Taxol-mediated augmentation of CD95 ligand-induced apoptosis of human malignant glioma cells: association with bcl-2 phosphorylation but neither activation of p53 nor G2/M cell cycle arrest

Abstract

Summary The anti-tumour alkaloid taxol shows strong cytotoxic and antiproliferative activity in two human malignant glioma cell lines, T98G and LN-229. CD95 (Fas/APO-1) ligand is a novel cytotoxic cytokine of the tumour necrosis factor (TNF) family that exerts prominent antiglioma activity. At clinically relevant taxol concentrations of 5-100 nM, taxol and CD95 ligand showed significant synergistic cytotoxicity and growth inhibition. High concentrations of taxol induced G/M cell cycle arrest in both cell lines. The synergy of taxol and CD95 ligand was independent of cell cycle effects of taxol as synergy was achieved at much lower taxol concentrations than G/M arrest and as cell cycle effects of taxol were unaffected by co-exposure to CD95 ligand. Similarly, high concentrations of taxol were required to induce p53 activity in the p53 wild-type cell line LN-229. This effect was not modulated by CD95 ligand, suggesting that synergy is also independent of p53 activation. However, taxol induced a mobility shift of the bcl-2 protein on immunoblot analysis, indicative of bcl-2 phosphorylation. Bcl-2 phosphorylation on serine was confirmed by immunoprecipitation and phosphoserine immunoblot analysis. Considering (1) that phosphorylation of bcl-2 interferes with its heterodimerization with bax and (2) the inhibition of CD95-mediated apoptosis by bcl-2, we propose that taxol sensitizes malignant glioma cells to CD95 ligand by increasing the functional bax/bcl-2 rheostat in favour of bax and thus cell death.

Fas mediated apoptosis of human Jurkat T-cells: intracellular events and potentiation by redox-active α-lipoic acid

“…Previously chemotherapeutic agents such as doxuribicin and vincristine, and the alkaloid taxol have been shown to facilitate Fas mediated cell death. 2,33 Doxorubicin, vincristine and taxol are anti-tumor drugs that are used for cancer therapy. At high concentrations these agents per se are toxic to cells.…”

Death receptor-independent cytochrome c release and caspase activation mediate thymidine kinase plus ganciclovir-mediated cytotoxicity in LN-18 and LN-229 human malignant glioma cells

“…Synergy was determined by isobologram analysis, 23 as described previously. 24 The non-infected and TK-infected cells were treated with different concentrations of each agent (GCV or cytotoxic drug) alone or with two agents in combination. The relative survival was assessed and the EC 50 values (median effect dosis) for each drug administered alone, or in combination with a fixed concentration of the second agent, were established from the concentrationeffect curves.…”

Secreted Frizzled-related proteins inhibit motility and promote growth of human malignant glioma cells

“…The glioma cells were maintained as described (Roth et al, 1998). Doubling times were determined during logarithmic growth in 24-well plates.…”

“…At day 9, the colonies were counted by an inverted microscope after staining with crystal violet. Acute cytotoxic cell death assays were performed as described (Roth et al, 1998). Glioma cells stably expressing human sFRP-1 or mouse sFRP-2 were obtained by lipofection with SuperFect (Qiagen, Hilden, Germany) using the hSARP2-pcDNA3 and the mSARP1-pcDNA3 plasmids (Melkonyan et al, 1997).…”