HEAT-SHOCK PROTEINS INCREASE RESISTANCE TO APOPTOSIS

Heat shock treatment of cells increases their survival and resistance to apoptosis. The kinetics of development of this resistance correlate s with the kinetics of synthesis of heat shock proteins (hsps). U937 a nd Wehi-s cells were cultured for 1 h at 42 degrees C, conditions whic h induced the synthesis of heat shock proteins 27, 70, and 90. The cel ls were subsequently permitted to recover for a 2-h period, prior to e xposure to the apoptosis inducing agents actinomycin-D (5 mu g/ml), ca mptothecin (5 mu g/ml), and etoposide (25 mu g/ml). Apoptosis was dete rmined by both DNA fragmentation and flow cytometric analysis, Heat-sh ocked cultures had a smaller number of apoptotic cells compared to con trol cultures when both were exposed to apoptosis inducing stimuli. Tr ansfected Wehi-s cells constitutively overexpressing human hsp 70 or 2 7 were then examined for their resistance to apoptosis induced by thes e drugs. Using the MTT assay, hsp 27 and 70 overexpressing cells exhib ited an increased resistance to cell death when compared to the parent al line. The parental line demonstrated features of apoptosis, that is , cell shrinkage and single- and double-strand DNA breaks. Taken toget her these results demonstrate that an increase in cellular levels of h sp 27 or 70, either by a mild heat shock treatment or by stable transf ection, increases the resistance of U937 and Wehi-s cells to apoptotic cell death. (C) 1996 Academic Press, Inc.