ACCUMULATION OF MAJOR STRESS PROTEIN 70KDA PROTECTS MYELOID AND LYMPHOID-CELLS FROM DEATH BY APOPTOSIS

The major heat shock protein, hsp70, is known to contribute to the mec hanisms of cell protection against a variety of stress and cytotoxic f actors, providing an increase of cell survival. Whether hsp70 could be implicated in the rescue of cells from stress-induced death proceedin g on apoptotic pathway is not well established. Here we report that su sceptibility of myeloid and lymphoid cell lines to apoptosis induced b y heat shock or ethanol coincides with hsp70 content and can be modula ted by changes in expression of this protein. Cells of lymphoid and my eloid lines differing in basal and inducible level of the protein were tested. The cells containing higher amounts of hsp70 (U937, Jurkat, M olt4) were more resistant to the apoptosis-inducing stimuli then cells which accumulate lower amounts of the protein (HL60) and especially t hose lacking the protein (NSO). Inhibition of hsp70 accumulation by qu ercetin made cells more susceptible to the same apoptotic inducer. Enh ancement of hsp70 expression by previous heating or by liposomal deliv ery of the exogenic protein to the cells lacking hsp70 made them more resistant to apoptosis. The possible mechanisms of the hsp70 protectiv e effect in apoptosis are discussed.