Initiation of Genome Instability and Preneoplastic Processes through Loss of Fhit Expression

Genomic instability drives tumorigenesis, but how it is initiated in sporadic neoplasias is unknown. In early preneoplasias, alterations at chromosome fragile sites arise due to DNA replication stress. A frequent, perhaps earliest, genetic alteration in preneoplasias is deletion within the fragile FRA3B/FHIT locus, leading to loss of Fhit protein expression. Because common chromosome fragile sites are exquisitely sensitive to replication stress, it has been proposed that their clonal alterations in cancer cells are due to stress sensitivity rather than to a selective advantage imparted by loss of expression of fragile gene products. Here, we show in normal, transformed, and cancer-derived cell lines that Fhit-depletion causes replication stress-induced DNA double-strand breaks. Using DNA combing, we observed a defect in replication fork progression in Fhit-deficient cells that stemmed primarily from fork stalling and collapse. The likely mechanism for the role of Fhit in replication fork progression is through regulation of Thymidine kinase 1 expression and thymidine triphosphate pool levels; notably, restoration of nucleotide balance rescued DNA replication defects and suppressed DNA breakage in Fhit-deficient cells. Depletion of Fhit did not activate the DNA damage response nor cause cell cycle arrest, allowing continued cell proliferation and ongoing chromosomal instability. This finding was in accord with in vivo studies, as Fhit knockout mouse tissue showed no evidence of cell cycle arrest or senescence yet exhibited numerous somatic DNA copy number aberrations at replication stress-sensitive loci. Furthermore, cells established from Fhit knockout tissue showed rapid immortalization and selection of DNA deletions and amplifications, including amplification of the Mdm2 gene, suggesting that Fhit loss-induced genome instability facilitates transformation. We propose that loss of Fhit expression in precancerous lesions is the first step in the initiation of genomic instability, linking alterations at common fragile sites to the origin of genome instability

Aquaculture governance: five engagement arenas for sustainability transformation

A greater focus on governance is needed to facilitate effective and substantive progress toward sustainability transformations in the aquaculture sector. Concerted governance efforts can help move the sector beyond fragmented technical questions associated with intensification and expansion, social and environmental impacts, and toward system-based approaches that address interconnected sustainability issues. Through a review and expert-elicitation process, we identify five engagement arenas to advance a governance agenda for aquaculture sustainability transformation: (1) setting sustainability transformation goals, (2) cross-sectoral linkages, (3) land–water–sea connectivity, (4) knowledge and innovation, and (5) value chains. We then outline the roles different actors and modes of governance can play in fostering sustainability transformations, and discuss action items for researchers, practitioners, and policymakers to operationalize activities within their engagement arenas

Rigorous monitoring is necessary to guide food system transformation in the countdown to the 2030 global goals

Food systems that support healthy diets in sustainable, resilient, just, and equitable ways can engender progress in eradicating poverty and malnutrition; protecting human rights; and restoring natural resources. Food system activities have contributed to great gains for humanity but have also led to significant challenges, including hunger, poor diet quality, inequity, and threats to nature. While it is recognized that food systems are central to multiple global commitments and goals, including the Sustainable Development Goals, current trajectories are not aligned to meet these objectives. As mounting crises further stress food systems, the consequences of inaction are clear. The goal of food system transformation is to generate a future where all people have access to healthy diets, which are produced in sustainable and resilient ways that restore nature and deliver just, equitable livelihoods. A rigorous, science-based monitoring framework can support evidence-based policymaking and the work of those who hold key actors accountable in this transformation process. Monitoring can illustrate current performance, facilitate comparisons across geographies and over time, and track progress. We propose a framework centered around five thematic areas related to (1) diets, nutrition, and health; (2) environment and climate; and (3) livelihoods, poverty, and equity; (4) governance; and (5) resilience and sustainability. We hope to call attention to the need to monitor food systems globally to inform decisions and support accountability for better governance of food systems as part of the transformation process. Transformation is possible in the next decade, but rigorous evidence is needed in the countdown to the 2030 SDG global goals

Initiation of Genome Instability and Preneoplastic Processes through Loss of Fhit Expression

Genomic instability drives tumorigenesis, but how it is initiated in sporadic neoplasias is unknown. In early preneoplasias, alterations at chromosome fragile sites arise due to DNA replication stress. A frequent, perhaps earliest, genetic alteration in preneoplasias is deletion within the fragile FRA3B/FHIT locus, leading to loss of Fhit protein expression. Because common chromosome fragile sites are exquisitely sensitive to replication stress, it has been proposed that their clonal alterations in cancer cells are due to stress sensitivity rather than to a selective advantage imparted by loss of expression of fragile gene products. Here, we show in normal, transformed, and cancer-derived cell lines that Fhit-depletion causes replication stress-induced DNA double-strand breaks. Using DNA combing, we observed a defect in replication fork progression in Fhit-deficient cells that stemmed primarily from fork stalling and collapse. The likely mechanism for the role of Fhit in replication fork progression is through regulation of Thymidine kinase 1 expression and thymidine triphosphate pool levels; notably, restoration of nucleotide balance rescued DNA replication defects and suppressed DNA breakage in Fhit-deficient cells. Depletion of Fhit did not activate the DNA damage response nor cause cell cycle arrest, allowing continued cell proliferation and ongoing chromosomal instability. This finding was in accord with in vivo studies, as Fhit knockout mouse tissue showed no evidence of cell cycle arrest or senescence yet exhibited numerous somatic DNA copy number aberrations at replication stress-sensitive loci. Furthermore, cells established from Fhit knockout tissue showed rapid immortalization and selection of DNA deletions and amplifications, including amplification of the Mdm2 gene, suggesting that Fhit loss-induced genome instability facilitates transformation. We propose that loss of Fhit expression in precancerous lesions is the first step in the initiation of genomic instability, linking alterations at common fragile sites to the origin of genome instability

Redox Signaling via Lipid Peroxidation Regulates Retinal Progenitor Cell Differentiation.

Reactive oxygen species (ROS) and downstream products of lipid oxidation are emerging as important secondary messengers in tissue homeostasis. However, their regulation and mechanism of action remain poorly studied in vivo during normal development. Here, we reveal that the fine regulation of hydrogen peroxide (H2O2) levels by its scavenger Catalase to mediate the switch from proliferation to differentiation in retinal progenitor cells (RPCs) is crucial. We identify 9-hydroxystearic acid (9-HSA), an endogenous downstream lipid peroxidation product, as a mediator of this effect in the zebrafish retina. We show that the 9-HSA proliferative effect is due to the activation of Notch and Wnt pathways through the inhibition of the histone deacetylase 1. We show that the local and temporal manipulation of H2O2 levels in RPCs is sufficient to trigger their premature differentiation. We finally propose a mechanism that links H2O2 homeostasis and neuronal differentiation via the modulation of lipid peroxidation

Genomic instability in Fhit-deficient cells correlates with onset of rapid proliferation and immortalization.

<p>(A) Analysis of <i>Fhit</i>^+/+ and <i>Fhit</i>^−/− 3T3 MEF cell lines (n = 3, cell lines established from 3 embryos for each mouse strain). Arrows mark the passage numbers when MEFs became immortalized. (B) Western blot of <i>Fhit</i>^+/+ MEFs for Fhit and GAPDH expression. Immunoblots were performed on lysates obtained at the indicated passage number. (C) Summary of copy number aberrations (CNAs) in pre- and post-senescence MEFs from <i>Fhit</i>^+/+ and <i>Fhit</i>^−/− mice. (D) The Fhit loss–induced genome instability model. Deletions in <i>FHIT</i> alleles occur due to FRA3B fragility causing loss of Fhit protein expression. Fhit loss causes dTTP pool insufficiency triggering replication stress, followed by stress-induced chromosomal instability. Chromosomal instability increases the likelihood of activating mutations in oncogenes and/or inactivating mutations in tumor suppressors, which are then selected for, facilitating cell transformation.</p

Loss of Fhit causes replication stress.

<p>(A) Cyclin A and γH2AX indirect immunofluorescence after Fhit knockdown. Representative images are shown; bars, 10 µm. (B) Data obtained in (A) were quantified from 3 independent experiments, and statistical significance was determined using a 2-sided T-test. Bar graphs represent the means, and error bars mark the standard deviations. (C) pATR immunofluorescence 2 days after Fhit knockdown in HEK293 cells. Representative images are shown; bars, 5 µm. (D) Quantification of cells positive for more than 5 pATR foci/cell from 3 independent experiments; statistical significance was determined using a 2-sided T-test. (E) Neutral comet assays in siRNA transfected HEK293 cells treated with 2 mM hydroxyurea for 4 h. Box plots show quantification of Tail moments. P-values were determined using the Mann-Whitney rank sum test. (F) Neutral comet assays in H1299 E1 and D1 cells with ponasterone A-induction treated with 2 mM hydroxyurea for 4 h. Box plots show quantification of Tail moments. P-values were determined using the Mann-Whitney rank sum test.</p