Trichostatin A induces differential cell cycle arrests but does not induce apoptosis in primary cultures of mitogen-stimulated rat hepatocytes

Background/Aims: The effects of Trichostatin A (TSA), a drug candidate for cancer therapy, on proliferation and survival of primary hepatocytes, the major site of xenobiotic biotransformation and primary target of drug-induced toxicity, were investigated. Methods: DNA replication was measured using [methyl-3H]-thymidine incorporation. Cell cycle markers were analyzed by Western and Northern blottings. Necrosis and apoptosis were monitored by LDH release, caspase-3-activation, respectively. Results: We identified two distinct cell cycle arrests, prior DNA replication, in two experimental conditions. First, perfusion of the liver in presence of TSA, prevented c-jun and cyclin D1 induction, characteristic for G1 entry and progression through late G1, respectively. Secondly, TSA treatment of isolated hepatocytes, located in early G1, led to an early S-phase arrest evidenced by the absence of the S/G2/M marker, CDK1. TSA upregulated the expression of the anti-apoptotic protein BclxL and did not increase caspase-3-activity and LDH release. Conclusions: TSA inhibits hepatocyte proliferation at different steps of the cell cycle. Our data suggest that this inhibition may involve downregulation of distinct subsets of genes. TSA does not induce apoptosis in primary hepatocytes, in contrast to what has been observed in hepatoma cells. This finding supports its use in the treatment of proliferative disorders.