CONSTITUTIVE EXPRESSION OF HUMAN HSP27, DROSOPHILA HSP27, OR HUMAN ALPHA-B-CRYSTALLIN CONFERS RESISTANCE TO TNF-INDUCED AND OXIDATIVE STRESS-INDUCED CYTOTOXICITY IN STABLY TRANSFECTED MURINE L929 FIBROBLASTS

Hyperthermia and other forms of stress that induce and/or stimulate he at shock or stress protein (hsp) expression enhance the cellular resis tance to TNF-alpha. One of the stress proteins, hsp70, has been shown to participate in the molecular mechanisms that regulate this phenomen on. Here we have tested the capability of small hsps from different sp ecies to protect against this cytokine in the TNF-sensitive L929 fibro sarcoma cells. The genes that encode human hsp27, Drosophila hsp27, an d human alpha B-crystallin were placed under the control of the consti tutive SV40 early promoter and were stably introduced into L929 cells. We observed that all clones that constitutively expressed the exogeno us small hsps exhibited a strong protection against TNF-mediated killi ng, which was proportional to the level of the expressed proteins. Thi s phenomenon did not correlate with altered binding of TNF-alpha to it s receptors, and no protection was observed as a consequence of the tr ansfection or selection procedures. In addition, the overexpression of the exogenous small hsps did not modify the level of the endogenous s tress proteins in the transfected clones. Remarkably, the small hsps a lso induced a protection against oxidative stresses generated by eithe r hydrogen peroxide or menadione. In L929 cells, the killing induced b y TNF-alpha and oxidative stress is thought to occur through the accum ulation of intracellular reactive oxygen intermediates. Hence, our dat a suggest that the small hsps from different species share the propert y to protect L929 cells against the deleterious effects of reactive ox ygen intermediates generated by either TNF-alpha or oxidative stress.