Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.8 (polynucleotide phosphorylase)
723 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Terminal differentiation and cellular senescence display common properties including irreversible growth arrest. To define the molecular and ultimately the biochemical basis of the complex physiological changes associated with terminal differentiation and senescence, an overlapping-pathway screen was used to identify genes displaying coordinated expression as a consequence of both processes. This approach involved screening of a subtracted cDNA library prepared from human melanoma cells induced to terminally differentiate by treatment with fibroblast IFN and mezerein with mRNA derived from senescent human progeria cells. This strategy identified old-35, which encodes an evolutionary conserved gene, human polynucleotide phosphorylase (hPNPase(old-35)), that is regulated predominantly by type I IFNs. The hPNPase(OLD-35) protein localizes in the cytoplasm of human cells and induces RNA degradation in vitro, as does its purified bacterial protein homologue. Ectopic expression of hPNPase(old-35) in human melanoma cells reduces colony formation, confirming inhibitory activity of this RNA-degradation enzyme. Identification of hPNPase(old-35), an IFN-inducible 3'-5' RNA exonuclease, provides additional support for a relationship between IFN action and RNA processing and suggests an important role for this gene in growth control associated with terminal differentiation and cellular senescence.
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PMID:Identification and cloning of human polynucleotide phosphorylase, hPNPase old-35, in the context of terminal differentiation and cellular senescence. 1247 48

Terminal differentiation and senescence share several common properties, including irreversible cessation of growth and changes in gene expression profiles. To identify molecules that converge in both processes, an overlapping pathway screening was employed that identified old-35, which is human polynucleotide phosphorylase (hPNPaseold-35), a 3',5'-exoribonuclease. We previously demonstrated that hPNPaseold-35 is a type I interferon-inducible gene that is also induced in senescent fibroblasts. In vitro RNA degradation assays confirmed its exoribonuclease properties, and overexpression of hPNPaseold-35 resulted in growth suppression in HO-1 human melanoma cells. The present study examined the molecular mechanism of the growth-arresting property of hPNPaseold-35. When overexpressed by means of a replication-incompetent adenoviral vector (Ad.hPNPaseold-35), hPNPaseold-35 inhibited cell growth in all cell lines tested. Analysis of cell cycle revealed that infection of HO-1 cells with Ad.hPNPaseold-35 resulted in arrest in the G1 phase and eventually apoptosis accompanied by marked reduction in the S phase. Infection with Ad.hPNPaseold-35 resulted in reduction in expression of the c-myc mRNA and Myc protein and modulated the expression of proteins regulating G1 checkpoint and apoptosis. In vitro mRNA degradation assays revealed that hPNPaseOLD-35 degraded c-myc mRNA. Overexpression of Myc partially but significantly protected HO-1 cells from Ad.hPNPaseold-35-induced growth arrest, indicating that Myc down-regulation might directly mediate the growth-inhibitory properties of Ad.hPNPaseold-35. Inhibition of hPNPaseold-35 by an antisense approach provided partial but significant protection against interferon-beta-mediated growth inhibition, thus demonstrating the biological significance of hPNPaseold-35 in interferon action.
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PMID:Down-regulation of Myc as a potential target for growth arrest induced by human polynucleotide phosphorylase (hPNPaseold-35) in human melanoma cells. 1272 1

An overlapping pathway screening (OPS) approach designed to identify and clone genes displaying parallel expression profiles as a function of induction of terminal differentiation and cellular senescence in human cells identified a novel gene old-35. Sequence and functional analysis indicates that old-35 encodes human polynucleotide phosphorylase, hPNPase(old-35). Polynucleotide phosphorylases comprise a family of phosphate dependent 3'-5' RNA exonucleases implicated in RNA regulation. Treatment of HO-1 human melanoma and additional diverse normal and tumor-derived human cell types with Type I interferon (IFN), IFN-beta or IFN-alpha, induces hPNPase(old-35) expression. To provide insights into the regulation of hPNPase(old-35), we cloned and analyzed the promoter region of this gene. These studies demonstrate that IFN-beta controls hPNPase(old-35) expression by transcriptional modulation rather than by altering mRNA stability. Transcriptional activation of hPNPase(old-35) by IFN-beta is primarily mediated by the interferon stimulatory response element (ISRE) present in its promoter. Analysis of hPNPase(old-35) expression in cell lines defective in various IFN signaling molecules confirms that hPNPase(old-35) expression is dependent upon the Janus activated kinase (JAK)/signal transducers and activators of transcription (STAT) pathway. Furthermore, gel shift analyses document that hPNPase(old-35) is a direct target of the interferon stimulated gene factor 3 (ISGF3) complex. The hPNPase(old-35) gene spans approximately 54 kb of genomic DNA and is distributed on 28 exons and 27 introns. hPNPase(old-35) maps to 2p15-2p16.1, a region implicated in hereditary nonpolyposis colorectal cancer, Carney complex, Doyne's honeycomb retinal dystrophy and several other diseases. To provide insights into PNPase function in vivo, we have also cloned the mouse PNPase(old-35) cDNA, mPNPase(old-35). Induction of hPNPase(old-35) by IFN treatment as well as during differentiation and senescence suggest that this gene may play a significant role in regulating cellular growth and that overlapping gene expression changes, also induced by IFN, may contribute to these important physiological processes.
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PMID:Expression regulation and genomic organization of human polynucleotide phosphorylase, hPNPase(old-35), a Type I interferon inducible early response gene. 1456 61

Chronic inflammation is a characteristic feature of aging, and the relationship between cellular senescence and inflammation, although extensively studied, is not well understood. An overlapping pathway screen identified human polynucleotide phosphorylase (hPNPase(old-35)), an evolutionary conserved 3',5'-exoribonuclease, as a gene up-regulated during both terminal differentiation and cellular senescence. Enhanced expression of hPNPase(old-35) via a replication-incompetent adenovirus (Ad.hPNPase(old-35)) in human melanoma cells and normal human melanocytes results in a characteristic senescence-like phenotype. Reactive oxygen species (ROS) play a key role in the induction of both in vitro and in vivo senescence. We now document that overexpression of hPNPase(old-35) results in increased production of ROS, leading to activation of the nuclear factor (NF)-kappaB pathway. Ad.hPNPase(old-35) infection promotes degradation of IkappaBalpha and nuclear translocation of NF-kappaB and markedly increases binding of the transcriptional activator p50/p65. The generation of ROS and activation of NF-kappaB by hPNPase(old-35) are prevented by treatment with a cell-permeable antioxidant, N-acetyl-l-cysteine. Infection with Ad.hPNPase(old-35) enhances the production of interleukin (IL)-6 and IL-8, two classical NF-kappaB-responsive cytokines, and this induction is inhibited by N-acetyl-l-cysteine. A cytokine array reveals that Ad.hPNPase(old-35) infection specifically induces the expression of proinflammatory cytokines, such as IL-6, IL-8, RANTES, and matrix metalloproteinase (MMP)-3. We hypothesize that hPNPase(old-35) might play a significant role in producing pathological changes associated with aging by generating proinflammatory cytokines via ROS and NF-kappaB. Understanding the relationship between hPNPase(old-35) and inflammation and aging provides a unique opportunity to mechanistically comprehend and potentially intervene in these physiologically important processes.
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PMID:Human polynucleotide phosphorylase (hPNPaseold-35): a potential link between aging and inflammation. 1549 72

To fully comprehend cellular senescence, identification of relevant genes involved in this process is mandatory. Human polynucleotide phosphorylase (hPNPase(OLD-35)), an evolutionarily conserved 3', 5' exoribonuclease mediating mRNA degradation, was first identified as a predominantly mitochondrial protein overexpressed during terminal differentiation and senescence. Overexpression of hPNPase(OLD-35) in human melanoma cells and melanocytes induces distinctive changes associated with senescence, potentially mediated by direct degradation of c-myc mRNA by this enzyme. hPNPase(OLD-35) contains two RNase PH (RPH) domains, one PNPase domain, and two RNA binding domains. Using deletion mutation analysis in combination with biochemical and molecular analyses we now demonstrate that the presence of either one of the two RPH domains conferred similar functional activity as the full-length protein, whereas a deletion mutant containing only the RNA binding domains was devoid of activity. Moreover, either one of the two RPH domains induced the morphological, biochemical, and gene expression changes associated with senescence, including degradation of c-myc mRNA. Subcellular distribution confirmed hPNPase(OLD-35) to be localized both in mitochondria and the cytoplasm. The present study elucidates how a predominantly mitochondrial protein, via its localization in both mitochondria and cytoplasm, is able to target a specific cytoplasmic mRNA, c-myc, for degradation and through this process induce cellular senescence.
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PMID:Defining the domains of human polynucleotide phosphorylase (hPNPaseOLD-35) mediating cellular senescence. 1605 41

Type I interferons (IFN-alpha/-beta) are capable of suppressing c-myc mRNA expression by modulating post-transcriptional processing. However, the molecular mechanism of this phenomenon is poorly understood. We previously established that human polynucleotide phosphorylase (hPNPase(old-35)), a type I IFN-inducible 3',5' exoribonuclease involved in mRNA degradation, induces G1 cell cycle arrest and eventually apoptosis by specifically degrading c-myc mRNA. We now demonstrate a close association between IFN-beta-induced hPNPase(old-35) upregulation and c-myc downregulation in human melanoma cells. Employing stable melanoma cell clones expressing hPNPase(old-35) small inhibitory RNA, we demonstrate that hPNPase(old-35) is a key molecule coupled with IFN-beta-mediated downregulation of c-myc mRNA. Inhibition of hPNPase(old-35) or overexpression of c-myc protects melanoma cells from IFN-beta-mediated growth inhibition, emphasizing the importance of hPNPase(old-35) upregulation and consequent c-myc downregulation in IFN-beta-induced growth inhibition and apoptosis induction. In these contexts, targeted overexpression of hPNPase(old-35) might be a novel therapeutic strategy for c-myc-overexpressing and IFN-resistant tumors, such as melanomas.
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PMID:Defining the mechanism by which IFN-beta dowregulates c-myc expression in human melanoma cells: pivotal role for human polynucleotide phosphorylase (hPNPaseold-35). 1641 Aug 5

Human mitochondrial polynucleotide phosphorylase (hPNPase) is an exoribonuclease localized in mitochondria. The exact physiological function of this enzyme is unknown. Recent studies have revealed the existence of a relationship between induction of hPNPase mRNA and both cellular senescence and growth arrest of melanoma cells following beta-interferon treatment. The aim of this study was to verify whether the augmented hPNPase mRNA level results in increase of the protein level. In several cell lines established from five metastatic melanoma patients we did not find any such correlation. However, an elevated level of hPNPase protein was observed in interferon-induced HeLa and Jurkat cells. This increase was correlated with a slight shortening of poly(A) tails of mitochondrial ND3 transcript.
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PMID:Up-regulation of human PNPase mRNA by beta-interferon has no effect on protein level in melanoma cell lines. 1650

Human polynucleotide phosphorylase (hPNPase(old-35)) is a type I IFN-inducible 3',5' exoribonuclease that mediates mRNA degradation. In melanoma cells, slow and sustained overexpression of hPNPase(old-35) induces G(1) cell cycle arrest ultimately culminating in apoptosis, whereas rapid overexpression of hPNPase(old-35) directly promotes apoptosis without cell cycle changes. These observations imply that inhibition of cell cycle progression and induction of apoptosis by hPNPase(old-35) involve multiple intracellular targets and signaling pathways. We now provide evidence that the apoptosis-inducing activity of hPNPase(old-35) is mediated by activation of double-stranded RNA-dependent protein kinase (PKR). Activation of PKR by hPNPase(old-35) precedes phosphorylation of eukaryotic initiation factor-2alpha and induction of growth arrest and DNA damage-inducible gene 153 (GADD153) that culminates in the shutdown of protein synthesis and apoptosis. Activation of PKR by hPNPase(old-35) also instigates down-regulation of the antiapoptotic protein Bcl-x(L). A dominant-negative inhibitor of PKR, as well as GADD153 antisense or bcl-x(L) overexpression, effectively inhibits apoptosis induction by hPNPase(old-35). These studies elucidate a novel pathway by which an evolutionary conserved RNA-metabolizing enzyme, hPNPase(old-35), regulates cell growth and viability.
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PMID:Activation of double-stranded RNA dependent protein kinase, a new pathway by which human polynucleotide phosphorylase (hPNPase(old-35)) induces apoptosis. 1780

MicroRNAs (miRNA), small noncoding RNAs, affect a broad range of biological processes, including tumorigenesis, by targeting gene products that directly regulate cell growth. Human polynucleotide phosphorylase (hPNPase(old-35)), a type I IFN-inducible 3'-5' exoribonuclease, degrades specific mRNAs and small noncoding RNAs. The present study examined the effect of this enzyme on miRNA expression in human melanoma cells. miRNA microarray analysis of human melanoma cells infected with empty adenovirus or with an adenovirus expressing hPNPase(old-35) identified miRNAs differentially and specifically regulated by hPNPase(old-35). One of these, miR-221, a regulator of the cyclin-dependent kinase inhibitor p27(kip1), displayed robust down-regulation with ensuing up-regulation of p27(kip1) by expression of hPNPase(old-35), which also occurred in multiple human melanoma cells upon IFN-beta treatment. Using both in vivo immunoprecipitation followed by Northern blotting and RNA degradation assays, we confirm that mature miR-221 is the target of hPNPase(old-35). Inhibition of hPNPase(old-35) by shRNA or stable overexpression of miR-221 protected melanoma cells from IFN-beta-mediated growth inhibition, accentuating the importance of hPNPase(old-35) induction and miR-221 down-regulation in mediating IFN-beta action. Moreover, we now uncover a mechanism of miRNA regulation involving selective enzymatic degradation. Targeted overexpression of hPNPase(old-35) might provide an effective therapeutic strategy for miR-221-overexpressing and IFN-resistant tumors, such as melanoma.
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PMID:Human polynucleotide phosphorylase selectively and preferentially degrades microRNA-221 in human melanoma cells. 2054 61

As a strategy to identify gene expression changes affected by human polynucleotide phosphorylase (hPNPase(old-35)), we performed gene expression analysis of HeLa cells in which hPNPase(old-35) was overexpressed. The observed changes were then compared to those of HO-1 melanoma cells in which hPNPase(old-35) was stably knocked down. Through this analysis, 90 transcripts, which positively or negatively correlated with hPNPase(old-35) expression, were identified. The majority of these genes were associated with cell communication, cell cycle, and chromosomal organization gene ontology categories. For a number of these genes, the positive or negative correlations with hPNPase(old-35) expression were consistent with transcriptional data extracted from the TCGA (The Cancer Genome Atlas) expression datasets for colon adenocarcinoma (COAD), skin cutaneous melanoma (SKCM), ovarian serous cyst adenocarcinoma (OV), and prostate adenocarcinoma (PRAD). Further analysis comparing the gene expression changes between Ad.hPNPase(old-35) infected HO-1 melanoma cells and HeLa cells overexpressing hPNPase(old-35) under the control of a doxycycline-inducible promoter, revealed global changes in genes involved in cell cycle and mitosis. Overall, this study provides further evidence that hPNPase(old-35) is associated with global changes in cell cycle-associated genes and identifies potential gene targets for future investigation.
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PMID:Analysis of global changes in gene expression induced by human polynucleotide phosphorylase (hPNPase(old-35)). 2472 70


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