[Effect of heat shock on cell differentiation and apoptosis in U-937 cells]

One of the most abundant cell protective systems is based on an inducible member of Hsp70 family of stress proteins. Proteins belonging to the family are known to participate in all processes of cell physiology including differentiation and apoptosis. Here data are presented concerning effect of heat shock accompanied by a high-level accumulation of Hsp70 on the phorbol ester-induced expression of surface antigens and on TNF-alpha mediated apoptosis. The data showed that heat shock at 43 degrees C for 60 min reduced the expression of CD11c and CD23 surface markers pre-established by phorbol ester; the latter is known to induce macrophage-like phenotype by 70-80% of the original level. Heating in the same conditions was also shown to markedly delay the outcome of apoptosis stimulated by TNF-alpha. Suggesting that Hsp70 by its binding transcription activators of NF-kappa B complex might transiently suppress both the processes, we determined the amount of p65 and c-Rel in nuclear fractions of cells subjected to various stimuli. It was found that both proteins were retarded in the cytoplasm and were not transported to nuclei in cells heated before the administration of PMA or TNF. It is concluded that Hsp70 accumulating in higher amounts is able to transiently protect cells of TNF-mediated cytotoxic effect by physical association with the proteins that serve as modulators of apoptosis.