[Show abstract][Hide abstract] ABSTRACT: The ARF tumour suppressor protein, the gene of which is frequently mutated in many human cancers, plays an important role in the cellular stress response by orchestrating up-regulation of p53 protein and consequently promoting cell-cycle delay. Although p53 protein function has been clearly linked to the cellular DNA damage response, the role of ARF protein in this process is unclear. Here, we report that arf gene transcription is induced by DNA strand breaks (SBs) and that ARF protein accumulates in response to persistent DNA damage. We discovered that poly(ADP-ribose) synthesis catalysed by PARP1 at the sites of unrepaired SBs activates ARF transcription through a protein signalling cascade, including the NAD(+)-dependent deacetylase SIRT1 and the transcription factor E2F1. Our data suggest that poly(ADP-ribose) synthesis at the sites of SBs initiates DNA damage signal transduction by reducing the cellular concentration of NAD(+), thus down-regulating SIRT1 activity and consequently activating E2F1-dependent ARF transcription. Our findings suggest a vital role for ARF in DNA damage signalling, and furthermore explain the critical requirement for ARF inactivation in cancer cells, which are frequently deficient in DNA repair and accumulate DNA damage.
[Show abstract][Hide abstract] ABSTRACT: ATM-mediated signaling in response to DNA damage is a barrier to tumorigenesis. Here we asked whether replication stress could also contribute to ATM signaling. We demonstrate that, in the absence of DNA damage, ATM responds to replication stress in a hypoxia-induced heterochromatin-like context. In certain hypoxic conditions, replication stress occurs in the absence of detectable DNA damage. Hypoxia also induces H3K9me3, a histone modification associated with gene repression and heterochromatin. Hypoxia-induced replication stress together with increased H3K9me3 leads to ATM activation. Importantly, ATM prevents the accumulation of DNA damage in hypoxia. Most significantly, we describe a stress-specific role for ATM in maintaining DNA replication rates in a background of increased H3K9me3. Furthermore, the ATM-mediated response to oncogene-induced replication stress is enhanced in hypoxic conditions. Together, these data indicate that hypoxia plays a critical role in the activation of the DNA damage response, therefore contributing to this barrier to tumorigenesis.
[Show abstract][Hide abstract] ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC) is characterised by an abundant stromal response also known as a desmoplastic reaction. Pancreatic stellate cells have been identified as playing a key role in pancreatic cancer desmoplasia. There is accumulating evidence that the stroma contributes to tumour progression and to the low therapeutic response of PDAC patients. In this review we described the main actors of the desmoplastic reaction within PDAC and novel therapeutic approaches that are being tested to block the detrimental function of the stroma.
[Show abstract][Hide abstract] ABSTRACT: Genomic integrity is crucial for correct chromosome segregation and physiological rates of cell proliferation. Mutations, deletions and translocations, hallmarks of human tumours, drive the aberrant proliferation and metastatic behaviour of cancer cells. These chromosomal rearrangements often occur at genomic sites susceptible to breakage during DNA replication, including regions with G-quadruplex (G4)-forming potential. G4s are stable secondary structures that guanine-rich single-stranded DNA can readily adopt in vitro. However, their formation in eukaryotic cells has remained elusive and thus a subject of debate ever since they were first described. Recent work has more convincingly implicated G4s in a variety of biological processes including telomere maintenance, gene expression, epigenetic regulation and DNA replication. However, the downside of employing thermodynamically very stable alternative DNA structures as regulatory entities lies in their potential to also interfere with normal DNA metabolic processes, such as transcription and replication, which require readability of each base to faithfully transmit genetic information. Indeed, it has become clear that G4 structures can pose prominent barriers to replication fork progression and that they are also intrinsically recombinogenic. Here, we discuss mechanisms that cells evolved to counteract these detrimental effects, thereby ensuring the faithful inheritance of G4-containing genomes.
[Show abstract][Hide abstract] ABSTRACT: In muscle-invasive bladder cancer there is an urgent need to identify relatively non-toxic radiosensitising agents for use in elderly patients. Histone deacetylase inhibitors radiosensitise tumour cells but not normal cells in vitro and variously downregulate DNA damage signalling, homologous recombination (HR) and non-homologous end-joining (NHEJ) repair proteins. We investigated panobinostat (PAN) as a potential radiosensitiser in bladder cancer cells.
Clonogenic assays were performed in RT112 bladder cancer cells, and RT112 cells stably knocked down for RAD51 or Ku80 by shRNAi. Resolution of γH2AX foci was determined by immunofluorescence confocal microscopy, cell cycle progression by FACS analysis and protein expression by western blotting.
PAN had a greater radiosensitising effect in Ku80KD than RT112 or RAD51KD cells; enhancement ratios 1.35 for Ku80KD at 10nM (IC20 for Ku80KD) and 1.31 for RT112 and RAD51KD at 25nM (IC40 for both). PAN downregulated MRE11, NBS1 and RAD51, but not Ku70 and Ku80, increased γH2AX foci formation in a dose-dependent manner and delayed γH2AX foci repair after ionising radiation.
PAN acts as a radiosensitiser in bladder cancer cell lines, and appears to target HR rather than NHEJ. As muscle-invasive bladder tumours have reduced Ku-DNA binding, PAN could be particularly useful as a radiosensitiser in bladder cancer.
[Show abstract][Hide abstract] ABSTRACT: The recent introduction of high-resolution molecular imaging technology is considered by many experts as a major breakthrough that will potentially lead to a revolutionary paradigm shift in health care and revolutionize clinical practice . This paper explores the challenges and strengths of the current major imaging modalities, as well as the biophysics engineering their repertoire of capabilities. Advancements in the mechanical aspects of both PET and SPECT imaging will advance molecular imaging diagnostic capabilities and have a direct impact on clinical and research practice . A better understanding of the strengths and limitations of functional imaging modalities in the context of their particular hardware and software mechanics will shed light onto how we can advance their diagnostic capabilities on a biological level. Herein, this paper demonstrates the fundamental biomechanical differences between PET and SPECT imaging, and how these fundamental differences translate into clinically relevant data acquisition for brain disorders.
Journal of nuclear medicine & radiation therapy. 07/2013; 4(3).
[Show abstract][Hide abstract] ABSTRACT: This review highlights recent progress in the development of anticancer radiopharmaceuticals. Molecularly targeted radiotherapy refers to the selective delivery of radionuclides that emit charged particles, such as α particles, β or Auger electrons, to cancer cells via a targeting vector. The discovery of new molecular targets through systems biology and other approaches has widened the scope for radiopharmaceutical development. Innovations in antibody engineering and humanisation, recombinant DNA technology, conjugation chemistry and, increasingly, nanotechnology have provided new approaches to the delivery of radionuclides to cancer cells. The increased availability of radioisotopes that have not traditionally been considered for therapy, such as α particle emitters, has also broadened the indications for targeted radiotherapy.
[Show abstract][Hide abstract] ABSTRACT: DNA damage of exposed tumour tissue leading to cell death is one of the detrimental effects of ionising radiation that is exploited, with beneficial consequences, for radiotherapy. The pattern of the discrete energy depositions during passage of the ionising track of radiation defines the spatial distribution of lesions induced in DNA with a fraction of the DNA damage sites containing clusters of lesions, formed over a few nanometres, against a background of endogenously induced individual lesions. These clustered DNA damage sites, which may be considered as a signature of ionising radiation, underlie the deleterious biological consequences of ionising radiation. The concepts developed rely in part on the fact that ionising radiation creates significant levels of clustered DNA damage, including complex double-strand breaks (DSB), to kill tumour cells as clustered damage sites are difficult to repair. This reduced repairability of clustered DNA damage using specific repair pathways is exploitable in radiotherapy for the treatment of cancer. We discuss some potential strategies to enhance radiosensitivity by targeting the repair pathways of radiation-induced clustered damage and complex DNA DSB, through inhibition of specific proteins that are not required in the repair pathways for endogenous damage. The variety and severity of DNA damage from ionising radiation is also influenced by the tumour microenvironment, being especially sensitive to the oxygen status of the cells. For instance, nitric oxide is known to influence the types of damage induced by radiation under hypoxic conditions. A potential strategy based on bioreductive activation of pro-drugs to release nitric oxide is discussed as an approach to deliver nitric oxide to hypoxic tumours during radiotherapy. The ultimate aim of this review is to stimulate thinking on how knowledge of the complexity of radiation-induced DNA damage may contribute to the development of adjuncts to radiotherapy.
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