Human hsp27, Drosophila hsp27 and human alpha B-crystallin expression-mediated increase in glutathione is essential for the protective activity of these proteins against TNF alpha-induced cell death

Expression of small stress proteins (shsp) enhances the survival of mammalian cells exposed to heat or oxidative injuries. Recently, we have shown that the expression of shsp from different species, such as human hsp27, Drosophila hsp27 or human alpha B-crystallin protected murine L929 cells against cell death induced by tumor necrosis factor (TNF alpha), hydrogen peroxide or menadione. Here, we report that, in growing L929 cell lines, the presence of these shsp decreased the intracellular level of reactive oxygen species (ROS). shsp expression also abolished the burst of intracellular ROS induced by TNF alpha. Several downstream effects resulting from the TNF alpha-mediated ROS increment, such as NF-kappa B activation, lipid peroxidation and protein oxidation, were inhibited by shsp expression. We also report that the expression of these different shsp raised the total glutathione level in both L929 cell lines and transiently transfected NIH 3T3-ras cells. This phenomenon was essential for the shsp-mediated decrease in ROS and resistance against TNF alpha. Our results therefore suggest that the protective activity shared by human hsp27, Drosophila hsp27 and human alpha B-crystallin against TNF alpha-mediated cell death and probably other types of oxidative stress results from their conserved ability to raise the intracellular concentration of glutathione.