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• Stop laser uranium enrichmentThe US Congress should discourage efforts to advance the technology to make fuel for nuclear reactors, say Francis Slakey and Linda R. Cohen ? the risks outweigh the benefits.
Nature Journals
• Transcription-independent ARF regulation in oncogenic stress-mediated p53 res...The tumour suppressor ARF is specifically required for p53 activation under oncogenic stress. Recent studies showed that p53 activation mediated by ARF, but not that induced by DNA damage, acts as a major protection against tumorigenesis in vivo under certain biological settings, suggesting that the ARF?p53 axis has more fundamental functions in tumour suppression than originally thought. Because ARF is a very stable protein in most human cell lines, it has been widely assumed that ARF induction is mediated mainly at the transcriptional level and that activation of the ARF?p53 pathway by oncogenes is a much slower and largely irreversible process by comparison with p53 activation after DNA damage. Here we report that ARF is very unstable in normal human cells but that its degradation is inhibited in cancerous cells. Through biochemical purification, we identified a specific ubiquitin ligase for ARF and named it ULF. ULF interacts with ARF both in vitro and in vivo and promotes the lysine-independent ubiquitylation and degradation of ARF. ULF knockdown stabilizes ARF in normal human cells, triggering ARF-dependent, p53-mediated growth arrest. Moreover, nucleophosmin (NPM) and c-Myc, both of which are commonly overexpressed in cancer cells, are capable of abrogating ULF-mediated ARF ubiquitylation through distinct mechanisms, and thereby promote ARF stabilization in cancer cells. These findings reveal the dynamic feature of the ARF?p53 pathway and suggest that transcription-independent mechanisms are critically involved in ARF regulation during responses to oncogenic stress.
• Spatial control of EGF receptor activation by reversible dimerization on livi...
Epidermal growth factor receptor (EGFR) is a type?I receptor tyrosine kinase, the deregulation of which has been implicated in a variety of human carcinomas. EGFR signalling is preceded by receptor dimerization, typically thought to result from a ligand-induced conformational change in the ectodomain that exposes a loop (dimerization arm) required for receptor association. Ligand binding may also trigger allosteric changes in the cytoplasmic domain of the receptor that is crucial for signalling. Despite these insights, ensemble-averaging approaches have not determined the precise mechanism of receptor activation in situ. Using quantum-dot-based optical tracking of single molecules combined with a novel time-dependent diffusivity analysis, here we present the dimerization dynamics of individual EGFRs on living cells. Before ligand addition, EGFRs spontaneously formed finite-lifetime dimers kinetically stabilized by their dimerization arms. The dimers were primed both for ligand binding and for signalling, such that after EGF addition they rapidly showed a very slow diffusivity state that correlated with activation. Although the kinetic stability of unliganded dimers was in principle sufficient for EGF-independent activation, ligand binding was still required for signalling. Interestingly, dimers were enriched in the cell periphery in an actin- and receptor-expression-dependent fashion, resulting in a peripheral enhancement of EGF-induced signalling that may enable polarized responses to growth factors.
• Heteroplasmic mitochondrial DNA mutations in normal and tumour cells
The presence of hundreds of copies of mitochondrial DNA (mtDNA) in each human cell poses a challenge for the complete characterization of mtDNA genomes by conventional sequencing technologies. Here we describe digital sequencing of mtDNA genomes with the use of massively parallel sequencing-by-synthesis approaches. Although the mtDNA of human cells is considered to be homogeneous, we found widespread heterogeneity (heteroplasmy) in the mtDNA of normal human cells. Moreover, the frequency of heteroplasmic variants varied considerably between different tissues in the same individual. In addition to the variants identified in normal tissues, cancer cells harboured further homoplasmic and heteroplasmic mutations that could also be detected in patient plasma. These studies provide insights into the nature and variability of mtDNA sequences and have implications for mitochondrial processes during embryogenesis, cancer biomarker development and forensic analysis. In particular, they demonstrate that individual humans are characterized by a complex mixture of related mitochondrial genotypes rather than a single genotype.
• ITPA gene variants protect against anaemia in patients treated for chronic he...
Chronic infection with the hepatitis C virus (HCV) affects 170?million people worldwide and is an important cause of liver-related morbidity and mortality. The standard of care therapy combines pegylated interferon (pegIFN) alpha and ribavirin (RBV), and is associated with a range of treatment-limiting adverse effects. One of the most important of these is RBV-induced haemolytic anaemia, which affects most patients and is severe enough to require dose modification in up to 15% of patients. Here we show that genetic variants leading to inosine triphosphatase deficiency, a condition not thought to be clinically important, protect against haemolytic anaemia in hepatitis-C-infected patients receiving RBV.
• Targeted deletion of the 9p21 non-coding coronary artery disease risk interva...
Sequence polymorphisms in a 58-kilobase (kb) interval on chromosome 9p21 confer a markedly increased risk of coronary artery disease (CAD), the leading cause of death worldwide. The variants have a substantial effect on the epidemiology of CAD and other life-threatening vascular conditions because nearly one-quarter of Caucasians are homozygous for risk alleles. However, the risk interval is devoid of protein-coding genes and the mechanism linking the region to CAD risk has remained enigmatic. Here we show that deletion of the orthologous 70-kb non-coding interval on mouse chromosome?4 affects cardiac expression of neighbouring genes, as well as proliferation properties of vascular cells. Chr4?70kb/?70kb mice are viable, but show increased mortality both during development and as adults. Cardiac expression of two genes near the non-coding interval, Cdkn2a and Cdkn2b, is severely reduced in chr4?70kb/?70kb mice, indicating that distant-acting gene regulatory functions are located in the non-coding CAD risk interval. Allele-specific expression of Cdkn2b transcripts in heterozygous mice showed that the deletion affects expression through a cis-acting mechanism. Primary cultures of chr4?70kb/?70kb aortic smooth muscle cells exhibited excessive proliferation and diminished senescence, a cellular phenotype consistent with accelerated CAD pathogenesis. Taken together, our results provide direct evidence that the CAD risk interval has a pivotal role in regulation of cardiac Cdkn2a/b expression, and suggest that this region affects CAD progression by altering the dynamics of vascular cell proliferation.
• p62, an autophagy hero or culprit?
The p62 protein recognizes toxic cellular waste, which is then scavenged by a sequestration process known as self-eating or autophagy. Lack of autophagy leads to accumulation of p62, which is not good for liver cells, as it induces a cellular stress response that leads to disease.
• The selective autophagy substrate p62 activates the stress responsive transcr...
Impaired turnover of the autophagy substrate p62 leads to liver injury. p62 inhibits the ubiquitin ligase Keap1, leading to stabilization of the transcription factor Nrf2. High levels of p62 in autophagy deficient animals leads to unusually high expression of Nrf2 targets genes and results in liver injury.
• Deciphering genetic susceptibility to frontotemporal lobar dementia
A genome-wide association study has identified a new genetic susceptibility factor for a subtype of frontotemporal lobar dementia characterized by TDP-43 inclusions. The work illustrates how high-quality phenotyping can increase power to detect risk alleles for rare heterogeneous diseases.
• Open chromatin and diabetes risk
A new study has identified a large number of open chromatin regions harboring active regulatory elements in human pancreatic islets. A type 2 diabetes?associated SNP in TCF7L2 was found to be located in a region of allele-specific open chromatin and shows allele-specific enhancer activity, suggesting a potential mechanism for this disease association.
• Common variants at 7p21 are associated with frontotemporal lobar degeneration...
Vivianna Van Deerlin and colleagues report that common variants at 7p21 are associated with a subtype of frontotemporal lobar degeneration marked by TDP-43 inclusions. They further show that the risk alleles are associated with elevated brain expression of TMEM106B, which resides at the peak of association on 7p21.
• Genome-wide association mapping identifies multiple loci for a canine SLE-rel...
Kerstin Lindblad-Toh and colleagues use genome-wide association mapping to identify risk loci for a canine systemic lupus erythematosus-related disease complex in Nova Scotia duck tolling retrievers. The study illustrates the power of using dog breeds for complex trait mapping.
• Vanilloid flavor for a good appetite?
Members of the transient receptor potential vanilloid ion-channel family are expressed in a wide variety of cells and function as sensors of mechanical stress. The second such family member, TVRP2, is now also linked to phagocytosis in macrophages.
• An essential role for the transcription factor HEB in thymocyte survival, Tcr...
Lymphocyte development requires transcription factors of the E2A family. Goldrath and colleagues identify a unique role for the E2 protein HEB in the generation and survival of invariant natural killer T cells.
• Pharmacological correction of a defect in PPAR-? signaling ameliorates diseas...
Defects in the ion transporter CFTR result in cystic fibrosis, which is marked by excessive mucous buildup in the lungs and colon and premature death. Christopher Glass and his colleagues now show that these aspects of the disease are associated with defects in PPAR-? signaling in epithelial cells and that a synthetic agonist of this nuclear receptor is sufficient to partially normalize signaling and improve survival of a mouse model (pages 267?268).
Nature Reviews
• Awakening dormant haematopoietic stem cellsHaematopoietic stem cells (HSCs) in mouse bone marrow are located in specialized niches as single cells. During homeostasis, signals from this environment keep some HSCs dormant, which preserves long-term self-renewal potential, while other HSCs actively self renew to maintain haematopoiesis. In response to haematopoietic stress,