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DNA damage checkpoints in the cell cycle may be important barriers against cancer progression in human cells. Fanconi anemia (FA) is an inherited DNA instability disorder that is associated with bone marrow failure and a strong predisposition to cancer. Although FA cells experience constitutive chromosomal breaks, cell cycle arrest at the [G.sub.2] DNA damage checkpoint, and an excess of cell death, some patients do become clinically stable, and the mechanisms underlying this, other than spontaneous reversion of the disease-causing mutation, are not well understood. Here we have defined a clonal phenotype, termed attenuation, in which FA patients acquire an abrogation of the [G.sub.2] checkpoint arrest. Attenuated cells expressed lower levels of CHK1 (also known as CHEK1) and p53. The attenuation could be recapitulated by modulating the ATR/CHK1 pathway, and CHK1 inhibition protected FA cells from cell death. FA patients who expressed the attenuated phenotype had mild bone marrow deficiency and reached adulthood, but several of them eventually developed myelodysplasia or leukemia. Better understanding of attenuation might help predict a patient's clinical course and guide choice of treatment. Our results also highlight the importance of evaluating the cellular DNA damage checkpoint and repair pathways in cancer therapies in general., Introduction Checkpoint pathways are complex biological pathways that regulate responses to DNA damage and other cellular events (1-3). The typical DNA damage checkpoint response triggers cell cycle arrest, allowing time [...]

DNA damage checkpoints in the cell cycle may be important barriers against cancer progression in human cells. Fanconi anemia (FA) is an inherited DNA instability disorder that is associated with bone marrow failure and a strong predisposition to cancer. Although FA cells experience constitutive chromosomal breaks, cell cycle arrest at the G2 DNA damage checkpoint, and an excess of cell death, some patients do become clinically stable, and the mechanisms underlying this, other than spontaneous reversion of the disease-causing mutation, are not well understood. Here we have defined a clonal phenotype, termed attenuation, in which FA patients acquire an abrogation of the G2 checkpoint arrest. Attenuated cells expressed lower levels of CHK1 (also known as CHEK1) and p53. The attenuation could be recapitulated by modulating the ATR/CHK1 pathway, and CHK1 inhibition protected FA cells from cell death. FA patients who expressed the attenuated phenotype had mild bone marrow deficiency and reached adulthood, but several of them eventually developed myelodysplasia or leukemia. Better understanding of attenuation might help predict a patient's clinical course and guide choice of treatment. Our results also highlight the importance of evaluating the cellular DNA damage checkpoint and repair pathways in cancer therapies in general. [ABSTRACT FROM AUTHOR]

Fanconi anemia (FA) is a genetic cancer-predisposition syndrome characterized by bone marrow failure and cellular and chromosomal hypersensitivity to DNA cross-linking agents. Seven FA genes have been isolated and their products associate to form a pathway that interacts functionally or physically with several DNA-damage response proteins involved in cell cycle checkpoints and/or DNA repair. These proteins include BLM, ATM, BRCA1, XPF and the MRE11/RAD50/NBS1 complex. In spite of several recent striking progresses in the biochemistry and the molecular biology of the disorder, the precise function(s) of the FA proteins remain(s) poorly determined. However, several recent data indicate that the FA pathway could be involved in the coordination of both cell cycle checkpoints and DNA repair. [Copyright &y& Elsevier]

Background Viral vector delivery of neurotrophic-expressing transgenes in the retina may retard or prevent the onset of blindness associated with photoreceptor degeneration. A key safety issue is to achieve regulated expression of these genes in the retina. The purpose of our study was to evaluate whether a single recombinant AAV-2 (rAAV) encoding for a tetracycline (Tet)-regulated destabilized reporter gene could provide quantitative profiles of gene regulation targeted to the rat neuroretina. Methods A rAAV vector carrying a destabilized green fluorescent protein ( dgfp) under a tet-regulatable promoter and the tetracycline-repressed transactivator (tTA) was generated (rAAVtetoff. dgfp) and administered intravitreally in nine Wistar rats. Retinas were monitored for 6 months using noninvasive fluorescence imaging and the animals were subjected to two cycles of doxycycline (Dox), a tetracycline analog. Eyes were ultimately examined by histology. Results Intravitreal injection of rAAVtetoff. dgfp resulted in effective transduction of ganglion cells. Following full expression of the transgene in the absence of Dox, 95% of the GFP signal was shut down 48 h post Dox administration and the signal was undetectable 7 days later. Initial levels of GFP expression were restored 21 days after Dox administration ceased. This pattern of expression was repeated twice over a period of 6 months. Conclusions This report demonstrates that rAAVtetoff. dgfp intravitreally injected rats displayed tight and sustained long-term regulation of the reporter gene in ganglion cells. These findings may have important implications regarding rAAV-mediated gene therapy using neuroprotective approaches for retinitis pigmentosa and glaucoma. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]