Overexpression of the R2 Subunit of Ribonucleotide Reductase in Human Nasopharyngeal Cancer Cells Reduces Radiosensitivity

Kuo, Mei Ling; Hwang, Hwa Shin; Sosnay, Patrick Ryan; Kunugi, Keith A.; Kinsella, Timothy J.

doi:10.1097/00130404-200307000-00010

Cited by 25 publications

(23 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been shown that an increase in RRM2 protein levels and RR activity in human nasopharyngeal cancer cells results in ionizing radiation resistance, which appears mediated by enhanced ionizing radiation damage repair during G2 phase of the cell cycle. However, overexpression of the large subunit, RRM1, of RR in these cells did not affect RR activity or ionizing radiation response (Kuo et al, 2003). RRM2 overexpression is also associated with gemcitabine chemoresistance in pancreatic adenocarcinoma cells, and that suppression of RRM2 expression using RNA interference enhances gemcitabine-induced cytotoxicity in vitro (Duxbury et al, 2004).…”

Section: Discussionmentioning

confidence: 85%

Integrated Bioinformatics for Radiation-Induced Pathway Analysis from Proteomics and Microarray Data

Hu¹,

Huang²,

Cheema³

et al. 2008

J Proteomics Bioinform

View full text Add to dashboard Cite

Functional analysis and interpretation of large-scale proteomics and gene expression data require effective use of bioinformatics tools and public knowledge resources coupled with expert-guided examination. An integrated bioinformatics approach was used to analyze cellular pathways in response to ionizing radiation. ATM, or ataxia-telangiectasia mutated , a serine-threonine protein kinase, plays critical roles in radiation responses, including cell cycle arrest and DNA repair. We analyzed radiation responsive pathways based on 2D-gel/MS proteomics and microarray gene expression data from fibroblasts expressing wild type or mutant ATM gene. The analysis showed that metabolism was significantly affected by radiation in an ATM dependent manner. In particular, purine metabolic pathways were differentially changed in the two cell lines. The expression of ribonucleoside-diphosphate reductase subunit M2 (RRM2) was increased in ATM-wild type cells at both mRNA and protein levels, but no changes were detected in ATM-mutated cells. Increased expression of p53 was observed 30min after irradiation of the ATM-wild type cells. These results suggest that RRM2 is a downstream target of the ATM-p53 pathway that mediates radiation-induced DNA repair. We demonstrated that the integrated bioinformatics approach facilitated pathway analysis, hypothesis generation and target gene/protein identification.

show abstract

Section: Discussionmentioning

confidence: 85%

Integrated Bioinformatics for Radiation-Induced Pathway Analysis from Proteomics and Microarray Data

Hu¹,

Huang²,

Cheema³

et al. 2008

J Proteomics Bioinform

View full text Add to dashboard Cite

show abstract

“…In contrast, Triapine is a considerably more potent RR inhibitor and is effective against hydroxyurea-resistant murine and human tumor cells (18,21). Moreover, Triapine is equally effective against the hRRM2 and p53R2 components of the R2 subunit of RR (11), and it is the R2 subunit that has been shown to protect against radiationinduced cell death (4). Triapine has undergone phase I clinical trials and has been shown to have a favorable pharmacokinetic and toxicity profile (22 -26).…”

Section: Discussionmentioning

confidence: 99%

“…With respect to radiosensitivity, Kuo et al (4) showed that whereas the overexpression of the R1 subunit has no effect on radiosensitivity, overexpression of the R2 subunit (in the form of hRRM2) protects against radiation-induced cell death, consistent with the R2 subunit of RR serving as a potential target for radiosensitization. Although a number of agents have been developed as RR inhibitors, hydroxyurea has received the most attention in preclinical and clinical studies.…”

mentioning

confidence: 99%

In vitro and In vivo Radiosensitization Induced by the Ribonucleotide Reductase Inhibitor Triapine (3-Aminopyridine-2-Carboxaldehyde-Thiosemicarbazone)

Barker

Burgan

Carter

et al. 2006

Clinical Cancer Research

View full text Add to dashboard Cite

Purpose: Because ribonucleotide reductase (RR) plays a role in DNA repair, it may serve as a molecular target for radiosensitization. Unlike previously investigated RR inhibitors, Triapine potently inhibits both RR holoenzymes.Therefore, the effects of Triapine on tumor cell radiosensitivity were investigated. Experimental Design: The effects of Triapine on the in vitro radiosensitivity of three human tumor cell lines and one normal cell line were evaluated using a clonogenic assay. Growth delay was used to evaluate the effects of Triapine on in vivo tumor radiosensitivity. The levels of the RR subunits were determined using immunoblot analysis and DNA damage and repair were evaluated using gH2AX foci. Results: Exposure of the tumor cell lines toTriapine before or immediately after irradiation resulted in an increase in radiosensitivity. In contrast,Triapine enhanced the radiosensitivity of the normal fibroblast cell line only when the exposure was before irradiation. There were no consistent differences between cell lines with respect to the expression of the RR subunits. Whereas Triapine had no effect on radiation-induced gH2AX foci at 1 hour, the number of gH2AX foci per cell was significantly greater in the Triapine-treated cells at 24 hours after irradiation, suggesting the presence of unrepaired DNA damage. Triapine administration to mice bearing tumor xenografts immediately after irradiation resulted in a greater than additive increase in radiation-induced tumor growth delay. Conclusions: These results indicate that Triapine can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect involves an inhibition of DNA repair.Radiotherapy continues to be a primary cancer treatment modality. Recent strategies aimed at increasing its efficacy have focused on targeting the molecules and processes that serve as determinants of cellular radiosensitivity. Among the fundamental processes that influence radiation-induced cell death is DNA repair; a critical molecule in this process is ribonucleotide reductase (RR). RR catalyzes the reduction of ribonucleotides to deoxyribonucleotides and thus provides an essential component for DNA synthesis and repair. RR is composed of two homodimer subunits (1). The R1 subunit (composed of two molecules of hRRM1) contains the ribonucleotide binding sites and allosteric effector sites. The R2 subunit, which contains a nonheme iron complexed with a tyrosyl free radical and is essential for catalytic activity, was initially defined as a homodimer of hRRM2. However, Tanaka et al. (2) recently identified the hRRM2 homologue, p53R2, which can serve as a functional alternative to hRRM2 as the R2 subunit (3). The circumstances that dictate whether the R2 subunit of RR is composed of hRRM2 or p53R2 have not been completely defined.With respect to radiosensitivity, Kuo et al. (4) showed that whereas the overexpression of the R1 subunit has no effect on radiosensitivity, overexpression of the R2 subunit (in the form of hRRM2) protects against radiation-in...

show abstract

“…As maximal DNA synthesis requires high concentrations of dNTPs, the RNR activity plays an important role in cell proliferation (31). On the other hand, increased RNR activity has been associated with malignant transformation and resistance to chemotherapy (12,14,25,56).The class I RNR holoenzymes are commonly found in eukaryotes and eubacteria and comprise two subunits, R1 and R2 (34). The active site and multiple binding sites for allosteric effectors reside in R1 (20), which can exist as a dimer, tetramer, and hexamer depending on the nucleotides present and their concentrations (21,37,47).…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Dif1 Controls Subcellular Localization of Ribonucleotide Reductase by Mediating Nuclear Import of the R2 Subunit

Huang

2008

Molecular and Cellular Biology

View full text Add to dashboard Cite

Fidelity in DNA replication and repair requires adequate and balanced deoxyribonucleotide pools that are maintained primarily by regulation of ribonucleotide reductase (RNR). RNR is controlled via transcription, protein inhibitor association, and subcellular localization of its two subunits, R1 and R2. Saccharomyces cerevisiae Sml1 binds R1 and inhibits its activity, while Schizosaccharomyces pombe Spd1 impedes RNR holoenzyme formation by sequestering R2 in the nucleus away from the cytoplasmic R1. Here we report the identification and characterization of S. cerevisiae Dif1, a regulator of R2 nuclear localization and member of a new family of proteins sharing separate homologous domains with Spd1 and Sml1. Dif1 is localized in the cytoplasm and acts in a pathway different from the nuclear R2-anchoring protein Wtm1. Like Sml1 and Spd1, Dif1 is phosphorylated and degraded in cells encountering DNA damage, thereby relieving inhibition of RNR. A shared domain between Sml1 and Dif1 controls checkpoint kinase-mediated phosphorylation and degradation of the two proteins. Abolishing Dif1 phosphorylation stabilizes the protein and delays damage-induced nucleus-to-cytoplasm redistribution of R2. This study suggests that Dif1 is required for nuclear import of the R2 subunit and plays an essential role in regulating the dynamic RNR subcellular localization.Maintenance of genomic stability depends on faithful replication of DNA and repair of lesions after damage. Fidelity of both DNA replication and repair is influenced by perturbation in the sizes and relative ratios of cellular deoxynucleotide triphosphate (dNTP) pools. Ribonucleotide reductase (RNR) catalyzes the essential step of converting ribonucleoside diphosphates to the corresponding deoxy forms and is largely responsible for maintaining cellular dNTP pools (34). As maximal DNA synthesis requires high concentrations of dNTPs, the RNR activity plays an important role in cell proliferation (31). On the other hand, increased RNR activity has been associated with malignant transformation and resistance to chemotherapy (12,14,25,56).The class I RNR holoenzymes are commonly found in eukaryotes and eubacteria and comprise two subunits, R1 and R2 (34). The active site and multiple binding sites for allosteric effectors reside in R1 (20), which can exist as a dimer, tetramer, and hexamer depending on the nucleotides present and their concentrations (21,37,47). R2 is a homodimer or heterodimer that houses a diferric-tyrosyl radical cofactor [(Fe) 2 -Y ⅐ ] essential for nucleotide reduction (36,40,42). Mammalian genomes contain a single R1 gene and two R2 genes; the cell cycle-regulated RRM2 is responsible for providing dNTPs in actively dividing cells, and the DNA damage-inducible p53R2 is required for replenishing dNTP pools in cells under genotoxic stress (9,22,44). Loss of p53R2 causes mitochondrial DNA depletion and increased apoptosis (22). The budding yeast Saccharomyces cerevisiae has two R1 genes, RNR1 and RNR3. RNR1 is essential for mitotic growth, while RNR3 is high...

show abstract

Overexpression of the R2 Subunit of Ribonucleotide Reductase in Human Nasopharyngeal Cancer Cells Reduces Radiosensitivity

Abstract: An increase in R2 protein levels and RR activity in KB/M2 cells results in IR resistance, which appears mediated by enhanced IR damage repair during G2. R1 protein overexpression in these isogenic human tumor cells (KB/M1) did not affect RR activity or IR response.

Cited by 25 publications

References 35 publications

Integrated Bioinformatics for Radiation-Induced Pathway Analysis from Proteomics and Microarray Data

Integrated Bioinformatics for Radiation-Induced Pathway Analysis from Proteomics and Microarray Data

In vitro and In vivo Radiosensitization Induced by the Ribonucleotide Reductase Inhibitor Triapine (3-Aminopyridine-2-Carboxaldehyde-Thiosemicarbazone)

Dif1 Controls Subcellular Localization of Ribonucleotide Reductase by Mediating Nuclear Import of the R2 Subunit

Contact Info

Product

Resources

About