Cross-talk between Interferon-alfa and Transforming Growth Factor-beta signaling in hepatocytes from preneoplastic rat livers

ALVAREZ, MARIA DE LUJAN; QUIROGA, ARIEL DARIO; PARODY, JUAN PABLO; RONCO, MARIA TERESA; FRANCES, DANIEL ELEAZAR ANTONIO; CARNOVALE, CRISTINA ESTER; CARRILLO, MARÍA CRISTINA

New Mexico, EEUU.

Simposio; Keystone Symposia: “TGF-ß Family in Homeostasis and Disease”; 2008

“Cross-talk between Interferon-alfa and Transforming Growth Factor-beta signaling in hepatocytes from preneoplastic rat livers.” Alvarez ML, Quiroga AD, Parody JP, Ronco MT, Francés DE, Carnovale CE, Carrillo MC.   Background/Aims: Interferon-a (IFN-a) signaling activation abrogates TGF-b1 responses in neoplastic and normal cells. These antagonistic effects could be due to the competition for interaction with limiting amounts of cellular coactivator p300. Otherwise, we observed that  IFN-a2b induces production and secretion of  TGF-b1 in hepatocytes form preneoplastic rat livers, with activation of both signaling pathways. It is of interest to elucidate the role of p300 in this experimental preneoplastic model. Methods: Isolated hepatocytes from rats subjected to an initiation-promotion model of hepatocarcinogenesis were cultured with and without IFN-a2b at 1, 4, 7, 15, 20 and 24 hours. Inhibitors of TGF-b1 signaling (SB431542 and anti-TGF-b1) were also used. Results: Activation of IFN-a signaling  was confirmed by the increment of phosphorylated Stat1 (+150%*) in nuclear extracts at 1 hour of culture. Levels of phosphorylated Smads2/3 augmented (+85%*) since 15 hours in hepatocytes treated with IFN-a2b, indicating TGF-b1 activation. This activation was completely blocked by TGF-b1 inhibitors. An increase in TGF-b1 receptor at protein (+60%*, at 15 hours) and mRNA (+100%*) levels was observed in plasma membranas of hepatocytes treated with IFN-a2b, with no changes in IFN-a receptor levels. Immunoprecipitation studies with p300 showed that in cells treated with IFN-a2b the coactivator is able to interact with both Stat1 and Smad2/3, indicating that it is a rate limiting factor for the activation of both pathways. The pool of endogenous p300 was significantly increased in hepatocytes from preneoplastic livers compared with hepatocytes from normal livers (+130%*, *p<0,05). Conclusions: the cellular abundance of coactivator p300 in hepatic preneoplasia allows the activacion of both IFN-a2b and TGF-b1 signaling, demonstrating in this case an independence of both pathways .