Hepatocyte-specific inhibition of NF-kappaB leads to apoptosis after TNF treatment, but not after partial hepatectomy.

One of the earliest TNF-dependent events to occur during liver regeneration is the activation of the transcription factor NF-kappaB through TNF receptor type 1. NF-kappaB activation in the liver can have both antiapoptotic and proliferative effects, but it is unclear which liver cell types, hepatocytes or nonparenchymal cells (NPCs), contribute to these effects. To specifically evaluate the role of hepatocyte NF-kappaB, we created GLVP/DeltaN-IkappaB(alpha) transgenic mice, in which expression of a deletion mutant of IkappaB(alpha) (DeltaN-IkappaB(alpha)) was induced in hepatocytes after injection of mifepristone. In control mice, injection of 25 microg/kg TNF caused NF-kappaB nuclear translocation in virtually all hepatocytes by 30 minutes and no detectable apoptosis, while in mice expressing DeltaN-IkappaB(alpha), NF-kappaB nuclear translocation was blocked in 45% of hepatocytes, leading to apoptosis 4 hours after TNF injection. In contrast, expression of DeltaN-IkappaBalpha in hepatocytes during the first several hours after partial hepatectomy did not lead to apoptosis or decreased proliferation. As NF-kappaB activation was not inhibited in liver NPCs, it is likely that these cells are responsible for mediating the proliferative and antiapoptotic effects of NF-kappaB during liver regeneration.