Doxorubicin and gamma rays increase the level of DNA topoisomerase IIalpha in nuclei of normal and xeroderma pigmentosum fibroblasts.

DNA topoisomerase IIalpha was monitored with the monoclonal antibody Ki-S1 in human fibroblasts after irradiation of cells with gamma rays from a 137Cs source or treatment with the DNA topoisomerase II inhibitor doxorubicin. DNA topoisomerase IIalpha was localized immunohistochemically as bright fluorescent dots in the karyoplasm. The fibroblasts investigated originated from normal human donors and a xeroderma pigmentosum (XP) patient (XP12BE). All cell lines examined showed a time- and dose-dependent increase in DNA topoisomerase IIalpha abundance after irradiation or treatment with doxorubicin. No principal difference in response was seen between normal and XP fibroblasts towards either treatment alone. After irradiation with 9 Gy, the effect was detectable after as little as 30 min and lasted for at least 6 h. After doxorubicin treatment, topoisomerase II overexpression occurred within less than 2 h. It passed through a maximum and began to decrease after approximately 6 h. In principle, the increase in DNA topoisomerase IIalpha may result from (i) architectural changes of interphase chromatin leading to enhanced accessibility of preformed enzyme to the antibody, (ii) enhanced gene expression, or (iii) enhanced stabilization of mRNA or protein molecules. The increase in enzyme levels may be part of the well-known DNA damage responses that operate in cell-protective or DNA-reparative pathways. Thus, the action of DNA topoisomerase II would serve to catalyze preparatory steps in DNA repair. We also found overexpression of the Bax protein and p16 predominantly in treated XP cells, suggesting that the DNA-damaging protocols elicited signals for apoptosis and cell-cycle arrest. From the simultaneous increase in DNA topoisomerase IIalpha and Bax, one may conclude that DNA topoisomerase IIalpha also plays role in apoptosis.

Nuclear morphometry in xeroderma pigmentosum-associated malignant melanomas.

Previous clinical observations have indicated that the metastatic potential for thick malignant melanoma is lower for patients with xeroderma pigmentosum than for other patients. In a prospective study using computerized image analysis to measure the morphometric characteristics of nuclei in these neoplasms, we found that the nuclei of malignant melanoma cells were smaller and more ovoid in patients with xeroderma pigmentosum than in other patients. Objective evaluation and grading of these subtle histopathologic variables could provide a means of establishing prognostic factors unrelated to the thickness of the neoplasm.

Correction of xeroderma pigmentosum repair defect by basal transcription factor BTF2 (TFIIH).

ERCC3 was initially identified as a gene correcting the nucleotide excision repair (NER) defect of xeroderma pigmentosum complementation group B (XP-B). The recent finding that its gene product is identical to the p89 subunit of basal transcription factor BTF2(TFIIH), opened the possibility that it is not directly involved in NER but that it regulates the transcription of one or more NER genes. Using an in vivo microinjection repair assay and an in vitro NER system based on cell-free extracts we demonstrate that ERCC3 in BTF2 is directly implicated in excision repair. Antibody depletion experiments support the idea that the p62 BTF2 subunit and perhaps the entire transcription factor function in NER. Microinjection experiments suggest that exogenous ERCC3 can exchange with ERCC3 subunits in the complex. Expression of a dominant negative K436-->R ERCC3 mutant, expected to have lost all helicase activity, completely abrogates NER and transcription and concomitantly induces a dramatic chromatin collapse. These findings establish the role of ERCC3 and probably the entire BTF2 complex in transcription in vivo which was hitherto only demonstrated in vitro. The results strongly suggest that transcription itself is a critical component for maintenance of chromatin structure. The remarkable dual role of ERCC3 in NER and transcription provides a clue in understanding the complex clinical features of some inherited repair syndromes.

Different rate of chromosome breakage in human fibroblast strains after storage in liquid nitrogen.

Cytogenetic investigation was carried out on fibroblasts stored in liquid nitrogen during a period of 7-99 months. Cell strains were from 9 individuals, 2 of whom were affected by xeroderma pigmentosum group C (XPC), and 2 XPC heterozygotes. In cell samples from 3 normal subjects and from 1 patient, high frequencies of abnormal mitoses were observed at the first passage after thawing, which returned to normal values after a few subcultures. The most frequent lesions were chromosome gaps and breaks. The cells damaged the most were those from one XP patient. These findings indicate that cells from some individuals are hypersensitive to clastogenic factors acting during freezing and thawing procedures. This sensitivity could be related to the genetic constitution, although the XP homozygous condition is not an essential or sufficient factor.

[The interrelation between changes in the structural organization of replicon clusters, a retarded fork displacement rate and the high level of spontaneous SCEs in form II of xeroderma pigmentosum]. / Vzaimosviaz' mezhdu izmeneniiami strukturnoi organizatsii klasterov replikonov, zamedlennoi skorost'iu prodvizheniia vilki replikatsii i vysokim urovnem spontannykh SKhO pri pigmentnoi kseroderme v forme II.

A cytogenetic observation, that the sister chromatid exchanges (SCE) occur 3 times more frequently in a special form of xeroderma pigmentosum--XPII than in the norm, prompted a study of DNA replication in this rare disease. Using DNA fiber autoradiography, the rate of fork movement and the frequency of initiation in the adjacent clusters of replicons were estimated. The rate of fork movement was significantly slower than that in classical XP and in normal cells. Here evidence was provided on another defect in DNA replication in XPII that involves a significantly decreased number of simultaneously operating adjacent clusters of replicons, which results in a decreased rate of DNA chain-growth. According to the Painter replication model for SCE, the exchanges arise due to double-strand DNA breaks occurring on the border between two adjacent clusters, respectively, completely and partially replicated. A retarded fork-displacement rate together with a decreased rate of DNA-chain growth may cause this situation to persist longer than in the norm. Thus, our data provide a further support of the replication model for SCE. A similar combination of cytogenetic and molecular defects has been obtained earlier in the Bloom syndrome cells.

Proximity of repair patches to persistent pyrimidine dimers in DNA of normal human and xeroderma pigmentosum cells.

The proximity of repair patches to persistent pyrimidine dimers in normal human cells and xeroderma pigmentosum group C and D cells was analyzed by sequential digestion of repaired DNA with Micrococcus luteus UV-endonuclease and Escherichia coli DNA polymerase I. Although this enzymatic digestion removed one-third of the pyrimidine dimers, less than 3% of the label associated with repair patches and a similar amount of uniformly labeled DNA were removed. The repair patches therefore appear to be similarly distant from persistent dimers in all cell types, and, in particular, are not adjacent to unexcised dimers in xeroderma pigmentosum group D cells. A previous model that suggested that patches are inserted adjacent to dimers in xeroderma pigmentosum group D cells receives no support from these results.

Ultrastructural studies of xeroderma pigmentosum.

Electron microscopic observations of both sun-exposed and sun-protected skin from a black patient with xeroderma pigmentosum (XP) revealed abnormal ultrastructural changes in the melanin pigmentary system, tonofibrillar-desmosome complexes, endoplasmic reticulum, mitochondria, and nucleoli of all keratinocytes. The difference between the cellular changes in the sun-exposed skin and that protected from sunlight was quantitative rather than qualitative in character. The most salient changes were seen in sun-exposed specimens: melanosomes limited by a membrane showed a high degree of polymorphism with a tendency to form large complexes, and many fibroblast-like cells displayed an intense phagocytic activity for melanosomes, the latter finding not previously reported. The present study supports the conclusions of other investigators that XP is a heterogeneous disease. Clarification of the XP entities by continued research may identify the defective gene and lead to methods of correction by the molecular biologist.

Size and frequency of gaps in newly synthesized DNA of xeroderma pigmentosum human cells irradiated with ultraviolet light.

Native newly synthesized DNA from human cells (xeroderma pigmentosum type) irradiated with ultraviolet light releases short pieces of DNA (L-DNA) when incubated with the single-strand specific S1 nuclease. This is not observed in the case of unirradiated cells. Previous experiments had shown that the L-DNA resulted from the action of S1 nuclease upon gaps, i.e., single-stranded DNA discontinuities in larger pieces of double-stranded DNA. We verified that the duplex L-DNA, that arises from the inter-gap regions upon S1 nuclease treatment, has a size which approximates the distance between two pyrimidine dimers on the same strand; this has been observed at different fluences of ultraviolet-light and indicates that the gap is related to or opposite the dimer. A method was devised to measure the size of the gaps. A Poisson distribution analysis of the percentage of the L-DNA produced as a function of S1 nuclease concentration made this possible. 65% of the gaps corresponded to stretches of 1,250 nucleotides and 35% to stretches of 150 nucleotides. These parameters have been considered in the proposition of a model for DNA synthesis on a template containing pyrimidine dimers.

[Ultrastructural aspects of the epidermis from a sun exposed and from a covered area in two cases of xeroderma pigmentosum (x. p.) and in two controls (author's transl)]. / Etude ultrastructurale de l'épiderme des parties découvertes et couvertes de deux malades noirs atteints de xeroderma pigmentosum (x. p.) et de deux sujets témoins.

Xeroderma pigmentosum is rare among Caucasoids and seems to be rarer among Negroes. Advantage was taken of the observation of two cases in the latters to study the ultrastructure of the epidermis and to verify whether the findings were similar to those observed in the formers. The skin exposed to sunlight (forearm) and that from an covered area (buttock) were studied in the two cases and also in two controls, obviously from the same race. The tissue material was coded after each biopsy and identified only when the ultrastructural study was completed. The authors have noted vacuolization and rarely necrosis of melanocytes, great increase and polymorphism of melanosomes, abnormal melanization sometimes large masses of melanosomes and pre-melanosomes, some other aspects already described in x.p. They have also observed melanosomes disposed as cluster or grapes, and large and strange shaped keratohyaline granules in the squamous cell layer. Even in the unexposed skin there were polymorphism and increased amount of melanosomes. The macroscopic and ultrastructural changes of x. p. in the two Negroes were apparently similar to those observed in Caucasoids.

Xeroderma pigmentosum. Ultrastructural study with special reference to abnormalities of the melanin pigmentary system.

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.