PROTEASE ACTIVATION FOLLOWING UV IRRADIATION IS LINKED TO HYPOMUTABILITY IN HUMAN-CELLS SELECTED FOR RESISTANCE TO COMBINATION OF UV AND ANTIPAIN

In order to examine the relationship between activation of an antipain -sensitive protease and suppression of mutability in UV (UVC)-irradiat ed human cells, a human cell variant with the high protease activity i nduced by UV was established and characterized for its susceptibility to W-induced mutagenicity. Cells of a hypermutable cell strain, RSa, w ere mutagenized with ethyl methanesulfonate and irradiated with 10 J/m (2) UV, followed by exposure to 20 mM antipain for 34 h. Whereas the c ombined treatment was totally lethal to RSa cells not treated with eth yl methanesulfonate, one surviving clone was isolated from the mutagen ized cells and designated UVAP-1. When fibrinolytic protease activity was measured from extracts of the cell, it was found that the protease activity was elevated promptly after UV irradiation, reaching the max imum at 10 min post-irradiation. This protease activity was inhibited by antipain. After UV irradiation the phenotypic mutation frequencies of UVAP-1 cells were much lower than those of the parent RSa cells, as evaluated by the generation of clones resistant to ouabain-killing. F urthermore, mutation at the K-ras codon 12 in genomic DNA was detected in RSa cells but not in UVAP-1 cells. Thus, the protease activation w as correlated with the decreased levels of UV-mutagenicity in UVAP-1 c ells, supporting the possible involvement of the antipain-sensitive pr otease activity in the regulation of cellular mutability following UV irradiation. (C) 1998 Elsevier Science B.V. All rights reserved.