Signalling steps in apoptosis by ether lipids

We have investigated the mechanisms of induction of apoptosis by the antine oplastic ether lipid ET-18-OCH3 (ALP) in sensitive S49(wt) mouse lymphoma c ells and ALP-resistant S49(ar) variants, both with wild-type p53, and in re lated L1210 cells with mutated p53. Ether lipid-resistant S49(ar) cells wer e cross-resistant to extracellular stress factors (cold shock, heat shock, H2O2, dimethylsulfoxide) and to radiation-induced apoptosis but not to phys iological apoptotic signals (dexamethasone, growth factor deprivation, thap sigargin, C-2-ceramide) and expressed similar levels of the apoptosis-regul ating proteins Bcl-2, Bcl-X, Bax, Bad and Bak as did the parent S49(wt) cel ls. The uptake of [H-3]-ALP was strongly reduced in the stress-resistant ce lls but this was not associated with significant differences in membrane ch olesterol:phospholipid content nor in membrane microviscosity. In S49(ar) c ells the activity of the antioxidant enzyme glutathione peroxidase (GSH-Px) was increased 4-fold and depletion of glutathione with the drug L-buthioni ne-S-R-sulfoximine (L-BSO) lowered the resistance of S49(ar) cells to ALP, stress factors and ionising radiation. The results indicate that ether lipi ds induce apoptosis by imposing a special form of physico-chemical stress, mediated by reactive oxygen species but independent of p53 status. The capa city of glutathione-dependent anti-oxidant defence appeared an important an d shared determinant of the sensitivity to ether lipids, several types of e xtracellular stress and ionising radiation.