HSP72 induction by heat stress is not universal in mammalian neural cell lines

Heat-induced expression of 72-kDa heat shock protein (HSP72) was investigated in a panel of neuronal and non-neuronal cell lines by immunoblotting and immunocytochemistry using monoclonal antibodies directed to HSP72. By immunoblotting, HSP72 expression was observed in most cell lines of mouse (SN6.1b, CL8c4.7, NSC34.6, B2A, C2C12), rat (PC12, C-6, L3), and human (NB-1, GOTO, IMR-32, HeLa) origin under the heat-stressed condition. The mouse neuroblastoma cell line N18TG2, however, did not express HSP72 under the heat-stressed condition. By immunocytochemistry, HSP72 was undetectable in the heat-stressed N18TG2 cells, while it was identified in the heat-stressed SN6.1b cells, a clonal hybrid neuron between N18TG2 and mouse septal cholinergic neuron. By exposure to a priming sublethal heat shock, SN6.1b cells but not N18TG2 cells acquired a significant level of tolerance to a subsequent lethal heat shock. These results suggest that heat-induced expression of HSP72 may contribute to acquisition of the thermotolerant state in SN6.1b cells.