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Diverse TNFalpha-induced death pathways are enhanced by inhibition of NF-kappaB
Mukta Katdare1, Elena V Efimova, Edwardine Labay
1Department of Surgery, Section of General Surgery, University of Chicago Hospitals, Chicago, IL 60637, USA.
Abstract:
TNFalpha was initially described as inducing necrotic death in tumors in vivo, and more recently as a cytokine that mediates cytoprotection and inflammation. The anti-tumor effects of TNFalpha are poorly characterized because TNFalpha-induced death of human tumor cells has largely been studied in the presence of agents that block transcription or protein synthesis. Also, most reports in model cell systems describe apoptosis within relatively early time points as the principal mode of cell death induced by TNFalpha. We investigated the cytotoxic effects of 10 ng/ml TNFalpha on human tumor cells of different histological types without concomitant exposure to these inhibitors. Eleven of 21 human tumor cell lines underwent TNFalpha-induced cell death which ranged from 41% to complete loss of viability. Only one cell line demonstrated caspase-dependent apoptosis within 24 h. Nine cell lines underwent death between 48 h and 21 days. Seven of these lines underwent caspase-3 independent death consistent with necrosis. One tumor line exhibited characteristics of senescence following TNFalpha exposure. Nine of 9 cell lines activated NF-kappaB following TNFalpha exposure by 24 h. In all cell lines studied, with the exception of the epidermoid carcinoma cell line that underwent early apoptosis, expression of one or more NF-kappaB target genes was demonstrated at 24-96 h. BMS-345541, a specific IKK inhibitor, increased TNFalpha killing in TNFalpha resistant tumor cell lines by increasing apoptosis, suggesting that inhibition of NF-kappaB may be an effective strategy to enhance the tumoricidal effects of TNFalpha.
Insights
Tumor necrosis factor-alpha (TNFalpha) can kill various human tumor cells through necrosis and apoptosis. Inhibiting NF-kappaB enhances TNFalpha
Area of Science:
- Oncology
- Immunology
- Cell Biology
Background:
- Tumor necrosis factor-alpha (TNFalpha) is a cytokine with dual roles in cytoprotection, inflammation, and tumor cell death.
- Previous studies on TNFalpha's anti-tumor effects were limited by the use of transcription/protein synthesis inhibitors and focused on early apoptosis.
- The precise mechanisms and diverse outcomes of TNFalpha-induced tumor cell death remain incompletely understood.
Purpose of the Study:
- To investigate the cytotoxic effects of TNFalpha on diverse human tumor cell lines without confounding inhibitors.
- To characterize the modes of cell death (apoptosis, necrosis, senescence) induced by TNFalpha.
- To explore the role of NF-kappaB signaling in TNFalpha-mediated tumor cell killing.
Main Methods:
- Treatment of 21 human tumor cell lines with 10 ng/ml TNFalpha.
- Assessment of cell viability, apoptosis (caspase-dependent), necrosis (caspase-independent), and senescence.
- Analysis of NF-kappaB activation and target gene expression.
- Evaluation of an IKK inhibitor (BMS-345541) in combination with TNFalpha.
Main Results:
- TNFalpha induced significant cell death (41%-100%) in 11 of 21 tumor cell lines.
- Cell death occurred through apoptosis (1 line), necrosis (7 lines), or senescence (1 line) over various time points (24h to 21 days).
- NF-kappaB was activated in all tested cell lines, with target gene expression observed in most lines; NF-kappaB inhibition enhanced TNFalpha-induced apoptosis.
Conclusions:
- TNFalpha exhibits potent, albeit variable, tumoricidal activity against human tumor cells, primarily through necrosis and delayed cell death mechanisms.
- NF-kappaB activation is a common response to TNFalpha, and its inhibition can sensitize resistant tumor cells to TNFalpha-mediated killing.
- Targeting NF-kappaB signaling presents a potential strategy to augment the anti-tumor efficacy of TNFalpha therapy.
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