The exquisite sensitivity of mitotic cancer cells to ionizing radiation (IR) underlies an important rationale for the widely used fractionated radiation therapy. However, the mechanism for this cell ...cycle-dependent vulnerability is unknown. Here we show that treatment with IR leads to mitotic chromosome segregation errors in vivo and long-lasting aneuploidy in tumour-derived cell lines. These mitotic errors generate an abundance of micronuclei that predispose chromosomes to subsequent catastrophic pulverization thereby independently amplifying radiation-induced genome damage. Experimentally suppressing whole-chromosome missegregation reduces downstream chromosomal defects and significantly increases the viability of irradiated mitotic cells. Further, orthotopically transplanted human glioblastoma tumours in which chromosome missegregation rates have been reduced are rendered markedly more resistant to IR, exhibiting diminished markers of cell death in response to treatment. This work identifies a novel mitotic pathway for radiation-induced genome damage, which occurs outside of the primary nucleus and augments chromosomal breaks. This relationship between radiation treatment and whole-chromosome missegregation can be exploited to modulate therapeutic response in a clinically relevant manner.
The caps on the ends of chromosomes, called telomeres, keep the ends of chromosomes from appearing as DNA double-strand breaks (DSBs) and prevent chromosome fusion. However, subtelomeric regions are ...sensitive to DSBs, which in normal cells is responsible for ionizing radiation-induced cell senescence and protection against oncogene-induced replication stress, but promotes chromosome instability in cancer cells that lack cell cycle checkpoints. We have previously reported that I-SceI endonuclease-induced DSBs near telomeres in a human cancer cell line are much more likely to generate large deletions and gross chromosome rearrangements (GCRs) than interstitial DSBs, but found no difference in the frequency of I-SceI-induced small deletions at interstitial and subtelomeric DSBs. We now show that inhibition of MRE11 3'-5' exonuclease activity with Mirin reduces the frequency of large deletions and GCRs at both interstitial and subtelomeric DSBs, but has little effect on the frequency of small deletions. We conclude that large deletions and GCRs are due to excessive processing of DSBs, while most small deletions occur during classical nonhomologous end joining (C-NHEJ). The sensitivity of subtelomeric regions to DSBs is therefore because they are prone to undergo excessive processing, and not because of a deficiency in C-NHEJ in subtelomeric regions.
Repair of DNA damage protects genomic integrity, which is key to tissue functional integrity. In cancer, the type and fidelity of DNA damage response is the fundamental basis for clinical response to ...cytotoxic therapy. Here we consider the contribution of transforming growth factor-beta (TGFβ), a ubiquitous, pleotropic cytokine that is abundant in the tumor microenvironment, to therapeutic response. The action of TGFβ is best illustrated in head and neck squamous cell carcinoma (HNSCC). Survival of HNSCC patients with human papilloma virus (HPV) positive cancer is more than double compared to those with HPV-negative HNSCC. Notably, HPV infection profoundly impairs TGFβ signaling. HPV blockade of TGFβ signaling, or pharmaceutical TGFβ inhibition that phenocopies HPV infection, shifts cancer cells from error-free homologous-recombination DNA double-strand-break (DSB) repair to error-prone alternative end-joining (altEJ). Cells using altEJ are more sensitive to standard of care radiotherapy and cisplatin, and are sensitized to PARP inhibitors. Hence, HPV-positive HNSCC is an experiment of nature that provides a strong rationale for the use of TGFβ inhibitors for optimal therapeutic combinations that improve patient outcome.
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•KOH modified Ascophyllum nodosum seaweed hydrochar is an effective V(V) adsorbent;•Weak binding of V(V) to the hydrochar indicates a reversible adsorption process;•The impact of ...co-existing cations had negligible impact on uptake of V(V);•Desorption and re-adsorption results indicate reusable potential for V(V) recovery.
Vanadium exists as a mobile and toxic trace metal in many alkaline residue leachates. Its removal and recovery not only reduces a global environmental risk but is also critical to the emergence of innovative technologies and the circular economy. In parallel, the use of treated biomass feedstock is receiving increased attention as a low cost adsorbent for toxic metals in wastewater. This study investigated the adsorption of Vanadium (V) from aqueous solution by KOH modified seaweed (Ascophyllum nodosum) hydrochar (HCKOH). The results showed that HCKOH is an effective V(V) adsorbent, achieving maximum uptake of 12.3 mg g−1 at solution pH 4, 60 min contact time and temperature 293 K. The kinetics followed a pseudo second order model with film diffusion controlling the overall adsorption rate. The type I adsorption isotherm was well fitted to a Langmuir model (qm = 12.3 mg g-1, R2 = 0.970, RMSE = 0.66) and a thermodynamic study indicated that the V(V) adsorption was both exothermic and spontaneous. The low enthalpy change (-10.97 kJ mol−1) indicated a weak binding of V(V) to HCKOH pointing to the possibility of V recovery. The impact of co-existing cations on V(V) uptake was negligible for Na(I) and Ga (III) but was reduced slightly for Al(III). Desorption and re-adsorption results (3 cycles) indicated that HCKOH has reusable potential to remove and recover V(V) from waste leachates.
The author is sad to announce the passing of one of University of California San Francisco's memorable and esteemed researchers, Robert B. Painter, who worked at UCSF from 1965 until retirement. ...Painter was a professor in the Department of Microbiology, and a researcher in the Laboratory of Radiobiology and Environmental Health. Although he would be the last to tell you, Painter was famous for many key discoveries in the fields of radiation biology and DNA repair. Painter's research laid the groundwork for the fields of DNA repair and the cellular response to DNA damage. In the 1950s, he was part of the team at Brookhaven National Laboratory that first synthesized tritiated thymidine, a radioactive DNA precursor, and used it to study DNA replication. This achievement was instrumental in defining and quantifying the cell cycle, and in demonstrating that chromosomes segregated as if they were single double helical DNA molecules.
Telomeres, repetitive nucleoprotein complexes that protect chromosomal termini and prevent them from activating inappropriate DNA damage responses (DDRs), shorten with cell division and thus with ...aging. Here, we characterized the human cellular response to targeted telomeric double-strand breaks (DSBs) in telomerase-positive and telomerase-independent alternative lengthening of telomere (ALT) cells, specifically in G1 phase. Telomeric DSBs in human G1 cells elicited early signatures of a DDR; however, localization of 53BP1, an important regulator of resection at broken ends, was not observed at telomeric break sites. Consistent with this finding and previously reported repression of classical non-homologous end-joining (c-NHEJ) at telomeres, evidence for c-NHEJ was also lacking. Likewise, no evidence of homologous recombination (HR)-dependent repair of telomeric DSBs in G1 was observed. Rather, and supportive of rapid truncation events, telomeric DSBs in G1 human cells facilitated formation of extensive tracks of resected 5' C-rich telomeric single-stranded (ss)DNA, a previously proposed marker of the recombination-dependent ALT pathway. Indeed, induction of telomeric DSBs in human ALT cells resulted in significant increases in 5' C-rich (ss)telomeric DNA in G1, which rather than RPA, was bound by the complementary telomeric RNA, TERRA, presumably to protect these exposed ends so that they persist into S/G2 for telomerase-mediated or HR-dependent elongation, while also circumventing conventional repair pathways. Results demonstrate the remarkable adaptability of telomeres, and thus they have important implications for persistent telomeric DNA damage in normal human G1/G0 cells (e.g., lymphocytes), as well as for therapeutically relevant targets to improve treatment of ALT-positive tumors.
Spontaneous telomere loss has been proposed as an important mechanism for initiating the chromosome instability commonly found in cancer cells. We have previously shown that spontaneous telomere loss ...in a human cancer cell line initiates breakage/fusion/bridge (B/F/B) cycles that continue for many cell generations, resulting in DNA amplification and translocations on the chromosome that lost its telomere. We have now extended these studies to determine the effect of the loss of a single telomere on the stability of other chromosomes. Our study showed that telomere acquisition during B/F/B cycles occurred mainly through translocations involving either the nonreciprocal transfer or duplication of the arms of other chromosomes. Telomere acquisition also occurred through small duplications involving the subtelomeric region of the other end of the same chromosome. Although all of these mechanisms stabilized the chromosome that lost its telomere, they differed in their consequences for the stability of the genome as a whole. Telomere acquisition involving nonreciprocal translocations resulted in the loss of a telomere on the donor chromosome, which consequently underwent additional translocations, isochromosome formation, or complete loss. In contrast, telomere acquisition involving duplications stabilized the genome, although the large duplications created substantial allelic imbalances. Thus, the loss of a single telomere can generate a variety of chromosome alterations commonly associated with human cancer, not only on a chromosome that loses its telomere but also on other chromosomes. Factors promoting telomere loss are therefore likely to have an important role in generating the karyotype evolution associated with human cancer.
•Nonhomologous end-joining protein Ku70 is similar at interstitial and subtelomeric DSBs.•Repair proteins RAD51, BRCA1 and CtIP are greatly increased at subtelomeric DSBs.•ATM is reduced at ...subtelomeric DSBs compared to interstitial DSBs.•ATR is increased at subtelomeric DSBs compared to interstitial DSBs.•DSBs near telomeres are more likely to be inappropriately processed.
Telomeres are nucleoprotein structures that are required to protect chromosome ends. Dysfunctional telomeres are recognized as DNA double-strand breaks (DSBs), and elicit the activation of a DNA damage response (DDR). We have previously reported that DSBs near telomeres are poorly repaired, resulting in a high frequency of large deletions and gross chromosome rearrangements (GCRs). Our previous genetic studies have demonstrated that this sensitivity of telomeric regions to DSBs is a result of excessive processing. In the current study, we have further investigated the sensitivity of telomeric regions to DSBs through the analysis of repair proteins associated with DSBs at interstitial and telomeric sites. Following the inducible expression of I-SceI endonuclease, chromatin immunoprecipitation (ChIP) and real-time quantitative PCR were used to compare the recruitment of repair proteins at I-SceI-induced DSBs at interstitial and subtelomeric sites. We observed that proteins that are specifically associated with processing of DSBs during homologous recombination repair, RAD51, BRCA1, and CtIP, are present at a much greater abundance at subtelomeric DSBs. In contrast, Ku70, which is specifically involved in classical nonhomologous end joining, showed no difference at interstitial and subtelomeric DSBs. Importantly, ATM was lower in abundance at subtelomeric DSBs, while ATR was in greater abundance at subtelomeric DSBs, consistent with the accumulation of processed DSBs near telomeres, since processing is accompanied by a transition from ATM to ATR binding. Combined, our results suggest that excessive processing is responsible for the increased frequency of large deletions and GCRs at DSBs near telomeres.
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