Nitric oxide upregulation of caspase-8 mRNA expression in lung endothelial cells: role of JAK2/STAT-1 signaling.

We recently reported that nitric oxide (NO) modulates expression of multiple genes associated with apoptotic pathways, including expression of caspase-8. The objective of the present study is to determine whether the NO-induced expression of the caspase-8 gene is regulated via signal transducers and activators of transcription-1 (STAT-1) signaling. The confluent monolayers of pulmonary artery endothelial cells (PAEC) were incubated with or without (control) 1 mM NOC-18, a NO donor, at 37 degrees C for 0-24 h. In some experiments PAEC were pretreated with a Janus kinase (JAK-2) inhibitor, AG490 (20 microM). Exposure of PAEC to NO-increased relative levels of caspase-8 mRNA as determined using quantitative real time PCR. Relative levels of phosphorylated STAT-1 at Serine (Ser)-727, but not total STAT-1 expression in NO-exposed cells, were upregulated significantly compared to control cells. AG490 attenuated NO-induced phosphorylation of STAT-1 at Ser 727 and expression of caspase-8 mRNA, suggesting JAK2 plays a role in the induction of caspase-8 mRNA. The promoter of caspase-8 has four gamma-activated sequence (GAS) and two interferon-stimulated response element (ISRE) transcription factor-binding sites. NO enhanced the STAT-1 binding activity to GAS/ISRE. Suppression of STAT-1 expression attenuated NO-induced elevation of caspase-8 mRNA. These studies demonstrate that a NO-dependent increase in caspase-8 mRNA levels is associated with phosphorylation of STAT-1 at Ser-727 and STAT1 binding to the caspase-8 promoter in cultured PAEC.