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TNFα induces survival through the FLIP-L-dependent activation of the MAPK/ERK pathway
F Marques-Fernandez1, L Planells-Ferrer, R Gozzelino
1Cell Signaling and Apoptosis Group, Fundació Institut de recerca de l'Hospital Universitari de la Vall d'Hebron, Edifici Collserola, Laboratori 203, Passeig Vall d'Hebron 119-129, 08035 Barcelona, Spain.
Abstract:
Activation of tumor necrosis factor receptor-1 can trigger survival or apoptosis pathways. In many cellular models, including the neuronal cell model PC12, it has been demonstrated that inhibition of protein synthesis is sufficient to render cells sensitive to apoptosis induced by TNFα. The survival effect is linked to the translocation of the transcription factor nuclear factor-kappa B (NF-κB) to the nucleus and activation of survival-related genes such as FLICE-like inhibitory protein long form (FLIP-L) or IAPs. Nonetheless, we previously reported an NF-κB-independent contribution of Bcl-xL to cell survival after TNFα treatment. Here, we demonstrate that NF-κB-induced increase in FLIP-L expression levels is essential for mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) activation. We demonstrate that FLIP-L behaves as a Raf-1 activator through both protein-protein interaction and Raf-1 kinase activation, without the requirement of the classical Ras activation. Importantly, prevention of FLIP-L increase by NF-κB inhibition or knockdown of endogenous FLIP-L blocks MAPK/ERK activation after TNFα treatment. From a functional point of view, we show that inhibition of the MAPK/ERK pathway and the NF-κB pathway are equally relevant to render PC12 cells sensitive to cell death induced by TNFα. Apoptosis induced by TNFα under these conditions is dependent on jun nuclear kinase1/2 JNK1/2-dependent Bim upregulation. Therefore, we report a previously undescribed and essential role for MAPK/ERK activation by FLIP-L in the decision between cell survival and apoptosis upon TNFα stimulation.
Insights
Tumor necrosis factor alpha (TNFα) triggers cell survival via nuclear factor-kappa B (NF-κB) and FLICE-like inhibitory protein long form (FLIP-L). FLIP-L activates MAPK/ERK, crucial for cell survival decisions.
Area of Science:
- Cellular biology
- Molecular signaling
- Apoptosis and cell survival pathways
Background:
- Tumor necrosis factor receptor-1 (TNFR1) activation can lead to either cell survival or apoptosis.
- Nuclear factor-kappa B (NF-κB) activation and subsequent gene expression (e.g., FLIP-L, IAPs) promote cell survival.
- Previous work indicated an NF-κB-independent role for Bcl-xL in TNFα-mediated survival.
Purpose of the Study:
- To elucidate the role of FLICE-like inhibitory protein long form (FLIP-L) in TNFα-induced cell survival pathways.
- To investigate the connection between NF-κB, FLIP-L, and mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) activation.
- To determine the functional significance of FLIP-L and MAPK/ERK in the TNFα-mediated cell fate decision.
Main Methods:
- Utilized the PC12 neuronal cell model.
- Investigated protein-protein interactions and kinase activation involving FLIP-L and Raf-1.
- Employed NF-κB inhibition and FLIP-L knockdown strategies.
- Analyzed the impact of pathway inhibition on apoptosis induction and Bim upregulation.
Main Results:
- NF-κB-dependent increase in FLIP-L expression is essential for TNFα-induced MAPK/ERK activation.
- FLIP-L directly activates Raf-1 kinase, independent of classical Ras activation.
- Inhibition of NF-κB or FLIP-L knockdown blocks MAPK/ERK activation following TNFα treatment.
- Both NF-κB and MAPK/ERK pathways are critical for rendering PC12 cells sensitive to TNFα-induced death.
- TNFα-induced apoptosis, under these conditions, relies on jun nuclear kinase (JNK)-dependent Bim upregulation.
Conclusions:
- FLIP-L plays a previously unrecognized, essential role in activating the MAPK/ERK pathway upon TNFα stimulation.
- FLIP-L acts as a key mediator linking NF-κB signaling to MAPK/ERK activation, influencing cell survival versus apoptosis.
- This study reveals a novel mechanism governing the cell fate decision in response to TNFα.
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