To elucidate cellular concepts for protection against ultraviolet (UV) light we investigated the effect of heat shock protein 70 (hsp70) overexpression on cell viability and on the secretion of UV-inducible immunological cytokines. Transfected murine fibrosarcoma cells (WEHI-S), overexpressing hsp70 or a sham transfected control were used. Overexpression of hsp70 was sufficient to markedly increase cell viability upon treatment with UVB (290-320 nm). Since long wave UV (UVA, 320-400 nm) as well as UVB turned out to stimulate the release of O2- radicals we studied the cell viability upon oxidative stress. Hsp70 overexpression increased viability upon treatment with hydrogen peroxide or menadione, but had no influence on UV-induced O2- release. UV-light is known to upregulate immunologic and proinflammatory cytokines such as IL-1 and IL-6. Oxidative stress appeared to exert a similar effect. Hsp70 overexpression markedly decreased the release of IL-6 induced by UVA, UVB and oxidative stress. To test whether the hsp70 mediated suppression is confined to events caused by UV-light we determined IL-1-mediated effects. IL-1-induced IL-6 release was reduced by hsp70 overexpression, whereas the IL-1 mediated activation of nuclear factor kappa B was not affected. Our data suggests that hsp70 plays a central role not only in cell protection against UV-light, but also in the regulation of proinflammatory cytokine release induced by UV-exposure.