopsis G3BP protein family.

Stress Granule-Mediated Oxidized RNA Decay in P-Body: Hypothetical Role of ADAR1, Tudor-SN, and STAU1

Reactive oxygen species (ROS) generated under oxidative stress (OS) cause oxidative damage to RNA. Recent studies have suggested a role for oxidized RNA in several human disorders. Under the conditions of oxidative stress, mRNAs released from polysome dissociation accumulate and initiate stress granule (SG) assembly. SGs are highly enriched in mRNAs, containing inverted repeat (IR) Alus in 3′ UTRs, AU-rich elements, and RNA-binding proteins. SGs and processing bodies (P-bodies) transiently interact through a docking mechanism to allow the exchange of RNA species. However, the types of RNA species exchanged, and the mechanisms and outcomes of exchange are still unknown. Specialized RNA-binding proteins, including adenosine deaminase acting on RNA (ADAR1-p150), with an affinity toward inverted repeat Alus, and Tudor staphylococcal nuclease (Tudor-SN) are specifically recruited to SGs under OS along with an RNA transport protein, Staufen1 (STAU1), but their precise biochemical roles in SGs and SG/P-body docking are uncertain. Here, we critically review relevant literature and propose a hypothetical mechanism for the processing and decay of oxidized-RNA in SGs/P-bodies, as well as the role of ADAR1-p150, Tudor-SN, and STAU1.

Translation of Tudor-SN, a novel terminal oligo-pyrimidine (TOP) mRNA, is regulated by the mTORC1 pathway in cardiomyocytes

The mechanisms that regulate cell-cycle arrest of cardiomyocytes during heart development are largely unknown. We have previously identified Tudor staphylococcal nuclease (Tudor-SN) as a cell-cycle regulator and have shown that its expression level was closely related to cell-proliferation capacity. Herein, we found that Tudor-SN was highly expressed in neonatal mouse myocardia, but it was lowly expressed in that of adults. Using Data Base of Transcription Start Sites (DBTSS), we revealed that Tudor-SN was a terminal oligo-pyrimidine (TOP) mRNA. We further confirmed that the translational efficiency of Tudor-SN mRNA was controlled by the mammalian target of rapamycin complex 1 (mTORC1) pathway, as revealed via inhibition of activated mTORC1 in primary neonatal mouse cardiomyocytes and activation of silenced mTORC1 in adult mouse myocardia; additionally, this result was recapitulated in H9c2 cells. We also demonstrated that the downregulation of Tudor-SN in adult myocardia was due to inactivation of the mTORC1 pathway to ensure that heart growth was in proportion to that of the rest of the body. Moreover, we revealed that Tudor-SN participated in the mTORC1-mediated regulation of cardiomyocytic proliferation, which further elucidated the correlation between Tudor-SN and the mTORC1 pathway. Taken together, our findings suggest that the translational efficiency of Tudor-SN is regulated by the mTORC1 pathway in myocardia and that Tudor-SN is involved in mTORC1-mediated regulation of cardiomyocytic proliferation and cardiac development.

The Tudor SND1 protein is an m6A RNA reader essential for replication of Kaposi's sarcoma-associated herpesvirus

N6-methyladenosine (m6A) is the most abundant internal RNA modification of cellular mRNAs. m6A is recognised by YTH domain-containing proteins, which selectively bind to m6A-decorated RNAs regulating their turnover and translation. Using an m6A-modified hairpin present in the Kaposi's sarcoma associated herpesvirus (KSHV) ORF50 RNA, we identified seven members from the 'Royal family' as putative m6A readers, including SND1. RIP-seq and eCLIP analysis characterised the SND1 binding profile transcriptome-wide, revealing SND1 as an m6A reader. We further demonstrate that the m6A modification of the ORF50 RNA is critical for SND1 binding, which in turn stabilises the ORF50 transcript. Importantly, SND1 depletion leads to inhibition of KSHV early gene expression showing that SND1 is essential for KSHV lytic replication. This work demonstrates that members of the 'Royal family' have m6A-reading ability, greatly increasing their epigenetic functions beyond protein methylation.

ATP-driven reactions are required for the assembly of large stress granules

Stress granules (SGs) are functional messenger ribonucleoprotein aggregates, and their assembly is an important cellular process required for remodeling the signaling network to cope with extensive environmental stresses. SG formation is a stepwise process that involves the formation of a stable core followed by a less stable outer shell, and this process is often hampered by faulty regulation of protein phosphorylation. It remains unclear, however, which kinase activity is essential for SG formation. Here, we screened small molecule library of kinase inhibitors using a well-validated fluorogenic SG probe. Our screen, time-lapse microscopy, and biochemical analyses identified an ATP-mimetic SG inhibitor that selectively interferes with the fusion and growth, rather than the initial assembly, of SG core structures into the large assemblies. Thus, SGs utilize ATP-dependent chemical reactions to achieve their functional architectures.

Global Tudor-SN transgenic mice are protected from obesity-induced hepatic steatosis and insulin resistance

In the current study, we explored the impact of Tudor-staphylococcal nuclease (SN) on obesity induced by a high-fat diet (HFD) in mice, because the functional involvement of Tudor-SN in lipid metabolism in vivo is unknown. HFD-transgenic (Tg) mice exhibited reductions in hepatic steatosis and systemic insulin resistance. There was no difference in hepatic lipid accumulation between chow-fed wild-type (WT) and chow-fed Tg mice; consistently, no difference in activation of the lipogenic pathway was detected. Overactivation of hepatic nuclear sterol regulatory element-binding protein (nSrebp2)-2, the central regulator of cholesterol metabolic proteins, was observed in HFD-Tg livers along with improved cholesterol homeostasis, but no such changes were observed in HFD-WT livers. Consistent results were observed in vitro in α-mouse liver 12 cells treated with palmitate mimicking the HFD state. In addition, global gene analysis indicated that various downstream targets of nSrebp2, were up-regulated in HFD-Tg livers. Moreover, HFD-WT mice displayed islet hypertrophy and suppression of glucose-induced insulin secretion from islets, whereas HFD-Tg mice had normal pancreatic islets. This finding suggests that the improved pancreatic metabolism of HFD-Tg mice is related to the systemic effect of insulin resistance, not to the autonomous influence of pancreatic cells. Tudor-SN is likely to be a key regulator for ameliorating HFD-induced hepatic steatosis and systemic insulin resistance in vivo.-Wang, X., Xin, L., Duan, Z., Zuo, Z., Wang, Y., Ren, Y., Zhang, W., Sun, X., Liu, X., Ge, L., Yang, X., Yao, Z., Yang, J. Global Tudor-SN transgenic mice are protected from obesity-induced hepatic steatosis and insulin resistance.

SND1 acts as an anti-apoptotic factor via regulating the expression of lncRNA UCA1 in hepatocellular carcinoma

Multifunctional SND1 (staphylococcal nuclease and tudor domain containing 1) protein is reportedly associated with different types of RNA molecules, including mRNA, miRNA, pre-miRNA, and dsRNA. SND1 has been implicated in a number of biological processes in eukaryotic cells, including cell cycle, DNA damage repair, proliferation, and apoptosis. However, the specific molecular mechanism regarding the anti-apoptotic role of SND1 in mammalian cells remains largely elusive. In this study, the analysis of the online HPA (human protein atlas) and TCGA (the cancer genome atlas) databases showed the significantly high expression of SND1 in liver cancer patients. We found that the downregulation or complete depletion of SND1 enhanced the apoptosis levels of HepG2 and SMMC-7721 cells upon stimulation with 5-Fu (5-fluorouracil), a chemotherapeutic drug for HCC (hepatocellular carcinoma). SND1 affected the 5-Fu-induced apoptosis levels of HCC cells by modulating the expression of UCA1 (urothelial cancer associated 1), which is a lncRNA (long non-coding RNA). Moreover, MYB (MYB proto-oncogene, transcription factor) may be involved in the regulation of SND1 in UCA1 expression. In summary, our study identified SND1 as an anti-apoptotic factor in hepatocellular carcinoma cells via the modulation of lncRNA UCA1, which sheds new light on the relationship between SND1 protein and lncRNA.

Deubiquitylases USP5 and USP13 are recruited to and regulate heat-induced stress granules through their deubiquitylating activities

Stress granules are transient cytoplasmic foci induced by various stresses that contain translation-stalled mRNAs and RNA-binding proteins. They are proposed to modulate mRNA translation and stress responses. Here, we show that the deubiquitylases USP5 and USP13 are recruited to heat-induced stress granules. Heat-induced stress granules also contained K48- and K63-linked ubiquitin chains. Depletion of USP5 or USP13 resulted in elevated ubiquitin chain levels and accelerated assembly of heat-induced stress granules, suggesting that these enzymes regulate the stability of the stress granules through their ubiquitin isopeptidase activity. Moreover, disassembly of heat-induced stress granules after returning the cells to normal temperatures was markedly repressed by individual depletion of USP5 or USP13. Finally, overexpression of a ubiquitin mutant lacking the C-terminal diglycine motif caused the accumulation of unanchored ubiquitin chains and the repression of the disassembly of heat-induced stress granules. As unanchored ubiquitin chains are preferred substrates for USP5, we suggest that USP5 regulates the assembly and disassembly of heat-induced stress granules by mediating the hydrolysis of unanchored ubiquitin chains while USP13 regulates stress granules through deubiquitylating protein-conjugated ubiquitin chains.This article has an associated First Person interview with the first author of the paper.

Oncoprotein Tudor-SN is a key determinant providing survival advantage under DNA damaging stress

Herein, Tudor-SN was identified as a DNA damage response (DDR)-related protein that plays important roles in the early stage of DDR. X-ray or laser irradiation could evoke the accumulation of Tudor-SN to DNA damage sites in a poly(ADP-ribosyl)ation-dependent manner via interaction with PARP-1. Additionally, we illustrated that the SN domain of Tudor-SN mediated the association of these two proteins. The accumulated Tudor-SN further recruited SMARCA5 (ATP-dependent chromatin remodeller) and GCN5 (histone acetyltransferase) to DNA damage sites, resulting in chromatin relaxation, and consequently activating the ATM kinase and downstream DNA repair signalling pathways to promote cell survival. Consistently, the loss-of-function of Tudor-SN attenuated the enrichment of SMARCA5, GCN5 and acetylation of histone H3 (acH3) at DNA break sites and abolished chromatin relaxation; as a result, the cells exhibited DNA repair and cell survival deficiency. As Tudor-SN protein is highly expressed in different tumours, it is likely to be involved in the radioresistance of cancer treatment.

Ethanol Induced Disordering of Pancreatic Acinar Cell Endoplasmic Reticulum: An ER Stress/Defective Unfolded Protein Response Model

BACKGROUND & AIMS

Heavy alcohol drinking is associated with pancreatitis, whereas moderate intake lowers the risk. Mice fed ethanol long term show no pancreas damage unless adaptive/protective responses mediating proteostasis are disrupted. Pancreatic acini synthesize digestive enzymes (largely serine hydrolases) in the endoplasmic reticulum (ER), where perturbations (eg, alcohol consumption) activate adaptive unfolded protein responses orchestrated by spliced X-box binding protein 1 (XBP1). Here, we examined ethanol-induced early structural changes in pancreatic ER proteins.

METHODS

Wild-type and Xbp1+/- mice were fed control and ethanol diets, then tissues were homogenized and fractionated. ER proteins were labeled with a cysteine-reactive probe, isotope-coded affinity tag to obtain a novel pancreatic redox ER proteome. Specific labeling of active serine hydrolases in ER with fluorophosphonate desthiobiotin also was characterized proteomically. Protein structural perturbation by redox changes was evaluated further in molecular dynamic simulations.

RESULTS

Ethanol feeding and Xbp1 genetic inhibition altered ER redox balance and destabilized key proteins. Proteomic data and molecular dynamic simulations of Carboxyl ester lipase (Cel), a unique serine hydrolase active within ER, showed an uncoupled disulfide bond involving Cel Cys266, Cel dimerization, ER retention, and complex formation in ethanol-fed, XBP1-deficient mice.

CONCLUSIONS

Results documented in ethanol-fed mice lacking sufficient spliced XBP1 illustrate consequences of ER stress extended by preventing unfolded protein response from fully restoring pancreatic acinar cell proteostasis during ethanol-induced redox challenge. In this model, orderly protein folding and transport to the secretory pathway were disrupted, and abundant molecules including Cel with perturbed structures were retained in ER, promoting ER stress-related pancreas pathology.

Aggregation of SND1 in Stress Granules is Associated with the Microtubule Cytoskeleton During Heat Shock Stimulus

Stress granules (SGs) are dynamic dense structures in the cytoplasm that form in response to a variety of environmental stress stimuli. Staphylococcal nuclease and Tudor domain containing 1 (SND1) is a type of RNA‐binding protein and has been identified as a transcriptional co‐activator. Our previous studies have shown that SND1 is a component of the stress granule, which forms under stress conditions. Here, we observed that SND1 granules were often surrounded by ɑ‐tubulin‐microtubules in 45°C‐treated HeLa cells at 15 min or colocalized with microtubules at 30 or 45 min. Furthermore, Nocodazole‐mediated microtubule depolymerization could significantly affect the efficient recruitment of SND1 proteins to the SGs during heat shock stress. In addition, the 45°C heat shock mediated the enhancement of eIF2α phosphorylation, which was not affected by treatment with Nocodazole, an agent that disrupts the cytoskeleton. The intact microtubule cytoskeletal tracks are important for the efficient assembly of SND1 granules under heat shock stress and may facilitate SND1 shuttling between cytoplasmic RNA foci. Anat Rec, 300:2192–2199, 2017. © 2017 The Authors The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

The Tudor Staphylococcal Nuclease Protein of Entamoeba histolytica Participates in Transcription Regulation and Stress Response

Entamoeba histolytica is the protozoa parasite responsible of human amoebiasis, disease that causes from 40,000 to 100,000 deaths annually worldwide. However, few are known about the expression regulation of molecules involved in its pathogenicity. Transcription of some virulence-related genes is positively controlled by the cis-regulatory element named URE1. Previously we identified the transcription factor that binds to URE1, which displayed a nuclear and cytoplasmic localization. This protein belongs to the Tudor Staphyococcal nuclease (TSN) family, which in other systems participates in virtually all pathways of gene expression, suggesting that this amoebic transcription factor (EhTSN; former EhURE1BP) could also play multiple functions in E. histolytica. The aim of this study was to identify the possible cellular events where EhTSN is involved. Here, we found that EhTSN in nucleus is located in euchromatin and close to, but not into, heterochromatin. We also showed the association of EhTSN with proteins involved in transcription and that the knockdown of EhTSN provokes a diminishing in the mRNA level of the EhRabB gene, which in its promoter region contains the URE1 motif, confirming that EhTSN participates in transcription regulation. In cytoplasm, this protein was found linked to the membrane of small vesicles and to plasma membrane. Through pull-down assays and mass spectrometry we identity thirty two candidate proteins to interact with EhTSN. These proteins participate in transcription, metabolism, signaling, and stress response, among other cellular processes. Interaction of EhTSN with some candidate proteins involved in metabolism, and signaling was validated by co-immunoprecipitation or co-localization. Finally we showed the co-localization of EhTSN and HSP70 in putative stress granules during heat shock and that the knockdown of EhTSN increases the cell death during heat shock treatment, reinforcing the hypothesis that EhTSN has a role during stress response. All data support the proposal that EhTSN is a multifunctional protein of E. histolytica.

Phosphorylation of Tudor-SN, a novel substrate of JNK, is involved in the efficient recruitment of Tudor-SN into stress granules

Posttranslational modifications of certain stress granule (SG) proteins are closely related to the assembly of SGs, a type of cytoplasmic foci structure. Our previous studies revealed that the Tudor staphylococcal nuclease (Tudor-SN) protein participates in the formation of SGs. However, the functional significance of potential Tudor-SN modifications during stress has not been reported. In this study, we demonstrated that the Tudor-SN protein was phosphorylated at threonine 103 (T103) upon stimulation with arsenite. In addition, c-Jun N-terminal kinase (JNK) was found to be responsible for Tudor-SN phosphorylation at the T103 site. We further illustrated that either a T103A mutation or the suppression of phosphorylation of T103 by the JNK inhibitor SP600125 inhibited the efficient recruitment of Tudor-SN into SGs. In addition, the T103A mutation could affect the physical binding of Tudor-SN with the G3BP (Ras-GAP SH3 domain-binding protein) protein but not with the HuR (Hu antigen R) protein and AGTR1-3'UTR (3'-untranslated region of angiotensin II receptor, type 1) mRNA cargo. These data suggested that JNK-enhanced Tudor-SN phosphorylation promotes the interaction between Tudor-SN and G3BP and facilitates the efficient recruitment of Tudor-SN into SGs under conditions of sodium arsenite-induced oxidative stress. This finding provides novel insights into the physiological function of Tudor-SN modification.

Tudor staphylococcal nuclease: biochemistry and functions

Tudor staphylococcal nuclease (TSN, also known as Tudor-SN, SND1 or p100) is an evolutionarily conserved protein with invariant domain composition, represented by tandem repeat of staphylococcal nuclease domains and a tudor domain. Conservation along significant evolutionary distance, from protozoa to plants and animals, suggests important physiological functions for TSN. It is known that TSN is critically involved in virtually all pathways of gene expression, ranging from transcription to RNA silencing. Owing to its high protein-protein binding affinity coexistent with enzymatic activity, TSN can exert its biochemical function by acting as both a scaffolding molecule of large multiprotein complexes and/or as a nuclease. TSN is indispensible for normal development and stress resistance, whereas its increased expression is closely associated with various types of cancer. Thus, TSN is an attractive target for anti-cancer therapy and a potent tumor marker. Considering ever increasing interest to further understand a multitude of TSN-mediated processes and a mechanistic role of TSN in these processes, here we took an attempt to summarize and update the available information about this intriguing multifunctional protein.

Malonate induces the assembly of cytoplasmic stress granules

Malonate, a classic inhibitor of respiratory electron transport chain, induces mitochondrial stress. Stress granules (SGs) are a kind of dynamic foci structure during stress. The study on the connection of mitochondrial stress and SG assembly is still limited. Here, we demonstrated that malonate treatment leads to SG formation and translation inhibition, apart from mitochondrial stress, including enhanced ROS formation, reduced mitochondrial Δψm and ATP level. The phosphorylation levels of eIF2α and 4EBP1 protein were affected upon mitochondrial dysfunction. However, knockdown of 4EBP1 affected SG formation, rather than eIF2α. In addition, an increase of ATP level under mitochondrial stress enhanced malonate-induced SG aggregation. Overall, malonate stimulation triggers mitochondrial stress and induces the assembly of non-canonical cellular SGs via 4EBP1 pathway.

Tudor-SN Regulates Milk Synthesis and Proliferation of Bovine Mammary Epithelial Cells

Tudor staphylococcal nuclease (Tudor-SN) is a highly conserved and ubiquitously expressed multifunctional protein, related to multiple and diverse cell type- and species-specific cellular processes. Studies have shown that Tudor-SN is mainly expressed in secretory cells, however knowledge of its role is limited. In our previous work, we found that the protein level of Tudor-SN was upregulated in the nucleus of bovine mammary epithelial cells (BMEC). In this study, we assessed the role of Tudor-SN in milk synthesis and cell proliferation of BMEC. We exploited gene overexpression and silencing methods, and found that Tudor-SN positively regulates milk synthesis and proliferation via Stat5a activation. Both amino acids (methionine) and estrogen triggered NFκB1 to bind to the gene promoters of Tudor-SN and Stat5a, and this enhanced the protein level and nuclear localization of Tudor-SN and p-Stat5a. Taken together, these results suggest the key role of Tudor-SN in the transcriptional regulation of milk synthesis and proliferation of BMEC under the stimulation of amino acids and hormones.

Profiling of promoter occupancy by the SND1 transcriptional coactivator identifies downstream glycerolipid metabolic genes involved in TNFα response in human hepatoma cells

The NF-κB-inducible Staphylococcal nuclease and tudor domain-containing 1 gene (SND1) encodes a coactivator involved in inflammatory responses and tumorigenesis. While SND1 is known to interact with certain transcription factors and activate client gene expression, no comprehensive mapping of SND1 target genes has been reported. Here, we have approached this question by performing ChIP-chip assays on human hepatoma HepG2 cells and analyzing SND1 binding modulation by proinflammatory TNFα. We show that SND1 binds 645 gene promoters in control cells and 281 additional genes in TNFα-treated cells. Transcription factor binding site analysis of bound probes identified motifs for established partners and for novel transcription factors including HSF, ATF, STAT3, MEIS1/AHOXA9, E2F and p300/CREB. Major target genes were involved in gene expression and RNA metabolism regulation, as well as development and cellular metabolism. We confirmed SND1 binding to 21 previously unrecognized genes, including a set of glycerolipid genes. Knocking-down experiments revealed that SND1 deficiency compromises the glycerolipid gene reprogramming and lipid phenotypic responses to TNFα. Overall, our findings uncover an unexpected large set of potential SND1 target genes and partners and reveal SND1 to be a determinant downstream effector of TNFα that contributes to support glycerophospholipid homeostasis in human hepatocellular carcinoma during inflammation.