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To date, 15 autosomal and 1 X-linked genes are designated as causative genes for FA, but the molecular structure of the FA pathway remains largely unclear. Lack of defined genetic model systems and a scarcity of recognizable protein domains in most FA proteins are among the major obstacles impeding the advance of FA biology. The main objective of this proposal is to establish the genetic framework of the FA pathway and to elucidate molecular functions of key FA proteins. We begin to approach these problems by systematically constructing somatic cellular knockout models. Our preliminary investigations insinuate a hypothesis that different FA proteins form distinct functional modules to accomplish the DNA damage-induced FA pathway activation, which enables the recruitment of DNA damage-processing enzymes.
We plan to test this hypothesis with three specific aims: 1 Define the epistatic relationships among classic FA gene products, which will mitigate a visible void in genetic connections among Fanconi anemia genes. Elucidation of the FA pathway should have a significant impact in advancing the understanding of fundamental cellular mechanisms protecting genome integrity.
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More importantly, FA pathway components are potential target for therapeutic intervention. This type of lesions is exemplified by DNA crosslinks most frequently generated by bifunctional alkylating chemotherapeutic modalities, such cisplatin and melphalan, and by DNA-protein crosslinks produced with high frequency from ionizing radiation exposure. For example, clinical response of many ovarian cancers to cisplatin treatment is dictated by their FA pathway status.
In summary, this project is aimed at delineating the molecular pathological mechanism of Fanconi anemia with the immediate benefit of uncovering novel therapeutic targets to the improve cancer treatment outcomes. This proposal investigates the molecular mechanism of Fanconi anemia, a complex cancer- prone hereditary disease with hematological defects underlined by deficiencies in repairing DNA damages.
Although sixteen different genes have been identified to cause Fanconi anemia, many of these genes have no clearly defined functions as to how they provide protection to cells exposed to DNA damaging reagents, which are broadly used chemotherapy drugs such as cisplatin and melphalan. The main objective of this project is to elucidate molecular functions of Fanconi anemia genes and explore their potential as novel targets to improve the efficacy of cancer treatment.
The percentage of untreated control was determined by dividing the number of colonies scored at each H 2 O 2 concentration by untreated controls. The data shown represent one of four independent experiments with similar results. The percentage base-line calculation was determined by dividing the number of colonies scored in hyperoxic conditions by the number of colonies counted from room air cultures. The cells were washed and plated in progenitor assays as described above.
The data represent one of three independent experiments.
Molecular basis of Fanconi anemia.
All of the error bars represent S. The percentage of untreated control was determined by dividing the number of MEFs scored at each H 2 O 2 concentration by untreated controls. The data shown represent the means of four experiments. B , H 2 O 2 -induced apoptosis. The mean of three independent experiments is shown. C , antioxidants and MEF viability assays. Viability was assessed by trypan blue exclusion.
D , SeMet pretreatment and apoptosis. One recognized function is to maintain normal alkylating agent sensitivity, which is associated with restoration of nuclear FA protein complex formation corrected by FANCC-EA mutant. The autoradiograph shown is representative of three separate transductions. Transduced MEFs were treated with increasing H 2 O 2 concentrations, and cell viability was determined by trypan blue exclusion. MEFs were then washed and lysed in nonionic lysis buffer.
The data shown are representative of five independent experiments. The data shown are representative of four independent transfection experiments with similar results. C , dominant negative ASK1 studies. At least cells were scored per condition per experiment. The data shown represent the means of three experiments.
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The first demonstration of oxygen hypersensitivity in FA cells was made over 20 years ago 33 ; however, since that initial report little progress has been made to understand the molecular mechanisms involved. In fact, contradictory data have led to significant debate 60 , Numerous reports in immortalized cell lines suggest that the loss of FA protein function may result in a pro-oxidant cellular environment 31 - 33 , 60 , 62 - In a reduced conformation GSTP1 inhibits stress-activated apoptotic signaling 50 , 72 , 73 , suggesting that the loss of FANCC may result in altered redox-dependent stress signaling.
In addition, CPR transfers electrons to cytochromes and molecular oxygen 74 - 77 ; hence increased CPR activity in FANCC deficient cells may subsequently result in a pro-oxidant cellular environment by generating increased reactive oxygen species.
Pang et al. Ichijo et al. Subsequent studies revealed that thioredoxin, in a reduced conformation, inhibits ASK1-dependent apoptosis by binding to ASK1 46 , which is the first demonstration that an apoptotic cascade is directly controlled by the cellular redox environment. Since this original description, it is now recognized that the redox regulation of ASK1 is complex, involving the direct interaction of ASK1 with multiple redox-dependent binding partners including thioredoxin, glutathione S -transferases, and glutaredoxin 45 - The precise physiologic role that individual negative regulators have in inhibiting ASK1 activity remains unclear.
However, there is evidence that these redox-dependent proteins may act as sensors for specific cellular redox stresses 46 , 49 , Previous studies showed that FANCC expression maintains GSTP1 in a reduced conformation during growth factor withdrawal and subsequently protects from apoptotic cell death Importantly, reduced glutathione S -transferases are critical for inhibition of ASK1 activation and consequently oxidant-induced apoptosis 45 , 50 , Interestingly, Gilot et al.
Future preclinical studies to test the potential of such an approach will be important. We gratefully acknowledge Dr. We also thank Drs. Smith Indiana University for many valuable discussions and thoughtful critique of the manuscript.
Fanconi Anemia - NORD (National Organization for Rare Disorders)
We thank Marsha Hippensteel and Arliene Britt for administrative support. The costs of publication of this article were defrayed in part by the payment of page charges. Section solely to indicate this fact. You'll be in good company. Journal of Lipid Research. Walnut St.
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