Inhibition of autophagy abrogates tumour necrosis factor alpha induced apoptosis in human T-lymphoblastic leukaemic cells

Abstract

The pattern and the sequence of tumour necrosis factor-alpha (TNF alpha) 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 TNF alpha-induced killing than its parental CCRF-CEM cell line. TNF alpha-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 codensed mitochondria occurred earlier than nuclear fragmentation. The specific inhibitor of autophagy, 3-methyladenine (3MA), inhibited the formation of autophagosomes. TNF alpha-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 TNF alpha-induced apoptosis. In addition, amino acid and protein deprivation enhanced TNF alpha-induced autophagy but not apoptosis. We propose that the early stages of autophagy are required for, but do not necessarily result in, TNF alpha-induced apoptosis.