• apoptosis;
  • autophagy;
  • 3-methyladenine (3MA);
  • tumour necrosis factor α (TNFα);
  • transmission electron microscopy (TEM)

The pattern and the sequence of tumour necrosis factor-α (TNFα) induced cell death in the acute T-lymphoblastic leukaemic cell line CCRF-CEM and its vinblastine-resistant subline CEM/VLB100 have been studied. Previously, we found that the CEM/VLB100 cell line was more sensitive to TNFα-induced killing than its parental CCRF-CEM cell line. TNFα-induced cell death showed an apoptotic pattern, as detected by agarose electrophoresis, flow cytometry and transmission electron microscopy (TEM). TEM images revealed that autophagy and condensed mitochondria occurred earlier than nuclear fragmentation. The specific inhibitor of autophagy, 3-methyladenine (3MA), inhibited the formation of autophagosomes. TNFα-induced DNA fragmentation and cytolysis were completely inhibited by 10 mM 3MA. Inhibition of the fusion of lysosomes with autophagosomes by asparagine did not block TNFα-induced apoptosis. In addition, amino acid and protein deprivation enhanced TNFα-induced autophagy but not apoptosis. We propose that the early stages of autophagy are required for, but do not necessarily result in, TNFα-induced apoptosis.