The Irreversible Inhibition of the MAPK p38 Pathway Downregulates LPS-augmented Release of Interleukin- Related Inflammatory Cytokines (IL-1β, IL-6): Immune Surveillance Unraveling IκB-α/NF-κB Phosphorylation State-independent Mechanism in vitro

Abstract

Background: The participation of signaling pathways involving the mitogen-activated protein kinases (MAPKs) in regulating the inflammatory response characterized by the release of cytokines is not well established in the alveolar epithelium. We have previously examined the effect of MAPK p38 blockade on the in vitro release of TNF-α, indicating the likely involvement of other pro-inflammatory cytokines. Methods: This study investigated the selective inhibition of MAPK p38 in modulating the release of interleukin-related inflammatory cytokines, including IL-1β and IL-6. LPS-mediated release of cytokines is closely associated with the blockade of MAPK by the compound SB203580, an irreversible and selective inhibitor of MAPK p38 , independent of MAPK ERK (p42/p44) and MAPK JNK . Results: Pre-treatment with ascending concentrations of SB203580 (0.1 – 100 μM) prior to LPS administration downregulated/attenuated the release of IL-1β, IL-6 and TNF-α in a dose-dependent and dose-independent manners. Furthermore, unraveling the immune molecular pathways likely involved with MAPK p38 -mediated secretion of cytokines revealed that SB203580 increased IκB-α phosphorylation, where IκB-α is considered the main cytosolic inhibitor of the transcription factor involved with regulating the processes of cellular inflammation, NF-κB. This upregulation of the phosphorylation status of IκB-α was accompanied by downregulating the cytosolic accumulation of the non-phosphorylated form of IκB-α, indicating normal nuclear translocation of the associated transcription factor. Conclusions: These results show that MAPK p38 is required, at least in part, for the release of inflammatory cytokines induced by LPS, a mechanism that is independent of the phosphorylation of IκB-α. In addition, the MAPK p38 -dependent release of cytokines seemingly does not require the activation of the NF-κB pathway.