Determination of the action spectrum for UV-induced plasminogen activator synthesis in mouse keratinocytes in vitro

Mouse epidermal keratinocyte-derived Pam 212 cells were irradiated with UV light, and the culture media were examined for plasminogen activator (PA) activity by measuring the capacity to convert exogenous plasminogen into plasmin. Exposure of cells to a broad spectrum of light in the UVB range induced a significant elevation of PA activity at 16 h after irradiation. A dose-response study revealed that a maximal enhancement, 15-fold higher than non-irradiated controls, was induced at a sublethal UVB dose of 100 J/m2, which significantly inhibited cell proliferation without affecting cell viability. Addition of 5 micrograms/ml of cycloheximide lowered the UV-induced elevation of PA activity, suggesting that protein synthesis is required for this phenomenon. Action spectra for PA synthesis were obtained by irradiating cells with monochromatic light ranging from 250 to 360 mm, and the data demonstrated that the action spectrum was 250-320 nm in length with a peak between 260 and 280 nm. The results suggest that UV exposure is an important physiological trigger for modulating PA synthesis in the epidermis.