Higher susceptibility to apoptosis following ultraviolet B irradiation of xeroderma pigmentosum fibroblasts is accompanied by upregulation of p53 and downregulation of Bcl-2

Apoptosis plays an important part as a defence mechanism in eliminating damaged cells. Among the complex factors which regulate apoptosis, the p53 tumour suppressor protein which is induced by DNA damage has been suggested to play a crucial part. Cells from xeroderma pigmentosum (XP) patients, which are defective in nucleotide excision repair, express higher levels of p53 and are highly susceptible to cell death after ultraviolet (UV) irradiation. To examine the relationships between DNA damage, p53 and apoptosis, normal and XP group A fibroblasts were exposed to UVB, and expressions of molecules involved in apoptosis were examined. Apoptosis of XP and normal cells was clearly detected at 48 h after irradiation with UVB at doses of 5 and 40 mJ/cm2, respectively. Cells were positive by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) staining under these exposure conditions. At 6 h after irradiation, p53 protein expression was induced in normal and XP cells at minimal doses of 10 and 2.5 mJ/cm2, respectively. Bcl-2 protein, an inhibitor of apoptosis, was downregulated prior to cell death following UVB exposure at doses that induced apoptosis in both cell types. These results suggest that DNA damage due to UVB induces apoptosis by upregulating proapoptotic molecules such as p53, and by downregulating anti-apoptotic molecules such as Bcl-2.     

XPD751基因多态性与中国人群肝细胞性肝癌易感性的Meta分析

目的探讨XPD基因多态性与中国人群肝细胞性肝癌患病风险的关系。方法计算机检索CBM、VIP、CNKI、Pubmed、Embase、Ovid等数据库,收集有关XPD Lys751Gln基因多态性与HCC易患性的病例对照研究,提取纳入文献的相关数据进行Meta分析。以病例组与对照组XPD Lys751Gln基因型分布的比值比(OR)为效应指标,检验其是否为肝细胞性肝癌的危险因素。结果共5篇研究符合纳入标准,累计病例1658例,对照1652例。Lys/Lys基因型与Gln/Gln+Lys/Gln基因型比较的OR为0.64(95%CI 0.36～1.14,P=0.13,I2=88%)。而Gln/Gln基因型与Lys/Lys+Lys/Gln基因型比较的OR为2.32(95%CI 1.71～3.15,P<0.01,I2=49%)。结论 XPD 751Gln/Gln是中国人群HCC的易感基因型,而XPD 751Lys/Lys可能是中国人群HCC的保护基因型。     

Truncated XPA protein detected in atypical group A xeroderma pigmentosum

XPA protein from a patient with typical group A xeroderma pigmentosum (XP) and three atypical group-A XP patients were analysed. Immunoblot analysis of XPA proteins revealed that a typical group-A XP patient showed no XPA protein band, while a smaller, truncated XPA protein, which appears to be responsible for mild skin lesions and minimal neurological abnormalities, was detected in cells from three atypical group-A XP patients. Furthermore, the difference in the amount of truncated XPA protein correlated with the mildness of neurological manifestations in these three atypical group-A XP patients. The results suggest a correlation between clinical manifestations and qualitative and quantitative abnormalities of XPA protein products.     

Evidence for excision repair-dependent and independent processes in ara C-induced chromosome rearrangements in G1 human lymphocytes

1-β-D-arabinofuranosylcytosine (ara C) enhances the formation of chromosome rearrangements such as translocations or dicentric chromosomes in G₁ cells containing DNA lesions. The formation of rearrangements is hypothesized to be the result of inhibition of excision repair. Ara C has also been known to lead to the formation of chromosome rearrangements in G₁ cells in the absence of induced DNA lesions. It is not known whether a common mechanism is involved in these two processes. In the present study, we used excision repair-deficient XP cells to investigate whether excision repair is involved in the formation of chromosome rearrangements in G₁ cells which do not contain induced DNA lesions. G₀ Lymphocytes from an XP patient were either treated with 4-nitroquinoline-1-oxide (4NQO) or left untreated. Cells were then cultured in the presence of ara C for about 18 h. Aphidicolin (APC), which induces chromosome rearrangements in cells containing 4NQO-induced DNA lesions, was used for comparison. The resulting frequency of dicentrics and rings (dic & ring) was determined at the first mitoses after culture initiation. In 4NQO-pretreated XP cells, the frequency of dic & ring was not increased by post-treatment with ara C or with APC. This result is thought to reflect the absence of excision repair in XP cells. However, normal induction of dic & ring was observed in XP cells not pretreated with 4NQO but treated with ara C. Thus, there seems to be two different processes involved in the induction of G₁ rearrangements: excision repair-dependent and excision repair-independent. UV-endonuclease is not involved in excision repair-independent rearrangements.     

DNA repair: Pathways and defects

Damaged DNA can be repaired by three different mechanisms: photoreactivation, excision repair and postreplication repair. Each mechanism is regulated by a highly specific set of enzymes. Defects within these systems result in diseases which have one common feature: affected individuals are cancer prone. Recently, newly developed methods not only make it possible to diagnose affected patients but also to detect individuals at risk. Furthermore, the results obtained elucidate some mechanisms of carcinogenesis. Clinical applications are discussed.     

Xeroderma pigmentosum

Summary Unusual changes in the melanin pigmentary system were observed on a warty papule biopsy taken from a patient with xeroderma pigmentosum (XP). Degenerated melanocytes full of lipids were observed from the basal layer up to the middle of the epidermis. The melanosomes were polymorphous, variable in size and shape with very strange aspects, such as spider-like and whirling configurations. The structure of the macromelanosomes suggests that they are large autophagosomes. These findings are discussed and compared with previous studies.     

Ocular Involvement in Xeroderma Pigmentosum

A 37-year-old, white woman with xeroderma pigmentosum had reduced vision for many years because of primary and secondary corneal epithelial edema and stromal haze. Corneal grafting was required, but was not successful. Numerous primary dermal tumors of various types involving the lids of both eyes had been excised surgically or treated by freezing with liquid nitrogen. Squamous cell carcinomas involving the limbal area of the globe and adjacent tissues were excised from the left eye at age 12, the right eye at age 32, and the left eye (again) at age 36. The right limbal tumor soon recurred and invaded the orbit despite radiation treatment; this required right orbital exenteration. The second left limbal tumor recurred one year later, soon after the recurrence of a left lower lid basal cell carcinoma. Left orbital exenteration was required. Corneal graft failures and recurrent ocular squamous cell carcinoma involving the eye in xeroderma pigmentosum can be difficult management problems.     

Evidence for repair of ultraviolet light-damaged herpes virus in human fibroblasts by a recombination mechanism

Human cells were either singly or multiply infected with herpes simplex virus (HSV-1) damaged by ultraviolet (UV) light, and the fraction of cells able to produce infectious virus was measured. The fraction of virus-producing cells was considerably greater for multiply infected cells than for singly infected cells at each UV dose examined. These high survival levels of UV-irradiated virus in multiply infected cells demonstrated that multiplicity-dependent repair, possibly due to genetic exchanges between damaged HSV-1 genomes, was occurring in these cells.To test whether UV light is recombinogenic for HSV-1, the effect of UV irradiation on the yield of temperature-resistant viral recombinants in cells infected with pairs of temperature-sensitive mutants was also investigated. Increased recombination frequencies were observed after UV irradiation of the parental viruses, indicating that damaged sites on the HSV-1 genome stimulate genetic exchanges. This stimulation provides strong support for the model that genetic recombination between lethally damaged HSV-1 chromosomes can lead to the production of undamaged virus. Experiments similar to those described above were performed with repair-deficient (xeroderma pigmentosum, group A, and xeroderma pigmentosum variant) cells. The results of these experiments showed that the defective functions in these mutant host cells are not required for multiplicity-dependent repair or UV-stimulated viral recombination in herpes-infected cells.     

Assessment of microsatellite instability in a cell line from a patient with xeroderma pigmentosum variant

Cells from patients with xeroderma pigmentosum (XP) variant are thought to be defective in postreplication repair. This DNA repair pathway is not well defined in human cells and the exact genetic defect of XP variant is unknown. In another cancer-prone hereditary disorder, hereditary nonpolyposis colon cancer, tumors are characterized by a DNA mismatch repair defect with microsatellite instability. Since there are some similarities between postreplication repair and mismatch repair, we investigated microsatellite instability, the hallmark of a DNA mismatch repair defect, in a lymphoblastoid cell line from a patient with XP variant. Two normal lines and one nucleotide excision repair-defective XP group A line were used as controls. In a host cell microsatellite instability assay, the recently developed shuttle vector pZCA29 was transfected into these cells and replicated plasmid recovered after 3 days. The plasmid contains two CA repeat tracts that interrupt the reading frame of the lacZ gene. Reversion to active β-galactosidase, detectable by a color reaction of bacterial transformants, represents the frequency of frameshift mutations in the CA repeat tracts during replication of the plasmid, and thereby the host cells’ microsatellite instability. We did not find any significant differences in the mutation frequencies of the plasmids after passage through either cell line. This indicates that there is no microsatellite instability in the examined XP variant cell line. Received: 8 August 1997     

Xeroderma pigmentosum patients from Germany: repair capacity of 45 XP fibroblast strains of the Mannheim XP Collection as measured by colony-forming ability and unscheduled DNA synthesis following treatment with methyl methanesulfonate and N-methyl-N-nitrosourea

Summary A total of 45 XP fibroblast strains from the Mannheim XP Collection (representatives of XP complementation groups A, C, D, E, F or G, I, and XP variants) were investigated for colony-forming ability (term: D₀ after treatment with up to ten doses of the methylating carcinogen MeSO₂OMe. As controls 16 fibroblast strains from normal donors were used. Except for 4 XP strains (1 from group C and 3 from group D) which, however, were borderline cases, none of the remaining 41 XP strains was found to be more sensitive than normal controls. This held true within the limits of an experimental accuracy (experimental variability of D₀ values) of ±7%. When weighted means were calculated for XP complementation groups and compared with that of normal donors at a significance level of 5%, no significant difference was detected. In contrast, after exposure of 6 XP group D strains to MeNOUr, a weighted mean D₀ value was obtained which was significantly decreasd by 27%. Unscheduled DNA synthesis (term: G₀ which serves as a measure of excision repair) after exposure to MeNOUr was quantitatively the same (exposure to MeNOUr was quantitatively the same (experimental varability: ±8%) both in the group of normal strains and in most of the XP complementation groups. Exceptions were group E and group F (or G) which had higher, and group I which had lower repair. Analogous G₀ values measured after exposure to MeSO₂OMe (experimental variability: ±13%), however, differed from that of the control strains: they were lower in XP complementation groups A, D, E, F (or G), and I. However, groups A, E, F (or G), and I including only 3 individual strains or less may be considered to be possibly ill-represented. Yet, group D including 11 XP strains did show reduction of the mean G₀ value by 35%. From this it is concluded that there are repair defects in XP group D strains with regrad to MeSO₂OMe-induced adducts. These defects seem to be small.Abbreviations XP xeroderma pigmentosum - MeSO₂OMe methyl methanesulfonate - MeNOUr N-methyl-N-nitrosourea - Me(NO)(NO₂)Gdn N-methyl-N-nitro-N-nitrosoguanidine - HEPES N-2-hydroxyethyl-piperazine-N-2-ethanesulfonic acid This work was supported by the Deutsche Forschungsgemeinschaft, SFB 136