Dual action of sphingosine 1-phosphate in eliciting proinflammatory responses in primary cultured rat intestinal smooth muscle cells

Sphingosine 1-phosphate (SIP) is involved in the local inflammatory response within the intestinal muscularis, which has been suggested to play a major role in the pathogenesis of postoperative ileus. The aim of the present study was to elucidate the role of SIP and the molecular mechanisms underlying regulation of inflammatory mediators in primary cultured rat intestinal smooth muscle (RISM) cells. Although our experimental data clearly show the mediatory role of sphingosine kinase (SK)-derived SIP in the TNF-alpha and the LPS induced activation of NF-kB, exogenously added SIP failed to trigger this transcription factor. Instead, exogenous SIP induced early growth response-1 (Egr-1), which was reported to play a proinflammatory role in postoperative ileus. Using RNA interference we found that Egr-1 is required primarily for S1P-induced expression of IL-1 and COX2. Conversely, IL-6 expression following SIP treatment was mediated by STAT3 (signal transducer and activator of transcription-3). In addition our data indicate that the proinflammatory effect of SIP is mediated by its receptors S1P(1-3) and requires activation of MAP-kinases. In conclusion, Egr-1 and STAT3 cooperatively mediate S1P-induced inflammatory responses in RISM cells, providing novel targets for attenuation of postoperative ileus. (C) 2010 Elsevier Inc. All rights reserved.