Background: Knowledge about the morphologic changes following ultraviolet irradiation in the earliest stages of melanomas is still lacking.
Methods: To investigate these changes, an in vitro system consisting of radial growth phase Wistar melanoma cell lines (WM35 and WM3211) was established. Cells were irradiated with a single erythemogenic dose of UVB (10 mJ/cm2) and evaluated for morphologic changes.
Results: When compared with the non-irradiated cells, inverted light microscopy revealed increased cellular branching, cytoplasmic size, and multinucleation in the irradiated cells. Transmission electron microscopy revealed the features of increased metabolic activity (hyperplasia of the mitochondria and Golgi) and those of ultrastructural atypia (pleomorphism of the nuclei and nucleoli, increased euchromatin, and nucleolar margination) in the irradiated cells. Moreover, UVB irradiation caused an increase in the apoptotic activity. These alterations were associated with up-regulation of p53, Bcl-2, and the second mismatch repair protein (hMSH2), as revealed by Western blot analysis.
Conclusions: UVB irradiation can induce apoptosis, morphologic changes, and altered expression of p53, Bcl-2, and hMSH2 in radial growth phase melanoma cell lines. Up-regulation of p53, Bcl-2, and hMSH2 suggests that these factors are involved in the altered balance between survival and apoptosis induced by UVB. Further investigation will be needed to determine if apoptosis and ultrastructural atypia reflect underlying DNA damage and genomic instability induced by UVB.