INDUCTION OF CELL-SURFACE PEPTIDASE ACTIVITY - A GLOBAL RESPONSE TO CELL STRESS CORRELATED WITH APOPTOSIS

We have previously characterized the stimulation of HeLa cell surface peptidase activity directed toward a nonapeptide substrate in response to low fluences of ultraviolet irradiation [Brown et al. (1993): J Ce ll Biochem 51:102-115]. To explore the hypothesis that this comprised a global response to cell stress featuring the interruption of DNA syn thesis, a variety of agents affecting macromolecular synthesis were ap plied to HeLa cell cultures. Actinomycin D,5,6-dichloro-1 beta-ribofur anosyl benzimadazole, mitomycin C, ultraviolet light, and cycloheximid e at doses which inhibited cell growth, but fell short of increasing t he proportion of cells which had lost cell membrane impermeability to trypan blue, resulted in the concentration dependent increase in both amino- and endo-peptidase activities of intact HeLa cell cultures. gam ma-Irradiation, despite inhibiting an increase in cell number over a 2 0-h observation period, had no effect on the expressed level of cell s urface peptidase activity nor did the accumulation of cells in S or G( 2) phase by thymidine parasynchronization. Some of these agents were f ound to increase the proportion of cells in the culture undergoing apo ptosis (programmed cell death), and a strong correlation was found bet ween the extent of apoptosis and the degree of elevation in cell surfa ce peptidase activity. Higher concentrations of perturbants in some in stances increased the percentage of cells that were nonviable and an a ssociated release of intracellular proteases overwhelmed the linear co rrelation with apoptotic cells. The present data do not distinguish be tween a homogeneous elevation of surface peptidase activity in all cel ls of treated cultures or the heterogeneous increase in only preapopto tic or apoptotic cells. Since sunburn of the skin increases both the o ccurrence of apoptotic keratinocytes (sunburn cells) in the affected e pidermis and the release of membrane bound cell activators such as tra nsforming growth factor alpha, it is suggested by way of extrapolation of these in vitro results, that the increase in cell surface proteoly tic activity plays an integral part in the reparative responses of the epidermal cells in vivo. (C) 1994 Wiley-Liss, Inc.