Heat shock-induced acquisition of thermotolerance at the levels of cell survival and translation in Xenopus A6 kidney epithelial cells

In this study we have investigated the acquisition of thermotolerance in a Xenopus laevis kidney A6 epithelial cell line at both the level of cell survival and translation. In cell survival studies, A6 cells were incubated at temperatures ranging from 22 to 35°C for 2 h followed by a thermal challenge at 39°C for 2 h and a recovery period at 22°C for 24 h. Optimal acquisition of thermotolerance occurred at 33°C. For example, exposure of A6 cells to 39°C for 2 h resulted in only 3.4% survival of the cells whereas prior exposure to 33°C for 2 h enhanced the survival rate to 69%. This state of thermotolerance in A6 cells was detectable after 1 h at 33°C and was maintained even after 18 h of incubation. Cycloheximide inhibited the acquisition of thermotolerance at 33°C suggesting the requirement for ongoing protein synthesis. The optimal temperature for the acquisition of translational thermotolerance also occurred at 33°C. Treatment of A6 cells at 39°C for 2 h resulted in an inhibition of labeled amino acid incorporation into protein which recovered to approximately 14% of control after 19 h at 22°C whereas cells treated at 33°C for 2 h prior to the thermal challenge recovered to 58% of control levels. These translationally thermotolerant cells displayed relatively high levels of the heat shock proteins hsp30, hsp70, and hsp90 compared to pretreatment at 22, 28, 30, or 35°C. These studies demonstrate that Xenopus A6 cells can acquire a state of thermotolerance and that it is correlated with the synthesis of heat shock proteins.Key words: Xenopus laevis, heat shock protein, hsps, A6 cells, chaperone, thermotolerance.