Activation of NF-kappa B in normal rat kidney epithelial (NRK52E) cells ismediated via a redox-insensitive, calcium-dependent pathway

Renal tubular epithelial cells are largely resistant to oxidant-induced inj ury 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 reac tive oxidants have been shown to promote the activation of NF-kappa B, a tr anscriptional factor that is known to mediate the inducible expression of a wide variety of genes that are involved in inflammatory and other cytotoxi c reactions in numerous cell types. NF-kappa B was found to be readily acti vated following exposure of cultured normal rat kidney epithelial (NRK52E) cells to bacterial lipopolysaccharide (LPS). However, in contrast to findin gs with many other cell types, the activation of NF-kappa B by LPS was not substantially altered either by pretreatment of cells with the thiol antiox idant, N-acetylcysteine, or by glutathione (GSH) depletion. Moreover, react ive oxidants and oxidative stress-generating chemicals were completely with out effect with respect to NF-kappa B activation in NRK52E cells, even foll owing GSH depletion. In contrast, LPS activation of NF-kappa B was substant ially attenuated by the intracellular Ca2+ chelator, Quin 2AM, and by the C a-channel inhibitor, ruthenium red. Moreover, thapsigargin, a Ca-ATPase inh ibitor, promoted NF-kappa B activation comparable to that observed by LPS. Additionally, staurosporine, a Ca-dependent protein kinase C inhibitor, sub stantially decreased LPS-mediated NF-kappa B activation. These results demo nstrate that the LPS-inducible expression of NF-kappa B in renal epithelial cells, in contrast to many other cell types, is not responsive to oxidativ e stress and is regulated, at least in part, by redox-insensitive modulatio n of intracellular calcium levels. These findings provide a basis for the h ighly tissue-specific expression and function of NF-kappa B in kidney epith elial cells, which may underlie their resistance to oxidant-mediated cytoto xicity. (C) 1999 Academic Press.