Ultraviolet A (UVA, 320-400 nm) radiation, an oxidizing component of sunlight, leads to an immediate increase in the labile iron in human skin fibroblasts. Exposure of skin fibroblasts to UVA radiation is also known to induce nuclear factor-kappaB (NF-kappaB) DNA-binding activity, although the underlying mechanism is unclear. We report here that in skin fibroblasts, the extent of NF-kappaB activation by UVA tightly correlates with the level of "UVA-induced" labile iron release as shown by both iron chelation and iron loading treatments. Furthermore, our data indicate that the slow kinetics of induction of NF-kappaB by UVA relative to other oxidants previously studied is due to a transient increase in permeability of nuclear membrane to proteins and occurs as a result of labile iron-mediated damage to nuclear membrane. Since in addition to iron chelators, lipid peroxidation inhibitors also decrease the UVA-mediated induction of NF-kappaB, we propose that the rapid release of labile iron by UVA might act as a catalyst to exacerbate the generation of lipid secondary messengers in skin cell membranes that are responsible for induction of NF-kappaB. This novel role for iron in amplifying NF-kappaB mobilization in response to UVA-induced oxidative stress aids understanding of its involvement in UV-induced skin inflammation.