Prostate cancer is the second leading cause of cancer-associated deaths among men in the western countries. Here, we report that human RecQL4 helicase, which is implicated in the pathogenesis of a subset of cancer-prone Rothmund-Thomson syndrome, is highly elevated in metastatic prostate cancer cell lines. Increased RecQL4 expression was also detected in human prostate tumor tissues as a function of tumor grade with the highest expression level in metastatic tumor samples, suggesting that RecQL4 may be a potential prognostic factor for advanced stage of prostate cancer. Transient and stable suppression of RecQL4 by small interfering RNA and short hairpin RNA vectors drastically reduced the growth and survival of metastatic prostate cancer cells, indicating that RecQL4 is a prosurvival factor for prostate cancer cells. RecQL4 suppression led to increased poly(ADP-ribose) polymerase (PARP) synthesis and RecQL4-suppressed prostate cancer cells underwent an extensive apoptotic death in a PARP-1-dependent manner. Most notably, RecQL4 knockdown in metastatic prostate cancer cells drastically reduced their cell invasiveness in vitro and tumorigenicity in vivo, showing that RecQL4 is essential for prostate cancer promotion. Observation of a direct interaction of retinoblastoma (Rb) and E2F1 proteins with RecQL4 promoter suggests that Rb-E2F1 pathway may regulate RecQL4 expression. Collectively, our study shows that RecQL4 is an essential factor for prostate carcinogenesis.

Solar UV radiation is a major mutagen that damages DNA through the formation of dimeric photoproducts between adjacent thymine and cytosine bases. A major effect of the GC content of the genome is thus anticipated, in particular in prokaryotes where this parameter significantly varies among species. We quantified the formation of UV-induced photolesions within both isolated and cellular DNA of bacteria of different GC content. First, we could unambiguously show the favored formation of cytosine-containing photoproducts with increasing GC content (from 28 to 72%) in isolated DNA. Thymine-thymine cyclobutane dimer was a minor lesion at high GC content. This trend was confirmed by an accurate and quantitative analysis of the photochemical data based on the exact dinucleotide frequencies of the studied genomes. The observation of the effect of the genome composition on the distribution of photoproducts was then confirmed in living cells, using two marine bacteria exhibiting different GC content. Because cytosine-containing photoproducts are highly mutagenic, it may be predicted that species with genomes exhibiting a high GC content are more susceptible to UV-induced mutagenesis.

UV radiation induced DNA damage (inferred from cyclobutane pyrimidine dimers, CPDs) in native marine virus communities was examined at 12 locations along a latitudinal transect from 41°S to 3°N in the southeastern Pacific Ocean. Surface waters were collected prior to sunrise each day and placed in UV transparent incubators kept at in situ seawater temperatures. A replicate treatment was prefiltered through a 0.2 µm filter to remove microbial host cells. Both treatments were exposed to ambient solar radiation until approximately 1 h before sunset. At the end of the day, the virus fraction was collected from each sample by filtration and concentration. DNA damage was determined in each fraction and compared to DNA damage in pre-dawn samples as well as DNA dosimeters exposed to an entire solar day's influence. CPDs in dosimeters and integrated solar irradiance were very highly correlated, as was DNA damage in the pre-sunrise virus community and latitude. A reduction in host cell abundance resulted in no consistent pattern or change in the CPD induction of virus particles, suggesting minimal host mediated repair in this natural virus community. The low daily induction of damage in virus incubations combined with the high residual damage suggests that the sunrise damage levels were the result of DNA damage accumulation over numerous days, indicating a long residence time for virus particles in surface waters in this region.KEY WORDS: Virus · DNA damage · Cyclobutane pyrimidine dimers · Southeastern Pacific Ocean · Marine microbiology Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 31: [1][2][3][4][5][6][7][8] 2003 viral infectivity in surface waters (Suttle & Chen 1992, Wommack et al. 1996, Noble & Fuhrman 1997, Garza & Suttle 1998, Wilhelm et al. 1998a, 2002. In fact, measured destruction rates of viral infectivity are so high that scientists had been left with a paradox concerning their existence: while estimates of UV-mediated destruction predicted viral clearance rates that should sterilize the water column on a daily basis, high titers of infectious viral particles continued to persist in these environments (Suttle et al. 1993). This problem was partially resolved by the realization that some UVmediated damage (as inferred from the formation of cyclobutane pyrimidine dimers, CPDs) could be repaired on a daily scale by host-cell-mediated repair mechanisms (Weinbauer et al. 1997).Early attempts to understand the persistence of viruses under significant UV pressures suggested that the temporal and spatial distribution of viral production, in consideration of water column mixing, were important (Murray & Jackson 1993). In part, the depth-dependent decay of viral infectivity (relative to the destruction of viral particles; Wommack et al. 1996) suggested an imbalance. If viral particles were destroyed at a lower rate than viral infectivity was lost from a community, and production of viral infectivity was a direct result of new viral particles, then the oce...

Histone H2A variant H2AX is a dose-dependent suppressor of oncogenic chromosome translocations. H2AX participates in DNA double-strand break repair, but its role in other DNA repair pathways is not known. In this study, role of H2AX in cellular response to alkylation DNA damage was investigated. Cellular sensitivity to two monofunctional alkylating agents (methyl methane sulfonate and N-methyl-N 0 -nitro-N-nitrosoguanidine (MNNG)) was dependent on H2AX dosage, and H2AX null cells were more sensitive than heterozygous cells. In contrast to wild-type cells, H2AX-deficient cells displayed extensive apoptotic death due to a lack of cell-cycle arrest at G 2 /M phase. Lack of G 2 /M checkpoint in H2AX null cells correlated well with increased mitotic irregularities involving anaphase bridges and gross chromosomal instability. Observation of elevated poly(ADP) ribose polymerase 1 (PARP-1) cleavage suggests that MNNG-induced apoptosis occurs by PARP-1-dependent manner in H2AX-deficient cells. Consistent with this, increased activities of PARP and poly(ADP) ribose (PAR) polymer synthesis were detected in both H2AX heterozygous and null cells. Further, we demonstrate that the increased PAR synthesis and apoptotic death induced by MNNG in H2AX-deficient cells are due to impaired activation of mitogen-activated protein kinase pathway. Collectively, our novel study demonstrates that H2AX, similar to PARP-1, confers cellular protection against alkylation-induced DNA damage. Therefore, targeting either PARP-1 or histone H2AX may provide an effective way of maximizing the chemotherapeutic value of alkylating agents for cancer treatment.

Please cite this paper as: Analysis of ionizing radiation‐induced DNA damage and repair in three‐dimensional human skin model system. Experimental Dermatology 2010; 19: e16–e22. Abstract:  Knowledge of cellular responses in tissue microenvironment is crucial for the accurate prediction of human health risks following chronic or acute exposure to ionizing radiation (IR). With this objective, we investigated the radio responses for the first time in three‐dimensional (3D) artificial human skin tissue microenvironment after γ‐rays radiation. IR‐induced DNA damage/repair response was assessed by immunological analysis of well‐known DNA double strand break (DSB) repair proteins, i.e. 53BP1 and phosphorylated ataxia telangiectasia mutatedser1981 (ATMser1981). Efficient 53BP1 and phosphorylated ATM foci formation was observed in human EpiDerm tissue constructs after low and high doses of γ‐rays. Interestingly, EpiDerm tissue constructs displayed less 53BP1 and ATM foci number at all radiation doses (0.1, 1, 2.5 and 5 Gy) than that observed for 2D human fibroblasts. DSB repair efficiency judged by the disappearance of 53BP1 foci declined with increasing doses of γ‐rays and tissue constructs irradiated with 2.5 and 5 Gy of γ‐rays displayed 53BP1 foci persisting up to 72 h of analysis. Pretreatment of EpiDerm tissue constructs with LY294002, [an inhibitor of phosphatidylinositol‐3 kinase and PI‐3 kinase like kinases (PIKK)] completely abolished IR‐induced 53BP1 foci formation and increased the apoptotic death. This observation indicates the importance of PIKK signalling pathway for efficient radiation responses in intact tissue constructs. In summary, we have successfully demonstrated the feasibility of monitoring the DNA damage response in human skin tissue microenvironment. In this system, 53BP1 can be used as a useful marker for monitoring the DSB repair efficiency.