Recent studies suggest that sodium arsenite downregulates NF-kappaB activity by inhibiting phosphorylation and subsequent degradation of IkappaBalpha. Many effects of sodium arsenite are secondary to induction of heat shock proteins. The role of the heat shock response in arsenite-induced inhibition of NF-kappaB, however, is not known. We examined the involvement of the heat shock response in arsenite-induced inhibition of NF-kappaB activity in IL-1beta-stimulated Caco-2 cells, a human colorectal adenocarcinoma cell line with enterocytic properties. Treatment of the cells with IL-1beta resulted in increased IkappaB kinase activity, reduced levels of IkappaBalpha and increased NF-kappaB DNA binding activity. Sodium arsenite blocked all of these responses to IL-1beta without inducing changes in heat shock factor activity or heat shock protein levels. Results from additional experiments showed that the protective effect of sodium arsenite on IkappaBalpha was not influenced by the oxygen radical scavenger catalase or by inhibitors of the MAP-kinase signaling pathway. The present results suggest that sodium arsenite stabilizes IkappaBalpha and prevents NF-kappaB activation in IL-1beta-stimulated Caco-2 cells independent of the heat shock response. In addition, stabilization of IkappaBalpha by sodium arsenite does not require oxygen radical formation or activation of the MAP kinase signaling pathway.
Copyright 2002 Wiley‐Liss, Inc.