Characterization of alternatively spliced isoforms of the type I interleukin-1 receptor on iNOS induction in rat hepatocytes.
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-kappaB. 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)-1beta 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-1beta. These results further suggest that the enhancement of IL-1RI isoforms may contribute to the regulation of iNOS induction in hepatocytes.
Yamada
Masanori
M
Department of Surgery, Kansai Medical University, Moriguchi, Osaka 570-8506, Japan.
Nishizawa
Mikio
M
Nakatake
Richi
R
Habara
Kozo
K
Yoshida
Hideyuki
H
Ozaki
Takashi
T
Matsui
Kosuke
K
Hamada
Yoshinori
Y
Kamiyama
Yasuo
Y
Ito
Seiji
S
Okumura
Tadayoshi
T
D000818:Animals; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic; D022781:Hepatocytes / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000235:genetics*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D020871:RNA Stability; D051381:Rats; D053573:Receptors, Interleukin-1 Type I / Q000235:genetics* / Q000502:physiology*; D012995:Solubility; D015533:Transcriptional Activation
D020033:Protein Isoforms; D053573:Receptors, Interleukin-1 Type I; D052247:Nitric Oxide Synthase Type II