Replication fork dynamics and the DNA damage response

Prevention and repair of DNA damage is essential for maintenance of genomic stability and cell survival. DNA replication during S-phase can be a source of DNA damage if endogenous or exogenous stresses impair the progression of replication forks. It has become increasingly clear that DNA-damage-response pathways do not only respond to the presence of damaged DNA, but also modulate DNA replication dynamics to prevent DNA damage formation during S-phase. Such observations may help explain the developmental defects or cancer predisposition caused by mutations in DNA-damage-response genes. The present review focuses on molecular mechanisms by which DNA-damage-response pathways control and promote replication dynamics in vertebrate cells. In particular, DNA damage pathways contribute to proper replication by regulating replication initiation, stabilizing transiently stalled forks, promoting replication restart and facilitating fork movement on difficult-to-replicate templates. If replication fork progression fails to be rescued, this may lead to DNA damage and genomic instability via nuclease processing of aberrant fork structures or incomplete sister chromatid separation during mitosis.</jats:p

Mechanisms of oncogene-induced replication stress:jigsaw falling into place

Oncogene activation disturbs cellular processes and accommodates a complex landscape of changes in the genome that contribute to genomic instability, which accelerates mutation rates and promotes tumorigenesis. Part of this cellular turmoil involves deregulation of physiologic DNA replication, widely described as replication stress. Oncogene-induced replication stress is an early driver of genomic instability and is attributed to a plethora of factors, most notably aberrant origin firing, replication–transcription collisions, reactive oxygen species, and defective nucleotide metabolism. Significance: Replication stress is a fundamental step and an early driver of tumorigenesis and has been associated with many activated oncogenes. Deciphering the mechanisms that contribute to the replication stress response may provide new avenues for targeted cancer treatment. In this review, we discuss the latest findings on the DNA replication stress response and examine the various mechanisms through which activated oncogenes induce replication stress

Diskriminierung aufgrund homosexueller Orientierungen: Exploration der Fremdwahrnehmung im Jugendalter

"Heterosexismus und dessen Folgen werden im wissenschaftlichen Diskurs bislang primär mit Blick auf die Selbstwahrnehmung nicht ausschließlich heterosexueller Menschen untersucht. In Erweiterung hierzu soll in der vorliegenden quantitativen Studie die Fremdwahrnehmung Jugendlicher (n=766) zur Diskriminierung homosexueller Altersgenossen in den für diese relevanten Umwelten (Schule, Peers, Ausbildung, Sport) exploriert werden; als zentrale kovariierende Merkmale wurden die Homonegativität der Probanden und die erlebte Homonegativität im Elternhaus erfasst. Die Ergebnisse verweisen bereichsübergreifend auf geringe bis moderate Ausprägungen von erlebtem Heterosexismus in der Fremdwahrnehmung Jugendlicher, lediglich die Peer-Group wird in höherem Maße als Setting von Heterosexismus wahrgenommen. Innerhalb der Stichprobe zeichnen sich Jugendliche mit eigener hoch ausgeprägter Homonegativität durch signifikant stärker erlebten Heterosexismus aus, die Homonegativität korrelierte zudem signifikant (positiv) mit dem im Elternhaus erlebten Ausmaß. Implikationen dieser explorativen Befunde werden abschließend mit Blick auf weiterführende Fragestellungen diskutiert." (Autorenreferat)"Heterosexism and related consequences are mainly objects of research with emphasis on the consequences for victims, i.e. not solely heterosexual individuals. The present empirical study therefore explores the perceptions of relevant others - teenagers and adolescents (n=766) - regarding discrimination of gay contemporaries in selected settings (school, peers, apprenticeship, Sport). Homonegativity of subjects as well as perceived parental homonegativity were assessed as relevant correlates. Results reveal a low to moderate level of perceived heterosexism across all settings. Specifically, referring to the peer-group higher levels of perceived heterosexism are reported. The subjects' homonegativity showed significant (positive) correlations with perceived parental homonegativity and with perceived heterosexism. Implications of explorative findings for future research are being discussed." (author's abstract

BRCA2 and RAD51 promote double-strand break formation and cell death in response to Gemcitabine

Replication inhibitors cause replication fork stalling and double-strand breaks (DSBs) that result from processing of stalled forks. During recovery from replication blocks, the homologous recombination (HR) factor RAD51 mediates fork restart and DSB repair. HR defects therefore sensitise cells to replication inhibitors, with clear implications for cancer therapy. Gemcitabine is a potent replication inhibitor used to treat cancers with mutations in HR genes such as BRCA2. Here we investigate why, paradoxically, mutations in HR genes protect cells from killing by Gemcitabine. Using DNA replication and -damage assays in mammalian cells, we show that even short Gemcitabine treatments cause persistent replication inhibition. BRCA2 and RAD51 are recruited to chromatin early after removal of the drug, actively inhibit replication fork progression and promote the formation of MUS81- and XPF-dependent DSBs that remain unrepaired. Our data suggest that HR intermediates formed at Gemcitabine-stalled forks are converted into DSBs and thus contribute to Gemcitabine-induced cell death, which could have implications for the treatment response of HR-deficient tumours

BET inhibition induces HEXIM1- and RAD51-dependent conflicts between transcription and replication

Summary: BET bromodomain proteins are required for oncogenic transcription activities, and BET inhibitors have been rapidly advanced into clinical trials. Understanding the effects of BET inhibition on processes such as DNA replication will be important for future clinical applications. Here, we show that BET inhibition, and specifically inhibition of BRD4, causes replication stress through a rapid overall increase in RNA synthesis. We provide evidence that BET inhibition acts by releasing P-TEFb from its inhibitor HEXIM1, promoting interference between transcription and replication. Unusually, these transcription-replication conflicts do not activate the ATM/ATR-dependent DNA damage response but recruit the homologous recombination factor RAD51. Both HEXIM1 and RAD51 promote BET inhibitor-induced fork slowing but also prevent a DNA damage response. Our data suggest that BET inhibitors slow replication through concerted action of transcription and recombination machineries and shed light on the importance of replication stress in the action of this class of experimental cancer drugs. : Bowry et al. show that BET inhibitors, emerging cancer therapeutics that target transcription programs, cause conflicts between transcription and replication by deregulating P-TEFb. These conflicts recruit the homologous recombination factor RAD51, which slows down replication and suppresses DNA damage. This highlights the importance of replication stress for BET inhibitor treatment. Keywords: JQ1, I-BET151, BRD4, P-TEFb, homologous recombination, replication fork, replication stress, DNA damage, cance

The German fibromyalgia consumer reports - a cross-sectional survey

Background: Consumer surveys provide information on effectiveness and side effects of medical interventions in routine clinical care. A report of fibromyalgia syndrome (FMS) consumers has not been carried out in Europe. Methods: The study was carried out from November 2010 to April 2011. Participants diagnosed with FMS rated the effectiveness and side effects of pharmacological and non-pharmacological FMS interventions on a 0 to 10 scale, with 10 being most efficacious (harmful). The questionnaire was distributed by the German League for people with Arthritis and Rheumatism and the German Fibromyalgia Association to their members and to all consecutive FMS patients of nine clinical centers of different levels of care. Results: 1661 questionnaires (95% women, mean age 54 years, mean duration since FMS diagnosis 6.8 years) were analysed. The most frequently used therapies were self-management strategies, prescription pain medication and aerobic exercise. The highest average effectiveness was attributed to whole body and local warmth therapies, thermal bathes, FMS education and resting. The highest average side effects were attributed to strong opioids, local cold therapy, gamma-amino-butyric acid analogues (pregabalin and gabapentin), tramadol and opioid transdermal systems. Conclusion: The German fibromyalgia consumer reports highlight the importance of non-pharmcological therapies in the long-term management of FMS, and challenges the strong recommendations for drug therapies given by FMS-guidelines

Increased global transcription activity as a mechanism of replication stress in cancer

Cancer is a disease associated with genomic instability that often results from oncogene activation. This in turn leads to hyperproliferation and replication stress. However, the molecular mechanisms that underlie oncogene-induced replication stress are still poorly understood. Oncogenes such as HRAS(V12) promote proliferation by upregulating general transcription factors to stimulate RNA synthesis. Here we investigate whether this increase in transcription underlies oncogene-induced replication stress. We show that in cells overexpressing HRAS(V12), elevated expression of the general transcription factor TATA-box binding protein (TBP) leads to increased RNA synthesis, which together with R-loop accumulation results in replication fork slowing and DNA damage. Furthermore, overexpression of TBP alone causes the hallmarks of oncogene-induced replication stress, including replication fork slowing, DNA damage and senescence. Consequently, we reveal that increased transcription can be a mechanism of oncogene-induced DNA damage, providing a molecular link between upregulation of the transcription machinery and genomic instability in cancer