CELL-CYCLE VARIATION OF HSP70 LEVELS IN HELA-CELLS AT 37-DEGREES-C AND AFTER A HEAT-SHOCK

The expression of the 72 kD inducible heat shock protein (hsp72) has b een reported to be cell cycle associated in unheated, synchronized HeL a cells. In this study, flow cytometry was used to investigate hsp72 l evels through the cell cycle in HeLa cells by dual labeling with propi dium iodide and antibodies against hsp72. The entire cell cycle distri bution of hsp72 could be measured in a single sample of asynchronously growing cells. For unheated cells, the level of hsp72 increased about 30% from G1 to S phase, with about a 65% increase in G2/M, probably d ue to cell size differences. Neither mitotic selection nor serum stimu lation induced a higher level of hsp72 than in the control cells. West ern blot analysis of hsp72 from Hoechst-stained cells sorted from G1, mid-S, or G2/M showed that G1 cells had the lowest level of hsp72, wit h about a 30% increase in S phase and a 60% increase in G2/M, in good agreement with the flow cytometry results. These data conflict with pr evious reports by other laboratories which showed a 3-fold higher leve l of hsp72 in S phase than in G1 or G2. In contrast, heat shock (both acute and chronic) led to a non-uniform increase in hsp72 through the cell cycle. Most cells in mid S phase had high levels of hsp72, and a larger range in the levels of hsp72 were found in G1 and late S/G2/M p hase cells. (C) 1995 Wiley-Liss, Inc.