Perfluorooctanoic acid (PFOA) affects distinct molecular signalling pathways in human primary hepatocytes
Perfluorooctanoic acid (PFOA) was shown to damage the liver of rodents and to impair embryonic development. At the molecular level, the hepatotoxic effects were attributed to the PFOA-mediated activation of peroxisome proliferator-activated receptor alpha (PPAR alpha). In general, PPAR alpha-dependent effects are less pronounced in humans than in rodents, and the hazard potential of PFOA for humans is controversially discussed. To analyse the effects of PFOA in human hepatocytes, a microarray analysis was conducted to screen for PFOA-mediated alterations in the transcriptome of human primary hepatocytes. A subsequent network analysis revealed that PFOA had an impact on several signalling pathways in addition to the well-known activation of PPARa. The microarray data confirmed earlier findings that PFOA: (i) affects the estrogen receptor ER alpha, (ii) activates the peroxisome proliferator-activated receptor gamma (PPAR gamma), and (iii) inhibits the function of the hepatocyte nuclear factor 4 alpha (HNF4 alpha) which is an essential factor for liver development and embryogenesis. Finally, as a novel finding, PFOA was shown to stimulate gene expression of the proto-oncogenes c-Jun and c-Fos. This was confirmed by using the HepG2 cell line as a model for human hepatocytes. PFOA stimulated cellular proliferation and the metabolic activity of the cells, and upregulated the expression of various cyclins which have a central function in the regulation of cell cycle control. Functional studies, however, indicated that PFOA had no impact on c-Jun and c-Fos phosphorylation and on AP-1-dependent gene transcription, thus demonstrating that PFOA-induced proliferation occurs largely independent of c-Jun and c-Fos.