NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

sources and effects of ionizing radiation

Of all types of DNA damage, DNA double-strand breaks (DSBs) pose the greatest challenge to cells. One might have, therefore, anticipated that a sizable number of DNA DSBs would be incompatible with cell proliferation. Yet recent experimental findings suggest that, in both precancerous lesions and cancers, activated oncogenes induce stalling and collapse of DNA replication forks, which in turn leads to formation of DNA DSBs. This continuous formation of DNA DSBs may contribute to the genomic instability that characterizes the vast majority of human cancers. In addition, in precancerous lesions, these DNA DSBs activate p53, which, by inducing apoptosis or senescence, raises a barrier to tumor progression. Breach of this barrier by various mechanisms, most notably by p53 mutations, that impair the DNA damage response pathway allows cancers to develop. Thus, oncogene-induced DNA damage may explain two key features of cancer: genomic instability and the high frequency of p53 mutations.

https://science.sciencemag.org/content/sci/319/5868/1352.full.pdf

An oncogene-induced DNA damage model for cancer development.

Ubiquitylation ? the conjugation of proteins with a small protein called ubiquitin ? touches upon all aspects of eukaryotic biology, and its defective regulation is manifest in diseases that range from developmental abnormalities and autoimmunity to neurodegenerative diseases and cancer. A few years ago, we could only have dreamt of the complex arsenal of enzymes dedicated to ubiquitylation. Why has nature come up with so many ways of doing what seems to be such a simple job?

/pdf/themes-and-variations-on-ubiquitylation-5ga1nh97p5.pdf

Themes and variations on ubiquitylation.

Acute myeloid leukaemia is a highly malignant haematopoietic tumour that affects about 13,000 adults in the United States each year. The treatment of this disease has changed little in the past two decades, because most of the genetic events that initiate the disease remain undiscovered. Whole-genome sequencing is now possible at a reasonable cost and timeframe to use this approach for the unbiased discovery of tumour-specific somatic mutations that alter the protein-coding genes. Here we present the results obtained from sequencing a typical acute myeloid leukaemia genome, and its matched normal counterpart obtained from the same patient's skin. We discovered ten genes with acquired mutations; two were previously described mutations that are thought to contribute to tumour progression, and eight were new mutations present in virtually all tumour cells at presentation and relapse, the function of which is not yet known. Our study establishes whole-genome sequencing as an unbiased method for discovering cancer-initiating mutations in previously unidentified genes that may respond to targeted therapies.

/pdf/dna-sequencing-of-a-cytogenetically-normal-acute-myeloid-3c4un65sna.pdf

DNA sequencing of a cytogenetically normal acute myeloid leukaemia genome

Genetic lesions that disable key regulators of G1 phase progression in mammalian cells are present in most human cancers. Mitogen-dependent, cyclin D-dependent kinases (cdk4 and cdk6) phosphorylate the retinoblastoma (Rb) tumor suppressor protein, helping to cancel its growth-inhibitory effects and enabling E2F transcription factors to activate genes required for entry into the DNA synthetic phase (S) of the cell division cycle. Among the E2F-responsive genes are cyclins E and A, which combine with and activate cdk2 to facilitate S phase entry and progression. Accumulation of cyclin D-dependent kinases during G1 phase sequesters cdk2 inhibitors of the Cip/Kip family, complementing the effects of the E2F transcriptional program by facilitating cyclin E-cdk2 activation at the G1-S transition. Disruption of "the Rb pathway" results from direct mutational inactivation of Rb function, by overexpression of cyclin D-dependent kinases, or through loss of p16(INK4a), an inhibitor of the cyclin D-dependent kinases. Reduction in levels of p27(Kip1) and increased expression of cyclin E also occur and carry a poor prognostic significance in many common forms of cancer. The ARF tumor suppressor, encoded by an alternative reading frame of the INK4a-ARF locus, senses "mitogenic current" flowing through the Rb pathway and is induced by abnormal growth promoting signals. By antagonizing Mdm2, a negative regulator of the p53 tumor suppressor, ARF triggers a p53-dependent transcriptional response that diverts incipient cancer cells to undergo growth arrest or apoptosis. Although ARF is not directly activated by signals that damage DNA, its loss not only dampens the p53 response to abnormal mitogenic signals but also renders tumor cells resistant to treatment by cytotoxic drugs and irradiation. Lesions in the p16--cyclin D-CDK4--Rb and ARF--Mdm2--p53 pathways occur so frequently in cancer, regardless of patient age or tumor type, that they appear to be part of the life history of most, if not all, cancer cells.

https://cancerres.aacrjournals.org/content/canres/60/14/3689.full.pdf

The Pezcoller lecture: cancer cell cycles revisited.

The ARF tumor suppressor protein stabilizes p53 by antagonizing its negative regulator, Mdm2 (Hdm2 in humans). Both mouse p19ARF and human p14ARF bind to the central region of Mdm2 (residues 210 to 304), a segment that does not overlap with its N-terminal p53-binding domain, nuclear import or export signals, or C-terminal RING domain required for Mdm2 E3 ubiquitin ligase activity. The N-terminal 37 amino acids of mouse p19ARF are necessary and sufficient for binding to Mdm2, localization of Mdm2 to nucleoli, and p53-dependent cell cycle arrest. Although a nucleolar localization signal (NrLS) maps within a different segment (residues 82 to 101) of the human p14ARF protein, binding to Mdm2 and nucleolar import of ARF-Mdm2 complexes are both required for cell cycle arrest induced by either the mouse or human ARF proteins. Because many codons of mouse ARF mRNA are not recognized by the most abundant bacterial tRNAs, we synthesized ARF minigenes containing preferred bacterial codons. Using bacterially produced ARF polypeptides and chemically synthesized peptides conjugated to Sepharose, residues 1 to 14 and 26 to 37 of mouse p19ARF were found to interact independently and cooperatively with Mdm2, while residues 15 to 25 were dispensable for binding. Paradoxically, residues 26 to 37 of mouse p19ARF are also essential for ARF nucleolar localization in the absence of Mdm2. However, the mobilization of the p19ARF-Mdm2 complex into nucleoli also requires a cryptic NrLS within the Mdm2 C-terminal RING domain. The Mdm2 NrLS is unmasked upon ARF binding, and its deletion prevents import of the ARF-Mdm2 complex into nucleoli. Collectively, the results suggest that ARF binding to Mdm2 induces a conformational change that facilitates nucleolar import of the ARF-Mdm2 complex and p53-dependent cell cycle arrest. Hence, the ARF-Mdm2 interaction can be viewed as bidirectional, with each protein being capable of regulating the subnuclear localization of the other.

Cooperative signals governing ARF-mdm2 interaction and nucleolar localization of the complex.

https://www.cell.com/molecular-cell/pdf/S1097-2765(03)00057-1.pdf

Nucleolar Arf Tumor Suppressor Inhibits Ribosomal RNA Processing

The Arf tumor suppressor protein (p19Arf in the mouse, and p14ARF in humans) antagonizes the functions of the p53-negative regulator Mdm2 to trigger p53-dependent cell-cycle arrest or apoptosis (Sherr 2001). Arf also has additional activities that are p53-independent, including an ability to inhibit ribosomal RNA (rRNA) processing (Sugimoto et al. 2003) and effects on gene expression (Eymin et al. 2001; Fatyol and Szalay 2001; Martelli et al. 2001; Datta et al. 2002; Kuo et al. 2003; Rocha et al. 2003). The p19Arf protein is unusual in several respects. It is encoded by the Ink4a locus (now designated Ink4a/Arf; Quelle et al. 1995), which also specifies a totally unrelated polypeptide, p16Ink4a, a potent inhibitor of cyclin D-dependent kinases (Serrano et al. 1993). Two transcripts initiated at separate promoters incorporate sequences from different first exons (1α and 1β) that are spliced to the products of a common downstream exon translated in alternative reading frames (from which Arf gets its name). Mouse p19Arf is a basic protein containing ∼22% arginine but only a single lysine residue that is not conserved in human p14ARF. Given its basic nature, p19Arf must be “buffered” by binding to other cellular proteins and/or nucleic acids. Most Arf protein localizes within the nucleolus where it is bound in complexes of high molecular mass (2–5 MDa) that include many other proteins (Weber et al. 1999; Bertwistle et al. 2004). Among the latter is nucleophosmin (NPM or B23), an abundant cellular protein which binds to p19Arf with high stoichiometry (Itahana et al. 2003; Bertwistle et al. 2004).

Expression of Arf transcripts is difficult to detect in developing mouse embryos (Zindy et al. 1997), and mice lacking the gene develop normally but are highly prone to tumor formation (Kamijo et al. 1997). The levels of p19Arf expressed in normal tissues in vivo are also quite low. Arf is induced by elevated and sustained oncogenic signals, such as those resulting from Myc overexpression (Zindy et al. 1998) or Ras mutation (Palmero et al. 1998) but not directly by other genotoxic stresses that lead to p53 stabilization. Studies using reporter mice in which a gene encoding green fluorescent protein (GFP) was substituted for Arf exon 1β have implied that Arf activation in vivo can efficiently eliminate incipient tumor cells (Zindy et al. 2003).

The p19Arf protein progressively accumulates when primary mouse embryo fibroblasts (MEFs) are passaged in culture, correlating with their decreasing proliferative capacity and eventual senescence. In contrast, Arf-null MEFs continue to proliferate much like established cell lines (Kamijo et al. 1997). Although one might imagine that p19Arf accumulation in senescing primary cells need not be accompanied by appreciable degradation, the mechanisms that regulate Arf turnover have not been elucidated. We show here that p19Arf is subject to more dynamic controls than previously thought, being degraded by the proteasome following N-terminal polyubiquitination.

/pdf/n-terminal-polyubiquitination-and-degradation-of-the-arf-1gt6e9zb9l.pdf

N-terminal polyubiquitination and degradation of the Arf tumor suppressor

Nucleophosmin (NPM or B23) plays key roles in ribosome biogenesis, centrosome duplication, and maintenance of genomic integrity. Mutations affecting the carboxylterminal domain of NPM occur in a significant percentage of adult patients with acute myeloid leukemia (AML), and these alterations create an additional nuclear export signal that relocalizes much of the protein from its normal nucleolar stores to the cytoplasm. When induced by oncogenic stress, the Arf tumor suppressor protein accumulates within the nucleolus, where it is physically associated with, and stabilized by, NPM. Ectopic overexpression of an NPM cytoplasmic mutant (NPMc) relocalized p19Arf and the endogenous NPM protein to the cytoplasm. NPMc-dependent export of p19Arf from the nucleus inhibited its functional interaction with the p53 negative regulator, Mdm2, and blunted Arf-induced activation of the p53 transcriptional program. Cytoplasmic NPM relocalization also attenuated Arf-induced sumoylation of Mdm2 and NPM and prevented wild type NPM from inhibiting p19Arf protein turnover. However, despite the ability of NPMc to interfere with these p53-dependent and independent activities of Arf, NPMc exhibited anti-proliferative activity in Arf-null NIH-3T3 cells. Overexpression of wild type NPM, but not NPMc, overcame premature senescence of Atm-null cells, a phenotype that can be rescued by inactivation of Arf or p53. Therefore, perturbation of Arf function appears to be insufficient to explain the oncogenic effects of the NPMc mutation. We favor the idea that NPMc also contributes to AML by dominantly perturbing other functions of the wild type NPM protein.

http://publicationslist.org/data/richard.williams/ref-15/2005-denBesten-CELL%20CYCLE.pdf

Myeloid leukemia-associated nucleophosmin mutants perturb p53-dependent and independent activities of the Arf tumor suppressor protein.

Nucleophosmin (NPM or B23) plays key roles in ribosome biogenesis, centrosome dupli-cation, and maintenance of genomic integrity. Mutations affecting the carboxylterminal domain of NPM occur in a significant percentage of adult patients with acute myeloid leukemia (AML), and these alterations create an additional nuclear export signal that relocalizes much of the protein from its normal nucleolar stores to the cytoplasm. When induced by oncogenic stress, the Arf tumor suppressor protein accumulates within the nucleolus, where it is physically associated with, and stabilized by, NPM. Ectopic overexpression of an NPM cytoplasmic mutant (NPMc) relocalized p19 Arf and the endogenous NPM protein to the cytoplasm. NPMc-dependent export of p19 Arf from the nucleus inhibited its functional interaction with the p53 negative regulator, Mdm2, and blunted Arf-induced activation of the p53 transcriptional program. Cytoplasmic NPM relocalization also attenuated Arf-induced sumoylation of Mdm2 and NPM and prevented wild type NPM from inhibiting p19 Arf protein turnover. However, despite the ability of NPMc to interfere with these p53-dependent and independent activities of Arf, NPMc exhibited anti-proliferative activity in Arf-null NIH-3T3 cells. Overexpression of wild type NPM, but not NPMc, overcame premature senescence of Atm-null cells, a phenotype that can be rescued by inactivation of Arf or p53. Therefore, perturbation of Arf function appears to be insufficient to explain the oncogenic effects of the NPMc mutation. We favor the idea that NPMc also contributes to AML by dominantly perturbing other functions of the wild type NPM protein.

Mei-Ling Kuo

Papers

Cooperative signals governing ARF-mdm2 interaction and nucleolar localization of the complex.

Nucleolar Arf Tumor Suppressor Inhibits Ribosomal RNA Processing

N-terminal polyubiquitination and degradation of the Arf tumor suppressor

Myeloid leukemia-associated nucleophosmin mutants perturb p53-dependent and independent activities of the Arf tumor suppressor protein.

Myeloid Leukemia-Associated Nucleophosmin Mutants Perturb p53-Dependent and Independent Activities of the Arf Tumor