Involvement of protease activation in modulating radiation-sensitivity of human cells

INTRODUCTION Molecular mechanisms that supervise radiation-susceptibility of human cells are one of the important problems in Radiation Protection Science. We previously hypothesized that proteases may play a key role in cellular functions triggered by radiation as well as those in SOS functions of E. coli (1). It has been found that the activity is detectable less than 1 min after irradiation with UV and continuously elevates up to 10 min, followed by being undetectable 30 min after far-ultraviolet C (UV, principally 254nm wavelength) irradiation in human cells (2-4). This time course is quite different from that in other previously reported proteases requiring more than several hours after UV irradiation (5-14). On the other hand, protease induction promptly after UV irradiation is associated with cellular hypomutable change (2-4, 1518). Therefore, it is highly important to characterize the UV-induced proteases. We have reported here partial purification of the UV-induced proteases and induction of other proteases in X-ray-irradiated human cells.