Transcriptional regulation of iNOS by IL-1 beta in cultured rat pulmonary artery smooth muscle cells. Am. J. Physiol. 271 (Lung Cell. Mol. Physiol. 15): L166-L171, 1996.-Interleukin-1 beta (IL-1 beta) is the critical cytokine affecting peripheral vascular expression of inducible nitric oxide synthase (iNOS). Accordingly, we sought to determine a role for IL-1 beta in stimulating iNOS transcription in cultured rat pulmonary artery smooth muscle cells (RPASMC). Treatment of RPASMC with IL-1 beta caused a concentration-dependent increase in iNOS gene expression by Northern and Western blotting. To demonstrate IL-1 beta-mediated transcriptional activation, we used transient liposome-mediated transfection of RPASMC with promoter-luciferase constructs containing deletional mutations of the murine macrophage iNOS 5' flanking promoter region. IL-1 beta increased promoter activity approximately two- to threefold over baseline in fragments ranging from -1592 (full-length) to -242 bp. Activity was lost, however, when the promoter fragment was shorter than -242 bp. IL-1 beta-mediated increases in steady-state iNOS mRNA were sensitive to pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappa B activation. Nuclear proteins from IL-1 beta-stimulated cells demonstrated PDTC-sensitive binding to an oligonucleotide containing the sequence for the NF-kappa B binding element present in the region between -242 and -42 bp. These data document that IL-1 beta, by itself, increases iNOS expression in RPASMC by transcriptional activation, mediated in part by NF-kappa B.