Abstract
Receptor interacting protein kinase 1 (RIPK1) regulates cell death and inflammatory responses downstream of TNFR1 and other receptors, and has been implicated in the pathogenesis of inflammatory and degenerative diseases. RIPK1 kinase activity induces apoptosis and necroptosis, however the mechanisms and phosphorylation events regulating RIPK1-dependent cell death signaling remain poorly understood. Here we show that RIPK1 autophosphorylation at serine 166 plays a critical role for the activation of RIPK1 kinase-dependent apoptosis and necroptosis. Moreover, we show that S166 phosphorylation is required for RIPK1 kinase-dependent pathogenesis of inflammatory pathologies in vivo in four relevant mouse models. Mechanistically, we provide evidence that trans autophosphorylation at S166 modulates RIPK1 kinase activation but is not by itself sufficient to induce cell death. These results show that S166 autophosphorylation licenses RIPK1 kinase activity to induce downstream cell death signaling and inflammation, suggesting that S166 phosphorylation can serve as a reliable biomarker for RIPK1 kinase-dependent pathologies.
Highlights
Receptor interacting protein kinase 1 (RIPK1) regulates cell death and inflammatory responses downstream of tumor necrosis factor receptor 1 (TNFR1) and other receptors, and has been implicated in the pathogenesis of inflammatory and degenerative diseases
Ripk1S166A/S166A mice were born at the expected Mendelian frequency and reached adulthood without showing signs of pathology, demonstrating that inhibition of RIPK1 phosphorylation at S166 does not interfere with normal mouse development and homeostasis under steady state conditions
These results suggest that the S166A mutation did not affect the scaffolding functions of RIPK1 that regulate proinflammatory signaling and tissue homeostasis
Summary
Receptor interacting protein kinase 1 (RIPK1) regulates cell death and inflammatory responses downstream of TNFR1 and other receptors, and has been implicated in the pathogenesis of inflammatory and degenerative diseases. RIPK1 kinase activity emerged as driver of ischemic injury[18,19,20] as well as neurodegenerative diseases such as multiple sclerosis (MS)[21], ALS (amyotrophic lateral sclerosis)[22] and Alzheimer’s disease[23] These studies identified RIPK1 kinase activity as a key factor contributing to the pathogenesis of inflammatory diseases, prompting the development of RIPK1 kinase inhibitors[24,25,26,27,28] that reached clinical trials for the treatment of inflammatory and neurodegenerative diseases as well as pancreatic cancer[24,25]. (MK2), transforming growth factor beta activating kinase 1 (TAK1), as well as TANK-binding kinase 1 (TBK1) and IKKε, limits TNF-induced RIPK1 kinase-dependent cell death and inflammation in vitro and in vivo[22,29,30,31,32,33,34,35] These results revealed that RIPK1 kinase activity is tightly controlled by a multitude of mechanisms, consistent with its strong cytotoxic potential
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