Paclitaxel (Taxol®)-induced apoptosis in human epithelioid sarcoma cell lines is enhanced by upregulation of CD95 ligand (FasL/Apo-1L)

Abstract

Metastasizing epithelioid sarcoma (ES) is an extremely aggressive tumor, because conventional chemotherapy and irradiation are largely ineffective. Here, we analyzed the impact of the CD95-mediated drug-induced apoptosis in ES cell lines. The effects of paclitaxel (Taxol) and 5-FU were determined by MTT assay. The extent of apoptosis was analyzed by light microscopy and Annexin V staining (flow cytometry). The expression of death receptors and ligands was defined by RT-PCR, Western blotting and flow cytometry. All cell lines expressed CD95, but not the CD95 ligand. The CD95 activation resulted in apoptosis and cell death in all cell lines. Both paclitaxel and 5-FU are able to trigger apoptosis, and furthermore, to upregulate CD95, whereas only paclitaxel increases CD95 ligand expression. Neutralizing antibodies directed against CD95 ligand effectively inhibited paclitaxel-induced cell death, thereby providing evidence for a direct involvement of the CD95 system in paclitaxel-induced apoptosis. Concomitant upregulation of CD95 receptor and ligand may significantly enhance the response of ES to anticancer drugs. As evident from the differential response of our clonal ES subpopulations to paclitaxel and 5-FU, effective activation of the CD95 system depends on intrinsic properties of both the chemotherapeutic agent and target cell population.