Transforming growth factor-beta1 induces hepatocyte apoptosis by a c-Jun independent mechanism.
BACKGROUND
During hepatic regeneration, transforming growth factor (TGF)-beta1 messenger RNA increases after the initial cycle of DNA synthesis, and it may control hepatocyte growth by inducing apoptosis. TGF-beta1 also induces c-Jun, a potential proapoptotic transcription factor. We hypothesized that autocrine expression of activated TGF-beta1 (Ad5aTGF-beta1) would increase c-jun expression in rat liver and limit hepatic regeneration by inducing apoptosis.


METHODS
Male rats (175 to 200 g) received portal venous injections with adenoviruses expressing either luciferase (Ad5Luc), as a control, or Ad5aTGF-beta1 at a dose of 6 x 10(9) plaque-forming units. Livers were harvested 24 or 48 hours after injection and nuclear extracts and total RNA isolated. TGF-beta1 expression was confirmed by Northern blot analysis in all TGF-beta1-injected rats.


RESULTS
A 2.5-fold increase in c-jun mRNA expression was detected in Ad5aTGF-beta1-infected rats compared with control rats. Transcriptional activity was assessed with an AP-1-responsive-reporter gene that increased 3-fold in rat primary hepatocytes infected with Ad5aTGF-beta1. C-Jun N-terminal kinase activity also increased 6- to 7-fold in Ad5aTGF-beta1-treated rats 24 and 48 hours after injection. Ad5aTGF-beta1-injected rats demonstrated increased AP-1 binding activity compared with Ad5Luc rats. Hepatocytes infected in vitro with Ad5aTGF-beta1 demonstrated increased apoptosis compared with Ad5Luc-infected hepatocytes (47% vs 27%) 36 hours after infection. Dual adenoviral infection with Ad5aTGF-beta1 and a dominant-negative c-Jun (Ad5TAM67) decreased AP-1-induced Ad5Luc activity but not hepatocyte apoptosis (46% with dominant-negative c-Jun and 47% without).


CONCLUSIONS
These data demonstrate that TGF-beta1 induces c-Jun, but c-Jun is not proapoptotic in hepatocytes.
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D022781:Hepatocytes / Q000473:pathology*; D008297:Male; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000502:physiology*
D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta