Catalase induces the expression of inducible nitric oxide synthase through activation of NF-KB and PI3K signaling pathway in Raw 264.7 cells

It has been reported that macrophages produce substantial amounts of nitrite and nitrate after addition of catalase, but the mechanism associated remains unclear. In present study, we investigated whether catalase modulates the expression of inducible nitric oxide synthase (iNOS), an enzyme that produces nitric oxide. Exposure of Raw 264.7 macrophages (Raw cells) to catalase induced high expression of iNOS mRNA as well as protein with enzymatic activity. Data of mechanical analyses, such as iNOS promoter-driven luciferase assay and actinomycin D chase experiments demonstrated that the induction was due to increased iNOS transcription and post-transcriptional iNOS mRNA stability. Of interest, catalase-induced iNOS protein expression was abrogated through inactivation of NF-kappaB pathway by MG132 or BAY 11-7085 and PI3K pathway by LY294002 or wortmannin, respectively. In particular, blockage of PI3K pathway by LY294002 down-regulated iNOS transcription and steady-state iNOS mRNA levels as well as iNOS mRNA stability induced by catalase, suggesting regulation of PI3K pathway in catalase-induced iNOS expression at the levels of iNOS transcription, steady-state mRNA status, and mRNA stability. Additional cell culture works in different types of cells indicated that iNOS expression by catalase might be cell typespecific, based on the facts that catalase induced iNOS expression in BV2 microglial macrophage-like cells, but not in HT-29 or A549, human colon or lung cancer epithelial-like cells. Together, these results demonstrate for the first time that catalase induces iNOS expression in Raw cells, which seems to be associated with the increase of iNOS transcription and mRNA stability as well as the activation of NF-kappaB and PI3K signaling pathways. (C) 2004 Elsevier Inc. All rights reserved.