The levels of two small stress proteins, hsp27 and alpha B crystallin, were low in C6 glioma cells confluency. However, the levels of the two proteins increased after exposure of cells to heat (42 degrees C for 30 min) or arsenite (50-100 microM for 1 h) stress. When cells were exposed to arsenite or heat in the presence of mastoparan, a peptide toxin from wasp venom, the induction of hsp27 and alpha B crystallin was markedly stimulated, as detected by means of specific immunoassays, Western blot analysis, and Northern blot analysis. The response of hsp70 to each stress was also enhanced in the presence of mastoparan. Treatment of cells with 40 microM mastoparan alone barely induced the accumulation of hsp27 and alpha B crystallin. The stimulatory effect of mastoparan was little affected in cells that had been treated with pertussis toxin, but it was strongly suppressed in the presence of quinacrine, an inhibitor of phospholipase A2. These results suggest that mastoparan, which is an activator of phospholipase A2, enhances the responses to stress of hsp27, alpha B crystallin and hsp70 by increasing the metabolic activity of the arachidonic acid cascade.