Chapter Seven - The Inflammatory Signal Adaptor RIPK3: Functions Beyond Necroptosis

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Abstract

Receptor interacting protein kinase 3 (RIPK3) is an essential serine/threonine kinase for necroptosis, a type of regulated necrosis. A variety of stimuli can cause RIPK3 activation through phosphorylation. Activated RIPK3 in turn phosphorylates and activates the downstream necroptosis executioner mixed lineage kinase domain-like (MLKL). Necroptosis is a highly inflammatory type of cell death because of the release of intracellular immunogenic contents from disrupted plasma membrane. Indeed, RIPK3-deficient mice exhibited reduced inflammation in many inflammatory disease models. These results have been interpreted as evidence that necroptosis is a key driver for RIPK3-induced inflammation. Interestingly, recent studies show that RIPK3 also regulates NF-κB, inflammasome activation, and kinase-independent apoptosis. These studies also reveal that these nonnecroptotic functions contribute significantly to disease pathogenesis. In this review, we summarize our current understanding of necroptotic and nonnecroptotic functions of RIPK3 and discuss how these effects contribute to RIPK3-mediated inflammation.

Introduction

In pathology, the term necrosis is used to describe gross histological damage caused by cell death. It is defined at the cellular and morphological level by cell and organelle swelling and membrane rupture. On the other hand, the term apoptosis describes cell death marked by cellular shrinkage, chromatin condensation, and cellular fragmentation (Kerr et al., 1972). Although the different cell death modes were originally defined by morphology, we now know that they also exhibit distinct biological functions and are regulated by unique mechanisms. Genetic studies in Caenorhabditis elegans laid the foundation for discovery of numerous apopotosis genes and the signaling network that regulates it. These discoveries unveiled the important physiological roles of apoptosis in embryonic development (Ellis and Horvitz, 1986), immune homeostasis (Burger et al., 2014), and cancer (Hockenbery et al., 1990, Tsujimoto et al., 1985). In contrast, since necrotic cell death is often observed when cells are exposed to excessive physical or chemical stresses, it was considered to be an unprogrammed and accidental cell death. However, accumulating evidence shows that necrosis can in fact be induced by dedicated regulatory signaling pathways and thus the long-standing dogma that necrosis represents unregulated cell death is being challenged.

Necroptosis is a type of regulated necrosis which is controlled by receptor interacting protein kinase 3 (RIPK3) and its downstream effector mixed lineage kinase domain-like (MLKL) (Chan et al., 2014). Upon ligand binding, a variety of cell surface receptors, such as tumor necrosis factor (TNF) superfamily death receptors (Vercammen et al., 1998a, Vercammen et al., 1998b), toll-like receptors (TLRs) (He et al., 2011), interferon receptors (IFNRs) (Thapa et al., 2011, Thapa et al., 2013), and T-cell receptor (Ch’en et al., 2011, Lu et al., 2011, Osborn et al., 2010, Zhang et al., 2011), induce necroptosis through phosphorylation-driven activation of the RIPK3-MLKL signaling pathway. Germline Ripk3-deficient (Ripk3−/−) mice are widely used to examine the physiological functions of necroptosis. Many infectious and noninfectious inflammatory disease models were attenuated in Ripk3−/− mice (Chan et al., 2014). These observations bolster the premise that RIPK3 promotes the release of intracellular immunogenic contents through necroptosis to elicit inflammatory responses (Kaczmarek et al., 2013). However, recent evidence indicates that RIPK3 also exhibits necroptosis-independent functions and that the amelioration of inflammatory phenotypes in Ripk3−/− mice could at least in part be attributed to these nonnecroptotic signaling functions (Moriwaki and Chan, 2014). In this review, we summarize our current knowledge of how RIPK3 executes necrotic and nonnecrotic functions. We will also discuss how these distinct functions of RIPK3 cooperate to promote inflammation in physiology.

Section snippets

Phosphorylation-Driven Activation of RIPK3

RIPK3 is a cytosolic serine/threonine kinase that consists of an active kinase domain at the amino terminus (Moriwaki and Chan, 2013). Essential amino acids for enzymatic activity of typical protein kinases are conserved in RIPK3, including the catalytic triad (Lys50, Glu60, and Asp160 in human RIPK3) and the DFG motif (Asp160, Phe161, and Gly162 in human RIPK3). RIPK3 also carries a unique homotypic protein–protein interaction domain, called RIP homotypic interaction motif (RHIM), at the

Endogenous Necroptosis Inhibitory Proteins

Necrotic cell death is a highly inflammatory type of cell death due to the release of intracellular immunogenic content that stimulates innate immune cells and subsequently inflammation. As such, there are cellular mechanisms put in place to keep in check the potential deleterious effects of necroptosis. For instance, the initiator caspase, caspase 8, not only induces apoptosis, but also has a critical role in necroptosis inhibition by cleavage of the crucial necroptosis regulators RIPK1,

How Does RIPK3 Promote Inflammation?

The germline Ripk3−/− mice generated by Newton and Dixit have been instrumental in the study of physiological functions of RIPK3 and necroptosis over the years (Newton et al., 2004). Ripk3−/− mice exhibited reduced inflammatory phenotypes in viral infection models as well as sterile inflammatory diseases in the kidney (Linkermann et al., 2013), heart (Luedde et al., 2014, Zhang et al., 2016), blood vessel (Lin et al., 2013, Meng et al., 2015), pancreas (He et al., 2009), brain (Vitner et al.,

RIPK3 in NF-κB Activation

RIPK3 was originally identified as an RIPK1 binding protein with homology to RIPK1 and RIPK2, both of which were known NF-κB inducers (Sun et al., 1999, Yu et al., 1999). Similar to these other RIP kinase family members, early studies showed that overexpression of RIPK3 also alters NF-κB activation (Kasof et al., 2000, Meylan et al., 2004, Sun et al., 1999, Yu et al., 1999). However, the results were confusing since different studies have shown activating as well as inhibitory effects on NF-κB

Concluding Remarks

Genetic evidence has provided strong rationale that RIPK3 is a therapeutic target in treating various inflammatory diseases. Indeed, several types of RIPK3 inhibitors targeting its kinase activity have been reported in recent years (Fauster et al., 2015, Mandal et al., 2014, Najjar et al., 2015, Rodriguez et al., 2016). However, as we have discussed here, RIPK3 can promote inflammation independent of its kinase activity and necroptosis. Therefore, it will be important to determine which RIPK3

References (118)

  • H.M. Ellis et al.

    Genetic control of programmed cell death in the nematode C. elegans

    Cell

    (1986)
  • S. Feng et al.

    Cleavage of RIP3 inactivates its caspase-independent apoptosis pathway by removal of kinase domain

    Cell. Signal.

    (2007)
  • M. Feoktistova et al.

    cIAPs block Ripoptosome formation, a RIP1/caspase-8 containing intracellular cell death complex differentially regulated by cFLIP isoforms

    Mol. Cell

    (2011)
  • H. Guo et al.

    Herpes simplex virus suppresses necroptosis in human cells

    Cell Host Microbe

    (2015)
  • S. He et al.

    Receptor interacting protein kinase-3 determines cellular necrotic response to TNF-alpha

    Cell

    (2009)
  • Z. Huang et al.

    RIP1/RIP3 binding to HSV-1 ICP6 initiates necroptosis to restrict virus propagation in mice

    Cell Host Microbe

    (2015)
  • A. Kaczmarek et al.

    Necroptosis: the release of damage-associated molecular patterns and its physiological relevance

    Immunity

    (2013)
  • T.B. Kang et al.

    Caspase-8 blocks kinase RIPK3-mediated activation of the NLRP3 inflammasome

    Immunity

    (2013)
  • G.M. Kasof et al.

    The RIP-like kinase, RIP3, induces apoptosis and NF-kappaB nuclear translocation and localizes to mitochondria

    FEBS Lett.

    (2000)
  • J. Li et al.

    The RIP1/RIP3 necrosome forms a functional amyloid signaling complex required for programmed necrosis

    Cell

    (2012)
  • J. Lin et al.

    A role of RIP3-mediated macrophage necrosis in atherosclerosis development

    Cell Rep.

    (2013)
  • P. Mandal et al.

    RIP3 induces apoptosis independent of pronecrotic kinase activity

    Mol. Cell

    (2014)
  • K. Moriwaki et al.

    The necroptosis adaptor RIPK3 promotes injury-induced cytokine expression and tissue repair

    Immunity

    (2014)
  • K. Moriwaki et al.

    Necrosis-dependent and independent signaling of the RIP kinases in inflammation

    Cytokine Growth Factor Rev.

    (2014)
  • K. Moriwaki et al.

    Regulation of RIPK3 and RHIM-dependent necroptosis by the proteasome

    J. Biol. Chem.

    (2016)
  • M. Najjar et al.

    Structure guided design of potent and selective ponatinib-based hybrid inhibitors for RIPK1

    Cell Rep.

    (2015)
  • S. Omoto et al.

    Suppression of RIP3-dependent necroptosis by human cytomegalovirus

    J. Biol. Chem.

    (2015)
  • D. Panayotova-Dimitrova et al.

    cFLIP regulates skin homeostasis and protects against TNF-induced keratinocyte apoptosis

    Cell Rep.

    (2013)
  • T. Samuel et al.

    Distinct BIR domains of cIAP1 mediate binding to and ubiquitination of tumor necrosis factor receptor-associated factor 2 and second mitochondrial activator of caspases

    J. Biol. Chem.

    (2006)
  • X. Sun et al.

    RIP3, a novel apoptosis-inducing kinase

    J. Biol. Chem.

    (1999)
  • X. Sun et al.

    Identification of a novel homotypic interaction motif required for the phosphorylation of receptor-interacting protein (RIP) by RIP3

    J. Biol. Chem.

    (2002)
  • T. Tenev et al.

    The Ripoptosome, a signaling platform that assembles in response to genotoxic stress and loss of IAPs

    Mol. Cell

    (2011)
  • J.W. Upton et al.

    Staying alive: cell death in antiviral immunity

    Mol. Cell

    (2014)
  • J.W. Upton et al.

    Cytomegalovirus M45 cell death suppression requires receptor-interacting protein (RIP) homotypic interaction motif (RHIM)-dependent interaction with RIP1

    J. Biol. Chem.

    (2008)
  • J.W. Upton et al.

    Virus inhibition of RIP3-dependent necrosis

    Cell Host Microbe

    (2010)
  • J.W. Upton et al.

    DAI/ZBP1/DLM-1 complexes with RIP3 to mediate virus-induced programmed necrosis that is targeted by murine cytomegalovirus vIRA

    Cell Host Microbe

    (2012)
  • J.E. Vince et al.

    TRAF2 must bind to cellular inhibitors of apoptosis for tumor necrosis factor (tnf) to efficiently activate nf-{kappa}b and to prevent tnf-induced apoptosis

    J. Biol. Chem.

    (2009)
  • J.E. Vince et al.

    Inhibitor of apoptosis proteins limit RIP3 kinase-dependent interleukin-1 activation

    Immunity

    (2012)
  • M.B. Afonso et al.

    Necroptosis is a key pathogenic event in human and experimental murine models of non-alcoholic steatohepatitis

    Clin. Sci. (Lond.)

    (2015)
  • M.L. Burger et al.

    T cell-specific inhibition of multiple apoptotic pathways blocks negative selection and causes autoimmunity

    eLife

    (2014)
  • I.L. Ch’en et al.

    Mechanisms of necroptosis in T cells

    J. Exp. Med.

    (2011)
  • F.K. Chan et al.

    Programmed necrosis in the cross talk of cell death and inflammation

    Annu. Rev. Immunol.

    (2014)
  • L. Dara et al.

    Receptor interacting protein kinase 1 mediates murine acetaminophen toxicity independent of the necrosome and not through necroptosis

    Hepatology

    (2015)
  • A. Degterev et al.

    Identification of RIP1 kinase as a specific cellular target of necrostatins

    Nat. Chem. Biol.

    (2008)
  • A. Degterev et al.

    Chemical inhibitor of nonapoptotic cell death with therapeutic potential for ischemic brain injury

    Nat. Chem. Biol.

    (2005)
  • M. Deutsch et al.

    Divergent effects of RIP1 or RIP3 blockade in murine models of acute liver injury

    Cell Death Dis.

    (2015)
  • F. Dufour et al.

    The ribonucleotide reductase R1 subunits of herpes simplex virus types 1 and 2 protect cells against TNFalpha- and FasL-induced apoptosis by interacting with caspase-8

    Apoptosis

    (2011)
  • A. Fauster et al.

    A cellular screen identifies ponatinib and pazopanib as inhibitors of necroptosis

    Cell Death Dis.

    (2015)
  • J. Gautheron et al.

    A positive feedback loop between RIP3 and JNK controls non-alcoholic steatohepatitis

    EMBO Mol. Med.

    (2014)
  • B. Gerlach et al.

    Linear ubiquitination prevents inflammation and regulates immune signalling

    Nature

    (2011)
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      It is important to consider nocodazole-challenged cells with enhanced p-MLKL is likely not necroptotic death but rather an accumulation of intracellular p-MLKL that fails to translocate from the nucleus to other cellular compartments over time due to nocodazole-altered microtubule dynamic instability (38, 47). Notably, staurosporine inhibited p-MLKL signal at 4 and 24 h with signal recovery by 48 h (Fig. 3D), which may be the result of cross talk between apoptotic and necroptotic signaling pathways (48, 49). Jurkat and MV-4-11 were more sensitive to induction of apoptotic effector cCAS3 than necroptotic effector p-MLKL (Fig. S5) and reflect cell type–specific responses with respect to leukemia subtypes.

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