Renal tubular epithelial cells are largely resistant to oxidant-induced injury despite their capacity to accumulate relatively high concentrations of potentially damaging prooxidant and thiol-depleting agents. In the present study, we tested the hypothesis that such resistance may be attributable to a lack or deficiency of signaling transduction pathways through which reactive oxidants have been shown to promote the activation of NF-kappaB, a transcriptional factor that is known to mediate the inducible expression of a wide variety of genes that are involved in inflammatory and other cytotoxic reactions in numerous cell types. NF-kappaB was found to be readily activated following exposure of cultured normal rat kidney epithelial (NRK52E) cells to bacterial lipopolysaccharide (LPS). However, in contrast to findings with many other cell types, the activation of NF-kappaB by LPS was not substantially altered either by pretreatment of cells with the thiol antioxidant, N-acetylcysteine, or by glutathione (GSH) depletion. Moreover, reactive oxidants and oxidative stress-generating chemicals were completely without effect with respect to NF-kappaB activation in NRK52E cells, even following GSH depletion. In contrast, LPS activation of NF-kappaB was substantially attenuated by the intracellular Ca2+ chelator, Quin 2AM, and by the Ca-channel inhibitor, ruthenium red. Moreover, thapsigargin, a Ca-ATPase inhibitor, promoted NF-kappaB activation comparable to that observed by LPS. Additionally, staurosporine, a Ca-dependent protein kinase C inhibitor, substantially decreased LPS-mediated NF-kappaB activation. These results demonstrate that the LPS-inducible expression of NF-kappaB in renal epithelial cells, in contrast to many other cell types, is not responsive to oxidative stress and is regulated, at least in part, by redox-insensitive modulation of intracellular calcium levels. These findings provide a basis for the highly tissue-specific expression and function of NF-kappaB in kidney epithelial cells, which may underlie their resistance to oxidant-mediated cytotoxicity.
Copyright 1999 Academic Press.