MK2 phosphorylation of RIPK1 regulates TNF-mediated cell death

Abstract

TNF is a master proinflammatory cytokine whose pathogenic role in inflammatory disorders can, in certain conditions, be attributed to RIPK1 kinase-dependent cell death. Survival, however, is the default response of most cells to TNF stimulation, indicating that cell demise is normally actively repressed and that specific checkpoints must be turned off for cell death to proceed. We identified RIPK1 as a direct substrate of MK2 in the TNFR1 signalling pathway. Phosphorylation of RIPK1 by MK2 limits cytosolic activation of RIPK1 and the subsequent assembly of the death complex that drives RIPK1 kinase-dependent apoptosis and necroptosis. In line with these in vitro findings, MK2 inactivation greatly sensitizes mice to the cytotoxic effects of TNF in an acute model of sterile shock caused by RIPK1-dependent cell death. In conclusion, we identified MK2-mediated RIPK1 phosphorylation as an important molecular mechanism limiting the sensitivity of the cells to the cytotoxic effects of TNF.

3‐O‐acetylrubianol C (3AR‐C) induces RIPK1‐dependent programmed cell death by selective inhibition of IKKβ

“…In complex‐I, ligation of TNFR1 induces various types of RIPK1 ubiquitination, which plays an essential role in recruiting the IKKs (IKKα/β/NEMO) and subsequent transcriptional induction of NF‐κB‐dependent pro‐survival genes including c‐FLIP, A20, and cIAP2 . In addition, transient phosphorylation of RIPK1 at Ser 25 by IKKs prevents its dissociation from complex‐I, and suppresses its Ser 166 ‐autophosphorylation‐dependent association with FADD to initiate formation of complex‐II/necrosome which functions as transcription‐independent players in TNF‐induced cell death . The kinase activity of RIPK1 is required for activation of RIPK3 that plays an essential role in necroptosis induction .…”

“…[6][7][8]48 In addition, transient phosphorylation of RIPK1 at Ser 25 by IKKs prevents its dissociation from complex-I, and suppresses its Ser 166 -autophosphorylationdependent association with FADD to initiate formation of complex-II/necrosome which functions as transcription-independent players in TNF-induced cell death. 18,22,49,50 The kinase activity of RIPK1 is required for activation of RIPK3 that plays an essential role in necroptosis induction. 14,15 Thus, discovery of small molecules regulating RIPK1 phosphorylation provides a basic research tool and substantiates the overall importance of early cell death checkpoint controlling apoptosis and necroptosis.…”

“…Subsequent biochemical analyses revealed that RIPK1 phosphorylation on Ser 321 or Ser 25 by TAK1 or IKKα/β in complex‐I prevented the RIPK1‐mediated assembly of the complex‐II/necrosome and then inhibited apoptosis/necroptosis in an NF‐κB‐independent manner . Furthermore, it has been proposed that MAPK‐activated protein kinase 2 (MK2) also induces RIPK1 phosphorylation in complex‐I and protects against complex‐II‐mediated cell death . It is now believed that RIPK1 phosphorylation by upstream kinases acts as an early cell death checkpoint to control the cytotoxic potential of TNF.…”

“…20,21 Furthermore, it has been proposed that MAPK-activated protein kinase 2 (MK2) also induces RIPK1 phosphorylation in complex-I and protects against complex-II-mediated cell death. [22][23][24] It is now believed that RIPK1 phosphorylation by upstream kinases acts as an early cell death checkpoint to control the cytotoxic potential of TNF. Thus, development of pharmacological agents targeting RIPK1 phosphorylation may provide a novel strategy to promote the therapeutic efficacy of TNF in cancers and inflammatory diseases.…”

Differentiated macrophages acquire a pro-inflammatory and cell death–resistant phenotype due to increasing XIAP and p38-mediated inhibition of RipK1

“…In contrast, during ripoptosome signaling in myeloid leukemia cells, p38MAPK has been shown to inhibit TNF expression, and inhibition of MK2 results in enhanced cell death of leukemia cells (59). It was subsequently shown that MK2 mediates an inhibitory phosphorylation of RipK1, which restricts ripoptosome induced cell death (60)(61)(62). Our results indicate that the phosphorylation of RipK1 in macrophages is dependent on MK2, and inhibition of MK2 results in augmentation of ripoptosome induced cell death, particularly on day 12 macrophages.…”