P60-c-src suppresses apoptosis through inhibition of caspase 8 activation in hepatoma cells, but not in primary hepatocytes

Background/Aims Failure to induce apoptosis triggered by members of the death receptor family has been described in hepatocellular carcinoma (HCC) and sensitization of malignant cells to pro-apoptotic molecules such as TRAIL has been proposed as an alternative cancer therapy. Limiting to this approach are the resistance of many tumor cells to TRAIL and safety concerns about the toxicity of TRAIL in normal hepatocytes. Methods We here explored the possibility that the protooncogene c-Src, known to be overexpressed in a variety of tumors, could be specifically responsible for the loss of response to receptor-mediated apoptosis. Results Cotreatment of several hepatoma cell lines with the Src inhibitor PP2 potently sensitized these cells to TRAIL and CD95, dramatically decreasing effective doses of TRAIL to as low as 1 ng/ml. Remarkably, Src-inhibition did not synergize with TRAIL signaling in primary hepatocytes. Specific siRNAs showed that the effect was due to blockade of p60c-Src and occurred through increased recruitment of caspase 8. Conclusions We provide evidence that p60c-Src is an important and effective suppressor of receptor-mediated apoptosis in hepatoma cells but not in primary human hepatocytes. Inhibition of Src sensitizes tumor cells to apoptosis and decreases effective doses of TRAIL to therapeutic concentrations.