Xeroderma pigmentosum: clues to understanding cancer initiation

AbstractXeroderma pigmentosum (XP) type C is a rare autosomal recessive disorder that occurs because of inactivation of the xeroderma pigmentosum group C (XPC) protein, which is an important DNA damage recognition protein involved in DNA nucleotide excision repair (NER). This defect, which prevents removal of a wide array of direct and indirect DNA lesions, is associated with a decrease in catalase activity. As a novel photoprotective approach, lentivirus-mediated catalase overexpression in XPC human keratinocytes results in a marked decrease in sunburn cell formation, caspase-3 activation, and p53 accumulation following UVB irradiation. While not correcting the gene defect, indirect gene therapy using antioxidant enzymes may be helpful in limiting photosensitivity in XP type C, as well as in other monogenic/polygenic photosensitive disorders characterized by reactive oxygen species (ROS) accumulation. Hypoxia-inducible factor-1 (HIF-1), a major transcription factor sensitive to oxygen levels, responds to various stress factors. As a common stressor of skin, UVB induces a biphasic HIF-1a variation through ROS generation in keratinocytes. HIF-1a has an important regulator effect on the expression of XPC protein and other NER genes, indicating indirect regulation of NER by ROS. The intrinsic genomic instability arising in XP type C provides a good opportunity to investigate the complex molecular mechanisms underlying the Warburg effect (the shift of mito-chondrial metabolism towards glycolysis). Overall, the monogenic disorder XP type C is a powerful tool for studying photoprotection and cancer

Approche préclinique de transfert de gène des enzymes antioxydantes en vue de photoprotection cutanée

Le rayonnement solaire atteignant la surface de la terre est le facteur de risque le plus important dand le développement du cancer de peau. Afin d'améliorer des stratégies de prévention et de thérapie des cancers de la peau, les rapports entre les voies de signalisation cellulaires qui modulent les réponses à l'irradiation UV ont besoin d'être mieux clarifiés. Compte tenu du rôle des espèces réactives de l'oxygène (ROS) dans la régulation de la réponse cellulaire au stress, soit en oxydant les macromolécules biologiques, soit en jouant le rôle de second messager, nos travaux ont été centrés sur l'étude des ROS dans la réponse cellulaire aux UV. Nos résultats montrent que l'irradiation UVB aboutit à une production de ROS en deux étapes : une vague apparaît immédiatement après irradiation puis une autre 3 heures après. Tandis que le premier pic est produit par l'induction d'une NADPH oxydase cytoplasmique, le deuxième est dépendant de l'activité mitochondriale. Les ROS UVB- induits déclenchent les deux voies (intrinsèque et extrinsèque) de la signalisation de l'apoptose. Nos résultats démontrent que la surexpression de la catalase dans les kératinocytes et dans les épidermes reconstruits réduit l'apoptose UVB- induite. Cette moindre apoptose est associée à une diminution de l'activation des caspases et de l'accumulation de p53. Nous avons également constaté que l'irradiation UVB induit une variation biphasique du facteur de transcription HIF- 1a (Hipoxia-inducible factor-1) dépendante de la génération et de l'origine des ROS. Nos expériences révèlent un rôle majeur de HIF-1a dans la modulation de l'apopotose UVB-induite et aussi l'existence d'une interaction entre p53 et HIF-1a dans les keratinocytes. L'impact de HIF-1a sur l'expression de nombreux gènes suggère que cetteprotéine puisse être un régulateur majeur des gènes UV-induits et de la photocarcinogenèse.The solar UV radiation reaching the earth's surface is the most important factor for the development of skin cancer. To improve the strategies of prevention and therapy of skin cancers, relationships between the cellular signaling pathways that modulate responses to UV irradiation in skin cells need a more in-depth understanding. Considering the effect of ROS in the regulation of cellular responses to stresses either through the oxidation of macromolecules or as a second messager, we investigated the role of reactive oxygen species (ROS) in keratinocyte responses to UV irradiation. Our results indicate that UVB induce an increase in ROS levels at two distinct stages ; immediately following irradiation and around 3 hours after irradiation. While the primary peak results from the activity of a cytoplasmic NADPH oxidase, the second originates from mitochondrial activity. UVB-induced ROS mediate apopotosis by triggering both intrinsic and extrinsic pathways. Reduction of apoptosis by catalase overexpression in keratinocyte as well as reconstructed epidermis is accompanied by a reduction of caspase-3 activation and a decrease in p53 accumulation. We also found that UVB induces a biphasic variation of the transcription factor HIF-1a (Hipoxia-inducible factor-1) through ROS generation. Our experiments reveal a key role of HIF-1a in mediating UVB- induced apoptosis and the existence of cross-talk between the tumor suppressor p53 and HIF-1a in keratinocytes. The broad impact of HIF-1a on gene expression suggests that it could be a key regulator of UV-responsive genes and photocarcinogenesis.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Diagnosis of Xeroderma Pigmentosum Groups A and C by Detection of Two Prevalent Mutations in West Algerian Population: A Rapid Genotyping Tool for the Frequent XPC Mutation c.1643_1644delTG

Xeroderma pigmentosum (XP) is a rare autosomal recessive disorder. Considering that XP patients have a defect of the nucleotide excision repair (NER) pathway which enables them to repair DNA damage caused by UV light, they have an increased risk of developing skin and eyes cancers. In the present study, we investigated the involvement of the prevalent XPA and XPC genes mutations—nonsense mutation (c.682C>T, p.Arg228X) and a two-base-pair (2 bp) deletion (c.1643_1644delTG or p.Val548Ala fsX25), respectively—in 19 index cases from 19 unrelated families in the West of Algeria. For the genetic diagnosis of XPA gene, we proceeded to PCR-RFLP. For the XPC gene, we validated a routine analysis which includes a specific amplification of a short region surrounding the 2 bp deletion using a fluorescent primer and fragment sizing (GeneScan size) on a sequencing gel. Among the 19 index cases, there were 17 homozygous patients for the 2 bp deletion in the XPC gene and 2 homozygous patients carrying the nonsense XPA mutation. Finally, XPC appears to be the major disease-causing gene concerning xeroderma pigmentosum in North Africa. The use of fragment sizing is the simplest method to analyze this 2 bp deletion for the DNA samples coming from countries where the mutation c.1643_1644delTG of XPC gene is prevalent

Harderoporphyria: a variant hereditary coproporphyria.

Three siblings with intense jaundice and hemolytic anemia at birth were found to excrete a high level of coproporphyrin in their urine and feces; the pattern of fecal porphyrin excretion was atypical for hereditary coproporphyria because the major porphyrin was harderoporphyrin (greater than 60%; normal value is less than 20%). The lymphocyte coproporphyrinogen III oxidase activity of each patient was 10% of control values, which suggests a homozygous state. Both parents showed only mild abnormalities in porphyrin excretion and lymphocyte coproporphyrinogen III oxidase activity decreased to 50% of normal values, as is expected in heterozygous cases of hereditary coproporphyria. Kinetic parameters of coproporphyrinogen III oxidase from these patients were clearly modified, with a Michaelis constant 15-20-fold higher than normal values when using coproporphyrinogen or harderoporphyrinogen as substrates. Maximal velocity was half the normal value, and we also observed a marked sensitivity to thermal denaturation. The possibility that a mutation affecting the enzyme on the active center which is specifically involved in the second decarboxylation (from harderoporphyrinogen to protoporphyrinogen) was eliminated by experiments on rat liver that showed that coproporphyrinogen and harderoporphyrinogen were metabolized at the same active center. The pattern of porphyrin excretion and the coproporphyrinogen oxidase from the three patients exhibited abnormalities that were different from the abnormalities found in another recently described homozygous case of hereditary coproporphyria. We suggest naming this variant of coproporphyrinogen oxidase defect "harderoporphyria.

Succès de la thérapie génique d’un modèle murin de porphyrie érythropoïétique congénitale

Les porphyries héréditaires représentent un ensemble de maladies métaboliques caractérisées par une synthèse, une accumulation et une excrétion accrues de porphyrines et/ou de leurs précurseurs, l’acide delta aminolévulinique et le porphobilinogène. Chacune de ces maladies a pu être reliée à un déficit spécifique d’une des enzymes de la biosynthèse de l’hème, et nous avons précédemment publié dans Médecine/Sciences les progrès effectués dans la connaissance des gènes, la pathologie moléculaire des porphyries ainsi que des modèles animaux indispensables pour des études physiopathologiques et thérapeutiques. Parmi les porphyries érythropoïétiques, la porphyrie érythropoïétique congénitale (PEC), ou maladie de Günther, la plus sévère des porphyries, est une maladie génétique caractérisée par un déficit en uroporphyrinogène III synthase (UROS). Elle est actuellement traitée par greffe de moelle osseuse allogénique dans les formes graves ; elle pourrait bénéficier dans le futur d’une thérapie génique ciblée sur les cellules souches/progénitrices hématopoïétiques. Les résultats d’une thérapie génique efficace dans un nouveau modèle murin de cette porphyrie sont exposés dans cet article

Hepcidin: immunoanalytic characteristics

International audienceHepcidin has progressively become essential in clinical practice for the diagnosis and follow-up of a large spectrum of diseases. Anyway, its own biochemical and structural characteristics have complicated and delayed the acquisition of a standardized quantifying tool of the peptide