VARIATION OF HEAT-SHOCK-PROTEIN-70 THROUGH THE CELL-CYCLE IN HL-60 CELLS AND ITS RELATIONSHIP TO APOPTOSIS

Cells respond to a heat shock by synthesizing heat shock proteins, whi ch help to protect the cells from further heating. Recent results indi cate that heat shock protein 70 (hsp70) may help to protect cells from apoptosis. We have used how cytometry to investigate the relationship between constitutive and inducible hsp70 and apoptosis through the ce ll cycle in HL-60 cells. Specific antibodies were used to measure hsp7 0 in cells costained with propidium iodide. In separate samples apopto sis was measured using the TdT assay. The apoptotic cells have a subdi ploid DNA content, which allows them to be identified also in the biva riate histograms of heat shock protein vs DNA content. After HL-60 cel ls were heated at 45.0 degrees C for 7.5 min and incubated for various times at 37 degrees C, many of them underwent apoptosis. The level of inducible hsp70 (hsp72) was lower in the apoptotic cells than in the nonapoptotic population, but constitutive hsp70 (hsp73) was the same i n both populations. Pretreatment with sodium vanadate increased the fr action of apoptotic: cells twofold, slightly increased the level of hs p72 in the nonapoptotic cells, but did not affect hsp73. These results suggest that hsp72, but not hsp73, is involved in the development or prevention of apoptosis. (C) 1997 Academic Press.