Expression of mitochondrial genes and DNA-repair-related nuclear genes is altered in xeroderma pigmentosum fibroblasts

Oxidative stress and mitochondrial dysfunction across broad-ranging pathologies: toward mitochondria-targeted clinical strategies

Beyond the disorders recognized as mitochondrial diseases, abnormalities in function and/or ultrastructure of mitochondria have been reported in several unrelated pathologies. These encompass ageing, malformations, and a number of genetic or acquired diseases, as diabetes and cardiologic, haematologic, organ-specific (e.g., eye or liver), neurologic and psychiatric, autoimmune, and dermatologic disorders. The mechanistic grounds for mitochondrial dysfunction (MDF) along with the occurrence of oxidative stress (OS) have been investigated within the pathogenesis of individual disorders or in groups of interrelated disorders. We attempt to review broad-ranging pathologies that involve mitochondrial-specific deficiencies or rely on cytosol-derived prooxidant states or on autoimmune-induced mitochondrial damage. The established knowledge in these subjects warrants studies aimed at elucidating several open questions that are highlighted in the present review. The relevance of OS and MDF in different pathologies may establish the grounds for chemoprevention trials aimed at compensating OS/MDF by means of antioxidants and mitochondrial nutrients.

Enhanced expression of the LDH-A gene after gravity-changing stress in human RSa cells

A major issue in radiation and space biology is whether gene expression levels are altered in cells exposed to gravity-changing stress. In the present study, genes up- or down-regulated in radiation-sensitive human RSa cells cultured under gravity-changing conditions, were identified using a PCR-based mRNA differential display method. Exposure of cells to gravity-changing stress was performed by free-fall with a drop-shaft facility or by an airplane-conducted parabolic flight. Among the candidates for gravity-changing stress-responsive genes obtained by the differential display analysis, the lactate dehydrogenase A gene (LDH-A) was confirmed by Northern blotting analysis to exhibit increased expression levels. The gravity-changing stress consisted of a combination of microgravity and hypergravity. However, exposure of the cells to hypergravity produced by centrifuge only slightly affected the LDH-A mRNA expression. Thus, LDH-A was found to be a candidate for the genes which play a role in the cellular response to gravity-changing stress, and mainly to microgravity.

Human DNA repair genes

DNA repair systems are essential for the maintenance of genome integrity. Consequently, the disregulation of repair genes can be expected to be associated with significant, detrimental health effects, which can include an increased prevalence of birth defects, an enhancement of cancer risk, and an accelerated rate of aging. Although original insights into DNA repair and the genes responsible were largely derived from studies in bacteria and yeast, well over 125 genes directly involved in DNA repair have now been identified in humans, and their cDNA sequence established. These genes function in a diverse set of pathways that involve the recognition and removal of DNA lesions, tolerance to DNA damage, and protection from errors of incorporation made during DNA replication or DNA repair. Additional genes indirectly affect DNA repair, by regulating the cell cycle, ostensibly to provide an opportunity for repair or to direct the cell to apoptosis. For about 70 of the DNA repair genes listed in Table I, both the genomic DNA sequence and the cDNA sequence and chromosomal location have been elucidated. In 45 cases single-nucleotide polymorphisms have been identified and, in some cases, genetic variants have been associated with specific disorders. With the accelerating rate of gene discovery, the number of identified DNA repair genes and sequence variants is quickly rising. This report tabulates the current status of what is known about these genes. The report is limited to genes whose function is directly related to DNA repair.

Modulation of DNA polymerases alpha, delta and epsilon by lactate dehydrogenase and 3-phosphoglycerate kinase

Literature documents that glycolytic enzymes (among them lactate dehydrogenase and 3-phosphoglycerate kinase) can reside in nuclei of mammalian cells and exert functions in DNA replication, transcription and DNA repair, in addition to their role as catalysts in the cytoplasm. Transfer of glycolytic enzymes to cell nuclei requires modification, for example phosphorylation. We studied the effects of phosphorylated lactate dehydrogenase and 3-phosphoglycerate kinase on (i) UV-induced DNA repair, using permeabilized human fibroblasts, and (ii) in vitro DNA synthesis catalyzed by purified DNA polymerases alpha, delta, and epsilon from proliferating rat liver. (i) Phosphorylated lactate dehydrogenase stimulated UV-induced DNA repair synthesis in normal fibroblasts in a dose-dependent manner; the unphosphorylated enzyme slightly inhibited. In repair-deficient xeroderma pigmentosum fibroblasts reparative synthesis was not enhanced whether lactate dehydrogenase was phosphorylated or not, indicating that reparative DNA synthesis must be possible in order to be stimulated. (ii) Activity of purified DNA polymerases alpha, delta, and epsilon was differentially stimulated or inhibited, according to the phosphorylation status of lactate dehydrogenase. DNA polymerases were also modulated by 3-phosphoglycerate kinase, depending on the primer-templates used which were gapped DNA (mimicking a repair mode of DNA synthesis) or single-stranded M13 DNA (representing the replicative mode of DNA synthesis). Since glycolytic enzymes in cell nuclei retain binding ability for their cofactors, cytoplasmic substrates and inhibitors, a regulatory linkage might exist between the energy state of a cell and its replicative and reparative functions.

Retroviral-mediated correction of DNA repair defect in xeroderma pigmentosum cells is associated with recovery of catalase activity

Xeroderma pigmentosum (XP) is a rare inherited disease associated with photosensitivity, a very high susceptibility to develop neoplasm on sun-exposed skin and neurological abnormalities for some patients. We previously reported that diploid cell lines established from XP skin biopsies present an abnormal low level of catalase activity, which is involved in the defense against oxygen free radicals. This biochemical dysfunction, probably involved in the skin cancer formation, has been difficult to be directly related to the nucleotide excision repair (NER) defect in XP. In this paper we report that the retroviral-mediated transduction of XP diploid cells by the XPC and XPD/ERCC2 cDNAs fully and stably corrects the NER defect in terms of survival and unscheduled DNA synthesis (UDS) after ultraviolet (UV) irradiation. The catalase activity in transduced cells was recovered up to normal levels only in cells transduced with repair genes correcting the repair defect. These results imply that: (i) the reduced catalase activity in XP, which might result from cellular depletion of its NADPH cofactor, is directly related to impaired DNA repair, and (ii) this depletion might be one of the multiple cellular consequences of XP inborn defect.

Expression of oxidative phosphorylation genes in renal tumors and tumoral cell lines

To investigate the regulation of genes encoding the proteins involved in energy metabolism in cancer cells, we studied the expression of several mitochondrial and nuclear genes involved in ATP production. Northern blot analysis was performed on renal tumors of different types: a clear cell carcinoma, an oncocytoma, and urothelial tumors at two different stages. The steady-state transcript patterns were compared with those observed in cell lines derived from renal tumors and in transformed cell lines. Striking differences were revealed among the three types of tumors, their respective controls, and the cultured renal cells. The levels of all mitochondrial transcripts were lower in tumor biopsies and tumoral cell lines than in the normal cell types. Moreover, a higher transcript level of nuclear genes involved in oxidative phosphorylation was observed in the oncocytomas and in the more malignant urothelial tumor. Different transcript patterns were observed in each of the tumoral and transformed cell lines, explaining the difference in metabolism between the different tumors and the tumoral or transformed cell lines. In particular, a high transcript level for the adenine nucleotide translocator isoform 2(ANT2) gene, which is usually not expressed in differentiated cells, was observed in oncocytoma and malignant urothelial renal tumor. This phenomenon was also observed in renal carcinoma cell lines and transformed cells. These data provide the first argument for the involvement of the ANT2 protein in glycolytic ATP uptake in cancer cell mitochondria and suggest a possible ANT2 antisense strategy for cancer therapy.

Human cytomegalovirus uracil DNA glycosylase is required for the normal temporal regulation of both DNA synthesis and viral replication

Human cytomegalovirus (CMV) encodes a gene, UL114, whose product is homologous to the uracil DNA glycosylase and is highly conserved in all herpesviruses. This DNA repair enzyme excises uracil residues in DNA that result from the misincorporation of dUTP or spontaneous deamination of cytosine. We constructed a recombinant virus, RC2620, that contains a large deletion in the UL114 open reading frame and carries a 1.2-kb insert containing the Escherichia coli gpt gene. RC2620 retains the capacity to replicate in primary human fibroblasts and reaches titers that are similar to those produced by the parent virus but exhibits a significantly longer replication cycle. Although the rate of expression of alpha and beta gene products appears to be unaffected by the mutation, DNA synthesis fails to proceed normally. Once initiated, DNA synthesis in mutant virus-infected cells proceeds at the same rate as with wild-type virus, but initiation is delayed by 48 h. The mutant virus also exhibits two predicted phenotypes: (i) hypersensitivity to the nucleoside analog 5-bromodeoxyuridine and (ii) retention of more uracil residues in genomic DNA than the parental virus. Together, these data suggest UL114 is required for the proper excision of uracil residues from viral DNA but in addition plays some role in establishing the correct temporal progression of DNA synthesis and viral replication. Although such involvement has not been previously observed in herpesviruses, a requirement for uracil DNA glycosylase in DNA replication has been observed in poxviruses.