Angiotensin II activates I kappaB kinase phosphorylation of RelA at Ser 536 to promote myofibroblast survival and liver fibrosis.
OBJECTIVE
The transcription factor nuclear factor-kappaB (NF)-kappaB promotes survival of hepatic myofibroblasts and fibrogenesis through poorly defined mechanisms. We investigated the activities of angiotensin II and I kappaB kinase (IKK) in regulation of NF-kappaB activity and the role of these proteins in liver fibrosis in rodents and humans.


METHODS
Phosphorylation of the NF-kappaB subunit RelA at serine 536 (P-Ser(536)-RelA) was detected by immunoblot and immunohistochemical analyses. P-Ser(536)-RelA function was assessed using vectors that expressed mutant forms of RelA, cell-permeable blocking peptides, and assays for RelA nuclear transport and apoptosis. Levels of P-Ser(536)-RelA were compared with degree of fibrosis in liver sections from chronically injured rats and patients with hepatitis C virus-mediated fibrosis who had been treated with the AT1 antagonist losartan.


RESULTS
Constitutive P-Ser(536)-RelA is a feature of human hepatic myofibroblasts, both in vitro and in situ in diseased livers. Autocrine angiotensin II stimulated IKK-mediated phosphorylation of RelA at Ser(536), which was required for nuclear transport and transcriptional activity of NF-kappaB. Inhibition of angiotensin II, the angiotensin II receptor type 1 (AT1), or IKK blocked Ser(536) phosphorylation and stimulated myofibroblast apoptosis. Treatment of fibrotic rodent liver with the angiotensin converting enzyme (ACE) inhibitor captopril or the IKK inhibitor sulphasalazine resulted in loss of P-Ser(536)-RelA-positive myofibroblasts and fibrosis regression. In human liver samples, increased numbers of P-Ser(536)-RelA-positive cells were associated with fibrosis that regressed following exposure to losartan.


CONCLUSIONS
An autocrine pathway that includes angiotensin II, IKK, and P-Ser(536)-RelA regulates myofibroblast survival and can be targeted to stimulate therapeutic regression of liver fibrosis.
Oakley
Fiona
F
Liver Research Group, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom.
Teoh
Victoria
V
Ching-A-Sue
Gemma
G
Bataller
Ramon
R
Colmenero
Jordi
J
Jonsson
Julie R
JR
Eliopoulos
Aristides G
AG
Watson
Martha R
MR
Manas
Derek
D
Mann
Derek A
DA
D000704:Analysis of Variance; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects; D022781:Hepatocytes / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008103:Liver Cirrhosis / Q000378:metabolism / Q000473:pathology*; D008297:Male; D018613:Microscopy, Confocal; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D011336:Probability; D012362:RNA, Transfer, Ser / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051996:Transcription Factor RelA / Q000378:metabolism*
D016328:NF-kappa B; D012362:RNA, Transfer, Ser; D051996:Transcription Factor RelA; D000804:Angiotensin II