UV stimulation of nucleophosmin/B23 expression is an immediate-early gene response induced by damaged DNA

Nucleophosmin Protein Dephosphorylation by DUSP3 Is a Fine-Tuning Regulator of p53 Signaling to Maintain Genomic Stability

The dual-specificity phosphatase 3 (DUSP3), an atypical protein tyrosine phosphatase (PTP), regulates cell cycle checkpoints and DNA repair pathways under conditions of genotoxic stress. DUSP3 interacts with the nucleophosmin protein (NPM) in the cell nucleus after UV-radiation, implying a potential role for this interaction in mechanisms of genomic stability. Here, we show a high-affinity binding between DUSP3-NPM and NPM tyrosine phosphorylation after UV stress, which is increased in DUSP3 knockdown cells. Specific antibodies designed to the four phosphorylated NPM’s tyrosines revealed that DUSP3 dephosphorylates Y29, Y67, and Y271 after UV-radiation. DUSP3 knockdown causes early nucleolus exit of NPM and ARF proteins allowing them to disrupt the HDM2-p53 interaction in the nucleoplasm after UV-stress. The anticipated p53 release from proteasome degradation increased p53-Ser15 phosphorylation, prolonged p53 half-life, and enhanced p53 transcriptional activity. The regular dephosphorylation of NPM’s tyrosines by DUSP3 balances the p53 functioning and favors the repair of UV-promoted DNA lesions needed for the maintenance of genomic stability.

Increased expression of nucleophosmin is associated with the pathophysiology of chronic rhinosinusitis with nasal polyposis

OBJECTIVE

Nucleophosmin (NPM1) has been suggested to be involved in the pathophysiologic mechanism of inflammatory disorders. We measured the expression level of NPM1 in nasal polyp (NP) tissues of patients with chronic rhinosinusitis with nasal polyposis (CRSwNP). We also assessed the correlation between NPM1 expression and other parameters such as eosinophilic infiltration, inflammatory cytokines, and clinical indicators such as Lund-Mackay computed tomography (CT) score.

METHODS

Thirty patients with CRSwNP were included. We performed pre-operative CT scan to determine Lund-Mackay CT scores. During endoscopic sinus surgery, we harvested NP tissues from patients with CRSwNP. We performed Sirius red staining to evaluate eosinophilia and conducted immunohistochemical staining for NPM1 and real-time PCR for cytokines including interleukin (IL)-5, IL-17A, and IL-32.

RESULTS

The mRNA expression of NPM1 was significantly up-regulated in eosinophilic NP tissues (RQ 0.58 ± 0.06), compared to non-eosinophilic NP tissues (RQ 0.38 ± 0.08, p < 0.05). In the epithelium of NP tissue, a significant positive correlation was observed between eosinophilic infiltration and NPM1 expression. The expression of NPM1 was significantly correlated with that of IL-5 (r = 0.6229, p = 0.0004), IL-17A (r = 0.5971, p = 0.001), and IL-32 (r = -0.5985, p = 0.0068). There was no significant correlation between the mRNA expression of NPM1 and the Lund-Mackay CT score (Spearman r = -0.2563, p = 0.1879).

CONCLUSION

Expression of NPM1 was significantly increased in eosinophilic NP tissues from patients with CRSwNP. We observed an association between NPM1 expression and various pro-inflammatory cytokines such as IL-5, IL-17, and IL-32 and eosinophilic infiltration, which is thought to contribute to the pathophysiology of NP.

Dipeptide repeat proteins inhibit homology-directed DNA double strand break repair in C9ORF72 ALS/FTD

BACKGROUND

The C9ORF72 hexanucleotide repeat expansion is the most common known genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), two fatal age-related neurodegenerative diseases. The C9ORF72 expansion encodes five dipeptide repeat proteins (DPRs) that are produced through a non-canonical translation mechanism. Among the DPRs, proline-arginine (PR), glycine-arginine (GR), and glycine-alanine (GA) are the most neurotoxic and increase the frequency of DNA double strand breaks (DSBs). While the accumulation of these genotoxic lesions is increasingly recognized as a feature of disease, the mechanism(s) of DPR-mediated DNA damage are ill-defined and the effect of DPRs on the efficiency of each DNA DSB repair pathways has not been previously evaluated.

METHODS AND RESULTS

Using DNA DSB repair assays, we evaluated the efficiency of specific repair pathways, and found that PR, GR and GA decrease the efficiency of non-homologous end joining (NHEJ), single strand annealing (SSA), and microhomology-mediated end joining (MMEJ), but not homologous recombination (HR). We found that PR inhibits DNA DSB repair, in part, by binding to the nucleolar protein nucleophosmin (NPM1). Depletion of NPM1 inhibited NHEJ and SSA, suggesting that NPM1 loss-of-function in PR expressing cells leads to impediments of both non-homologous and homology-directed DNA DSB repair pathways. By deleting NPM1 sub-cellular localization signals, we found that PR binds NPM1 regardless of the cellular compartment to which NPM1 was directed. Deletion of the NPM1 acidic loop motif, known to engage other arginine-rich proteins, abrogated PR and NPM1 binding. Using confocal and super-resolution immunofluorescence microscopy, we found that levels of RAD52, a component of the SSA repair machinery, were significantly increased iPSC neurons relative to isogenic controls in which the C9ORF72 expansion had been deleted using CRISPR/Cas9 genome editing. Western analysis of post-mortem brain tissues confirmed that RAD52 immunoreactivity is significantly increased in C9ALS/FTD samples as compared to controls.

CONCLUSIONS

Collectively, we characterized the inhibitory effects of DPRs on key DNA DSB repair pathways, identified NPM1 as a facilitator of DNA repair that is inhibited by PR, and revealed deficits in homology-directed DNA DSB repair pathways as a novel feature of C9ORF72-related disease.

Insights into the Relationship between Nucleolar Stress and the NF-κB Pathway

The nuclear organelle the nucleolus and the transcription factor nuclear factor of κ-light-chain-enhancer of activated B cells (NF-κB) are both central to the control of cellular homeostasis, dysregulated in common diseases and implicated in the ageing process. Until recently, it was believed that they acted independently to regulate homeostasis in health and disease. However, there is an emerging body of evidence suggesting that nucleoli and NF-κB signalling converge at multiple levels. Here we will review current understanding of this crosstalk. We will discuss activation of the NF-κB pathway by nucleolar stress and induction of apoptosis by nucleolar sequestration of NF-κB/RelA. We will also discuss the role of TIF-IA, COMMD1, and nucleophosmin, which are key players in this crosstalk, and the therapeutic relevance, particularly with respect to the antitumour effects of aspirin.

RNA-Binding Protein HuR Regulates Rac1 Nucleocytoplasmic Shuttling Through Nucleophosmin in the Intestinal Epithelium

BACKGROUND & AIMS

The mammalian intestinal epithelium is a rapidly self-renewing tissue in the body, and its homeostasis is tightly regulated via well-controlled mechanisms. The RNA-binding protein HuR is essential for maintaining gut epithelial integrity, and targeted deletion of HuR in intestinal epithelial cells (IECs) disrupts mucosal regeneration and delays repair after injury. Here, we defined the role of HuR in regulating subcellular distribution of small guanosine triphosphatase Rac1 and investigated the implication of nucleophosmin (NPM) as a molecular chaperone in this process.

METHODS

Studies were conducted in intestinal epithelial tissue-specific HuR knockout (IE-HuR^-/-) mice and cultured IEC-6 cells, derived from rat small intestinal crypts. Functions of HuR and NPM in vitro were investigated via their gene silencing and overexpression.

RESULTS

The abundance of cytoplasmic Rac1 in the small intestinal mucosa increased significantly in IE-HuR^-/- mice, although HuR deletion did not alter total Rac1 levels. HuR silencing in cultured IECs also increased the cytoplasmic Rac1 levels, without an effect on whole-cell Rac1 content. In addition, HuR deficiency in the intestinal epithelium decreased the levels of NPM in IE-HuR^-/- mice and cultured IECs. NPM physically interacted with Rac1 and formed the NPM/Rac1 complex. NPM silencing decreased the NPM/Rac1 association and inhibited nuclear accumulation of Rac1, along with an increase in cytoplasmic abundances of Rac1. In contrast, ectopically expressed NPM enhanced Rac1 nuclear translocation and restored Rac1 subcellular localization to near normal in HuR-deficient cells.

CONCLUSIONS

These results indicate that HuR regulates Rac1 nucleocytoplasmic shuttling in the intestinal epithelium by altering NPM expression.

B23/Nucleophosmin promotes reconstitution of synaptic path in hippocampus after injury

B23, also known as nucleophosmin (NPM), is multifunctional protein directly implicated in cell proliferation, cell cycle progression, and cell survival. In the current study, in addition to confirming its anti-apoptotic function in neuronal survival, we demonstrated that the spatial-temporal expression profile of B23 during development of hippocampal neurons is high in the embryonic stage, down-regulated after birth, and preferentially localized at the tips of growing neuritis and branching points. Overexpression of B23 promotes axon growth with abundant branching points in growing hippocampal neurons, but depletion of B23 impairs axon growth, leading to neuronal death. Following injury to the trisynaptic path in hippocampal slice, overexpression of B23 remarkably increased the number and length of regenerative fibers in the mossy fiber path. Our study suggests that B23 expression in developing neurons is essential for neuritogenesis and axon growth and that up-regulation of B23 may be a strategy for enhancing the reconstitution of synaptic paths after injury to hippocampal synapses.

Phosphoproteome Profiling Reveals Multifunctional Protein NPM1 as part of the Irradiation Response of Tumor Cells

To fight resistances to radiotherapy, the understanding of escape mechanisms of tumor cells is crucial. The aim of this study was to identify phosphoproteins that are regulated upon irradiation. The comparative analysis of the phosphoproteome before and after irradiation brought nucleophosmin (NPM1) into focus as a versatile phosphoprotein that has already been associated with tumorigenesis. We could show that knockdown of NPM1 significantly reduces tumor cell survival after irradiation. NPM1 is dephosphorylated stepwise within 1 hour after irradiation at two of its major phosphorylation sites: threonine-199 and threonine-234/237. This dephosphorylation is not the result of a fast cell cycle arrest, and we found a heterogenous intracellular distribution of NPM1 between the nucleoli, the nucleoplasm, and the cytoplasm after irradiation. We hypothesize that the dephosphorylation of NPM1 at threonine-199 and threonine-234/237 is part of the immediate response to irradiation and of importance for tumor cell survival. These findings could make NPM1 an attractive pharmaceutical target to radiosensitize tumor cells and improve the outcome of radiotherapy by inhibiting the pathways that help tumor cells to escape cell death after gamma irradiation.

Oncogene c-fos and mutant R175H p53 regulate expression of Nucleophosmin implicating cancer manifestation

Nucleophosmin (NPM1) is a nucleolar protein that is frequently overexpressed in various types of solid tumors. NPM1 is involved in several cellular processes that might contribute significantly to the increased proliferation potential of cancers. Previous reports suggest that NPM1 expression is highly increased in response to mitogenic and oncogenic signals, the mechanisms of which have not been elucidated extensively. Using constructs incorporating different fragments of the NPM1 promoter upstream to a Luciferase reporter gene, we have identified the minimal promoter of NPM1 and candidate transcription factors regulating NPM1 promoter activity by luciferase reporter assays. We have validated the roles of a few candidate factors at the transcriptional and protein level by quantitative reverse transcriptase PCR, immunoblotting and immunohistochemistry, and explored the mechanism of regulation of NPM1 expression using immunoprecipitation and chromatin immunoprecipitation assays. We show here that the expression of NPM1 is regulated by transcription factor c-fos, a protein that is strongly activated by growth factor signals. In addition, mutant p53 (R175H) overexpression also enhances NPM1 expression possibly through c-myc and c-fos. Moreover, both c-fos and mutant p53 are overexpressed in oral tumor tissues that showed NPM1 overexpression. Collectively, our results suggest that c-fos and mutant p53 R175H positively regulate NPM1 expression, possibly in synergism, that might lead to oncogenic manifestation.

Prohibitin 2 localizes in nucleolus to regulate ribosomal RNA transcription and facilitate cell proliferation in RD cells

Prohibitin 2 (PHB2), as a conserved multifunctional protein, is traditionally localized in the mitochondrial inner membrane and essential for maintenance of mitochondrial function. Here, we investigated the role of PHB2 in human rhabdomyosarcoma (RMS) RD cells and found substantial localization of PHB2 in the nucleolus. We demonstrated that PHB2 knockdown inhibited RD cell proliferation through inducing cell cycle arrest and suppressing DNA synthesis. Meanwhile, down-regulation of PHB2 also induced apoptosis and promoted differentiation in fractions of RD cells. In addition, PHB2 silencing led to altered nucleolar morphology, as observed by transmission electron microscopy, and impaired nucleolar function, as evidenced by down-regulation of 45S and 18S ribosomal RNA synthesis. Consistently, upon PHB2 knockdown, occupancy of c-Myc at the ribosomal DNA (rDNA) promoter was attenuated, while more myoblast determination protein 1 (MyoD) molecules bound to the rDNA promoter. In conclusion, our findings suggest that nucleolar PHB2 is involved in maintaining nucleolar morphology and function in RD cells by regulating a variety of transcription factors, which is likely to be one of the underlying mechanisms by which PHB2 promotes tumor proliferation and represses differentiation. Our study provides new insight into the pathogenesis of RMS and novel characterizations of the highly conserved PHB2 protein.

mTOR transcriptionally and post-transcriptionally regulates Npm1 gene expression to contribute to enhanced proliferation in cells with Pten inactivation

The mammalian target of rapamycin (mTOR) plays essential roles in the regulation of growth-related processes such as protein synthesis, cell sizing and metabolism in both normal and pathological growing conditions. These functions of mTOR are thought to be largely a consequence of its cytoplasmic activity in regulating translation rate, but accumulating data highlight supplementary role(s) for this serine/threonine kinase within the nucleus. Indeed, the nuclear activities of mTOR are currently associated with the control of protein biosynthetic capacity through its ability to regulate the expression of gene products involved in the control of ribosomal biogenesis and proliferation. Using primary murine embryo fibroblasts (MEFs), we observed that cells with overactive mTOR signaling displayed higher abundance for the growth-associated Npm1 protein, in what represents a novel mechanism of Npm1 gene regulation. We show that Npm1 gene expression is dependent on mTOR as demonstrated by treatment of wild-type and Pten inactivated MEFs cultured with rapamycin or by transient transfections of small interfering RNA directed against mTOR. In accordance, the mTOR kinase localizes to the Npm1 promoter gene in vivo and it enhances the activity of a human NPM1-luciferase reporter gene providing an opportunity for direct control. Interestingly, rapamycin did not dislodge mTOR from the Npm1 promoter but rather strongly destabilized the Npm1 transcript by increasing its turnover. Using a prostate-specific Pten-deleted mouse model of cancer, Npm1 mRNA levels were found up-regulated and sensitive to rapamycin. Finally, we also showed that Npm1 is required to promote mTOR-dependent cell proliferation. We therefore proposed a model whereby mTOR is closely involved in the transcriptional and posttranscriptional regulation of Npm1 gene expression with implications in development and diseases including cancer.

Proteomic Analysis and Functional Studies of Baicalin on Proteins Associated with Skin Cancer

Abundant evidence supports the key role of ultraviolet radiation (UVR) in skin cancer development. The human skin, especially the epidermal layer, is the main defense against UV radiation. Baicalin is a major bioactive component of Scutellaria baicalensis Georgi, a plant which has been found to exhibit antitumor activity. The anticarcinogenic mechanism of baicalin is not completely understood. We have reported that baicalin inhibited UVB-induced photo-damage and apoptosis in HaCaT cells (human skin keratinocytes). The aim of the present study is to investigate the cellular gene targets responsible for baicalin’s antitumor activity by performing two-dimensional electrophoresis liquid chromatography-mass spectrometry/mass spectrometry (2-DE LC-MS/MS) with HaCaT cells following UVB and baicalin exposure. Two-DE for protein separation was performed, followed by matrix-assisted laser desorption/ionization mass spectrometry and database searches. Nucleophosmin (NPM)-specific siRNA was designed and synthesized, and the small interfering RNA was transfected into skin squamous cancer A431 cells to knockdown the NPM expression. Proliferation and cell cycle status were assessed by CCK8 and flow cytometric analyses, respectively. We have identified 38 protein spots that are differentially expressed in HaCaT cells exposed to baicalin and/or UVB irradiation These proteins are involved in detoxification, proliferation, metabolism, cytoskeleton and motility. In particular, we found several proteins that have been linked to tumor progression and resistance, such as NPM. Baicalin treatment reduced the cellular proliferation rate and induced arrest during the S-phase of the cell cycle in A431 cells. NPM1 silencing significantly enhanced the effect of baicalin. Our data indicated that baicalin results in the significant inhibition of tumor growth in the A431 cell line, which may be associated with the regulation of the NPM gene expression.

Crosstalk between the nucleolus and the DNA damage response

Nucleolar function and the cellular response to DNA damage have long been studied as distinct disciplines. New research and a new appreciation for proteins holding multiple functional roles, however, is beginning to change the way we think about the crosstalk among distinct cellular processes. Here, we focus on the crosstalk between the DNA damage response and the nucleolus, including a comprehensive review of the literature that reveals a role for conventional DNA repair proteins in ribosome biogenesis, and conversely, ribosome biogenesis proteins in DNA repair. Furthermore, with recent advances in nucleolar proteomics and a growing list of proteins that localize to the nucleolus, it is likely that we will continue to identify new DNA repair proteins with a nucleolar-specific role. Given the importance of ribosome biogenesis and DNA repair in essential cellular processes and the role that they play in diverse pathologies, continued elucidation of the overlap between these two disciplines will be essential to the advancement of both fields and to the development of novel therapeutics.

Downregulation of NPM expression by Her-2 reduces resistance of gastric cancer to oxaliplatin

Nucleophosmin (NPM) and human epidermal growth factor receptor-2 (Her-2) are abnormally expressed in various types of human malignant tumors, including gastric cancer, and have been closely associated with cancer chemoresistance. However, their interaction and roles in oxaliplatin resistance are not fully understood. Therefore, the present study aimed to elucidate the relationship between NPM and Her-2 in gastric cancer cell lines and clinical samples, and further investigated their role in the resistance of gastric cancer to oxaliplatin. Western blotting and reverse transcription-quantitative polymerase chain reaction confirmed that NPM and Her-2 expression were significantly upregulated in gastric cancer cells and clinical samples, and that their expression levels were strongly correlated. However, Her-2 expression was not affected by upregulation or downregulation of NPM expression in gastric cancer cells. Cell counting kit-8 assays demonstrated that the cell sensitivity to oxaliplatin decreased simultaneously with an increase in NPM expression. Furthermore, inhibition of Her-2 expression using trastuzumab significantly increased the sensitivity of the cells to oxaliplatin, which occurred simultaneously with the downregulation of NPM. These results indicated that inhibition of NPM, as a Her-2 downstream signal, may be a novel strategy to overcome oxaliplatin-resistant gastric cancer, and that trastuzumab and oxaliplatin may exhibit a synergistic antitumor effect in Her-2-positive gastric cancer cells.

Nucleophosmin: from structure and function to disease development

Nucleophosmin (NPM1) is a critical cellular protein that has been implicated in a number of pathways including mRNA transport, chromatin remodeling, apoptosis and genome stability. NPM1 function is a critical requirement for normal cellular biology as is underlined in cancer where NPM1 is commonly overexpressed, mutated, rearranged and sporadically deleted. Consistent with a multifunctional role within the cell, NPM1 can function not only as a proto-oncogene but also as a tumor suppressor. The aim of this review is to look at the less well-described role of NPM1 in the DNA repair pathways as well as the role of NPM1 in the regulation of apoptosis and its mutation in cancers.

Can ecological history influence response to pollutants? Transcriptomic analysis of Manila clam collected in different Venice lagoon areas and exposed to heavy metal

Chronic exposure to environmental pollutants can exert strong selective pressures on natural populations, favoring the transmission over generations of traits that enable individuals to survive and thrive in highly impacted environments. The lagoon of Venice is an ecosystem subject to heavy anthropogenic impact, mainly due to the industrial activities of Porto Marghera (PM), which led to a severe chemical contamination of soil, groundwater, and sediments. Gene expression analysis on wild Manila clams collected in different Venice lagoon areas enabled to identify differences in gene expression profiles between clams collected in PM and those sampled in clean areas, and the definition of molecular signatures of chemical stress. However, it remains largely unexplored to which extent modifications of gene expression patterns persists after removing the source of contamination. It is also relatively unknown whether chronic exposure to xenobiotics affects the response to other chemical pollutants. To start exploring such issues, in the present study a common-garden experiment was coupled with transcriptomic analysis, to compare gene expression profiles of PM clams with those of clams collected in the less impacted area of Chioggia (CH) during a period under the same control conditions. Part of the two experimental groups were also exposed to copper for seven days to assess whether different "ecological history" does influence response to such pollutant. The results obtained suggest that the chronic exposure to chemical pollution generated a response at the transcriptional level that persists after removal for the contaminated site. These transcriptional changes are centered on key biological processes, such as defense against either oxidative stress or tissue/protein damage, and detoxification, suggesting an adaptive strategy for surviving in the deeply impacted environment of Porto Marghera. On the other hand, CH clams appeared to respond more effectively to copper exposure than PM animals, proposing that chronic exposure to chemical toxicants either lowers the sensitivity to additional toxicants or blunts the capacity to respond to novel chemical challenges in PM clams.

The expression of B23 and EGR1 proteins is functionally linked in tumor cells under stress conditions

BACKGROUND

The nucleolus is a multi-domain enriched with proteins involved in ribosome biogenesis, cell cycle and apoptosis control, viral replication and differentiation of stem cells. Several authors have suggested a role for the nucleolus also in malignant transformation. We have recently demonstrated that under specific circumstances the transcriptional factor EGR1 is shuttled to the nucleolus where it functions as a negative regulator of RNA polymerase I. Since this activity is hampered in ARF -/- cells, and ARF transcription is regulated by EGR1 while the turnover of ARF protein is under the control of B23, we speculated that some sort of cooperation between EGR1 and B23 might also exist.

RESULTS

In this work we identified a canonical EGR1 binding site on the B23 promoter through experiments of transactivation and in vitro DNA binding assay. We then found that the levels of B23 expression are directly correlated with those of EGR1, and that this correlation applies to several cellular types and to different stress conditions. Furthermore, we showed that EGR1 stability and accumulation within the nucleolus is in turn regulated by B23 through proteasome involvement, similarly to ARF turnover.

CONCLUSION

Our results highlight EGR1 as a regulator of B23 expression actively playing within the newly discovered nucleolar B23-ARF-EGR1 network.

Humoral autoimmune response to nucleophosmin in the immunodiagnosis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a worldwide prevalent cancer with an exremely poor prognosis. Detection of serum α-fetoprotein (AFP) and liver imaging techniques are the conventional methods used clinically for the identification of this malignancy. However, these techniques are not reliable for early diagnosis, and particularly the sensitivity and specificity of AFP in HCC diagnosis are not optimal. Therefore, there is an urgent need for the development of more sensitive and specific methods that can improve AFP quantification in the early detection of HCC. In the present study, autoantibody responses to nucleophosmin (NPM1) in HCC patients were evaluated by enzyme-linked immunosorbent assay (ELISA), western blotting and indirect immunofluorescence. Immunohistochemistry (IHC) with tissue array slides was also performed to analyze protein expression of NPM1 in HCC and control tissues. The prevalence of autoantibodies against NPM1 was 22.4% (17/76) in HCC, which was significantly higher than that in sera from patients with liver cirrhosis (LC), chronic hepatitis (CH) and systemic lupus erythematosus (SLE) (P<0.01). The average titer of autoantibodies against NPM1 in HCC sera was higher compared to that in LC, CH, SLE and normal human sera (NHS) (P<0.01). In addition, anti-NMP1 autoantibodies were detected in sera from several HCC patients with serial bleeding samples. A stronger reactive band corresponding to NMP1 was visualized in the western blot analyses, utilizing sera from patients 3–6 months before the clinical diagnosis of HCC. Our data indicate that NPM1 and the anti-NPM1 system may have potential as an early-stage biomarker for HCC screening and diagnosis.

Granulocyte colony-stimulating factor improves neuron survival in experimental spinal cord injury by regulating nucleophosmin-1 expression

Granulocyte colony-stimulating factor (G-CSF) and its related mechanisms were investigated to assess the potential for this factor to exert neuroprotective effects against spinal cord injury in mice. Recombinant human granulocyte colony-stimulating factor (rhG-CSF) was injected into mice spinal cord hemisection models. Locomotor activity was assessed by using the Basso-Bettie-Bresnahan scale. Neurons isolated from spinal cords were cultured in vitro and used in a neuronal mechanical injury model. Three treatment groups were compared with this model, 1) G-CSF, 2) G-CSF + NSC348884 (a nucleophosmin 1-specific inhibitor), and 3) NSC348884. Immunofluorescence staining and Western blotting were performed to analyze the expression of G-CSF and nucleophosmin 1 (Npm1). TUNEL staining was performed to analyze apoptosis after G-CSF treatment. We found that the G-CSF receptor (G-CSFR) and Npm1 were expressed in neurons and that Npm1 expression was induced after G-CSF treatment. G-CSF inhibited neuronal apoptosis. NSC348884 induced p53-dependent cell apoptosis and partially blocked the neuroprotective activity of G-CSF on neurons in vitro. G-CSF promoted locomotor recovery and demonstrated neuroprotective effects in an acute spinal cord injury model. The mechanism of G-CSF's neuroprotection may be related in part to attenuating neuronal apoptosis by NPM1.

Physical and functional interaction of the TPL2 kinase with nucleophosmin

Tumor Progression Locus 2 (TPL2) is widely recognized as a cytoplasmic mitogen-activated protein 3 kinase with a prominent role in the regulation of inflammatory and oncogenic signal transduction. Herein we report that TPL2 may also operate in the nucleus as a physical and functional partner of nucleophosmin (NPM/B23), a major nucleolar phosphoprotein with diverse cellular activities linked to malignancy. We demonstrate that TPL2 mediates the phosphorylation of a fraction of NPM at threonine 199, an event required for its proteasomal degradation and maintenance of steady-state NPM levels. Upon exposure to ultraviolet C, Tpl2 is required for the translocation of de-phosphorylated NPM from the nucleolus to the nucleoplasm. NPM is an endogenous inhibitor of HDM2:p53 interaction and knockdown of TPL2 was found to result in reduced binding of NPM to HDM2, with concomitant defects in p53 accumulation following genotoxic or ribosomal stress. These findings expand our understanding of the function of TPL2 as a negative regulator of carcinogenesis by defining a nuclear role for this kinase in the topological sequestration of NPM, linking p53 signaling to the generation of threonine 199-phosphorylated NPM.

Proteomic, cellular, and network analyses reveal new DUSP3 interactions with nucleolar proteins in HeLa cells

DUSP3 (or Vaccinia virus phosphatase VH1-related; VHR) is a small dual-specificity phosphatase known to dephosphorylate c-Jun N-terminal kinases and extracellular signal-regulated kinases. In human cervical cancer cells, DUSP3 is overexpressed, localizes preferentially to the nucleus, and plays a key role in cellular proliferation and senescence triggering. Other DUSP3 functions are still unknown, as illustrated by recent and unpublished results from our group showing that this enzyme mediates DNA damage response or repair processes. In this study, we sought to identify new interactions between DUSP3 and proteins directly or indirectly involved in or correlated with its biological roles in HeLa cells exposed to gamma or UV radiation. By using GST-DUSP as bait, we pulled down interacting proteins and identified them by LC-MS/MS. Of the 46 proteins obtained, six hits were extensively validated by immune techniques; the proteins Nucleophosmin, HnRNP C1/C2, and Nucleolin were the most promising targets found to directly interact with DUSP3. We then analyzed the DUSP3 interactomes using physical protein-protein interaction networks using our hits as the seed list. The validated hits as well as unvalidated hits fluctuated on the DUSP3 interactomes of HeLa cells, independent of the time post radiation, which confirmed our proteomic and experimental data and clearly showed the proximity of DUSP3 to proteins involved in processes intimately related to DNA repair and senescence, such as Ku70 and Tert, via interactions with nucleolar proteins, which were identified in this study, that regulate DNA/RNA structure and functions.

Enhanced levels of double-strand DNA break repair proteins protect ovarian cancer cells against genotoxic stress-induced apoptosis

BACKGROUND

Earlier, proteomic profiling of a Serous Ovarian Carcinoma (SeOvCa) progression model in our lab had identified significantly enriched expression of three double-strand break (DSB) -repair proteins viz. RAD50, NPM1, and XRCC5 in transformed cells over pre-transformed, non-tumorigenic cells. Analysis of the functional relevance of enhanced levels of these proteins was explored in transformed ovarian cancer cells.

METHODS

Expression profiling, validation and quantitation of the DSB-repair proteins at the transcriptional and protein levels were carried out. Further analyses included identification of their localization, distribution and modulation on exposure to Estradiol (E2) and cisplatin. Effects on silencing of each of these under conditions of genomic-stress were studied with respect to apoptosis, alterations in nuclear morphology and DNA fragmentation; besides profiling known mitotic and spindle check-point markers in DSB-repair.

RESULTS

We identified that levels of these DSB-repair proteins were elevated not only in our model, but generally in cancer and are specifically triggered in response to genotoxic stress. Silencing of their expression led to aberrant DSB repair and consequently, p53/p21 mediated apoptosis. Further compromised functionality generated genomic instability.

CONCLUSIONS

Present study elucidates a functional relevance of NPM1, RAD50 and XRCC5 DSB-repair proteins towards ensuring survival and evasion of apoptosis during ovarian transformation, emphasizing their contribution and association with disease progression in high-grade SeOvCa.

S-nitrosylation of B23/nucleophosmin by GAPDH protects cells from the SIAH1-GAPDH death cascade

S-nitrosylation of B23/nucleophosmin mediates neuroprotective effects by binding SIAH1, displacing GAPDH, and preventing SIAH1 E3 ligase activity.

B23/nucleophosmin is a multifunctional protein that participates in cell survival signaling by shuttling between the nucleolus/nucleoplasm and nucleus/cytoplasm. In this paper, we report a novel neuroprotective function of B23 through regulation of the SIAH1–glyceraldehyde-3-phosphate dehydrogenase (GAPDH) death cascade. B23 physiologically bound to both SIAH1 and GAPDH, disrupting the SIAH1–GAPDH complex in the nucleus in response to nitrosative stress. S-nitrosylation of B23 at cysteine 275 by trans-nitrosylation from GAPDH dramatically reduced the interaction between SIAH1 and GAPDH. S-nitrosylation of B23 enhanced B23–SIAH1 binding and mediated the neuroprotective actions of B23 by abrogating the E3 ligase activity of SIAH1. In mice, overexpression of B23 notably inhibited N-methyl-d-aspartate–mediated neurotoxicity, whereas expression of the C275S mutant, which is defective in binding to SIAH1, did not prevent neurotoxicity. Thus, B23 regulates neuronal survival by preventing SIAH1–GAPDH death signaling under stress-induced conditions in the brain.

Nucleophosmin (NPM1/B23) interacts with activating transcription factor 5 (ATF5) protein and promotes proteasome- and caspase-dependent ATF5 degradation in hepatocellular carcinoma cells

Nucleophosmin (NPM1/B23) and the activating transcription factor 5 (ATF5) are both known to subject to cell type-dependent regulation. NPM1 is expressed weakly in hepatocytes and highly expressed in hepatocellular carcinomas (HCC) with a clear correlation between enhanced NPM1 expression and increased tumor grading and poor prognosis, whereas in contrast, ATF5 is expressed abundantly in hepatocytes and down-regulated in HCC. Re-expression of ATF5 in HCC inhibits cell proliferation. We report here that using an unbiased approach, tandem affinity purification (TAP) followed with mass spectrometry (MS), we identified NPM1 as a novel ATF5-interacting protein. Unlike many other NPM1-interacting proteins that interact with the N-terminal oligomerization domain of NPM1, ATF5 binds via its basic leucine zipper to the C-terminal region of NPM1 where its nucleolar localization signal is located. NPM1 association with ATF5, whose staining patterns partially overlap in the nucleoli, promotes ATF5 protein degradation through proteasome-dependent and caspase-dependent pathways. NPM1-c, a mutant NPM1 that is defective in nucleolar localization, failed to stimulate ATF5 polyubiquitination and was unable to down-regulate ATF5. NPM1 interaction with ATF5 displaces HSP70, a known ATF5-interacting protein, from ATF5 protein complexes and antagonizes its role in stabilization of ATF5 protein. NPM1-promoted ATF5 down-regulation diminished ATF5-mediated repression of cAMP-responsive element-dependent gene transcription and abrogates ATF5-induced G(2)/M cell cycle blockade and inhibition of cell proliferation in HCC cells. Our study establishes a mechanistic link between elevated NPM1 expression and depressed ATF5 in HCC and suggests that regulation of ATF5 by NPM1 plays an important role in the proliferation and survival of HCC.

Ultraviolet C irradiation induces different expression of cyclooxygenase 2 in NIH 3T3 cells and A431 cells: the roles of COX-2 are different in various cell lines

Ultraviolet C (UVC) is a DNA damage inducer, and 20 J/m² of UVC irradiation caused cell growth inhibition and induced cell death after exposure for 24–36 h. The growth of NIH 3T3 cells was significantly suppressed at 24 h after UVC irradiation whereas the proliferation of A431 cells was inhibited until 36 h after UVC irradiation. UVC irradiation increased COX-2 expression and such up-regulation reached a maximum during 3–6 h in NIH 3T3 cells. In contrast, UVC-induced COX-2 reached a maximum after 24–36 h in A431 cells. Measuring prostaglandin E2 (PGE2) level showed a biphasic profile that PGE2 release was rapidly elevated in 1–12 h after UVC irradiation and increased again at 24 h in both cell lines. Treatment with the selective COX-2 inhibitor, SC-791, during maximum expression of COX-2 induction, attenuated the UVC induced-growth inhibition in NIH 3T3 cells. In contrast, SC-791 treatment after UVC irradiation enhanced death of A431 cells. These data showed that the patterns of UVC-induced PGE2 secretion from NIH 3T3 cells and A431 cells were similar despite the differential profile in UVC-induced COX-2 up-regulation. Besides, COX-2 might play different roles in cellular response to UVC irradiation in various cell lines.

An extensive tumor array analysis supports tumor suppressive role for nucleophosmin in breast cancer

Nucleophosmin (NPM) is a multifunctional protein involved in a complex network of interactions. The role of NPM in oncogenesis is controversial. The NPM gene (NPM1) is mutated or rearranged in a number of hematological disorders, but such changes have not been detected in solid cancers. However, experiments with cultured NPM-null cells and with mice carrying a single inactivated NPM allele indicate a tumor suppressor function for NPM. To resolve the role of NPM in solid cancers, we examined its expression and localization in histologically normal breast tissue and a large array of human breast carcinoma samples (n = 1160), and also evaluated its association with clinicopathological variables and patient survival. The intensity and localization (nucleolar, nuclear, cytoplasmic) of NPM varied across clinical samples. No mutations explaining the differences were found, but the present findings indicate that expression levels of NPM affected its localization. Our study also revealed a novel granular staining pattern for NPM, which was an independent prognostic factor of poor prognosis. In addition, reduced levels of NPM protein were associated with poor prognosis. Furthermore, luminal epithelial cells of histologically normal breast displayed high levels of NPM and overexpression of NPM in the invasive MDA-MB-231 cells abrogated their growth in soft agar. These results support a tumor suppressive role for NPM in breast cancer.

Knockdown of NPM1 by RNA interference inhibits cells proliferation and induces apoptosis in leukemic cell line

Nucleophosmin (NPM1) is an abundant and ubiquitously expressed phosphoprotein that is known to influence solid tumors progression. However, little is known about the role of NPM1 in leukemia. Here, we knocked down the NPM1 expression by RNA interference to investigate the role of NPM1 in leukemic cells proliferation and apoptosis. The interference vector pNPM1-shRNA was constructed and transfected into the human leukemic K562 cell line. The expression levels of NPM1 mRNA and protein were detected by quantitative real-time PCR and Western blot, respectively. Cells proliferation potential in vitro was assessed by methyl thiazolyl tetrazolium (MTT) and colony formation assays. Flow cytometry was used to detect the distribution of cell cycle. Cellular apoptosis was reflected by the relative activities of caspase-3 and caspase-8. The results showed that the expression levels of NPM1 mRNA and protein in K562 cells were significantly reduced after pNPM1-shRNA transfection. The cells growth was significantly inhibited in a time-dependent manner and the number of colonies was significantly reduced in the pNPM1-shRNA transfected cells. Meanwhile, the percentage of cells in G1 phase in the K562/pNPM1-shRNA cells was significantly increased. In addition, there were higher relative activities of caspase-3/8 in the pNPM1-shRNA transfected cells. These results indicate that down-regulation of NPM1 expression inhibits leukemic cells proliferation, blocks cell cycle progression and induces cellular apoptosis. It may implicate a potential target for leukemia gene therapy.

Detection of nucleophosmin and FMS-like tyrosine kinase-3 gene mutations in acute myeloid leukemia

BACKGROUND AND OBJECTIVES

Nucleophosmin gene mutations are frequently reported in acute myeloid leukemia (AML) patients with normal karyotype, which is also frequently associated with internal tandem duplication mutations in the FMS-like tyrosine kinase-3 gene. We sought to detect the nucleophosmin and FMS-like tyrosine kinase-3 (FLT3) internal tandem duplication (ITD) mutations among Iranian patients with AML and to assess the relationship between these mutations and the subtypes of the disease.

DESIGN AND SETTING

Cross-sectional study of patients referred during 2007 through 2009.

PATIENTS AND METHODS

Bone marrow and peripheral blood samples of 131 AML patients were randomly collected at the time of diagnosis and prior to treatment and the DNA extracted. After amplifying the nucleophosmin and FLT3 gene regions, positive cases were screened by conformation-sensitive gel electrophoresis and agarose gel electrophoresis techniques.

RESULTS

Of 131 patients, 23 (17.5%) (0.95% CI=0.107-0.244) had nucleophosmin gene mutations. The highest frequency of such mutations was found among the subtypes of M4 (30.4%), M3 (21.7%) and M5 (17.4%). There was a high frequency of these mutations in the M3 subtype as well as a high frequency of allele D in all subtypes. Also, 21 (16.0%) samples (0.95% CI=0.092-0.229) had FLT3/ITD mutation, of which 8 samples had mutant nucleophosmin (8 of 23, 35%), and another 13 samples had wild-type nucleophosmin gene (13 of 108, 12%). There was a high degree of association between the occurrence of nucleophosmin and FLT3/ITD mutations (P=.012).

CONCLUSION

Our data showed a high frequency of NPM1 mutations in the monocytic subtypes of AML, as well as a high degree of association between the occurrence of NPM1 and FLT3/ITD mutations.

The Multifunctional Nucleolar Protein Nucleophosmin/NPM/B23 and the Nucleoplasmin Family of Proteins

The nucleophosmin (NPM)/nucleoplasmin family of nuclear chaperones has three members: NPM1, NPM2, and NPM3. Nuclear chaperones serve to ensure proper assembly of nucleosomes and proper formation of higher order structures of chromatin. In fact, this family of proteins has such diverse functions in cellular processes such as chromatin remodeling, ribosome biogenesis, genome stability, centrosome replication, cell cycle, transcriptional regulation, apoptosis, and tumor suppression. Of the members of this family, NPM1 is the most studied and is the main focus of this review. NPM2 and NPM3 are less well characterized, and are also discussed wherever appropriate. The structure–function relationship of NPM proteins has largely been worked out. Other than the many processes in which NPM1 takes part, the major interest comes from its involvement in human cancers, particularly acute myeloid leukemia (AML). Its significance stems from the fact that AML with mutated NPM1 accounts for ∼30% of all AML cases and usually has good prognosis. Its clinical importance also comes from its involvement in virus replication, particularly in the era of outbreaks of infectious diseases.

Dephosphorylation of nucleophosmin by PP1β facilitates pRB binding and consequent E2F1-dependent DNA repair

We report a new pathway through which PP1β signals to nucleophosmin (NPM) in response to DNA damage. UV induces dephosphorylation of NPM at multiple sites, leading to enhancement of complex formation between NPM and retinoblastoma tumor suppressor protein and the subsequent upregulation of E2F1. Consequently, such signaling pathway potentiates the cellular DNA repair capacity.

Nucleophosmin (NPM) is an important phosphoprotein with pleiotropic functions in various cellular processes. Although phosphorylation has been postulated as an important functional determinant, possible regulatory roles of this modification on NPM are not fully characterized. Here, we find that NPM is dephosphorylated on various threonine residues (Thr199 and Thr234/237) in response to UV-induced DNA damage. Further experiments indicate that the serine/threonine protein phosphatase PP1β is a physiological NPM phosphatase under both the genotoxic stress and growth conditions. As a consequence, NPM in its hypophosphorylated state facilitates DNA repair. Finally, our results suggest that one possible mechanism of this protective response lies in enhanced NPM-retinoblastoma tumor suppressor protein (pRB) interaction, leading to the relief of the repressive pRB–E2F1 circuitry and the consequent transcriptional activation of E2F1 and several downstream DNA repair genes. Thus, this study unveils a key phosphatase of NPM and highlights a novel mechanism by which the PP1β–NPM pathway contributes to cellular DNA damage response.

Involvement of nucleophosmin/B23 in the cellular response to curcumin

Nucleophosmin (NPM/B23) is a nucleolar phosphoprotein involved in cellular response to many different stimuli. Herein, we studied the molecular mechanism of NPM/B23 induction by curcumin, a natural AP-1 inhibitor with antitumor properties. Exposure to 5-30 μM curcumin significantly and dose-dependently increased the level of NPM/B23 in non-transformed NIH 3T3 cells but not HeLa cells and F9 cells. Besides, the transformed F9 and HeLa cells are more sensitive to curcumin-induced cell death and growth inhibition than NIH 3T3 cells. Overexpression of c-Jun, but not c-Fos, decreased ∼40% of NPM/B23 and enhanced the sensitivity of NIH 3T3 cells to 30 μM curcumin. Furthermore, down-regulation of NPM/B23 by transfection with NPM/B23 antisense plasmid enhanced the sensitivity to curcumin-induced cell death and growth inhibition. These results indicated that NPM/B23 expression regulates cellular sensitivity to curcumin. Besides, NPM/B23 knockdown may facilitate as a novel strategy to promote the sensitivity of cancer cells to curcumin.

Expression of the cytoplasmic NPM1 mutant (NPMc+) causes the expansion of hematopoietic cells in zebrafish

Mutations in the human nucleophosmin (NPM1) gene are the most frequent genetic alteration in adult acute myeloid leukemias (AMLs) and result in aberrant cytoplasmic translocation of this nucleolar phosphoprotein (NPMc+). However, underlying mechanisms leading to leukemogenesis remain unknown. To address this issue, we took advantage of the zebrafish model organism, which expresses 2 genes orthologous to human NPM1, referred to as npm1a and npm1b. Both genes are ubiquitously expressed, and their knockdown produces a reduction in myeloid cell numbers that is specifically rescued by NPM1 expression. In zebrafish, wild-type human NPM1 is nucleolar while NPMc+ is cytoplasmic, as in human AML, and both interact with endogenous zebrafish Npm1a and Npm1b. Forced NPMc+ expression in zebrafish causes an increase in pu.1(+) primitive early myeloid cells. A more marked perturbation of myelopoiesis occurs in p53(m/m) embryos expressing NPMc+, where mpx(+) and csf1r(+) cell numbers are also expanded. Importantly, NPMc+ expression results in increased numbers of definitive hematopoietic cells, including erythromyeloid progenitors in the posterior blood island and c-myb/cd41(+) cells in the ventral wall of the aorta. These results are likely to be relevant to human NPMc+ AML, where the observed NPMc+ multilineage expression pattern implies transformation of a multipotent stem or progenitor cell.

Interaction with checkpoint kinase 1 modulates the recruitment of nucleophosmin to chromatin

The Checkpoint kinase 1 (Chk1) plays a central role in the cellular response to DNA damage and also contributes to the efficacy of DNA replication in the absence of genomic stress. However, we have only limited knowledge regarding the molecular mechanisms that regulate differential Chk1 function in the absence and presence of DNA damage. To address this, we used vertebrate cells with compromised Chk1 function to analyze how altered Chk1 activity influences protein interactions in chromatin. Avian and mammalian cells with compromised Chk1 activity were used in combination with genomic stress, induced by UV, and DNA-associated proteomes were analyzed using 2-DE/MS proteomics and Western-blot analysis. Only one protein, the histone chaperone nucelophosmin, was altered consistently in line with changes in chromatin-associated Chk1 and increased in response to DNA damage. Purified Chk1 and NPM were shown to interact in vitro and strong in vivo interactions were implied from immunoprecipitation analysis of chromatin extracts. During chromatin immunoprecipitation, coassociation of the major cell cycle regulator proteins p53 and CDC25A with both Chk1 and NPM suggests that these proteins are components of complex interaction networks that operate to regulate cell proliferation and apoptosis in vertebrate cells.

A proteomics approach for the identification of nucleophosmin and heterogeneous nuclear ribonucleoprotein C1/C2 as chromatin-binding proteins in response to DNA double-strand breaks

Double-strand breaks (DSBs) of chromosomal DNA trigger the cellular response that activates the pathways for DNA repair and cell-cycle checkpoints, and sometimes the pathways leading to cell death if the damage is too severe to be tolerated. Evidence indicates that, upon generation of DNA DSBs, many nuclear proteins that are involved in DNA repair and checkpoints are recruited to chromatin around the DNA lesions. In the present study we used a proteomics approach to identify DNA-damage-induced chromatin-binding proteins in a systematic way. Two-dimensional gel analysis for protein extracts of chromatin from DNA-damage-induced and control HeLa cells identified four proteins as the candidates for DNA-damage-induced chromatin-binding proteins. MALDI-TOF (matrix-assisted laser-desorption ionization-time-of-flight) MS analysis identified these proteins to be NPM (nucleophosmin), hnRNP (heterogeneous nuclear ribonucleoprotein) C1, hnRNP C2 and 37-kDa laminin-receptor precursor, and the identity of these proteins was further confirmed by immunoblot analysis with specific antibodies. We then demonstrated with chromatin-binding assays that NPM and hnRNP C1/C2, the abundant nuclear proteins with pleiotropic functions, indeed bind to chromatin in a DNA-damage-dependent manner, implicating these proteins in DNA repair and/or damage response. Immunofluorescence experiments showed that NPM, normally present in the nucleoli, is mobilized into the nucleoplasm after DNA damage, and that neither NPM nor hnRNP C1/C2 is actively recruited to the sites of DNA breaks. These results suggest that NPM and hnRNP C1/C2 may function at the levels of the global context of chromatin, rather than by specifically targeting the broken DNA.

Identifying apoptosis-evasion proteins/pathways in human hepatoma cells via induction of cellular hormesis by UV irradiation

Evading apoptosis is pivotal in both of carcinogenesis and resistance to anticancer therapy. We investigated the molecules and pathways of apoptosis evasion in human hepatoma cells by irradiating hepatoma cells with optimized UV (so-called "hormetic responses"). Proteins and pathways related to hormetic responses were identified via proteomic approaches followed by reconstruction of function-networks. Of the 2326 defined protein spots, 42 distinct proteins significantly changed their expression. Eleven hormetic response proteins (HINT1, PHB, CTSD, ANXA1, LGASL1, TPT1, NPM, PRDX2, UCHL1, CERK, and C1QBP) were involved in 5 death-regulatory pathways, including the p53-dependent apoptotic pathway, protein ubiquinization, cellular redox, calcium-mediated signaling pathway, and sphingomyelin-metabolism pathway. Knockdown of HINT1 expression via RNA interference increased tumor cell resistance to apoptosis induction, while silencing NPM, UCHL1, or CERK greatly sensitized tumor cells to apoptosis induction. In conclusion, NPM, UCHL1, and CERK act as apoptosis-evasion proteins that may serve as therapeutic targets for hepatoma. Silencing their expression would increase therapeutic efficacy, thereby reducing the corresponding doses and side-effects of anticancer therapy. This model of induction of cellular hormetic responses to identify apoptosis-evasion molecules/pathways via proteomic approaches can be applied to other modalities of anticancer therapy.

Heat induced ‘masking’ of redox sensitive component(s) of the DNA-nuclear matrix anchoring complex

The 'masking effect' is the observation that heat shock reduces or masks the apparent expression of ionizing radiation (IR) damage to DNA. The mechanism of this effect is thought to involve the aggregation of proteins to the nuclear matrix or chromatin, thereby stabilizing these structures and masking actual DNA damage from assays and presumably from DNA repair complexes. Previously, using the 'halo assay', it has been shown that nucleoids treated with 1 mM dithiothreitol (DTT) and/or inhibited the rewinding of DNA supercoils and that this effect was masked in nucloids isolated from heated cells. Here it is reported that treatment of living cells with reducing agents diminishes the interaction between DNA and Protein Disulphide Isomerase (PDI) and that hyperthermia restored the PDI-DNA interaction, indicating that the masking effect occurred in vivo. PDI is a nuclear matrix protein which binds MAR DNA sequences and may be involved in regulating the degree of DNA supercoiling. It is hypothesized that heat-induced stabilization of PDI-DNA interaction will mask changes in supercoiling observed with reducing reagents and also IR. This stabilization may be affected through either the heat-induced association or enhancement of the binding of proteins to MAR DNA at the NM. Several proteins, including B23 and Hsp60, have been identified whose interaction with DNA increased following heat shock. Further work will be needed to determine if these proteins do, in fact, play a role in the masking effect.

Nucleophosmin blocks mitochondrial localization of p53 and apoptosis

Activation of p53 is an important mechanism in apoptosis. However, whether the presence of p53 in mitochondria plays an important role in p53-mediated apoptosis is unclear. Here, we demonstrate that overexpression of NPM (nucleophosmin) significantly suppresses 12-O-tetradecanoylphorbol 13-acetate (TPA)-mediated apoptosis, in part, by blocking the mitochondrial localization of p53. Within 1 h following TPA treatment of skin epithelial (JB6) cells, p53 accumulated in mitochondria. Expression of NPM enhances p53 levels in the nucleus but reduces p53 levels in mitochondria, as detected by immunocytochemistry and Western blot analysis. The suppressive effect of NPM on p53 mitochondrial localization is also observed in TPA-treated primary epithelial cells and in JB6 cells treated with doxorubicin. NPM enhances the expression of p53 target gene p21 and bax. However, the increase in Bax level in the absence of p53 in mitochondria did not lead to an increase in TPA-induced apoptosis, suggesting that the presence of p53 in mitochondria is important. Suppression of NPM by NPM small interfering RNA leads to an increase of p53 levels in mitochondria and apoptosis. Furthermore, suppression of NPM in tumor cells with a high constitutive level of NPM results in p53 translocation to mitochondria and enhances TPA-mediated apoptosis. The results demonstrate the effect of NPM on p53 localization in mitochondria and apoptosis. Together, the data indicate that the presence of p53 in mitochondria plays an important role in stress-induced apoptosis and suggest that NPM may protect cells from apoptosis by reducing the mitochondrial level of p53.

A phylogenetically conserved DNA damage response resets the circadian clock

The mammalian circadian clock influences the timing of many biological processes such as the sleep/wake cycle, metabolism, and cell division. Environmental cues such as light exposure can influence the timing of this system through the posttranslational modification of key components of the core molecular oscillator. We have previously shown that DNA damage can reset the circadian clock in a time-of-day-dependent manner in the filamentous fungus Neurospora crassa through the modulation of negative regulator FREQUENCY levels by PRD-4 (homologue of mammalian Chk2). We show that DNA damage, generated with either the radiomimetic drug methyl methane sulfonate or UV irradiation, in mouse embryonic fibroblasts isolated from PER2::LUC transgenic mice or in the NIH3T3 cell line, elicits similar responses. In addition to induction of phase advances, DNA damage caused a decrease in luciferase signal in PER2::LUC mouse embryonic fibroblast cells that is indicative of PER2 degradation. Finally, we show that the activity of the BMAL1 promoter is enhanced during DNA damage. These findings provide further evidence that the DNA damage-mediated response of the clock is conserved from lower eukaryotes to mammals.

Differential proteomic analysis of cyclosporine A-induced toxicity in renal proximal tubule cells

BACKGROUND

The use of cyclosporine A (CsA) as a potent immunosuppressant has been limited by its severe nephrotoxic effects. The mechanisms involved are haemodynamic but also related to direct toxic effects of CsA on proximal tubule epithelial cells. We focused on defining a proteomic profile in CsA-treated proximal tubule cells to distinguish the direct impact of CsA on these cells from overlapping haemodynamically mediated phenomena that occur in an in vivo system.

METHODS

By means of high-throughput differential proteomic analyses and mass spectrometry techniques in CsA and vehicle-treated proximal tubule-derived cell lines of human and mouse origin, we determined proteins that change their expression in the presence of CsA.

RESULTS

CsA-induced toxicity analyses revealed that 10 mM CsA for 24 h was the threshold condition to induce significant changes in cell viability and proteomic profile. We identified 38 differentially expressed proteins on CsA-treated mouse PCT3 and human HK-2 cells, related to protein metabolism, response to damage, cell organization and cytoskeleton, energy metabolism, cell cycle and nucleobase/nucleoside/nucleotidic metabolism. 1D and 2D western blot assays in crude extracts from CsA-treated cells or kidneys with impaired function upon CsA treatment revealed a correlation with proteomic changes or differential isoform expression, in randomly selected proteins.

CONCLUSIONS

Proteins identified in this work might be useful markers to eventually distinguish CsA toxicity from chronic allograft nephropathy in protocol biopsies of transplanted patients, facilitating the adjustment of CsA doses to non-toxic ranges, as well as to study the impact of potential therapeutic interventions in an animal model.

Inflammation and endothelial dysfunction during aging: role of NF-kappaB

One of the major conceptual advances in our understanding of the pathogenesis of age-associated cardiovascular diseases has been the insight that age-related oxidative stress may promote vascular inflammation even in the absence of traditional risk factors associated with atherogenesis (e.g., hypertension or metabolic diseases). In the present review we summarize recent experimental data suggesting that mitochondrial production of reactive oxygen species, innate immunity, the local TNF-alpha-converting enzyme (TACE)-TNF-alpha, and the renin-angiotensin system may underlie NF-kappaB induction and endothelial activation in aged arteries. The theme that emerges from this review is that multiple proinflammatory pathways converge on NF-kappaB in the aged arterial wall, and that the transcriptional activity of NF-kappaB is regulated by multiple nuclear factors during aging, including nuclear enzymes poly(ADP-ribose) polymerase (PARP-1) and SIRT-1. We also discuss the possibility that nucleophosmin (NPM or nuclear phosphoprotein B23), a known modulator of the cellular oxidative stress response, may also regulate NF-kappaB activity in endothelial cells.

Ribosomal protein S9 is a novel B23/NPM-binding protein required for normal cell proliferation

B23 (NPM/nucleophosmin) is a multifunctional nucleolar protein and a member of the nucleoplasmin superfamily of acidic histone chaperones. B23 is essential for normal embryonic development and plays an important role in genomic stability, ribosome biogenesis, and anti-apoptotic signaling. Altered protein expression or genomic mutation of B23 is encountered in many different forms of cancer. Although described as multifunctional, a genuine molecular function of B23 is not fully understood. Here we show that B23 is associated with a protein complex consisting of ribosomal proteins and ribosome-associated RNA helicases. A novel, RNA-independent interaction between ribosomal protein S9 (RPS9) and B23 was further investigated. We found that S9 binding requires an intact B23 oligomerization domain. Depletion of S9 by small interfering RNA resulted in decreased protein synthesis and G(1) cell cycle arrest, in association with induction of p53 target genes. We determined that S9 is a short-lived protein in the absence of ribosome biogenesis, and proteasomal inhibition significantly increased S9 protein level. Overexpression of B23 facilitated nucleolar storage of S9, whereas knockdown of B23 led to diminished levels of nucleolar S9. Our results suggest that B23 selectively stores, and protects ribosomal protein S9 in nucleoli and therefore could facilitate ribosome biogenesis.

Ebp1 association with nucleophosmin/B23 is essential for regulating cell proliferation and suppressing apoptosis

Ebp1 and NPM/B23 are essential for cell proliferation and survival. Ebp1 possesses p42 and p48 isoforms. Whereas p42 exclusively resides in the cytoplasm, p48 localizes in both the cytoplasm and the nucleolus. Here, we show that Ebp1 forms a complex with B23, and this complex plays a critical role in cell proliferation and survival. p42 specifically associates with B23 upon epidermal growth factor stimulation, while p48 constantly binds B23. Moreover, Ser360 phosphorylation in p42, but not p48, is critical for the interaction. p48 constitutively binds B23 in the nucleolus, for which B23 Lys263 sumoylation is indispensable. By contrast, p42 selectively binds unsumoylated B23 mutants. Interestingly, B23 K263R, an unsumoylated mutant, triggers p42 nuclear translocation and interacts with it in the nucleus even in the absence of epidermal growth factor. In contrast, the nucleolar residency of p48 is abolished in B23 K263R cells. During the cell cycle, p42 selectively colocalizes with B23 in the mitotic cells, correlating with its phosphorylation status in mitosis. Knocking down of B23 or Ebp1 substantially decreases ribosome biogenesis and cell survival. Thus, B23 distinctively binds Ebp1 isoforms and regulates cell proliferation and survival through p42 and p48, respectively.

Activation of Holliday junction recognizing protein involved in the chromosomal stability and immortality of cancer cells

We identified a novel gene HJURP (Holliday junction-recognizing protein) whose activation seemed to play a pivotal role in the immortality of cancer cells. HJURP was considered a possible downstream target for ataxia telangiectasia mutated signaling, and its expression was increased by DNA double-strand breaks (DSB). HJURP was involved in the homologous recombination pathway in the DSB repair process through interaction with hMSH5 and NBS1, which is a part of the MRN protein complex. HJURP formed nuclear foci in cells at S phase and those subjected to DNA damage. In vitro assays implied that HJURP bound directly to the Holliday junction and rDNA arrays. Treatment of cancer cells with small interfering RNA (siRNA) against HJURP caused abnormal chromosomal fusions and led to genomic instability and senescence. In addition, HJURP overexpression was observed in a majority of lung cancers and was associated with poor prognosis as well. We suggest that HJURP is an indispensable factor for chromosomal stability in immortalized cancer cells and is a potential novel therapeutic target for the development of anticancer drugs.

Proteome analysis of proliferative response of bystander cells adjacent to cells exposed to ionizing radiation

Recently (Cytometry 2003, 56A, 71-80), we reported that direct cell-to-cell contact is required for stimulating proliferation of bystander rat liver cells (WB-F344) cocultured with irradiated cells, and neither functional gap junction intercellular communication nor long-range extracellular factors appear to be involved in this proliferative bystander response (PBR). The molecular basis for this response is unknown. Confluent monolayers of WB-F344 cells were exposed to 5-Gray (Gy) of gamma-rays. Irradiated cells were mixed with unirradiated cells and co-cultured for 24 h. Cells were harvested and protein expression was examined using 2-DE. Protein expression was also determined in cultures of unirradiated and 5-Gy irradiated cells. Proteins were identified by MS. Nucleophosmin (NPM)-1, a multifunctional nucleolar protein, was more highly expressed in bystander cells than in either unirradiated or 5-Gy irradiated cells. Enolase-alpha, a glycolytic enzyme, was present in acidic and basic variants in unirradiated cells. In bystander and 5-Gy irradiated cells, the basic variant was weakly expressed, whereas the acidic variant was overwhelmingly present. These data indicate that the presence of irradiated cells can affect NPM-1 and enolase-alpha in adjacent bystander cells. These proteins appear to participate in molecular events related to the PBR and suggest that this response may involve cellular defense, proliferation, and metabolism.