Synergistic effect of TNF-α and ceramide on the production of IL-8 in A549 cells and A549 cells transfected with human ceramide kinase (CERK). (90.11)

Abstract

Abstract Many inducers of the stress response result in ceramide (Cer) accumulation as a result of activation of either sphingolyelinases (SMases) or the de novo pathway. Recently, there is strong evidence for a role of sphingolipids in inflammatory responses such as leukocyte recruitment. The attraction of leukocytes to tissues is essential for inflammation and the host response to infection. Following stimulation by TNF-?, the production of IL-8 increased over time in a concentration dependent manner. Simultaneously, Cer levels increased gradually from 7.56 % during 15 minute stimulation to 35% for 16 hour stimulation. Using Fumonisin B1, an inhibitor of de novo synthesis of Cer, which inhibits Cer synthesis by 25%, we observed 17% decrease of IL-8 expression. When the inhibitor for neutral (SMase) GW4869 was used on A549 cells, there was a significant reduction of Cer as well as IL-8. Subsequently, two serine-threonine phosphatases (PPas), protein phosphatase-1 (PP1) and protein phosphatase-2A (PP2A) have been shown to be Cer responsive in vitro and in vivo. These results suggest that TNF-? stimulates the production of IL-8 by a mechanism that involves the sphingomyelin-Cer system. Cer may be important in increasing the production of IL-8 in A 549 cells. Since Cer can be phosphorylated by CERK to C1P, we predict that CERK expression may affect the balance between these sphingolipids and influence the Cer dependent PPas.