Akt Regulates TNFα Synthesis Downstream of RIP1 Kinase Activation during Necroptosis

Abstract

Necroptosis is a regulated form of necrotic cell death that has been implicated in the pathogenesis of various diseases including intestinal inflammation and systemic inflammatory response syndrome (SIRS). In this work, we investigated the signaling mechanisms controlled by the necroptosis mediator receptor interacting protein-1 (RIP1) kinase. We show that Akt kinase activity is critical for necroptosis in L929 cells and plays a key role in TNFα production. During necroptosis, Akt is activated in a RIP1 dependent fashion through its phosphorylation on Thr308. In L929 cells, this activation requires independent signaling inputs from both growth factors and RIP1. Akt controls necroptosis through downstream targeting of mammalian Target of Rapamycin complex 1 (mTORC1). Akt activity, mediated in part through mTORC1, links RIP1 to JNK activation and autocrine production of TNFα. In other cell types, such as mouse lung fibroblasts and macrophages, Akt exhibited control over necroptosis-associated TNFα production without contributing to cell death. Overall, our results provide new insights into the mechanism of necroptosis and the role of Akt kinase in both cell death and inflammatory regulation.

RIPK1 and RIPK3 Kinases Promote Cell-Death-Independent Inflammation by Toll-like Receptor 4

“…Similar to previous data in L929 cells (Christofferson et al, 2012; McNamara et al, 2013), silencing of cJun abrogated inflammatory responses induced by LPS with zVAD in BMDMs (Fig. S5C).…”

“…In contrast to the well-established roles for kinase activities of RIPK1 and RIPK3 in directing cell death, evidence also hints at the possibility for additional roles for RIPK1 and RIPK3 in the direct regulation of pro-inflammatory signaling (Christofferson et al, 2012; Lukens et al, 2013; McNamara et al, 2013; Wong et al, 2014). Among various inducers of RIPK1 and RIPK3, signaling by TLR3 and TLR4 members of the TLR family of Pattern Recognition Receptors (PRRs) in macrophages engages the RIPK1, RIPK3, and MLKL pathway directly in a manner that is dependent on the RHIM-containing adaptor protein TRIF in the presence of the pan-caspase inhibitor zVAD.fmk (zVAD) (He et al, 2011; Kaiser et al, 2013; Schworer et al, 2014).…”

Structure Guided Design of Potent and Selective Ponatinib-Based Hybrid Inhibitors for RIPK1

“…It has also been found to promote synthesis of TNFα at the mRNA level independent of cell death regulation (Biton and Ashkenazi, 2011; Christofferson et al, 2012; McNamara et al, 2013). This and other cell death-independent pro-inflammatory activities of RIPK1 kinase are also emerging as potentially clinically relevant targets.…”

Cucurbitacin E inhibits TNF-α-induced inflammatory cytokine production in human synoviocyte MH7A cells via suppression of PI3K/Akt/NF-κB pathways

“…Akt kinase is specifically engaged in the signaling downstream from RIP1 kinase, which exerts its activity through promoting a selective increase in Akt phosphorylation of Thr308. TNF-α-triggered signaling also involved TRAF2-RIP-NIK-IKK or TRAF2-RIP-MEKK-IKK pathway [32]. Therefore, RIP1 is a multi-functional signal transducer involved in mediating NF-κB activation.…”