Translocation of hsp-70 and protein synthesis during continuous heating at mild temperatures in HeLa cells

We have investigated intracellular translocation of hsp-70 and the synthesis of hsp-70 and total protein during heating at moderate temperatures in HeLa cells. When cells were heated at temperatures above 41 degrees C, hsp-70 translocated from the cytoplasm into the nuclei and apparently accumulated in nucleoli within 10 min. At temperatures above 42 degrees C, hsp-70 remained in the nuclei during heating. When cells were heated at 41 degrees C, the hsp-70 which had translocated into the nuclei returned gradually to the cytoplasm during heating. Synthesis of hsp-70 increased to three- to fourfold that in control cells, then decreased to the control level by 6-8 h. Total protein synthesis first decreased to 60% of the control level, then gradually recovered by 4 h. This indicates the acquisition of translational tolerance during heating at 41 degrees C. The return of hsp-70 to the cytoplasm is related to the recovery of total protein synthesis. Similar results were obtained at 42 degrees C heating in heat-induced thermotolerant cells. From these results, it is suggested that translocation of hsp-70 into the nuclei is very important for the recovery of protein synthesis (acquisition of translational tolerance) during heating at moderate temperatures. Also, cycloheximide and puromycin appeared to lower the temperature threshold about 1 degree C with respect to the translocation of hsp-70.