Related Experiment Videos
Stimulus-dependent synergism of the antiapoptotic tumor necrosis factor receptor-associated factor 2 (TRAF2) and
S Y Lee1, D R Kaufman, A L Mora
1Department of Pathology, Hallym Medical School, Choonchun, Kangwon-do, 200-702, Korea.
Abstract:
Tumor necrosis factor (TNF) signaling leads to pleiotropic responses in a wide range of cell types, in part by activating antiapoptotic and proapoptotic signaling pathways. Thus, although TNF can cause apoptosis and may prove useful in the treatment of malignancies, most cells are resistant to TNF-induced cell death unless de novo protein synthesis is inhibited. Previous studies suggested that TNF activation of the nuclear factor (NF)-kappaB transcription factor family antagonizes the proapoptotic signals initiated by TNF-alpha. TNF receptor-associated factor (TRAF)2 has also been shown to mediate crucial antiapoptotic signals during TNF stimulation, yet is not essential in activation of NF-kappaB under physiologic conditions, thus raising questions about the relationship between these antiapoptotic pathways. We report here that inhibition of TRAF2 and NF-kappaB function in primary cells, by coexpression of a constitutive repressor of multiple NF-kappaB/Rel proteins (IkappaBalpha.DN) and a dominant negative form of TRAF2 (TRAF2.DN), synergistically enhanced TNF-induced apoptosis. The effects were stimulus dependent, such that neither inhibitory molecule affected Fas- and daunorubicin-induced apoptosis to the same degree as TNF-induced death. These findings indicate that the NF-kappaB and TRAF2 pathways activate independent antiapoptotic mechanisms which act in concert to suppress the proapoptotic signals induced by TNF-alpha.
Insights
Tumor necrosis factor (TNF) can induce cancer cell death, but cells are often resistant. Inhibiting nuclear factor-kappaB (NF-kappaB) and TNF receptor-associated factor 2 (TRAF2) pathways synergistically enhances TNF-induced apoptosis.
Area of Science:
- Cellular biology
- Molecular signaling
- Immunology
Background:
- Tumor necrosis factor (TNF) signaling triggers diverse cellular responses, including anti- and pro-apoptotic pathways.
- Most cells resist TNF-induced apoptosis unless protein synthesis is inhibited, suggesting complex regulatory mechanisms.
- Nuclear factor-kappaB (NF-kappaB) activation by TNF is thought to antagonize pro-apoptotic signals, while TNF receptor-associated factor 2 (TRAF2) also mediates anti-apoptotic signals.
Purpose of the Study:
- To investigate the relationship between NF-kappaB and TRAF2 in mediating anti-apoptotic signaling during TNF stimulation.
- To determine if these pathways act independently or dependently to suppress TNF-induced apoptosis.
- To elucidate the mechanisms underlying cellular resistance to TNF-alpha-induced cell death.
Main Methods:
- Coexpression of a constitutive repressor of NF-kappaB/Rel proteins (IkappaBalpha.DN) and a dominant-negative form of TRAF2 (TRAF2.DN) in primary cells.
- Assessment of the synergistic effect of inhibiting both pathways on TNF-induced apoptosis.
- Comparison of the effects of these inhibitors on apoptosis induced by other stimuli like Fas and daunorubicin.
Main Results:
- Inhibition of both TRAF2 and NF-kappaB function synergistically enhanced TNF-induced apoptosis in primary cells.
- The combined inhibition was more effective in sensitizing cells to TNF-induced death compared to Fas- or daunorubicin-induced apoptosis.
- Neither IkappaBalpha.DN nor TRAF2.DN alone significantly sensitized cells to TNF-induced apoptosis to the same extent as their combined inhibition.
Conclusions:
- The NF-kappaB and TRAF2 signaling pathways activate independent antiapoptotic mechanisms.
- These independent pathways function in concert to suppress the pro-apoptotic signals initiated by TNF-alpha.
- Targeting both NF-kappaB and TRAF2 may represent a strategy to overcome resistance to TNF-based cancer therapies.