Do Fanconi anemia genes control cell response to cross-linking agents by modulating cytochrome P-450 reductase activity?

Mechanistic and biological considerations of oxidatively damaged DNA for helicase-dependent pathways of nucleic acid metabolism

Cells are under constant assault from reactive oxygen species that occur endogenously or arise from environmental agents. An important consequence of such stress is the generation of oxidatively damaged DNA, which is represented by a wide range of non-helix distorting and helix-distorting bulkier lesions that potentially affect a number of pathways including replication and transcription; consequently DNA damage tolerance and repair pathways are elicited to help cells cope with the lesions. The cellular consequences and metabolism of oxidatively damaged DNA can be quite complex with a number of DNA metabolic proteins and pathways involved. Many of the responses to oxidative stress involve a specialized class of enzymes known as helicases, the topic of this review. Helicases are molecular motors that convert the energy of nucleoside triphosphate hydrolysis to unwinding of structured polynucleic acids. Helicases by their very nature play fundamentally important roles in DNA metabolism and are implicated in processes that suppress chromosomal instability, genetic disease, cancer, and aging. We will discuss the roles of helicases in response to nuclear and mitochondrial oxidative stress and how this important class of enzymes help cells cope with oxidatively generated DNA damage through their functions in the replication stress response, DNA repair, and transcriptional regulation.

Fanconi Anemia: A DNA repair disorder characterized by accelerated decline of the hematopoietic stem cell compartment and other features of aging

Fanconi Anemia (FA) is a rare autosomal genetic disorder characterized by progressive bone marrow failure (BMF), endocrine dysfunction, cancer, and other clinical features commonly associated with normal aging. The anemia stems directly from an accelerated decline of the hematopoietic stem cell compartment. Although FA is a complex heterogeneous disease linked to mutations in 19 currently identified genes, there has been much progress in understanding the molecular pathology involved. FA is broadly considered a DNA repair disorder and the FA gene products, together with other DNA repair factors, have been implicated in interstrand cross-link (ICL) repair. However, in addition to the defective DNA damage response, altered epigenetic regulation, and telomere defects, FA is also marked by elevated levels of inflammatory mediators in circulation, a hallmark of faster decline in not only other hereditary aging disorders but also normal aging. In this review, we offer a perspective of FA as a monogenic accelerated aging disorder, citing the latest evidence for its multi-factorial deficiencies underlying its unique clinical and cellular features.

The p38 pathway partially mediates caspase-3 activation induced by reactive oxygen species in Fanconi anemia C cells

Because Fanconi anemia (FA) cells display hypersensitivity to oxidative stress and reactive oxygen species (ROS) that act as second messengers in cellular signaling, we investigated c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) activation in two FA-C lymphocyte cell lines (HSC536/N and PD149L) and one FA-A cell line (HSC99) exposed to interferon (IFN)-gamma or H2O2. IFN-gamma induced accumulation of ROS and activation of JNK and p38 in HSC536/N and PD149L but not in HSC99 cells. Higher concentrations of H2O2 were needed to induce moderate intracellular levels of ROS and phosphorylation of MAPKs in FA-A than in FA-C cells. Pre-incubation with dehydroascorbic acid resulted in reduced intracellular ROS levels and inhibition of MAPK activation induced by the above treatments. To define the functional role of JNK and p38 in IFN-gamma signaling, the effects of pharmacological inhibition of the MAPKs on induction of IFN-gamma and anti-Fas antibody responses were determined. Treatment of HSC536/N cells with p38-specific inhibitors partially inhibited caspase-3 activation while pre-incubation with specific inhibitors of JNK had no effect. Altogether, these results suggest that FA-C cells are hypersensitive to IFN-gamma and are more sensitive to oxidative stress than FA-A cells and that IFN-gamma and anti-Fas antibody mediate signals for apoptosis in FA-C cells via p38 but not JNK pathways.

Cisplatin triggers apoptotic or nonapoptotic cell death in Fanconi anemia lymphoblasts in a concentration-dependent manner

Cells derived from Fanconi anemia (FA) patients are hypersensitive for cross-linking agents, such as cisplatin, that are potent inducers of programmed cell death (PCD). Here, we studied cisplatin hypersensitivity in FA in relation to the mechanism of PCD in lymphoblastoid cells representing FA groups A and C. In FA cells, a low concentration of cisplatin caused chromatin condensation, phosphatidylserine (PS) externalization, and the expression of an 18-kDa variant of Bax, all indicators of apoptotic cell death, and the latter suggesting the involvement of a mitochondrial route. However, procaspases-3, -8, and -9, and PARP were not cleaved, although small increases in caspase activity could be detected. At a high concentration of cisplatin, both FA and corrected cells showed a robust cleavage of procaspases and PARP. DNA fragmentation was clearly visible under high cisplatin conditions and to some extent at a low concentration in FA-A cells, but not in the FA-C cell line regardless of the presence of functional FANCC, suggesting an unknown deficiency in these cells. We conclude that hypersensitivity in FA cells is associated with a mixture of necrotic and apoptotic features that is best described as apoptotic-like cell death, and that a defective FA pathway does not interfere with the proper activation of caspase-mediated cell death.

Differential diagnosis of Fanconi anemia by nitrogen mustard and diepoxybutane

Fanconi anemia (FA) is an autosomal recessive inherited disorder which is associated with a variety of congenital anomalies. These include morphometric abnormalities involving mainly the head and face, skeletal malformations particularly of the radial ray, growth retardation, abnormal skin pigmentation, deafness, and renal, ocular, genital, and cardiac defects. The cardinal clinical feature is a severe progressive pancytopenia. The overall aim of our study was to compare two different alkylating agents that would permit rapid and unequivocal detection of FA. A total of 271 patients underwent nitrogen mustard (NTM) and diepoxybutane (DEB) tests in our laboratory; baseline chromosomal breakage was studied for all of them. After the results of the chromosomal breakage studies, 72 patients were diagnosed as affected and 136 patients as unaffected by FA. We also studied 63 family members of FA patients. According to our study, NTM seems more specific to identify chromosomal breakages in FA parents than DEB.

Fanconi anemia group A and C double-mutant mice: functional evidence for a multi-protein Fanconi anemia complex

OBJECTIVE

Fanconi anemia (FA) is a genetically heterogeneous disorder associated with defects in at least eight genes. The biochemical function(s) of the FA proteins are unknown, but together they define the FA pathway, which is involved in cellular responses to DNA damage and in other cellular processes. It is currently unknown whether all FA proteins are involved in controlling a single function or whether some of the FA proteins have additional roles. The aim of this study was 1) to determine whether the FA group A and group C genes have identical or partially distinct functions, and 2) to have a better model for human FA.

MATERIALS AND METHODS

We generated mice with a targeted mutation in fanca and crossed them with fancc disrupted animals. Several phenotypes including sensitivity to DNA cross linkers and ionizing radiation, hematopoietic colony growth, and germ cell loss were analyzed in fanca-/-, fancc-/-, fanca/fancc double -/-, and controls.

RESULTS

Fibroblast cells and hematopoietic precursors from fanca/fancc double-mutant mice were not more sensitive to MMC than those of either single mutant. fanca/fancc double mutants had no evidence for an additive phenotype at the cellular or organismal level.

CONCLUSIONS

These results support a model where both FANCA and FANCC are part of a multi-protein nuclear FA complex with identical function in cellular responses to DNA damage and germ cell survival.

Mitochondrial alterations in fanconi anemia fibroblasts following ultraviolet A or psoralen photoactivation

The genetic disease Fanconi anemia (FA), generally considered to be a DNA repair defect, has also been related to a deficiency in cellular defense against reactive oxygen species (ROS). Results show that mitochondrial matrix densification occurs rapidly and transiently in FA fibroblasts following 8-methoxypsoralen (8-MOP) photoreaction or ultraviolet A (320 to 380 nm) (UVA) irradiation. This effect is oxygen dependent because it is more important under 20 than under 5% oxygen tension. In contrast, in normal fibroblasts very little, if any, densification of mitochondrial matrix is induced by treatments even at the highest oxygen tension. The changes in matrix density in FA cells are accompanied by some modifications in transmembrane potential, linked to a Fenton-like reaction, and in mitochondrial cardiolipin content, differing from the responses of normal cells. These data are indicative of some sort of membrane damage induced by 8-MOP photoreaction and UVA irradiation, to which FA cells appear to be particularly sensitive.