COINDUCTION OF 2 LOW-MOLECULAR-WEIGHT STRESS PROTEINS, ALPHA-B-CRYSTALLIN AND HSP28, BY HEAT OR ARSENITE STRESS IN HUMAN GLIOMA-CELLS

The responses of two low-molecular-weight stress proteins, alpha B crystallin and HSP28, to various types of stress were determined quantitatively by specific immunoassays in a human glioblastoma cell line (U118 MG;). Levels of alpha B crystallin (2-4 ng/mg protein) and HSP28 (1-1.5 mu g/mg protein) in the soluble fraction from cells that had been cultured at 37 degrees C increased about 100-fold and 3-fold, respectively, within 24 h after heat treatment for 15 min at 45 degrees C, with a temporary decrease, due to redistribution to the insoluble fraction, during the heat treatment. Exposure of cells to arsenite (NaAsO2, 100 mu M for 1h) also induced the two proteins with a time course similar to that observed after heat stress, but without a decrease during the stress period. L-Azetidine-2-carboxylate (5 mM for 5 h) was also effective in inducing the two proteins, but to a lesser extent. Other chemicals, including CdCl2, ZnCl2, AlCl3, ethanol, caffeine, nicotine, NaN3, dibutyryl 3',5'-cyclic AMP, forskolin, and a phorbol ester, did not induce the two proteins. Expression of alpha B crystallin and HSP28 mRNAs in cells was enhanced after heat stress and after exposure to arsenite. When cells were challenged with heat stress in the presence of arsenite, the effect on the induction of the two proteins was synergistic. Ethanol (1-2%) enhanced the responses to heat stress or arsenite stress. Glycerol (10% or 1.38 M), added to the culture medium during the stress period, completely blocked the expression of the mRNA for alpha B crystallin and the induction of the two proteins by heat stress, but not that by arsenite stress. These results indicate that the two low-molecular-weight stress proteins, alpha B crystallin and HSP28, respond analogously to heat and chemical stressors in U118 MG cells, but suggest that the events associated with activation of the heat shock genes by heat stress are different from those associated with the activation by chemical (arsenite) stress.