Characterization of alternatively spliced isoforms of the type I interleukin-1 receptor on iNOS induction in rat hepatocytes

Abstract: In animal models of liver injury, proinflammatory cytokines are implicated in inducing iNOS, which is followed by the production of NO in hepatocytes. Previously we have reported that the up-regulation of type I IL-1 receptor (IL-1RI) is required for the transcriptional activation of iNOS gene, in concert with the activation of transcription factor NF-κB. In this study, we found three alternatively spliced isoforms of IL-1RI in primary cultured rat hepatocytes: two (long and short) membrane-bound and one soluble IL-1RI. Interleukin (IL)-1β markedly augmented the mRNA levels of long and short IL-1RI with time, but was less effective for soluble IL-1RI. Two membrane-bound IL-1RI were localized in the intracellular fraction, whereas soluble IL-1RI was released into the culture medium. Cotransfection experiments with iNOS promoter-luciferase constructs revealed that the overexpression of long and short IL-1RI, but not soluble IL-1RI, significantly increased the transactivation of iNOS promoter and the stabilization of its mRNA. In contrast, the addition of conditioned medium containing soluble IL-1RI reduced the induction of iNOS and NO production stimulated by IL-1β. These results further suggest that the enhancement of IL-1RI isoforms may contribute to the regulation of iNOS induction in hepatocytes. [Copyright &y& Elsevier]