DIFFERENTIAL EFFECT OF UV-B AND UV-C ON DNA-DAMAGE IN L-132 CELLS

Ultraviolet radiation is known to induce skin cancer. The induction of DNA damage caused by UV-B and UV-C was investigated using cultured L- 132 cells, DNA strand breaks assayed by the alkaline elution procedure occurred in a dose-dependent manner, the extent of the strand breaks were inversely well correlated with the number of viable L-132 cells a fter 24 h incubation, About a 10-fold dose of UV-B irradiation was req uired to induce a similar degree of strand breaking to that induced by UV-C, Similarly about a 10-fold dose of W-B was required to produce a similar amount of pyrimidine dimers, such as cyclobutane-type dimers and pyrimidine-(6-4)-pyrimidone photoproducts, which were determined b y ELISA using the specific monoclonal antibody, to that produced by UV -C, Strand breaks induced by UV-B, however, were not fully repaired in viable cells remaining after incubation of cells for a longer period of time, although UV-C-induced strand breaks were repaired in a time-d ependent manner, Furthermore, an experiment with a cell-free system, w here the induction of strand breaks by repair enzymes did not take pla ce, indicated that UV-B caused significantly more direct DNA strand br eaks than that caused by one-tenth the dose of UV-C. The data shown he re suggest that UV-B-induced DNA damage is mediated, at least in part, in a different mechanism from the UV-C induced one.