Received for publication August 30, 2005.
Revised December 11, 2005.
Accepted for publication December 13, 2005.

Janus Kinase-Signal Transducer and Activator of Transcription Mediates Phosphatidic Acid-Induced IL-1 and IL-6 Production

Abstract

Previously, we found that phosphatidic acid (PA) can induce inflammatory mediators like cytokines, which implies that PA plays a role in inflammatory response. In the present study, we provide evidence of the PA-mediated activation of the JAK-STAT signaling pathway, which results in the production of IL-1 and IL-6 from macrophages. PA was found to cause the rapid phosphorylations of JAK2 and STAT1/3, and the subsequent nuclear translocation of STAT1/3. Macrophages that had been transiently transfected with a luciferase reporter construct containing eight consecutive -interferon activating sequence (GAS) elements, a known STAT-binding site, exhibited enhanced reporter gene activity in response to PA stimulation, which further supports the involvement of JAK-STAT activation in the PA-induced signaling pathway. Of the inflammatory cytokines, IL-1, IL-6, and TNF-were detected in media from macrophages stimulated with PA. Moreover, the JAK2 inhibitor, AG490, abolished PA-induced IL-1 and IL-6 release, but had no effect on TNF- production, which is consistent with the notion that IL-1 and IL-6, but not TNF-, contain an STAT-binding element in their promoter region. The knock-down of JAK2 in macrophages by small interfering (si) RNA significantly attenuated PA-induced IL-1 and IL-6 production. In addition, JAK2 inhibitor suppressed PA-induced Akt phosphorylation and the Akt inhibitor, LY294002, blocked GAS activation (GAS contains a promoter that responds to PA), suggesting that PA-mediated JAK2 activation leads to PI3K/Akt phosphorylation and STAT activation, and the subsequent translocation of STAT to the nucleus. Taken together, our data demonstrate that PA-activated macrophages produce IL-1 and IL-6, and that these processes require the activation of the JAK2-STAT1/3 or JAK2-Akt-STAT signaling pathways.

Key words: Interleukins, Jak/Stats, Stat activated transcriptional events