In vivo role of RIPK1 in the regulation of the murine intestinal epithelium

Rezeptor-interagierendes Protein Kinase 1 (RIPK1) ist involviert in Signalkaskaden die Zelltod und Entzündungen regulieren. RIPK1 reguliert NF-κB Aktivierung, interagiert mit RIPK3 um Nekroptose zu steuern und vermittelt Apoptose in einer RIP1 Kinase Aktivität abhängigen Art und Weise. Das intestinale Epithel ist eine einzellige Schicht, die den luminalen Inhalt von sub-epithelien Immunzellen separiert. Um Gewebehomöostase und die intestinale Barriereintegrität zu gewährleisten, muss der Zelltod von intestinalen Epithelzellen streng reguliert sein. Die in vivo Funktion von RIPK1 für die Regulierung von Zelltod und Homöostase in Epithelgewebe ist weitgehend unbekannt. Um die Funktion von RIPK1 im intestinalen Epithel zu studieren wurde das Cre-loxP System benutzt um Mäuse zu generieren, die defizitär für RIPK1 spezifisch in intestinalen Epithelzellen sind. Mäuse mit einer IEZ-spezifischen RIPK1 Deletion (RIPK1IEZ-KO) zeigten erhöhte IEZ Apoptose begleitet von Villus Atrophie, Krypt Hyperproliferation und eine milde Entzündung im Kolon und Ileum, was zu einem frühzeitigem Tod innerhalb des ersten Lebensmonat führte. Die intestinal Pathologie war teilweise abhängig von TNFR1-vermittelter Signalübertragung aber entwickelte sich unabhängig von der Microbiota und der MyD88-abhängigen Signalübertragung. Epithelzellpezifische Deletion von FADD verhinderte IEZ Apoptose, aber RIPK1IEZ-KO/FADDIEZ-KO Doppelknockout Mäuse zeigten IEZ Nekroptose und entwickelten Colitis ulcerosa. Zusätzliche Deletierung von RIPK3 verhinderte intestinale Entzündung und IEZ Nekroptose, was darauf hindeutet, dass IEZs in RIPK1IEZ-KO/FADDIEZ-KO Mäusen durch RIPK1-unabhängige RIPK3-abhängige Nekroptose starben. Daher besitzt RIPK3-vermittelte Nekroptose in IEZs eine höhere Immunogenizität als FADD-vermittelte Apoptose. RIPK1-defizitäre IEZs zeigten den Abbau von den überlebensfördernden Proteinen TRAF2, cIAP1 und cFLIP, was direkt mit dem Tod von IEZs assoziiert sein könnte. Zusammenfassend, die Ergebnisse in dieser Arbeit offenbaren eine neue gerüstartige Funktion von RIPK1 für die Regulation von intestinaler Homöostase durch die Verhinderung von FADD-vermittelter Apoptose

Molecular and in vivo Functions of the CDK8 and CDK19 Kinase Modules

CDK8 and its paralog, CDK19, collectively termed ‘Mediator Kinase,’ are cyclin-dependent kinases that have been implicated as key rheostats in cellular homeostasis and developmental programming. CDK8 and CDK19 are incorporated, in a mutually exclusive manner, as part of a 4-protein complex called the Mediator kinase module. This module reversibly associates with the Mediator, a 26 subunit protein complex that regulates RNA Polymerase II mediated gene expression. As part of this complex, the Mediator kinases have been implicated in diverse process such as developmental signaling, metabolic homeostasis and in innate immunity. In recent years, dysregulation of Mediator kinase module proteins, including CDK8/19, has been implicated in the development of different human diseases, and in particular cancer. This has led to intense efforts to understand how CDK8/19 regulate diverse biological outputs and develop Mediator kinase inhibitors that can be exploited therapeutically. Herein, we review both context and function of the Mediator kinases at a molecular, cellular and animal level. In so doing, we illuminate emerging concepts underpinning Mediator kinase biology and highlight certain aspects that remain unsolved

NEMO Prevents RIP Kinase 1-Mediated Epithelial Cell Death and Chronic Intestinal Inflammation by NF-kappaB-Dependent and -Independent Functions

Intestinal epithelial cells (IECs) regulate gut immune homeostasis, and impaired epithelial responses are implicated in the pathogenesis of inflammatory bowel diseases (IBD). IEC-specific ablation of nuclear factor kappaB (NF-kappaB) essential modulator (NEMO) caused Paneth cell apoptosis and impaired antimicrobial factor expression in the ileum, as well as colonocyte apoptosis and microbiota-driven chronic inflammation in the colon. Combined RelA, c-Rel, and RelB deficiency in IECs caused Paneth cell apoptosis but not colitis, suggesting that NEMO prevents colon inflammation by NF-kappaB-independent functions. Inhibition of receptor-interacting protein kinase 1 (RIPK1) kinase activity or combined deficiency of Fas-associated via death domain protein (FADD) and RIPK3 prevented epithelial cell death, Paneth cell loss, and colitis development in mice with epithelial NEMO deficiency. Therefore, NEMO prevents intestinal inflammation by inhibiting RIPK1 kinase activity-mediated IEC death, suggesting that RIPK1 inhibitors could be effective in the treatment of colitis in patients with NEMO mutations and possibly in IBD

Zhongguo-tianran-yaowu : = Chinese journal of natural medicines

Receptor-interacting protein kinase (RIPK) 1 functions as a key mediator of tissue homeostasis via formation of Caspase-8 activating ripoptosome complexes, positively and negatively regulating apoptosis, necroptosis, and inflammation. Here, we report an unanticipated cell-death-and inflammation- independent function of RIPK1 and Caspase-8, promoting faithful chromosome alignment in mitosis and thereby ensuring genome stability. We find that ripoptosome complexes progressively form as cells enter mitosis, peaking at metaphase and disassembling as cells exit mitosis. Genetic deletion and mitosis-specific inhibition of Ripk1 or Caspase-8 results in chromosome alignment defects independently of MLKL. We found that Polo-like kinase 1 (PLK1) is recruited into mitotic ripoptosomes, where PLK1's activity is controlled via RIPK1-dependent recruitment and Caspase-8-mediated cleavage. A fine balance of ripoptosome assembly is required as deregulated ripoptosome activity modulates PLK1-dependent phosphorylation of downstream effectors, such as BUBR1. Our data suggest that ripoptosome-mediated regulation of PLK1 contributes to faithful chromosome segregation during mitosis

RIPK1 maintains epithelial homeostasis by inhibiting apoptosis and necroptosis

Necroptosis has emerged as an important pathway of programmed cell death in embryonic development, tissue homeostasis, immunity and inflammation(1-8). RIPK1 is implicated in inflammatory and cell death signalling(9-13) and its kinase activity is believed to drive RIPK3-mediated necroptosis(14,15). Here we show that kinase-independent scaffolding RIPK1 functions regulate homeostasis and prevent inflammation in barrier tissues by inhibiting epithelial cell apoptosis and necroptosis. Intestinal epithelial cell (IEC)-specific RIPK1 knockout caused IEC apoptosis, villus atrophy, loss of goblet and Paneth cells and premature death in mice. This pathology developed independently of the microbiota and of MyD88 signalling but was partly rescued by TNFR1 (also known as TNFRSF1A) deficiency. Epithelial FADD ablation inhibited IEC apoptosis and prevented the premature death of mice with IEC-specific RIPK1 knockout. However, mice lacking both RIPK1 and FADD in IECs displayed RIPK3-dependent IEC necroptosis, Paneth cell loss and focal erosive inflammatory lesions in the colon. Moreover, a RIPK1 kinase inactive knock-in delayed but did not prevent inflammation caused by FADD deficiency in IECs or keratinocytes, showing that RIPK3-dependent necroptosis of FADD-deficient epithelial cells only partly requires RIPK1 kinase activity. Epidermis-specific RIPK1 knockout triggered keratinocyte apoptosis and necroptosis and caused severe skin inflammation that was prevented by RIPK3 but not FADD deficiency. These findings revealed that RIPK1 inhibits RIPK3-mediated necroptosis in keratinocytes in vivo and identified necroptosis as a more potent trigger of inflammation compared with apoptosis. Therefore, RIPK1 is a master regulator of epithelial cell survival, homeostasis and inflammation in the intestine and the skin