Expression of antisense hsp70 is a major determining factor in heat-induced cell death of P-19 carcinoma cells

Overexpressed heat shock protein 70 (Hsp70) is known to be associated with thermoprotection in a number of cell lines and transgenic animals. We hypot hesized that because overexpression of Hsp70 protects cells from lethal hea t stress, inhibition of expression should make cells susceptible to heat st ress. The model used for this study was a stably transfected P-19 carcinoma cell line expressing antisense hsp70 under the control of the hsp70b promo ter. The results showed marked inhibition of Hsp70 expression after heat sh ock correlated with heat-induced cell death. Hsp90 and Hsc70 protein expres sion were not affected by the antisense construct. Unexpectedly, heme oxyge nase (HO-1), another highly inducible heat shock protein, was not induced a fter heat shock in the antisense hsp70 cell line. Heat shock transcription factor-1 (HSF-1) was in a highly phosphorylated state in the antisense cell line before and after heat shock. This was in contrast to the untransfecte d control P-19 cells where HSF-I was primarily highly phosphorylated after heat shock. A control cell line expressing only the vector, pMAMneo, withou t the antisense construct also showed partial loss of Hsp70 induction but n ot increased cell death after heat shock. The findings support the role of Hsp70 in thermoresistance.