Proteomic analysis of differential protein expression in primary hepatocytes induced by EGF, tumour necrosis factor alpha or the peroxisome proliferator nafenopin

Peroxisome proliferators are nongenotoxic rodent-liver carcinogens that hav e been shown to cause both an induction of hepatocyte proliferation and a s uppression of apoptosis. Both epidermal growth factor (EGF) and the peroxis ome proliferator nafenopin induce DNA replication in primary rat hepatocyte cultures, but apparently through different signalling pathways. However, b oth EGF and nafenopin require tumour necrosis factor alpha (TNF alpha) sign alling to induce DNA replication. By examining proteins isolated from rat p rimary hepatocyte cultures using two-dimensional gel electrophoresis and ma ss spectrometry, we found that proteins showing an altered expression patte rn in response to nafenopin differed from those showing altered expression in response to EGF. However, many proteins showing altered expression upon stimulation with TNF alpha were common to both the EGF and nafenopin respon ses. These proteome profiling experiments contribute to a better understand ing of the molecular mechanisms involved in the response to peroxisome prol iferators. We found 32 proteins with altered expression upon stimulation wi th nafenopin, including muscarinic acetylcholine receptor 3, intermediate f ilament vimentin and the beta subunit of the ATP synthase. These nonperoxis omal protein targets offer insights into the mechanisms of peroxisome proli ferator-induced carcinogenesis in rodents and provide opportunities to iden tify toxicological markers to facilitate early identification of nongenotox ic carcinogens.