Phosphoinositide 3-kinase activity leads to silica-induced NF-κB activation through interacting with tyrosine-phosphorylated IκB-&agr; and contributing to tyrosine phosphorylation of p65 NF-κB.

The role of the subunits of phosphoinositide (PI) 3-kinase in NF-κB activation in silica-stimulated RAW 264.7 cells was investigated. Results indicate that PI3-kinase activity was increased in response to silica. The p85&agr; subunit of PI3-kinase interacted with tyrosine-phosphorylated IκB-&agr; in silica-stimulated cells. PI3-kinase specific inhibitors, such as wortmannin and LY294003, substantially blocked both silica-induced PI3-kinase and NF-κB activation. The inhibition of NF-κB activation by PI3-kinase inhibitors was also observed in pervanadate-stimulated but not in LPS-stimulated cells. Furthermore, tyrosine phosphorylation of NF-κB p65 was enhanced in cells stimulated with silica, pervanadate or LPS, and wortmannin substantially inhibited the phosphorylation event induced by the first two stimulants but not LPS. Antioxidants, such as superoxide dismutase (SOD), N-acetylcysteine (NAC) and pyrrolidine dithiocarbamate (PDTC), blocked silica-induced PI3-kinase activation, suggesting that reactive oxygen species may be important regulatory molecules in NF-κB activation by mediating PI3-kinase activation. Our data suggest that p85 and p110 subunits of PI3-kinase play a role in NF-κB activation through interaction with tyrosine-phosphorylated IκB-&agr; and contributing to tyrosine phosphorylation of p65 NF-κB. [ABSTRACT FROM AUTHOR]