Fibroblasts derived from patients with dysplastic nevus syndrome are not more sensitive towards 254-nm and 312-nm ultraviolet light than fibroblasts from normal donors

Ectopic expression of tyrosinase increases melanin synthesis and cell death following UVB irradiation in fibroblasts from familial atypical multiple mole and melanoma (FAMMM) patients

Patients with familial atypical multiple mole and melanoma (FAMMM) [so-called familial dysplastic naevus syndrome (FDNS)] have a high risk for the development of malignant melanoma. The underlying gene defect has an autosomal dominant inheritance with variable expression and incomplete penetrance. Fibroblasts derived from FAMMM patients have high sensitivity to UVC and mutagens, e.g. 4-nitroquinoline-1-oxide. We were interested in identifying how the combination of inherent sensitivity to UV light and abnormal melanin synthesis interacts in the development of melanoma in FAMMM patients. Intermediates of melanin synthesis produce free radicals that are toxic to cells. Atypical moles (dysplastic naevi) are engaged in the biosynthesis of abnormal melanin pigments. This study examined whether there was any abnormal melanin pigmentation or cell damage after the ectopic expression of tyrosinase in fibroblasts from FAMMM patients when compared with fibroblasts from normal subjects. Fibroblasts from FAMMM patients (3012T and 3072T) were associated with a higher sensitivity than normal human fibroblasts to the toxicity of UVB. When cells were infected with tyrosinase-expressing adenovirus (Ad-HT) and irradiated with UVB, FAMMM fibroblasts showed higher tyrosinase activity, produced more melanin pigments and were degraded more significantly than normal human fibroblasts. Western blot analysis revealed that Ad-HT-infected 3072T produced a larger amount of tyrosinase protein than did Ad-HT-infected normal fibroblasts after UVB irradiation. Our findings suggest: (1) that FAMMM fibroblasts have an unknown machinery which enhances tyrosinase expression by UVB irradiation; and (2) that the resulting increase in melanin synthesis affects the cytotoxicity of UVB to FAMMM fibroblasts. All of these processes may be involved in the genomic instability and development of melanoma in FAMMM patients.

Comet assay demonstrates a higher ultraviolet B sensitivity to DNA damage in dysplastic nevus cells than in common melanocytic nevus cells and foreskin melanocytes

We used the single cell gel electrophoresis assay (comet assay) to study ultraviolet B (UVB)-induced DNA damage in pigment cells. This assay detects DNA damage, mainly DNA strand breaks and alkali labile sites in the DNA molecule. We studied the effect of biologically relevant doses (comparable to 2-3 MED (minimal erythemal dose) for in vivo irradiated full-thickness skin) of monochromatic UVB light of 302 nm on cultured melanocytes derived from foreskin, common melanocytic nevi, and dysplastic nevi. We were able to demonstrate a linear dose-response relationship between UV dose and the migration coefficient of the comet tail in all three types of pigment cells. Nevus cells originating from dysplastic nevi showed the highest sensitivity to UVB irradiation: 65% higher induction of DNA damage compared to the induction in foreskin melanocytes. Common melanocytic nevus cells were most resistant and showed a 30% lower induction of DNA damage in comparison to foreskin melanocytes. Differences in chromatin structure and cell cycle profile may influence the results of the comet assay. Control experiments with x-ray irradiation, which is well known to produce direct DNA strand breaks via radical formation, revealed only small differences between the three types of melanocytic cells. It is unlikely, therefore, that intrinsic nuclear characteristics may account for the observed differences.

DNA repair synthesis following irradiation with 254-nm and 312-nm ultraviolet light is not diminished in fibroblasts from patients with dysplastic nevus syndrome

The DNA excision repair capacity of 23 primary fibroblast lines from patients with dysplastic nevus syndrome was investigated and DNA repair synthesis ("unscheduled DNA synthesis") was determined after UV exposure. Seventeen fibroblast lines from normal donors served as controls. The dose/response experiments included up to ten dose levels and two wavelength ranges: UV-C (using a low-pressure mercury lamp emitting predominantly 254-nm light) and UV-B (artificial "sunlamp" radiation centering around 312-nm light). For each dose level, silver grains over fibroblast nuclei were counted by visual inspection. Twelve cell lines were also evaluated for both UV wavelength ranges using a new semi-automatic image analyzing system. This system included components for rapid sequential identification of both fibroblast nuclei and silver grains sited above them. Silver grains over 100 nuclei were determined for each UV dose level. Dose/response curves were established and analyzed by linear regression. As a quantitative term for assessing DNA excision repair capacity of a cell line we calculated the linear increase (G0) in the number of grains per nucleus, when the UV dose was multiplied by the factor e (i.e. 2.72). The sensitivity of grain detection and resolution of overlapping grains was approximately threefold better in visual than in automatic counting, especially when there were more than 70 grains over nuclei. The time required for visual counting, however, was tenfold that of automatic counting. The variance-weighted mean G0v.w of all fibroblast lines from patients with dysplastic nevus syndrome was found to be 79.1 (+/- 1.8- grains/nucleus, that of fibroblast lines from normal donors was 74.2 (+/- 1.7) grains/nucleus. This difference revealed a slightly better repair capability for cell lines from patients but was at the borderline of detection and, therefore, should not be overinterpreted. From the experimental accuracy achieved by determination of the variance-weighted means of the two groups, we would have been able to detect a difference of 7 and more grains [> 2 x (sigma normal+sigma patients)]. The variance-weighted mean G0v.w of all fibroblast lines from patients with dysplastic nevus syndrome was found to be 76.4 (+/- 1.4) grains/nucleus, whereas that of fibroblast lines from normal donors was only 66.6 (+/- 1.8) grains/nucleus. This difference was statistically significant and, contrary to expectation, revealed better, not worse post-UV DNA repair capability in cell lines from patients that in those from normal donors.(ABSTRACT TRUNCATED AT 400 WORDS)

A potential laboratory test for dysplastic nevus syndrome: ultraviolet hypermutability of a shuttle vector plasmid

The diagnosis of the melanoma-prone disorder dysplastic nevus syndrome (DNS) is based currently on a combination of clinical and histopathologic examinations of patients. To develop a potential laboratory test for DNS, we utilized the observation that an ultraviolet light (UV)-treated mutagenesis plasmid shuttle vector has an abnormally increased frequency of mutations after transfection into lymphoblastoid cells from a patient with familial DNS. pSP189 (containing the bacterial suppressor tRNA gene supF as a marker for mutations and a gene for ampicillin resistance for selection) was treated with UV and transfected into familial DNS, xeroderma pigmentosum complementation group A (XP-A), and normal lymphoblastoid cells by electroporation or diethylaminoethyl (DEAE) dextran. Untreated plasmid pZ189K (containing a gene for kanamycin resistance) was co-transfected as an internal standard to reduce the variability of plasmid survival measurements. After 2 d, plasmids were extracted, used to transform an indicator strain of Escherichia coli, and assayed on plates containing ampicillin or kanamycin. Counting light blue or white colonies (containing mutated supF in the plasmid) and blue colonies (with wild type supF) permitted measurement of the plasmid survival and mutation frequency. Transfection by electroporation or DEAE dextran resulted in abnormally reduced survival of UV-treated plasmid after passage through the XP-A but normal survival in the three DNS lines. Transfection of UV-treated plasmid by DEAE dextran yielded a greater hypermutability with the familial DNS lines than by electroporation. These results suggest that pSP189 UV hypermutability with normal UV survival using DEAE dextran transfection may form the basis of a potential laboratory assay for familial DNS.