INHIBITION OF AUTOPHAGY ABROGATES TUMOR-NECROSIS-FACTOR-ALPHA INDUCEDAPOPTOSIS IN HUMAN T-LYMPHOBLASTIC LEUKEMIC-CELLS

The pattern and the sequence of tumour necrosis factor-alpha (TNF alph a) induced cell death in the acute T-lymphoblastic leukaemic cell line CCRF-CEM and its vinblastine-resistant subline CEM/VLB100 have been s tudied. Previously, we found that the CEM/VLB100 cell line was more se nsitive to TNF alpha-induced killing than its parental CCRF-CEM cell l ine. TNF alpha-induced cell death showed an apoptotic pattern, as dete cted by agarose electrophoresis, flow cytometry and transmission elect ron microscopy (TEM). TEM images revealed that autophagy and condensed mitochondria occurred earlier than nuclear fragmentation. The specifi c inhibitor of autophagy, 3-methyladenine (3MA), inhibited the formati on of autophagosomes. TNF alpha-induced DNA fragmentation and cytolysi s were completely inhibited by 10 mM 3MA. Inhibition of the fusion of lysosomes with autophagosomes by asparagine did not block TNF alpha-in duced apoptosis. In addition, amino acid and protein deprivation enhan ced TNF alpha-induced autophagy but not apoptosis. We propose that the early stages of autophagy are required for, but do not necessarily re sult in, TNF alpha-induced apoptosis.