Effects of epidermal growth factor on CYP inducibility by xenobiotics, DNA replication, and caspase activations in collagen I gel sandwich cultures of rat hepatocytes.

In this study, we investigated the combined effects of EGF and collagen I gel on the phenotype of cultured rat hepatocytes and we focussed our investigations on the regulation of xenobiotic-mediated induction of CYP, cell cycle progression and activation of capases 8 and 3. We found that EGF, added to basal culture medium or phenobarbital (3.2 mM) containing medium, provoked a moderate decrease of CYP1A1 and CYP2B1/2 activities. However, EGF did not exert any inhibitory effect on 3-methylcholantrene (5 microM) and beta-naphtoflavone (25 microM) induction of CYP1A1 activities. In collagen gel sandwich cultures, hepatocytes remained arrested in mid-G1 phase of the cell cycle, even in the presence of EGF. In conventional primary cultures, caspases 8 and 3 were activated at 3 and 5 days after plating respectively. In collagen gel sandwich cultures, we found that neither collagen I nor EGF prevented activation of caspase 8 while collagen I gel inhibited activation of caspase 3, preventing spontaneous apoptosis of cultured rat hepatocytes. In contrast, EGF transiently increased caspase 3 activity at day 1 after plating. Altogether, our data demonstrate that collagen I gel triggers intracellular signals which strongly affect cultured hepatocyte phenotype, leading to a cell cycle arrest in G1 phase and long-term survival through the inhibition of caspase 3 activation and that EGF-free medium improves survival and liver-specific gene expression in hepatocytes maintained in collagen I gel sandwich cultures.