A model for heterogeneous nuclear ribonucleoproteins in telomere and telomerase regulation

Interferon-Regulated Expression of Cellular Splicing Factors Modulates Multiple Levels of HIV-1 Gene Expression and Replication

Type I interferons (IFN-Is) are pivotal in innate immunity against human immunodeficiency virus I (HIV-1) by eliciting the expression of IFN-stimulated genes (ISGs), which encompass potent host restriction factors. While ISGs restrict the viral replication within the host cell by targeting various stages of the viral life cycle, the lesser-known IFN-repressed genes (IRepGs), including RNA-binding proteins (RBPs), affect the viral replication by altering the expression of the host dependency factors that are essential for efficient HIV-1 gene expression. Both the host restriction and dependency factors determine the viral replication efficiency; however, the understanding of the IRepGs implicated in HIV-1 infection remains greatly limited at present. This review provides a comprehensive overview of the current understanding regarding the impact of the RNA-binding protein families, specifically the two families of splicing-associated proteins SRSF and hnRNP, on HIV-1 gene expression and viral replication. Since the recent findings show specifically that SRSF1 and hnRNP A0 are regulated by IFN-I in various cell lines and primary cells, including intestinal lamina propria mononuclear cells (LPMCs) and peripheral blood mononuclear cells (PBMCs), we particularly discuss their role in the context of the innate immunity affecting HIV-1 replication.

Dysregulated RNA processing and metabolism: a new hallmark of ageing and provocation for cellular senescence

The human genome is capable of producing hundreds of thousands of different proteins and non-coding RNAs from <20 000 genes, in a co-ordinated and regulated fashion. This is achieved by a collection of phenomena known as mRNA processing and metabolism, and encompasses events in the life cycle of an RNA from synthesis to degradation. These factors are critical determinants of cellular adaptability and plasticity, which allows the cell to adjust its transcriptomic output in response to its internal and external environment. Evidence is building that dysfunctional RNA processing and metabolism may be a key contributor to the development of cellular senescence. Senescent cells by definition have exited cell cycle, but have gained functional features such as the secretion of the senescence-associated secretory phenotype (SASP), a known driver of chronic disease and perhaps even ageing itself. In this review, I will outline the impact of dysregulated mRNA processing and metabolism on senescence and ageing at the level of genes, cells and systems, and describe the mechanisms by which progressive deterioration in these processes may impact senescence and organismal ageing. Finally, I will present the evidence implicating this important process as a new hallmark of ageing, which could be harnessed in the future to develop new senotherapeutic interventions for chronic disease.

hnRNPA1/UP1 Unfolds KRAS G-Quadruplexes and Feeds a Regulatory Axis Controlling Gene Expression

Recent studies have proven that the genetic landscape of pancreatic cancer is dominated by the KRAS oncogene. Its transcription is controlled by a G-rich motif (called 32R) located immediately upstream of the TSS. 32R may fold into a G-quadruplex (G4) in equilibrium between two G4 conformers: G9T (T _M = 61.2 °C) and G25T (T _M = 54.7 °C). We found that both G4s bind to hnRNPA1 and its proteolytic fragment UP1, promoting several contacts with the RRM protein domains. 1D NMR analysis of DNA imino protons shows that, upon binding to UP1, G25T is readily unfolded at both 5' and 3' tetrads, while G9T is only partially unfolded. The impact of hnRNPA1 on KRAS expression was determined by comparing Panc-1 cells with two Panc-1 knockout cell lines in which hnRNPA1 was deleted by the CRISPR/Cas9 technology. The results showed that the expression of KRAS is inhibited in the knockout cell lines, indicating that hnRNPA1 is essential for the transcription of KRAS. In addition, the knockout cell lines, compared to normal Panc-1 cells, show a dramatic decrease in cell growth and capacity of colony formation. Pull-down and Western blot experiments indicate that conformer G25T is a better platform than conformer G9T for the assembly of the transcription preinitiation complex with PARP1, Ku70, MAZ, and hnRNPA1. Together, our data prove that hnRNPA1, being a key transcription factor for the activation of KRAS, can be a new therapeutic target for the rational design of anticancer strategies.

Effect of hnRNPA2/B1 on the proliferation and apoptosis of glioma U251 cells via the regulation of AKT and STAT3 pathways

Glioma is the most common malignant tumor in the human central nervous system. Although heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1) was previously presumed to be a tumor-promoting gene, the relationship between hnRNPA2/B1 and glioma is unclear. Targeting hnRNPA2/B1 interference in glioma cells can significantly inhibit proliferation and increase apoptosis of human glioma cells in vitro. In a tumor xenograft model, knockdown of hnRNPA2/B1 suppressed tumor growth in glioma cells in vivo. In terms of a mechanism, the knockdown of hnRNPA2/B1 led to inactivation of the AKT and STAT3 signaling pathways, which ultimately reduced the expression of B-cell lymphoma-2 (Bcl-2), CyclinD1 and proliferating cell nuclear antigen (PCNA). Collectively, these data suggest that the inhibition of hnRNPA2/B1 can reduce the growth of gliomas through STAT3 and AKT signaling pathways, and this inhibition is expected to be a therapeutic target for gliomas.

lncRNA ST3GAL6‑AS1 promotes invasion by inhibiting hnRNPA2B1‑mediated ST3GAL6 expression in multiple myeloma

Multiple myeloma (MM) is an incurable disease caused by the infiltration of malignant plasma B cells into bone marrow, whose pathogenesis remains largely unknown. Long non‑coding RNAs (lncRNAs) have emerged as important factors in pathogenesis. Our previous study validated that lncRNA ST3 β‑galactoside α‑2,3‑sialyltransferase 6 antisense RNA 1 (ST3GAL6‑AS1) was upregulated markedly in MM. Therefore, the aim of the study was to investigate the molecular mechanisms of ST3GAL6‑AS1 in MM cells. ST3GAL6‑AS1 expression levels in MM cells was detected using reverse transcription‑quantitative PCR. ST3GAL6‑AS1 antisense oligonucleotides and small interfering RNAs were transfected into MM cells to downregulate expression. In vitro assays were performed to investigate the functional role of ST3GAL6‑AS1 in MM cells. RNA pull‑down, RNA immunoprecipitation and comprehensive identification of RNA‑binding proteins using mass spectrometry assays were used to determine the mechanism of ST3GAL6‑AS1‑mediated regulation of underlying targets. It was reported that knockdown of ST3GAL6‑AS1 suppressed the adhesion, migration and invasion ability of MM cells in vitro. Expression of ST3GAL6 was significantly reduced when ST3GAL6‑AS1 was knock downed in MM cells. Moreover, mechanistic investigation showed that ST3GAL6‑AS1 could suppress ST3GAL6 mRNA degradation via interacting with heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1). The present results suggested that upregulated lncRNA ST3GAL6‑AS1 promotes adhesion and invasion of MM cells by binding with hnRNPA2B1 to regulate ST3GAL6 expression.

Crucial roles of different RNA-binding hnRNP proteins in Stem Cells

The self-renewal, pluripotency and differentiation of stem cells are regulated by various genetic and epigenetic factors. As a kind of RNA binding protein (RBP), the heterogeneous nuclear ribonucleoproteins (hnRNPs) can act as "RNA scaffold" and recruit mRNA, lncRNA, microRNA and circRNA to affect mRNA splicing and processing, regulate gene transcription and post-transcriptional translation, change genome structure, and ultimately play crucial roles in the biological processes of cells. Recent researches have demonstrated that hnRNPs are irreplaceable for self-renewal and differentiation of stem cells. hnRNPs function in stem cells by multiple mechanisms, which include regulating mRNA stability, inducing alternative splicing of mRNA, epigenetically regulate gene expression, and maintaining telomerase activity and telomere length. The functions and the underlying mechanisms of hnRNPs in stem cells deserve further investigation.

Single-stranded DNA-binding proteins in plant telomeres

Telomere single-stranded DNA-binding proteins bind to the terminal single-stranded DNA of telomeres, maintaining and protecting the chromosomal end in eukaryotes. This paper focuses on the protective mechanism of single-stranded DNA-binding proteins in plant telomeres. This review summarizes the roles of plant single-stranded DNA-binding proteins and their influence on telomere length and telomerase. This review provides insights into the mechanism and development of single-stranded DNA-binding proteins in plants.

HnRNPA2/B1 Is a Novel Prognostic Biomarker for Breast Cancer Patients

Aims: Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1) is highly expressed in multiple types of tumor tissues and could potentially be used as a biomarker for the early detection of lung cancer. However, there is little evidence supporting its clinical significance as a prognostic marker in breast cancer. Materials and Methods: We retrospectively analyzed the protein expression and localization of hnRNPA2/B1 protein in breast cancer tissues and adjacent normal tissues from 50 patients with Stage II and III breast cancer who were treated at Shanxi Provincial People's Hospital from May 2018 to May 2019 using western blot, and immunofluorescent and immunohistochemical staining assays. In addition, bioinformatic analyses using the Affymetrix Human Genome database were performed to examine the mRNA levels of hnRNPA2/B1 in normal and breast cancer tissues, and to determine their correlation with the survival rates of breast cancer patients. Results: Based on the cohort of 50 patients, HnRNPA2/B1 protein was expressed in both the cytoplasm and nucleus of breast cancer cells. The protein levels of hnRNPA2/B1 in breast cancer tissues were significantly higher than those in adjacent normal tissues (p < 0.001). Furthermore, bioinformatic analyses of hnRNPA2/B1 mRNA expression levels demonstrated that they were negatively correlated with overall survival and disease-specific survival rates in breast cancer patients. Conclusion: Our study indicates that hnRNPA2/B1 could serve as a novel prognostic biomarker for breast cancer.

Identification of rare variants in novel candidate genes in pulmonary atresia patients by next generation sequencing

Pulmonary atresia (PA) is a rare congenital heart defect (CHD) with complex manifestations and a high mortality rate. Since the genetic determinants in the pathogenesis of PA remain elusive, a thorough identification of the genetic factors through whole exome sequencing (WES) will provide novel insights into underlying mechanisms of PA. We performed WES data from PA/VSD (n = 60), PA/IVS (n = 20), TOF/PA (n = 20) and 100 healthy controls. Rare variants and novel genes were identified using variant-based association and gene-based burden analysis. Then we explored the expression pattern of our candidate genes in endothelium cell lines, pulmonary artery tissues, and embryonic hearts. 56 rare damage variants of 7 novel candidate genes (DNAH10, DST, FAT1, HMCN1, HNRNPC, TEP1, and TYK2) were certified to have function in PA pathogenesis for the first time. In our research, the genetic pattern among PA/VSD, PA/IVS and TOF/PA were different to some degree. Taken together, our findings contribute new insights into the molecular basis of this rare congenital birth defect.

Chemotherapy Resistance in Advanced Ovarian Cancer Patients

Ovarian cancer is the seventh most common gynaecologic malignancy seen in women. Majority of the patients with ovarian cancer are diagnosed at the advanced stage making prognosis poor. The standard management of advanced ovarian cancer includes tumour debulking surgery followed by chemotherapy. Various types of chemotherapeutic regimens have been used to treat advanced ovarian cancer, but the most promising and the currently used standard first-line treatment is carboplatin and paclitaxel. Despite improved clinical response and survival to this combination of chemotherapy, numerous patients either undergo relapse or succumb to the disease as a result of chemotherapy resistance. To understand this phenomenon at a cellular level, various macromolecules such as DNA, messenger RNA and proteins have been developed as biomarkers for chemotherapy response. This review comprehensively summarizes the problem that pertains to chemotherapy resistance in advanced ovarian cancer and provides a good overview of the various biomarkers that have been developed in this field.

Functional roles of hnRNPA2/B1 regulated by METTL3 in mammalian embryonic development

Heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1) plays an important role in RNA processing via in m⁶A modification of pre-mRNA or pre-miRNA. However, the functional role of and relationship between m⁶A and hnRNPA2/B1 in early embryonic development are unclear. Here, we found that hnRNPA2/B1 is crucial for early embryonic development by virtue of regulating specific gene transcripts. HnRNPA2/B1 was localized to the nucleus and cytoplasm during subsequent embryonic development, starting at fertilization. Knockdown of hnRNPA2/B1 delayed embryonic development after the 4-cell stage and blocked further development. RNA-Seq analysis revealed changes in the global expression patterns of genes involved in transcription, translation, cell cycle, embryonic stem cell differentiation, and RNA methylation in hnRNPA2/B1 KD blastocysts. The levels of the inner cell mass markers OCT4 and SOX2 were decreased in hnRNPA2/B1 KD blastocysts, whereas that of the differentiation marker GATA4 was decreased. N6-Adenosine methyltransferase METTL3 knock-down caused embryonic developmental defects similar to those in hnRNPA2/B1 KD embryos. Moreover, METTL3 KD blastocysts showed increased mis-localization of hnRNPA2/B1 and decreased m⁶A RNA methylation. Taken together, our results suggest that hnRNPA2/B1 is essential for early embryogenesis through the regulation of transcription-related factors and determination of cell fate transition. Moreover, hnRNPA2/B1 is regulated by METTL3-dependent m⁶A RNA methylation.

SERPINA3 is a key modulator of HNRNP-K transcriptional activity against oxidative stress in HCC

Most studies about serpin peptidase inhibitor, clade A member 3 (SERPINA3) has been limited to its inhibitory functions and mechanisms. Herein, we report a novel role of SERPINA3 in transcriptional regulation of HCC progression-related genes. Among 19 selected genes through HCC cell isolation system based on telomere length, microarray analyses, and cell-based studies, SERPINA3 was the strongest determinant of increases in telomere length, HCC cell proliferation, survival, migration, and invasion. We also found that SERPINA3 strongly interacted with heterogeneous nuclear ribonucleoprotein K (HNRNP-K) under H₂O₂ exposure, and the oxidation-elicited SERPINA3-HNRNP-K complex enhanced the promoter activities and transcript levels of a telomere-relating gene (POT1) and HCC-promoting genes (UHRF1 and HIST2H2BE). Intriguingly, the inhibition of SERPINA3 oxidation rendered the transcriptional activity of the SERPINA3-HNRNP-K complex suppressed. Moreover, the co-immunoprecipitated HNRNP-K with SERPINA3 quantitatively correlated with not only the level of SERPINA3 oxidation but also the level of POT1, UHRF1, and HIST2H2BE transcripts and telomere length in HCC tissues. Therefore, the upregulated transcriptional activity of HNRNP-K mediated by SERPINA3 promotes HCC cell survival and proliferation and could be an indicator of poor prognosis for HCC patients.

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SERPINA3-HNRNP-K complex promotes HCC survival and proliferation.

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Oxidation of SERPINA3 accentuated the role of complex on target regulatory DNA.

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Blockade of the SERPINA3-HNRNP-K complex could be valuable in HCC therapy.

d-/l-Isothymidine incorporation in the core sequence of aptamer BC15 enhanced its binding affinity to the hnRNP A1 protein

The heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) was reported to participate in the development of a variety of tumors. BC15 is a DNA aptamer targeting hnRNP A1. Firstly, through sequence truncation, we identified 31-mer sequence BC15-31 as the core sequence of BC15 with a strong binding affinity and high selectivity to the hnRNP A1 protein. Isothymidine (isoT) modification was then applied for the structural optimization of BC15-31, systematic modification and biological evaluation were carried out. Incorporation of isoT in the 1,3 sites at the 5'-end of BC15-31 can significantly enhance the protein affinity. Chemical modifications close to the 3'-end can greatly improve the stability of the aptamer. Furthermore, BC15-31 modified with isoT at both the 5'-end and 3'-end displayed an additive effect with enhanced bioactivity and stability at the same time. Our study strategy on BC15 provides a useful guideline for chemical modification and optimization of the aptamer for further clinical application.

Mechanism of the natural product moracin-O derived MO-460 and its targeting protein hnRNPA2B1 on HIF-1α inhibition

Hypoxia-inducible factor-1α (HIF-1α) mediates tumor cell adaptation to hypoxic conditions and is a potentially important anticancer therapeutic target. We previously developed a method for synthesizing a benzofuran-based natural product, (R)-(-)-moracin-O, and obtained a novel potent analog, MO-460 that suppresses the accumulation of HIF-1α in Hep3B cells. However, the molecular target and underlying mechanism of action of MO-460 remained unclear. In the current study, we identified heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1) as a molecular target of MO-460. MO-460 inhibits the initiation of HIF-1α translation by binding to the C-terminal glycine-rich domain of hnRNPA2B1 and inhibiting its subsequent binding to the 3’-untranslated region of HIF-1α mRNA. Moreover, MO-460 suppresses HIF-1α protein synthesis under hypoxic conditions and induces the accumulation of stress granules. The data provided here suggest that hnRNPA2B1 serves as a crucial molecular target in hypoxia-induced tumor survival and thus offer an avenue for the development of novel anticancer therapies.

A synthetic analog of a chemical found in fruit suppresses tumor growth by targeting an RNA-binding protein (hnRNPA2B1) and preventing the production of a pro-cancer regulatory factor. Nak-Kyun Soung from the Korea Research Institute of Bioscience and Biotechnology, Cheongju, South Korea, and coworkers built on their previous discovery that a compound derived from a medicinal plant metabolite can suppress the activity of hypoxia-inducible factor-1α (HIF-1α). This protein, which is involved in many aspects of cancer biology, is activated in the low-oxygen microenvironments found inside tumors. The researchers show that the compound binds to a protein that helps with the conversion of HIF-1α–encoding RNA transcripts into HIF-1α proteins. Liver cancer cells treated with the compound grew slowly and produced less HIF-1α under both normal and low-oxygen culture conditions, highlighting the potential of this anti-cancer strategy.

Heterogeneous Nuclear Ribonucleoproteins Involved in the Functioning of Telomeres in Malignant Cells

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are structurally and functionally distinct proteins containing specific domains and motifs that enable the proteins to bind certain nucleotide sequences, particularly those found in human telomeres. In human malignant cells (HMCs), hnRNP-A1-the most studied hnRNP-is an abundant multifunctional protein that interacts with telomeric DNA and affects telomerase function. In addition, it is believed that other hnRNPs in HMCs may also be involved in the maintenance of telomere length. Accordingly, these proteins are considered possible participants in the processes associated with HMC immortalization. In our review, we discuss the results of studies on different hnRNPs that may be crucial to solving molecular oncological problems and relevant to further investigations of these proteins in HMCs.

Prognostic value and oncogene function of heterogeneous nuclear ribonucleoprotein A1 overexpression in HBV-related hepatocellular carcinoma

Previous study has shown heterogeneous nuclear ribonucleoprotein A1(HNRNPA1) is highly expressed in various human cancers. In order to study the clinical value and potential function of HNRNPA1 in HBV-related hepatocellular carcinoma (HCC), three datasets from the GEPIA, GEO and TCGA were analyzed. HNRNPA1 expression was found to be significantly higher in HBV-positive HCC samples, which was supported with IHC validation. Both GO and KEGG analyses demonstrated that HNRNPA1 co-expressed genes were involved in translation, ribonucleoprotein complex biogenesis and assembly, ribosome biogenesis, RNA processing, RNA splicing, etc. Survival analysis showed a significant reduction in overall survival of patients with high HNRNPA1 expression from both the GSE14520 cohort and 151 patients with HBV-related HCC cohort. Furthermore, Gene set enrichment analysis (GSEA) revealed that HNRNPA1 may regulate HCC progression by influencing the cell cycle and WNT signaling pathway, etc. HNRNPA1 overexpression has diagnostic value in distinguishing between HCC and non-HCC liver tissue (AUC = 0.730). Finally, HNRNPA1 was a directly target gene of miR-22 manifested by the reduced luciferase activity and decreased HNRNPA1 expression in the cells with overexpression of miR-22. HNRNPA1 might function as an oncogene through the EGFR signaling pathway in HBV-related HCC, which has not been reported in previous studies.

Prognostic value of heterogeneous ribonucleoprotein A1 expression and inflammatory indicators for patients with surgically resected hepatocellular carcinoma: Perspectives from a high occurrence area of hepatocellular carcinoma in China

Heterogeneous ribonucleoproteinA1 (hnRNPA1) is a documented tumor biomarker known to be aberrantly expressed in a number of types of human cancer. However, to the best of our knowledge, its prognostic value for surgically resected HCC (RHCC) in the high incidence areas of China has not been described; the association between hnRNPA1 expression, pre-operative neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) is also not understood. In the present study, hnRNPA1 expression was retrospectively measured in two independent cohorts of patients with hepatocellular carcinoma (HCC) who underwent surgery to remove the primary cancer at one center in Fujian, an area with a high incidence of HCC in China. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting and immunohistochemistry (IHC) were used to quantify hnRNPA1 expression in RHCC tissues. The survival curves were plotted using the Kaplan-Meier method, and the prognostic significance of hnRNPA1, NLR and PLR was analyzed using the log-rank test. The relevant prognostic factors were identified by multivariate Cox regression analysis. RT-qPCR and western blotting revealed that hnRNPA1 was upregulated in HCC tissues (P<0.001), and particularly overexpressed in tumor tissues of patients with recurrent HCC (P<0.001) (cohort 1; 54 patients). Differential hnRNPA1 expression was measured in 426HCC tissues with IHC; 259 exhibited high hnRNPA1 expression and 167 exhibited low expression. High hnRNPA1 expression was significantly associated with Tumor-Node-Metastasis stage (P=0.024), tumor size (P=0.027), vascular invasion (P<0.001), Edmonson grade (P<0.001), pre-operative serum α-fetoprotein (AFP) (P<0.001), NLR (P<0.001) and PLR (P<0.001). In addition, multivariate Cox regression analysis confirmed that high hnRNPA1 expression was associated with relapse-free survival (RFS; HR, 0.685; 95% CI, 0.506-0.928; P=0.015) and overall survival (OS; HR, 0.629; 95% CI, 0.454-0.871; P=0.005). Multivariate analysis confirmed that higher pre-operative serum AFP had an unfavorable impact on RFS (HR, 1.350; 95% CI, 1.006-1.811; P=0.045) and OS (HR=1.564; 95% CI, 1.151-2.126; P=0.004), while higher pre-operative NLR had an unfavorable impact on OS (HR, 1.758; 95% CI, 1.161-2.661; P=0.008) (cohort 2;426 patients). The expression of hnRNPA1 was also positively correlated with NLR (Spearman's correlation; r=0.122, P=0.012) and PLR (Spearman's correlation; r=0.140, P=0.004). In conclusion, high hnRNPA1 expression was revealed as prognostic for poor survival in patients with RHCC, and detection of hnRNPA1 protein in tumor tissues demonstrated potential in estimating survival for patients with RHCC in areas with high incidence rates. Furthermore, the combination of high hnRNPA1 expression and pre-operative serum AFP levels (>400 µg) proved to be a good diagnostic and prognostic biomarker for this specific population of patients. Finally, a correlation may also exist between hnRNPA1 expression and other markers of systemic inflammation.

Identification of Potential Anticancer Protein Targets in Cytotoxicity Mediated by Tropical Medicinal Fern Extracts

Background:

Medicinal fern species represent a potentially important source for both food and medicinal applications. Previously, two underutilized tropical fern species (Blechnum orientale and Phymatopteris triloba) were reported with cytotoxic activities against selected cancer cell lines. However, the exact mechanism remains elusive.

Objective:

In this paper, we reported the identification of six differentially expressed proteins isolated from cancer cells, following exposure to the cytotoxic fern extracts.

Materials and Methods:

The identities of these cancer proteins were determined by matrix-assisted laser desorption ionization time-of-flight protein sequencing.

Results:

The cancer proteins were identified as follows: elongation factor 1-γ, glyceraldehydes-3-phosphate dehydrogenase, heat shock protein 90-β, heterogeneous nuclear ribonucleoprotein-A2/B1, truncated nucleolar phosphoprotein B23, and tubulin-β chain. To the best of our knowledge, this paper represents the first time these cancer proteins are being reported, following exposure to the aforementioned cytotoxic fern extracts.

Conclusion:

It is hoped that further efforts in this direction could lead to the identification and development of target-specific chemotherapeutic agents.

SUMMARY

Cytotoxic fern extracts were tested in anti-cancer proteomic works.

Six differentially-expressed cancer proteins were identified.

Potential anti-cancer protein targets were reported.

Abbreviations used: EF: Elongation factor; HRP: Horseradish peroxidase; HSP: Heat shock protein; MALDI: Matrix-assisted laser desorption/ionization.

Insight meditation and telomere biology: The effects of intensive retreat and the moderating role of personality

A growing body of evidence suggests that meditation training may have a range of salubrious effects, including improved telomere regulation. Telomeres and the enzyme telomerase interact with a variety of molecular components to regulate cell-cycle signaling cascades, and are implicated in pathways linking psychological stress to disease. We investigated the effects of intensive meditation practice on these biomarkers by measuring changes in telomere length (TL), telomerase activity (TA), and telomere-related gene (TRG) expression during a 1-month residential Insight meditation retreat. Multilevel analyses revealed an apparent TL increase in the retreat group, compared to a group of experienced meditators, similarly comprised in age and gender, who were not on retreat. Moreover, personality traits predicted changes in TL, such that retreat participants highest in neuroticism and lowest in agreeableness demonstrated the greatest increases in TL. Changes observed in TRGs further suggest retreat-related improvements in telomere maintenance, including increases in Gar1 and HnRNPA1, which encode proteins that bind telomerase RNA and telomeric DNA. Although no group-level changes were observed in TA, retreat participants' TA levels at post-assessment were inversely related to several indices of retreat engagement and prior meditation experience. Neuroticism also predicted variation in TA across retreat. These findings suggest that meditation training in a retreat setting may have positive effects on telomere regulation, which are moderated by individual differences in personality and meditation experience. (ClinicalTrials.gov #NCT03056105).

Small molecule modulation of splicing factor expression is associated with rescue from cellular senescence

Background

Altered expression of mRNA splicing factors occurs with ageing in vivo and is thought to be an ageing mechanism. The accumulation of senescent cells also occurs in vivo with advancing age and causes much degenerative age-related pathology. However, the relationship between these two processes is opaque. Accordingly we developed a novel panel of small molecules based on resveratrol, previously suggested to alter mRNA splicing, to determine whether altered splicing factor expression had potential to influence features of replicative senescence.

Results

Treatment with resveralogues was associated with altered splicing factor expression and rescue of multiple features of senescence. This rescue was independent of cell cycle traverse and also independent of SIRT1, SASP modulation or senolysis. Under growth permissive conditions, cells demonstrating restored splicing factor expression also demonstrated increased telomere length, re-entered cell cycle and resumed proliferation. These phenomena were also influenced by ERK antagonists and agonists.

Conclusions

This is the first demonstration that moderation of splicing factor levels is associated with reversal of cellular senescence in human primary fibroblasts. Small molecule modulators of such targets may therefore represent promising novel anti-degenerative therapies.

Electronic supplementary material

The online version of this article (10.1186/s12860-017-0147-7) contains supplementary material, which is available to authorized users.

Emerging roles of hnRNPA1 in modulating malignant transformation

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA-binding proteins associated with complex and diverse biological processes such as processing of heterogeneous nuclear RNAs (hnRNAs) into mature mRNAs, RNA splicing, transactivation of gene expression, and modulation of protein translation. hnRNPA1 is the most abundant and ubiquitously expressed member of this protein family and has been shown to be involved in multiple molecular events driving malignant transformation. In addition to selective mRNA splicing events promoting expression of specific protein variants, hnRNPA1 regulates the gene expression and translation of several key players associated with tumorigenesis and cancer progression. Here, we will summarize our current knowledge of the involvement of hnRNPA1 in cancer, including its roles in regulating cell proliferation, invasiveness, metabolism, adaptation to stress and immortalization. WIREs RNA 2017, 8:e1431. doi: 10.1002/wrna.1431 For further resources related to this article, please visit the WIREs website.

Splicing regulatory factors, ageing and age-related disease

Alternative splicing is a co-transcriptional process, which allows for the production of multiple transcripts from a single gene and is emerging as an important control point for gene expression. Alternatively expressed isoforms often have antagonistic function and differential temporal or spatial expression patterns, yielding enormous plasticity and adaptability to cells and increasing their ability to respond to environmental challenge. The regulation of alternative splicing is critical for numerous cellular functions in both pathological and physiological conditions, and deregulated alternative splicing is a key feature of common chronic diseases. Isoform choice is controlled by a battery of splicing regulatory proteins, which include the serine arginine rich (SRSF) proteins and the heterogeneous ribonucleoprotein (hnRNP) classes of genes. These important splicing regulators have been implicated in age-related disease, and in the ageing process itself. This review will outline the important contribution of splicing regulator proteins to ageing and age-related disease.

Critical role of hnRNP A1 in activating KRAS transcription in pancreatic cancer cells: A molecular mechanism involving G4 DNA

KRAS is one of the most mutated genes in human cancer. Its crucial role in the tumourigenesis of pancreatic ductal adenocarcinoma (PDAC) has been widely demonstrated. As this deadly cancer does not sufficiently respond to conventional chemotherapies, it is important to increase our knowledge of pancreatic cancer biology, in particular how oncogenic KRAS is regulated. The promoter of KRAS contains a GA-element composed of runs of guanines that fold into a G4 structure. This unusual DNA conformation is recognized by several nuclear proteins, including MAZ and hnRNP A1. Recent data have revealed that KRAS is interconnected to ILK and hnRNP A1 in a circuitry that enables pancreatic cancer cells to maintain an aggressive phenotype. The present review illustrates recent advances on how KRAS is regulated in pancreatic cancer cells, focusing on the formation of G4 structures in the KRAS promoter and their interaction with hnRNP A1. The newly discovered KRAS-ILK-hnRNP A1 regulatory loop is discussed, emphasizing its potential as a therapeutic target for PDAC-specific molecules. This article is part of a Special Issue entitled "G-quadruplex" Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

Nuclear distribution of eIF3g and its interacting nuclear proteins in breast cancer cells

Eukaryotic translation initiation factor 3 subunit g (eIF3g) is a core subunit of the eukaryotic translation initiation factor 3 complex, and is important in the initiation of translation. It is also involved in caspase-mediated apoptosis, and is upregulated in multidrug-resistant cancer cells. In the present study, the nuclear distribution of eIF3g was determined by performing co-immunoprecipitation of proteins that potentially interact with eIF3g in the nucleus. Mass spectrometry characterization showed that three proteins, heterogeneous nuclear ribonucleoprotein U/scaffold attachment factor A, HSZFP36/zinc finger protein 823 and β-actin, were among the candidate eIF3g-interacting proteins in the nucleus. The protein-protein interaction was further confirmed by cross-linking and a glutathione S-transferase pull-down assay, followed by western blotting. The co-localization of these proteins was determined by confocal microscopy. These findings provide novel insight into the possible functions of eIF3g in the nucleus and serves as an important first step for further investigation of the roles of eIF3g in cancer development.

M. PfGBP: una proteína de unión al telómero de Plasmodium falciparum

Los telómeros son estructuras complejas de ADN y proteína localizadas en el extremo de los cromosomas eucariotes. Su principal función es proteger el extremo cromosomal de ser reconocido y procesado como ADNs fracturado, evitando así eventos de recombinación y fusión que conducen a inestabilidad cromosomal. El ADN telomérico consta de secuencias cortas, repetidas una tras otra, ricas en guanina; la cadena rica en guanina se extiende formando una región de cadena sencilla denominada extremo 3´ protuberante. Las proteínas por su parte, se pueden clasificar en: dsBPs, o proteínas de unión a la cadena doble, GBPs aquellas que reconocen específicamente el extremo protuberante y, proteínas que las interconectan mediante interacciones proteína-proteína. El gen PF3D7_1006800 de <em>Plasmodium falciparum</em> codifica para una proteína putativa similar a una GBP de <em>Criptosporidium parvum</em>, con el fin de establecer si esta proteína de <em>P. falciparum</em> presenta la capacidad de unión al ADN telomérico del parásito, se produjo una proteína recombinante a partir de la región codificante del gen, se purificó y se utilizó en ensayos de unión a ADN, y en la generación de anticuerpos policlonales específicos contra PfGBP. Nuestros resultados indican que la proteína de <em>P. falciparum</em> es una proteína nuclear con capacidad de unión al ADN telomérico <em>in vitro, </em>por lo<em> </em>que podría ser<em> </em>parte del complejo proteico encargado de proteger y/o mantener el telómero <em>in vivo</em>.

The hnRNP A1 homolog Hrb87F/Hrp36 is important for telomere maintenance in Drosophila melanogaster

Unlike the telomerase-dependent mammalian telomeres, HeT-A, TART, and TAHRE (HTT) retroposon arrays regulate Drosophila telomere length. Cap prevents telomeric associations (TAs) and telomeric fusions (TFs). Our results suggest important roles of Hrb87F in telomeric HTT array and cap maintenance in Drosophila. All chromosome arms, except 2L, in Df(3R)Hrb87F homozygotes (Hrb87F-null) displayed significantly elongated telomeres with amplified HTT arrays and high TAs, all of which resolved without damage. Presence of FLAG-tagged Hrb87F (FLAG-Hrb87F) on cap and subtelomeric regions following hsFLAG-Hrb87F transgene expression in Df(3R)Hrb87F homozygotes suppressed TAs without affecting telomere length. A normal X-chromosome telomere expanded within five generations in Hrb87F-null background and displayed high TAs, but not when hsFLAG-Hrb87F was co-expressed. Tel (1) /Gaiano line or HP1 loss-of-function mutant-derived expanded telomeres carry Hrb87F on cap and HTT arrays while Hrb87F-null telomeres have HP1 and HOAP on caps and expanded HTT arrays. ISWI, seen only on cap on normal telomeres, was abundant on Hrb87F-null expanded HTT arrays. Extended telomeres derived from Tel (1) (Gaiano) or HP1-null mutation background interact with those from Hrb87F-null, since while the end association frequency was negligible in Df(3R)Hrb87F/+ nuclei, it increased significantly in co-presence of Tel (1) or HP1-null-based expanded telomere/s. Together, these suggest complex interactions between members of the proteome of telomere so that absence of any key member leads to telomere expansion and/or enhanced TAs/TFs. HTT expansion in Hrb87F-null condition is not developmental but a germline event presumably because absence of Hrb87F in germline may deregulate HTT retroposition/replication leading to telomere elongation.

Heterogeneous nuclear ribonucleoproteins in amyotrophic lateral sclerosis: what do we know?

ABSTRACT: Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset motor neuron disease that results from the progressive loss of motor neurons in the brainstem and spinal cord, and of upper motor neurons in the motor cortex. TDP-43 was the first protein identified in ALS. It is present in cytoplasmic inclusions in motor neurons of affected patient brains and spinal cords, a hallmark feature of this disease. Successive studies have identified missense mutations in TARDBP, and, to date, more than 40 mutations have been identified. Recent studies have indicated that altered RNA metabolism is a key feature of ALS. This article reviews an emerging role of heterogeneous nuclear ribonucleoproteins driving disease pathogenesis that include TDP-43, FUS, hnRNPA1, hnRNPA2/B1 and hnRNPA3. Determining the molecular pathways involved may provide a promising prospect for heterogeneous nuclear ribonucleoproteins being potential biomarkers in ALS in order to develop therapeutic strategies for mitigating this disease, for which there is currently no cure.

Expression profile of telomere-associated genes in multiple myeloma

To further contribute to the understanding of multiple myeloma, we have focused our research interests on the mechanisms by which tumour plasma cells have a higher survival rate than normal plasma cells. In this article, we study the expression profile of genes involved in the regulation and protection of telomere length, telomerase activity and apoptosis in samples from patients with monoclonal gammopathy of undetermined significance, smouldering multiple myeloma, multiple myeloma (MM) and plasma cell leukaemia (PCL), as well as several human myeloma cell lines (HMCLs). Using conventional cytogenetic and fluorescence in situ hybridization studies, we identified a high number of telomeric associations (TAs). Moreover, telomere length measurements by terminal restriction fragment (TRF) assay showed a shorter mean TRF peak value, with a consistent correlation with the number of TAs. Using gene expression arrays and quantitative PCR we identified the hTERT gene together with 16 other genes directly involved in telomere length maintenance: HSPA9, KRAS, RB1, members of the Small nucleolar ribonucleoproteins family, A/B subfamily of ubiquitously expressed heterogeneous nuclear ribonucleoproteins, and 14-3-3 family. The expression levels of these genes were even higher than those in human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs), which have unlimited proliferation capacity. In conclusion, the gene signature suggests that MM tumour cells are able to maintain stable short telomere lengths without exceeding the short critical length, allowing cell divisions to continue. We propose that this could be a mechanism contributing to MM tumour cells expansion in the bone marrow (BM).

hnRNP C1/C2 and Pur-beta proteins mediate induction of senescence by oligonucleotides homologous to the telomere overhang

Background

Experimental disruption of the telomere overhang induces a potent DNA damage response and is the target of newly emerging cancer therapeutics. Introduction of T-oligo, an eleven-base oligonucleotide homologous to the 3′-telomeric overhang, mimics telomere disruption and induces DNA damage responses through activation of p53, p73, p95/Nbs1, E2F1, pRb, and other DNA damage response proteins. ATM (ataxia telangiectasia mutated) was once thought to be the primary driver of T-oligo-induced DNA damage responses; however, recent experiments have highlighted other key proteins that may also play a significant role.

Methods

To identify proteins associated with T-oligo, MM-AN cells were treated with biotinylated T-oligo or complementary oligonucleotide, cell lysates were run on SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis), and the protein bands observed after treatment of cells with T-oligo or complementary oligonucleotide were analyzed using mass spectrometry. To study the effect of T-oligo on expression of hnRNP C1/C2 (heterogeneous nuclear ribonucleoprotein C1 and C2) and purine-rich element binding proteins (Pur proteins), cells were treated with T-oligo, and immunoblotting experiments were performed. To determine their role in senescence, cells were treated with shRNA (short hairpin ribonucleic acid) against these proteins, and senescence was studied using the senescence associated beta-galactosidase assay.

Results

Using mass spectrometry, RNA-binding hnRNP C1/C2 and DNA-binding Pur proteins were found to associate with T-oligo. hnRNP C1/C2 exhibited increased expression (3.6–12.0-fold) in non-small-cell lung cancer (NSCLC) and in melanoma cells (4.5–5.2-fold), and Pur proteins exhibited increased expression of 2.2-fold in NSCLC and 2.0-fold in melanoma cells after T-oligo treatment. Experimental knockdown of hnRNP C1/C2 and Pur-beta completely abrogated T-oligo induced senescence in both MU melanoma and H358 NSCLC cells. Additionally, knockdown of Pur-beta prevented T-oligo-induced phosphorylation of p53, hypophosphorylation of pRb, and upregulation of E2F1, p21, and p53.

Conclusion

These novel findings highlight proteins essential to T-oligo’s anticancer effects that may be of interest in telomere biology and cancer therapeutics.

hnRNP A2/B1 interacts with influenza A viral protein NS1 and inhibits virus replication potentially through suppressing NS1 RNA/protein levels and NS1 mRNA nuclear export

The NS1 protein of influenza viruses is a major virulence factor and exerts its function through interacting with viral/cellular RNAs and proteins. In this study, we identified heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1) as an interacting partner of NS1 proteins by a proteomic method. Knockdown of hnRNP A2/B1 by small interfering RNA (siRNA) resulted in higher levels of NS vRNA, NS1 mRNA, and NS1 protein in the virus-infected cells. In addition, we demonstrated that hnRNP A2/B1 proteins are associated with NS1 and NS2 mRNAs and that knockdown of hnRNP A2/B1 promotes transport of NS1 mRNA from the nucleus to the cytoplasm in the infected cells. Lastly, we showed that knockdown of hnRNP A2/B1 leads to enhanced virus replication. Our results suggest that hnRNP A2/B1 plays an inhibitory role in the replication of influenza A virus in host cells potentially through suppressing NS1 RNA/protein levels and NS1 mRNA nucleocytoplasmic translocation.

Mitochondrial retrograde signaling at the crossroads of tumor bioenergetics, genetics and epigenetics

Mitochondria play a central role not only in energy production but also in the integration of metabolic pathways as well as signals for apoptosis and autophagy. It is becoming increasingly apparent that mitochondria in mammalian cells play critical roles in the initiation and propagation of various signaling cascades. In particular, mitochondrial metabolic and respiratory states and status on mitochondrial genetic instability are communicated to the nucleus as an adaptive response through retrograde signaling. Each mammalian cell contains multiple copies of the mitochondrial genome (mtDNA). A reduction in mtDNA copy number has been reported in various human pathological conditions such as diabetes, obesity, neurodegenerative disorders, aging and cancer. Reduction in mtDNA copy number disrupts mitochondrial membrane potential (Δψm) resulting in dysfunctional mitochondria. Dysfunctional mitochondria trigger retrograde signaling and communicate their changing metabolic and functional state to the nucleus as an adaptive response resulting in an altered nuclear gene expression profile and altered cell physiology and morphology. In this review, we provide an overview of the various modes of mitochondrial retrograde signaling focusing particularly on the Ca(2+)/Calcineurin mediated retrograde signaling. We discuss the contribution of the key factors of the pathway such as Calcineurin, IGF1 receptor, Akt kinase and HnRNPA2 in the propagation of signaling and their role in modulating genetic and epigenetic changes favoring cellular reprogramming towards tumorigenesis.

A three-state model for the regulation of telomerase by TERRA and hnRNPA1

Telomeres, the physical ends of eukaryotic chromosomes, are transcribed into telomeric repeat-containing RNA (TERRA), a large non-coding RNA, which forms an integral part of telomeric heterochromatin. In vitro, naked TERRA molecules are efficient inhibitors of human telomerase, base-pairing via their 5'-UUAGGG-3' repeats with the template sequence of telomerase RNA, in addition to contacting the telomerase reverse transcriptase protein subunit. In vivo, however, TERRA-mediated inhibition of telomerase can be prevented by unknown mechanisms. Also, heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) has been implicated in telomere length control. In vivo, TERRA is partially associated with hnRNPA1, and hnRNPA1 is also detected at telomeres. We demonstrate that on binding of TERRA, hnRNPA1 can alleviate the TERRA-mediated inhibition of telomerase. However, when in excess over TERRA, hnRNPA1 becomes itself an inhibitor of telomere extension, on binding of the telomeric DNA substrate. Yet, hnRNPA1 has no notable direct effects on the telomerase catalysis. Our in vitro results suggest that TERRA-mediated telomerase inhibition may be prevented by hnRNPA1 in vivo. Telomere extension by telomerase may require balanced levels of TERRA and hnRNPA1 at telomeres. Thus, TERRA and hnRNPA1 can function as a bimolecular regulator to turn telomerase and the telomere on and off.

Functions of heterogeneous nuclear ribonucleoproteins in stem cell potency and differentiation

Stem cells possess huge importance in developmental biology, disease modelling, cell replacement therapy, and tissue engineering in regenerative medicine because they have the remarkable potential for self-renewal and to differentiate into almost all the cell types in the human body. Elucidation of molecular mechanisms regulating stem cell potency and differentiation is essential and critical for extensive application. Heterogeneous nuclear ribonucleoproteins (hnRNPs) are modular proteins consisting of RNA-binding motifs and auxiliary domains characterized by extensive and divergent functions in nucleic acid metabolism. Multiple roles of hnRNPs in transcriptional and posttranscriptional regulation enable them to be effective gene expression regulators. More recent findings show that hnRNP proteins are crucial factors implicated in maintenance of stem cell self-renewal and pluripotency and cell differentiation. The hnRNPs interact with certain sequences in target gene promoter regions to initiate transcription. In addition, they recognize 3′UTR or 5′UTR of specific gene mRNA forming mRNP complex to regulate mRNA stability and translation. Both of these regulatory pathways lead to modulation of gene expression that is associated with stem cell proliferation, cell cycle control, pluripotency, and committed differentiation.

Proteomic analysis of novel targets associated with TrkA-mediated tyrosine phosphorylation signaling pathways in SK-N-MC neuroblastoma cells

Tropomyosin-related kinase A (TrkA) is a receptor-type protein tyrosine kinase and exploits pleiotypic roles via nerve growth factor (NGF)-dependent or NGF-independent mechanisms in various cell types. Here, we showed that the inhibition of TrkA activity by GW441756 resulted in the suppression of tyrosine phosphorylation of cellular proteins including extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK). To find novel targets associated with TrkA-mediated tyrosine phosphorylation signaling pathways, we investigated GW441756 effects on TrkA-dependent targets in SK-N-MC neuroblastoma cells by proteomic analysis. The major TrkA-dependent protein spots controlled by GW441756 were determined by PDQuest image analysis, identified by MALDI-TOF MS and MALDI-TOF/TOF MS/MS, and verified by 2DE/Western blot analysis. Thus, we found that most of the identified protein spots were modified forms in a normal condition, and their modifications were regulated by TrkA activity. Especially, our results demonstrated that the modifications of α-tubulin and heterogeneous nuclear ribonucleoproteins C1/C2 (hnRNP C1/C2) were significantly upregulated by TrkA, whereas α-enolase modification was downregulated by TrkA, and it was suppressed by GW441756, indicating that TrkA activity is required for their modifications. Taken together, we suggest here that the major novel TrkA-dependent targets such as α-tubulin, hnRNP C1/C2, and α-enolase could play an essential role in TrkA-mediated tyrosine phosphorylation signaling pathways via regulation of their posttranslational modifications.

TERRA, hnRNP A1, and DNA-PKcs Interactions at Human Telomeres

Maintenance of telomeres, repetitive elements at eukaryotic chromosomal termini, and the end-capping structure and function they provide, are imperative for preserving genome integrity and stability. The discovery that telomeres are transcribed into telomere repeat containing RNA (TERRA) has revolutionized our view of this repetitive, rather unappreciated region of the genome. We have previously shown that the non-homologous end-joining, shelterin associated DNA dependent protein kinase catalytic subunit (DNA-PKcs) participates in mammalian telomeric end-capping, exclusively at telomeres created by leading-strand synthesis. Here, we explore potential roles of DNA-PKcs and its phosphorylation target heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) in the localization of TERRA at human telomeres. Evaluation of co-localized foci utilizing RNA-FISH and three-dimensional (3D) reconstruction strategies provided evidence that both inhibition of DNA-PKcs kinase activity and siRNA depletion of hnRNP A1 result in accumulation of TERRA at individual telomeres; depletion of hnRNP A1 also resulted in increased frequencies of fragile telomeres. These observations are consistent with previous demonstrations that decreased levels of the nonsense RNA-mediated decay factors SMG1 and UPF1 increase TERRA at telomeres and interfere with replication of leading-strand telomeres. We propose that hTR mediated stimulation of DNA-PKcs and subsequent phosphorylation of hnRNP A1 influences the cell cycle dependent distribution of TERRA at telomeres by contributing to the removal of TERRA from telomeres, an action important for progression of S-phase, and thereby facilitating efficient telomere replication and end-capping.

Telomerase-dependent 3' G-strand overhang maintenance facilitates GTBP1-mediated telomere protection from misplaced homologous recombination

At the 3'-end of telomeres, single-stranded G-overhang telomeric repeats form a stable T-loop. Many studies have focused on the mechanisms that generate and regulate the length of telomere 3' G-strand overhangs, but the roles of G-strand overhang length control in proper T-loop formation and end protection remain unclear. Here, we examined functional relationships between the single-stranded telomere binding protein GTBP1 and G-strand overhang lengths maintained by telomerase in tobacco (Nicotiana tabacum). In tobacco plants, telomerase reverse transcriptase subunit (TERT) repression severely worsened the GTBP1 knockdown phenotypes, which were formally characterized as an outcome of telomere destabilization. TERT downregulation shortened the telomere 3' G-overhangs and increased telomere recombinational aberrations in GTBP1-suppressed plants. Correlatively, GTBP1-mediated inhibition of single-strand invasion into the double-strand telomeric sequences was impaired due to shorter single-stranded telomeres. Moreover, TERT/GTBP1 double knockdown amplified misplaced homologous recombination of G-strand overhangs into intertelomeric regions. Thus, proper G-overhang length maintenance is required to protect telomeres against intertelomeric recombination, which is achieved by the balanced functions of GTBP1 and telomerase activity.

Telomere- and telomerase-interacting protein that unfolds telomere G-quadruplex and promotes telomere extension in mammalian cells

Telomere extension by telomerase is essential for chromosome stability and cell vitality. Here, we report the identification of a splice variant of mammalian heterogeneous nuclear ribonucleoprotein A2 (hnRNP A2), hnRNP A2*, which binds telomeric DNA and telomerase in vitro. hnRNP A2* colocalizes with telomerase in Cajal bodies and at telomeres. In vitro assays show that hnRNP A2* actively unfolds telomeric G-quadruplex DNA, exposes 5 nt of the 3' telomere tail and substantially enhances the catalytic activity and processivity of telomerase. The expression level of hnRNP A2* in tissues positively correlates with telomerase activity, and overexpression of hnRNP A2* leads to telomere elongation in vivo. Thus, hnRNP A2* plays a positive role in unfolding telomere G-quadruplexes and in enhancing telomere extension by telomerase.

Analysis of protein expression profiles in the thymus of chickens infected with Marek's disease virus

BACKGROUND

Marek's disease virus (MDV) is a highly cell-associated oncogenic α-herpesvirus that causes a disease characterised by T-cell lymphomas. The pathogenesis, or the nature of the interaction of the virus and the host, in the thymus are still unclear.

RESULTS

In this study, we identified 119 differentially expressed proteins using two-dimensional electrophoresis and mass spectrometry from the thymuses of chickens infected with the RB1B strain of MDV. These differentially expressed proteins were found mainly at 21, 28 and 35 days post-infection. More than 20 of the differentially expressed proteins were directly associated with immunity, apoptosis, tumour development and viral infection and replication. Five of these proteins, ANXA1, MIF, NPM1, OP18 and VIM, were further confirmed using real-time PCR. The functional associations and roles in oncogenesis of these proteins are discussed.

CONCLUSIONS

This work provides a proteomic profiling of host responses to MDV in the thymus of chickens and further characterises proteins related to the mechanisms of MDV oncogenesis and pathogenesis.

Overexpression of HnRNP A1 promotes tumor invasion through regulating CD44v6 and indicates poor prognosis for hepatocellular carcinoma

Heterogeneous ribonucleoprotein (hnRNP) A1 is a member of the A/B subfamily of ubiquitously expressed hnRNPs, which have a wide variety of functions in gene expression and signal transduction. To investigate the biological function and clinical significance of hnRNP A1 in hepatocellular carcinoma (HCC), we measured hnRNP A1 expression in four HCC cell lines and two independent cohorts of HCC patients. We found that hnRNP A1 was overexpressed in the highly metastatic HCC cell lines and in tumor tissues of patients with recurrent HCC. Knockdown of hnRNP A1 in highly metastatic HCC cells caused a significant decrease in cell invasion, while upregulation of hnRNP A1 in poorly metastatic HCC cells led to a significant increase in their invasive capacity. We found that this effect may occur through the regulation of CD44v6 expression by hnRNP A1 in HCC cells. Both quantitative reverse transcription-polymerase chain reaction (qRT-RCR) and immunohistochemistry revealed that hnRNP A1 was upregulated in HCC tissues and coincided with overexpression of CD44v6. HCC patients with high hnRNP A1 tended to have higher levels of CD44v6, shorter overall survival (OS) and higher rates of tumor recurrence. Multivariate analyses revealed that hnRNP A1 alone or in combination with CD44v6 were independent prognostic indicators for OS and time to recurrence and have potential as therapeutic targets. In conclusion, overexpression of hnRNP A1 promotes HCC invasion by regulating the level of CD44v6 and indicates a poor prognosis for HCC patients after curative resection.

A new function of ROD1 in nonsense-mediated mRNA decay

RNA-binding proteins play a crucial role in the post-transcriptional regulation of gene expression. Polypyrimidine tract binding protein (PTB in humans) has been extensively characterized as an important splicing factor, and has additional functions in 3' end processing and translation. ROD1 is a PTB paralog containing four RRM (RNA recognition motif) domains. Here, we discover a function of ROD1 in nonsense-mediated mRNA decay (NMD). We show that ROD1 and the core NMD factor UPF1 interact and co-regulate an extensive number of target genes. Using a reporter system, we demonstrate that ROD1, similarly to UPF1 and UPF2, is required for the destabilization of a known NMD substrate. Finally, we show through RIP-seq that ROD1 and UPF1 associate with a significant number of common transcripts.

Telomerase regulation

The intimate connection between telomerase regulation and human disease is now well established. The molecular basis for telomerase regulation is highly complex and entails multiple layers of control. While the major target of enzyme regulation is the catalytic subunit TERT, the RNA subunit of telomerase is also implicated in telomerase control. In addition, alterations in gene dosage and alternative isoforms of core telomerase components have been described. Finally, telomerase localization, recruitment to the telomere and enzymology at the chromosome terminus are all subject to modulation. In this review we summarize recent advances in understanding fundamental mechanisms of telomerase regulation.

Proteomic identification of paclitaxel-resistance associated hnRNP A2 and GDI 2 proteins in human ovarian cancer cells

Ovarian cancer is a gynecological malignancy with the highest mortality. Chemoresistance is an important subject for the treatment of ovarian cancer, because obtaining significant drug resistance to the first line chemotherapy, paclitaxel, causes major therapeutic obstacles. It is essential to improve the survival rate of ovarian cancer patients by mining the biomarkers indicating the drug resistance and prognosis, and by further understanding underlying mechanisms of drug resistance. In the present study, we established paclitaxel-resistant subline (SKpac) from human epithelial ovarian cancer cell line, SKOV3, and performed comparative analysis of whole proteomes between paclitaxel-resistant SKpac sublines and paclitaxel-sensitive parental SKOV3 cells to identify differentially expressed proteins and useful biomarkers indicating chemoresistance. Proteins related to chemoresistant process were identified by two-dimensional gel electrophoresis (2DE) with mass spectrometry (MALDI-TOF and LC-MS/MS). Eighteen spots were differentially expressed and were identified in SKpac chemoresistant cells compared to SKOV3. The expressions of ALDH 1A1, annexin A1, hnRNP A2, and GDI 2 proteins were validated by Western blot, which was consistent with proteomic analysis. Among the selected proteins, downregulation of hnRNP A2 and GDI 2 was found to be the most significant finding in SKpac cells and chemoresistant ovarian cancer tissues. Our results suggest that hnRNP A2 and GDI 2 may represent potential biomarkers of the paclitaxel-resistant ovarian cancers for tailored cancer therapy.

Functional diversity of the hnRNPs: past, present and perspectives

The hnRNPs (heterogeneous nuclear ribonucleoproteins) are RNA-binding proteins with important roles in multiple aspects of nucleic acid metabolism, including the packaging of nascent transcripts, alternative splicing and translational regulation. Although they share some general characteristics, they vary greatly in terms of their domain composition and functional properties. Although the traditional grouping of the hnRNPs as a collection of proteins provided a practical framework, which has guided much of the research on them, this approach is becoming increasingly incompatible with current knowledge about their structural and functional divergence. Hence, we review the current literature to examine hnRNP diversity, and discuss how this impacts upon approaches to the classification of RNA-binding proteins in general.

An Arabidopsis splicing RNP variant STEP1 regulates telomere length homeostasis by restricting access of nuclease and telomerase

Telomere is an essential DNA-protein complex composed of repetitive DNA and binding proteins to protect the chromosomal ends in eukaryotes. Telomere length is regulated by a specialized RNA-dependent DNA polymerase, telomerase and associated proteins. We show here a potential role of STEP1 that was previously isolated by affinity chromatography in controlling telomere length. While STEP1 requires both RNA-binding domains for telomere binding and subsequent DNA protection, it requires only one RBD to interact with telomerase. The differential telomerase inhibitory activity depending on STEP1 concentrations may suggest that STEP1 contributes to controlling telomere length homeostasis, likely by limiting the accessibility of nuclease or telomerase to telomeric DNA.

Selective suppression of cervical cancer Hela cells by 2-O-β-D-glucopyranosyl-L-ascorbic acid isolated from the fruit of Lycium barbarum L

Lycium barbarum fruit has been used as a Chinese traditional medicine and dietary supplement for centuries. 2-O-β-D-Glucopyranosyl-L-ascorbic acid (AA-2βG), a novel stable vitamin C analog, is one of the main biologically active components of the fruit. In this report, we investigated the cytotoxic and antiproliferative effect of AA-2βG against cancer cells in vitro and identified the proteins with significantly differential expression in the cervical cancer cells (Hela) cultured in the presence of AA-2βG proteomic analysis. Our results demonstrated that the cytotoxic and antiproliferative activity of AA-2βG on cancer cell lines were in a cell type-, time-, and dose-dependent manner. Similar to vitamin C, the AA-2βG selectively induced cell death repressed the proliferation of Hela cells by the mechanism of cell apoptosis and cell cycle arrest induced by AA-2βG through a mechanism of stabilizing p53 protein. However, the biological activity of inhibition of cell proliferation in other malignant cancer cell lines or primary cells were varied, as demonstrated by either moderate inhibition or slight promotion following treatment with AA-2βG. Comparative analysis of the proteomic profiles and immunoblot analysis identified 15 proteins associated with repressing cell apoptosis and/or stimulating cell proliferation in Hela cells that were downregulated in the presence of AA-2βG or vitamin C. These data indicate that a mechanism of the AA-2βG and vitamin C mediated antitumor activity by downregulating the expression of proteins involved in cell apoptosis and proliferation and consequently inducing Hela cell apoptosis and cell cycle arrest, suggesting that AA-2βG and vitamin C may share a similar mechanism of inducing Hela cell apoptosis. These results also suggest that the L. barbarum fruit may be a potential dietary supplement and anticancer agent aimed at the prevention and treatment of cervical cancer.