Up-regulation of IL-1 receptor through PI3K/Akt is essential for the induction of iNOS gene expression in hepatocytes.
OBJECTIVE
Nuclear translocation and DNA binding of NF-kappaB is essential, as interleukin-1beta (IL-1beta) stimulates the induction of inducible nitric oxide synthase (iNOS) gene expression in hepatocytes. However, recent evidence indicates that the activation of NF-kappaB is not sufficient to induce the NF-kappaB-dependent transcription, and the existence of a second signaling is postulated.


METHODS
Primary cultured hepatocytes were treated with IL-1beta, and the expression of iNOS and type 1 IL-1 receptor (IL-1R1) was analyzed in the presence of antisense of IL-1R1, phosphatidylinositol 3-kinase (PI3K) inhibitor, proteasome inhibitor and hypoxia. Moreover, the activities of Akt and NF-kappaB were recorded and the cotransfection was carried out.


RESULTS
Antisense experiment revealed that IL-1R1 was required for iNOS transcription. IL-1beta markedly stimulated the induction of IL-1R1, which preceded the induction of iNOS. The IL-1R1 induction was found to be PI3K/Akt-dependent but NF-kappaB-independent. The up-regulation of IL-1R1 was associated with the second activation of Akt, which accelerated the phosphorylation of NF-kappaB p65 subunit. Cotransfection experiments revealed that Akt increased the transcriptional activity of iNOS gene promoter.


CONCLUSIONS
These results indicate that the up-regulation of IL-1R1 in concert with the activation of NF-kappaB is required for the transcriptional activation of iNOS gene.
Teshima
Shigeru
S
Department of Surgery, Kansai Medical University, Osaka 570-8506, Japan.
Nakanishi
Hideki
H
Nishizawa
Mikio
M
Kitagawa
Katsuhiko
K
Kaibori
Masaki
M
Yamada
Masanori
M
Habara
Kozo
K
Kwon
A-Hon
AH
Kamiyama
Yasuo
Y
Ito
Seiji
S
Okumura
Tadayoshi
T
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D007375:Interleukin-1 / Q000494:pharmacology; D008954:Models, Biological; D016328:NF-kappa B / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics*; D052247:Nitric Oxide Synthase Type II; D020319:Oligodeoxyribonucleotides, Antisense / Q000235:genetics / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017472:Receptors, Interleukin-1 / Q000235:genetics*; D053573:Receptors, Interleukin-1 Type I; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction; D015854:Up-Regulation
D004247:DNA; D007375:Interleukin-1; D016328:NF-kappa B; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D020319:Oligodeoxyribonucleotides, Antisense; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017472:Receptors, Interleukin-1; D053573:Receptors, Interleukin-1 Type I; D011994:Recombinant Proteins; C496318:Nos2 protein, rat; C494920:Akt1 protein, rat