TNFα induces survival through the FLIP-L-dependent activation of the MAPK/ERK pathway

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 TNF alpha. The survival effect is linked to the translocation of the transcription factor nuclear factor-kappa B (NF-kappa B) 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-kappa B-independent contribution of Bcl-xL to cell survival after TNF alpha treatment. Here, we demonstrate that NF-kappa B-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-kappa B inhibition or knockdown of endogenous FLIP-L blocks MAPK/ERK activation after TNF alpha treatment. From a functional point of view, we show that inhibition of the MAPK/ERK pathway and the NF-kappa B pathway are equally relevant to render PC12 cells sensitive to cell death induced by TNF alpha. Apoptosis induced by TNF alpha 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 TNF alpha stimulation. Cell Death and Disease (2013) 4, 493; doi:10.1038/cddis.2013.25; published online 14 February 2013