Heat stress upregulates chaperone heat shock protein 70 and antioxidant manganese superoxide dismutase through reactive oxygen species (ROS), p38MAPK, and Akt

Chinese hamster lung fibroblasts V79 cells were treated with heat stress for 4 weeks with short duration (15 min) heat shock every alternate day in culture. It was observed that Hsp 70 and the antioxidant enzyme MnSOD became overexpressed during the chronic heat stress period. Both p38 MAPK and Akt became phosphorylated by chronic heat stress exposure. Simultaneous exposure to SB203580, a potent and specific p38MAPK inhibitor drastically inhibited the phosphorylation of p38MAPK and Akt. Furthermore, exposure to SB203580 also blocked the increase in Hsp70 and MnSOD levels and the elevated SOD activity brought about by chronic heat stress. Heat shock factor 1 (HSF1) transcriptional activity and nuclear translocation of HSF1 were prominently augmented by chronic heat stress, and this amplification is markedly reduced by concomitant exposure to SB203580. Also, activations of p38MAPK and Akt and upregulations of Hsp70 and MnSOD were observed on exposure to heat shock for a single exposure of longer duration (40 min). siRNA against p38MAPK notably reduced Akt phosphorylation by single exposure to heat stress and drastically diminished the rise in Hsp70 and MnSOD levels. Similarly, siRNA against Akt also eliminated the augmentation in Hsp70 and MnSOD levels but p38MAPK levels remained unaffected. Heat stress produced reactive oxygen species (ROS) in V79 fibroblasts. N-acetyl cysteine blocked the increase in phosphorylation of p38MAPK, amplification of Hsp70, and MnSOD levels by heat stress. Therefore, we conclude that heat stress-activated p38MAPK which in turn activated Akt. Akt acted downstream of p38MAPK to increase Hsp70 and MnSOD levels. Concise summary: Thermal injury of the skin over a long period of time has been associated with development of cancerous lesions. Also, in many cancers, the cytoprotective genes Hsp70 and MnSOD have been found to be overexpressed. Therefore, we considered it important to identify the signaling elements upstream of the upregulated survival genes in heat stress. We conclude that heat stress activated p38MAPK which in turn activated Akt. Akt mediated an augmentation in Hsp70 and MnSOD levels working downstream of p38MAPK.