ABSTRACT
In this report we show that mithramycin considerably increases the direct cytotoxic effect of tumour necrosis factor (TNF) on tumour cells in vitro. Sensitisation to TNF-induced apoptosis was prevented by the broad caspase inhibitor zVAD-fmk, whereas overexpression of Bcl-2 had no effect. Mithramycin also potentiated cell death induced by Fas agonistic antibodies. In contrast, mithramycin reduced the percentage of cells undergoing apoptosis due to factor withdrawal. TNF-induced activation of NF-kappaB (NF-kappaB)-dependent gene expression was not modulated by mithramycin treatment. Concomitantly with the increased sensitivity, the protein level of the short-spliced cFLIP variant was downregulated. These results indicate that mithramycin enhances TNF-induced cell death in an NF-kappaB-independent manner, and suggest that the Fas-associated death domain protein plays a crucial role in the TNF-sensitising effect of mithramycin.
Subject(s)
Adaptor Proteins, Signal Transducing , Apoptosis/drug effects , Carrier Proteins/pharmacology , Plicamycin/analogs & derivatives , Plicamycin/pharmacology , Tumor Necrosis Factor-alpha/pharmacology , Drug Resistance, Neoplasm , Fas-Associated Death Domain Protein , Gene Expression Regulation, Neoplastic/drug effects , Humans , Leukemia, Erythroblastic, Acute/pathology , Leukemia, Promyelocytic, Acute/pathology , Tumor Cells, Cultured , fas ReceptorABSTRACT
Resistance genes allow plants to recognize specific pathogens. Recognition results in the activation of a variety of defence responses, including localized programmed cell death (the hypersensitive response), synthesis of pathogenesis-related proteins and induction of systemic acquired resistance. These responses are co-ordinated by a branching signal transduction pathway. In tobacco, one branch activates virus resistance, and might require the mitochondrial alternative oxidase to operate. Here we discuss the evidence for this virus-specific branch of the transduction pathway and assess what must be done to further understand virus resistance and the role of the alternative oxidase in its induction.