Odile Chevallier-Lagente

Clues to epidermal cancer proneness revealed by reconstruction of DNA repair-deficient xeroderma pigmentosum skin in vitro

Sun exposure has been clearly implicated in premature skin aging and neoplastic development. These features are exacerbated in patients with xeroderma pigmentosum (XP), a hereditary disease, the biochemical hallmark of which is a severe deficiency in the nucleotide excision repair of UV-induced DNA lesions. To develop an organotypic model of DNA repair deficiency, we have cultured several strains of primary XP keratinocytes and XP fibroblasts from skin biopsies of XP patients. XP skin comprising both a full-thickness epidermis and a dermal equivalent was succesfully reconstructed in vitro. Satisfactory features of stratification were obtained, but the expression of epidermal differentiation products, such as keratin K10 and loricrin, was delayed and reduced. In addition, the proliferation of XP keratinocytes was more rapid than that of normal keratinocytes. Moreover, increased deposition of cell attachment proteins, α-6 and β-1 integrins, was observed in the basement membrane zone, and β-1 integrin subunit, the expression of which is normally confined to basal keratinocytes, extended into several suprabasal cell layers. Most strikingly, the in vitro reconstructed XP skin displayed numerous proliferative epidermal invasions within dermal equivalents. Epidermal invasion and higher proliferation rate are reminiscent of early steps of neoplasia. Compared with normal skin, the DNA repair deficiency of in vitro reconstructed XP skin was documented by long-lasting persistence of UVB-induced DNA damage in all epidermal layers, including the basal layer from which carcinoma develops. The availability of in vitro reconstructed XP skin provides opportunities for research in the fields of photoaging, photocarcinogenesis, and tissue therapy.

Retrovirus-mediated gene transfer corrects DNA repair defect of xeroderma pigmentosum cells of complementation groups A, B and C.

With the aim to devise a long-term gene therapy protocol for skin cancers in individuals affected by the inherited autosomal recessive xeroderma pigmentosum, we transferred the human DNA repair XPA, XPB/ERCC3 and XPC cDNAs, by using the recombinant retroviral vector LXSN, into primary and immortalized fibroblasts obtained from two XP-A, one XP-B (associated with Cockayne’s syndrome) and two XP-C patients. After transduction, the complete correction of DNA repair deficiency and functional expression of the transgenes were monitored by UV survival, unscheduled DNA synthesis and recovery of RNA synthesis, and Western blots. The results show that the recombinant retroviruses are highly efficient vectors to transfer and stably express the human DNA repair genes in XP cells and correct the defect of DNA repair of group A, B and C. With our previous results with XPD/ERCC2, the present work extends further promising issues for the gene therapy strategy for most patients suffering from this cancer-prone syndrome.

Genetic correction of DNA repair-deficient/cancer-prone xeroderma pigmentosum group C keratinocytes.

Xeroderma pigmentosum (XP) is a rare photosensitive and cancer-prone syndrome transmitted as an autosomal recessive trait. Most cancers developed by XP patients are basal and squamous cell carcinoma strikingly restricted to sun-exposed parts of the skin. Cells from patients with classic XP are deficient in nucleotide excision repair, a versatile biochemical mechanism for removal of ultraviolet-induced DNA lesions. Among the seven classic XP complementation groups known to date (XP-A to XP-G), XP-C is the most common one in Europe and North Africa and XP-C patients remain free of neurologic problems often seen in other XP complementation groups. This has prompted us to undertake genetic correction of XP-C fibroblasts and particularly keratinocytes, which are the most relevant cells in relation to skin cancer and have proven recently to be capable of reconstructing XP-C skin in vitro. In this study, we demonstrate that DNA repair capacity, cell survival properties, and transition from proliferative to abortive keratinocyte colonies toward UVB irradiation can be fully recovered in keratinocytes from patients with XPC transduced with a retroviral vector stably driving the expression of the wild-type XPC protein. In addition, we show that in the absence of UV, XP-C keratinocytes exhibit intrinsic cell cycle abnormalities, and beta(1)-integrin overexpression, defects that are also both fully reversed after genetic correction. Together with full correction of the defects in XP-C corrected keratinocytes, in vitro reconstruction of skin from these cells open a rational perspective to XP tissue therapy.

Long-term complementation of DNA repair deficient human primary fibroblasts by retroviral transduction of the XPD gene

Due to their limited life time in culture and their relative resistance to DNA transfection, primary fibroblasts derived from UV-hypersensitive patients could not be used for cloning DNA repair gene and studying stable complementation with wild-type DNA repair genes. Primary cells were only used for complementation analysis after transient expression through cell fusion. DNA microinjection and transfection. We report the retroviral-mediated highly efficient transfer and stable expression of XPD/ERCC2 gene in fibroblast strains from eight different patients using the LXPDSN retroviral vector. Cells derived from skin biopsies of xeroderma pigmentosum and trichothiodystrophy patients were incubated with vector-containing suspension and selected with the neomycin-analog G418. LXPDSN vector specifically complemented cells belonging to the XP-D group. Long-term reversion of repair-deficient phenotype, monitored by UV survival and UDS analysis, has been achieved in these diploid fibroblasts. We demonstrate this methodology is a powerful tool to study phenotypic reversion of nucleotide excision repair-deficient cells such as cellular DNA repair properties and we suggest that it may be used to study other cellular parameters (cell cycle regulation, p53 stability or immunosurveillance-controlling factors) involved in UV-induced skin cancers and which reliability requires the use of untransformed cells.

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.

Stable SV40-transformation and characterisation of some DNA repair properties of fibroblasts from a trichothiodystrophy patient

To characterize nucleotide excision repair properties of cells from trichothiodystrophy (TTD) patients genetically-related to the xeroderma pigmentosum (XP) group D, TTD skin fibroblasts from two unrelated patients (TTD1VI and TTD2VI) belonging to the TTD/XPD group were transformed with a plasmid containing SV40 large T antigen-coding sequences and some DNA repair properties, such as unscheduled DNA synthesis (UDS), UV-survival, in vitro repair synthesis of cell extracts and reactivation of UV-irradiated reporter plasmid were studied. Results showed that: a) both untransformed and transformed TTD cells present a reduced UV-survival, compared to wild-type cells, but at significantly less reduced levels than XP-D cells; b) reduced repair activities were detected in both TTD and XP-D transformed cells by using in vitro cell free extract repair and reactivation of UV-irradiated plasmid procedures, and these relative reduced extents correlated with respective UV-survival; c) surprisingly, near wild-type UDS levels were detected in TTD2VILas transformed cells at different passages after the crisis, suggesting a phenotypic reversion of this transformed cell line; d) fluoro-cytometric analysis of TTD2VILas cells revealed a strong increase of a cell population containing a DNA amount more than twice as high than that of untransformed cells; finally, e) when UDS data were normalized to the DNA content in TTD2VILas cells, it appeared that the repair efficiency was only slightly higher than in untransformed cells. This implies that in transformed cells DNA repair properties should be evaluated, taking into account additional parameters. We obtained an immortalized TTD cell line which maintains DNA repair properties similar to those of parental untransformed cells and may be used to characterize the TTD defect at genetic, molecular and biochemical levels.

Complementation Assays Adapted for DNA Repair-Deficient Keratinocytes

Genetic alterations affecting nucleotide excision repair, the most versatile DNA-repair mechanism responsible for removal of bulky DNA adducts including ultraviolet (UV) light-induced DNA lesions, may result in the rare, recessively inherited autosomal syndromes xeroderma pigmentosum (XP), Cockayne syndrome (CS), or trichothiodystrophy (TTD). Classical approaches such as somatic cell fusions or microinjection assays have formalized the genetic complexity of these related but clinically distinct syndromes, and contributed to the determination of seven, five, and three complementation groups for XP, CS, and TTD, respectively. XP patients are highly susceptible to photoinduced cutaneous cancers of epidermal origin. To better study the responses to UV irradiation of XP keratinocytes, and to objectively determine the extent to which cutaneous gene therapy may be realized, we set up experimental procedures adapted to ex vivo genetic complementation of keratinocytes from XP patients. We provide here detailed rationales and procedures for these approaches.