Phospholipases are activated during cell destruction by human alpha-lymphotoxin in vitro

These studies investigate the molecular mechanism of destruction of transformed cells induced by recombinant human alpha-lymphotoxin (LT) in vitro. They focus on steps subsequent to binding of LT to specific plasma membrane receptors. L929 cell membrane phospholipids were prelabelled with 14C arachidonic acid and then the cells were treated with lethal levels of LT. We found 14C labelled fatty acids were released into the media soon after LT treatment and levels continued to climb as cells were destroyed. At various time intervals lipid extracts of these same cell cultures were made and separated by thin layer chromatography. Autoradiography revealed that LT-treated cells contain increased levels of free fatty acids first detectable at 4-6 hrs after LT treatment and the levels continued to rise through 21 hrs. Untreated cultures and cultures killed by alternate methods did not show elevated free fatty acid levels in either the media or intracellularly. These results indicate that cellular phospholipases are activated when LT-induced cell destruction occurs and that this activation does not occur when cells are killed by various other methods.