Selective stimulation of Hsp27 and alphaB-crystallin but not Hsp70 expression by p38 MAP kinase activation.

The levels of Hsp27 and alphaB-crystallin in C6 rat glioma cells, that had been heated at 43 degrees C for 30 min with a subsequent culture for 16 h at 37 degrees C, were markedly increased. The exposure of the cells to a low concentration (0.1-3 microg/ml) of anisomycin for a few hours after heat stress stimulated the accumulation of the small stress proteins Hsp27 and alphaB-crystallin, but not that of Hsp70. The levels of mRNAs for Hsp27 and alphaB-crystallin but not that for Hsp70 increased in cells that had been exposed to heat and subsequently for 2 h to 0.1-3 microg/ml anisomycin. The results of a reporter assay, using an alphaB-crystallin promotor fused to a luciferase reporter gene, suggested that the increase in level of alphaB-crystallin mRNA was due to the production of new mRNA. The activation of the binding of heat shock factors to heat shock elements induced in cells that had been heat stressed was barely affected by subsequent exposure to anisomycin at 0.3 microg/ml. The stimulatory effects of anisomycin were also observed in cells that had been exposed to NaAsO2 or CdCl2. The active form of p38 mitogen activated protein (MAP) kinase was increased in cell that had been subjected to heat shock and subsequent exposure to 0.3 microg/ml of anisomycin. The heat-induced accumulations of Hsp27 and alphaB-crystallin were also stimulated by cycloheximide, another stimulator of p38 MAP kinase. SB202190, a specific inhibitor of p38 MAP kinase, suppressed the stimulation by anisomycin of the heat stress-induced expressions of Hsp27 and alphaB-crystallin. These results suggest that the signal transduction pathway of the stress-induced expressions of Hsp27 and alphaB-crystallin in C6 glioma cells includes a process that is sensitive to p38 MAP kinase.