The basal and the mutagen-induced levels of ADP-ribosyl transferase activity are not modified in Fanconi's anemia cells

The cellular control enzyme polyADP ribosyl transferase is eliminated in cultured Fanconi anemia fibroblasts at confluency

Fanconi anemia (FA) is a hereditary disease of unknown pathogenic mechanisms, although mutations in seven different genes can be causative. Six of these genes have been cloned and sequenced. Only slight homology to the DNA of any other known gene has been found with the exception of FANCG which is identical to XRCC9. The function of these genes, including XRCC9, is presently unknown. Since pADP ribosyl transferase (pADPRT) plays a role in apoptosis, and apoptosis is affected in FA cells, we studied the correlation between pADPRT and FA cells. We reinvestigated the previously reported lack of pADPRT activity in fibroblasts from patients with Fanconi anemia. Here we describe the role of the lower redox potential of FA cells and demonstrate that this is an efficient strategy in the prevention of cell death due to the lack of energy under oxidative stress. This strategy is advantageous for the cells under the nonreplicative condition of confluency in which the risk of mutation is low and the prevention of apoptosis permits cell survival. pADPRT is not diminished to the same extent in all complementation groups of FA. It is prominent in FANCA, FANCG and FANCF cells, indicating that these genes control pADPRT diminution. Our experiments suggest that the pADPRT level is linked with the oxidoreduction reactions seen in FA.

Is Fanconi anemia caused by a defect in the processing of DNA damage?

Fanconi anemia (FA) is an autosomal genetic disease characterized by a complex array of developmental disorders, a high predisposition to bone marrow failure and to acute myelogenous leukemia. The chromosomal instability and the hypersensitivity to DNA cross-linking agents led to its classification with the DNA repair disorders. This review aimed at establishing whether it is still appropriate to consider 1/approximately FA within a DNA repair framework taking into account the recently discovered genetic heterogeneity characteristics of the defect (eight complementation groups). We discuss the possibility that the FA proteins interact to form a complex which may control different functions, including the processing of specific DNA lesions. Such a complex may act as a sensor to initiate protective systems as well as transcription of specific genes specifying, among others proteins, growth factors. Such steps may be organized as a linear cascade or more likely under the form of a web network.

Cellular responses to hematoporphyrin-induced photooxidative damage in Fanconi anemia, xeroderma pigmentosum and normal human fibroblasts

Several observations reported in the literature suggest that singlet oxygen (1O2) might play a role in the clastogenic process in Fanconi anemia (FA) cells, and that the antioxidant status of xeroderma pigmentosum (XP) may also be altered. In order to test the ability of FA and XP cells, relative to normal cells, to cope with 1O2 damage, the effects of photosensitization by hematoporphyrin (HP) have been determined (i) on host cell reactivation (HCR) of damaged infecting herpes simplex virus (HSV) or transfecting SV40 DNA, and (ii) on DNA template capability and clonogenicity of treated cells. Results showed no significant difference among the three types of cells, either for the survival of HP-photosensitized HSV, or for the yields of SV40 virus following transfection of cultures with damaged viral DNA. The treatment of cells with HP plus 365-nm light leads to a dose-dependent, homothetic reduction of 18S and 28S ribosomal RNA (rRNA) synthesis, presumably through a mechanism other than the formation of transcription termination sites. After a 24-h post-exposure incubation, the rate of rRNA synthesis was restored to higher than normal levels in all cell lines. Finally, two FA cell lines showed a higher survival to HP photosensitization than two normal cell lines. Another FA cell line and XP-A and XP-C cells were in the range of sensitivity of the two normal strains for this treatment. These results indicate that FA cells possess an antioxidant defense system at least as efficient as that of normal cells for processing 1O2-induced damage.