Chronic UVA irradiation of human HaCaT keratinocytes induces malignant transformation associated with acquired apoptotic resistance

Abstract

Ultraviolet A (UVA, 315-400 nm), constituting about 95% of ultraviolet irradiation in natural sunlight, represents a major environmental challenge to the skin and is clearly associated with human skin cancer. It has proven difficult to show direct actions of UVA as a carcinogen in human cells. Here, we demonstrate that chronic UVA exposures at environmentally relevant doses in vitro can induce malignant transformation of human keratinocytes associated with acquired apoptotic resistance. As evidence of carcinogenic transformation, UVAlong-treated (24 J/cm 2 once/week for 18 weeks) HaCaT (ULTH) cells showed increased secretion of matrix metalloproteinase (MMP-9), overexpression of keratin 13, altered morphology and anchorage-independent growth. Malignant transformation was established by the production of aggressive squamous cell carcinomas after inoculation of ULTH cells into nude mice (NC r -nu). ULTH cells were resistant to apoptosis induced not only by UVA but also by UVB and arsenite, two other human skin carcinogens. ULTH cells also became resistant to apoptosis induced by etoposide, staurosporine and doxorubicin hydrochloride. Elevated phosphorylation of protein kinase B (PKB, also called AKT) and reduced expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) were detected in ULTH cells. The resistance of ULTH cells to UVA-induced apoptosis was reversed by either inhibition of phosphatidylinositol 3-kinase (PI-3K) or adenovirus expression of PTEN or dominant negative AKT. These data indicate that UVA has carcinogenic potential in human keratinocytes and that the increased AKT signaling and decreased PTEN expression may contribute to this malignant transformation. Further comparisons between the transformed ULTH and control cells should lead to a better understanding of the mechanism of UVA carcinogenesis and may help identify biomarkers for UVA-induced skin malignancies.

The effects of phototherapy and melanocytes on keratinocytes

“…Furthermore, treatment with UV radiation may induce intracellular mutations, which may in turn induce malignant transformation. The results of previous studies have suggested that environmentally relevant doses of UVA (>20 J/cm 2 ) irradiation may induce highly pernicious transformation, including anchorage-independent growth, the hypersecretion or overexpression of carcinogenic factors, and alterations in the morphology and apoptosis of keratinocytes (33,34). However, in the present study, clinical doses of UVA irradiation negative influences in HaCaT cells; they promoted the expression of Nrf2 and cellular antioxidant levels.…”

UVA radiation causes DNA strand breaks, chromosomal aberrations and tumorigenic transformation in HaCaT skin keratinocytes

“…Albino hairless mice exposed to UVA irradiation (330 nm) developed tumors after >400 days and even long-wave UVA irradiation (>340 nm) has been found to induce skin carcinomas (for review see de Gruijl, 2002). Furthermore, the immortal human HaCaT keratinocytes became tumorigenic when irradiated with 24 J/cm 2 UVA for 18 weeks (He et al, 2006).…”

Genotoxic changes in peripheral lymphocytes after therapeutic exposure to crude coal tar and ultraviolet radiation

“…However, the results of recent studies have shown that the UVA can also be a potent inductor of DNA damage and may be associated with skin cancer 9 . Protracted exposure to UVA leads to lysosomal dysfunction in human fibroblasts 10 , malignant transformation in human cultured keratinocytes 11 and the formation of skin carcinomas in hairless mice in vivo 12 . Unlike the shorter-wavelength UVB photons, which are almost completely absorbed by the epidermis, the longerwave length UVA photons can reach deeper dermal layer of skin and its blood vessels.…”