Mixed lineage kinase domain-like protein is a prognostic biomarker for cervical squamous cell cancer

Background: The mixed lineage kinase domain-like protein (MLKL) has recently been identified as a key RIP3 (receptor interacting protein 3) downstream component of tumor necrosis factor (TNF)-induced necroptosis. Objective: To evaluate the expression and clinical significance of MLKL in cervical squamous cell carcinoma.Methods: The expression of MLKL in 54 cervical squamous carcinoma samples was detected by immuneohistochemical method. Chi-square, correlation analysis and kaplan-Meier method were used to analyze the data. Results: The MLKL expression in cervical squamous cell carcinoma was higher than that in normal cervical tissues (P = 0.004). The MLKL expression was negatively correlated with histological grade, lymphatic metastasis (P<0.05). Survival analysis showed the low expression of MLKL indicated poor prognosis. Conclusion: MLKL was a prognostic biomarker for cervical squamous cell carcinoma.     

Smac mimetics and TRAIL cooperate to induce MLKL-dependent necroptosis in Burkitt's lymphoma cell lines

Burkitt''s lymphoma (BL) is a highly aggressive form of B-cell non-Hodgkin''s lymphoma. The clinical outcome in children with BL has improved over the last years but the prognosis for adults is still poor, highlighting the need for novel treatment strategies. Here, we report that the combinational treatment with the Smac mimetic BV6 and TRAIL triggers necroptosis in BL when caspases are blocked by zVAD.fmk (TBZ treatment). The sensitivity of BL cells to TBZ correlates with MLKL expression. We demonstrate that necroptotic signaling critically depends on MLKL, since siRNA-induced knockdown and CRISPR/Cas9-mediated knockout of MLKL profoundly protect BL cells from TBZ-induced necroptosis. Conversely, MLKL overexpression in cell lines expressing low levels of MLKL leads to necroptosis induction, which can be rescued by pharmacological inhibitors, highlighting the important role of MLKL for necroptosis execution. Importantly, the methylation status analysis of the MLKL promoter reveals a correlation between methylation and MLKL expression. Thus, MLKL is epigenetically regulated in BL and might serve as a prognostic marker for treatment success of necroptosis-based therapies. These findings have crucial implications for the development of new treatment options for BL.     

Recent Advances in Pathology: the 2019 Annual Review Issue of The Journal of Pathology

In this Annual Review Issue of The Journal of Pathology, we present 15 invited reviews on topical aspects of pathology, ranging from the impacts of the microbiome in human disease through mechanisms of cell death and autophagy to recent advances in immunity and the uses of genomics for understanding, classifying and treating human cancers. Each of the reviews is authored by experts in their fields and our intention is to provide comprehensive updates in specific areas of pathology in which there has been considerable recent progress. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

程序性细胞坏死参与急慢性损伤脑内神经元死亡的研究进展

 程序性细胞坏死是一种新发现的细胞死亡形式。这类死亡细胞形态类似坏死,而其死亡过程受胞内主动机制的调节,由此改变了坏死细胞不受内在机制调控的经典概念。当细胞膜上死亡受体与其配体结合,细胞内凋亡因子caspase-8被抑制时,激活受体相互作用蛋白（receptor interaction protein,RIPK1/RIPK3）激酶及关键底物——混合谱系激酶结构域样蛋白（mixed lineage kinase domain-like protein,MLKL）的信号通路,从而触发细胞发生程序性细胞坏死。后者参与多种疾病的病理过程,如肿瘤、免疫炎症、神经退行性疾病、脑缺血损伤等。本文就程序性细胞坏死的信号通路、重要调控分子及在神经损伤相关疾病致病机制进行综述,并对研究方法和分析工具药物进行了归纳总结。     

Protective action of ultrasound-guided intraparenchymal transplantation of BMSCs in adriamycin nephropathy rats through the RIPK3/MLKL and NLRP3 pathways

BackgroundBone marrow stromal cells (BMSCs) are an effective new strategy for the treatment of kidney diseases. At present, noninvasive and efficient transplantation approaches to homing BMSCs to the renal parenchyma is still a serious challenge. The aim of this study was to investigate the feasibility and potential mechanism of ultrasound-guided intraparenchymal transplantation of BMSCs for the treatment of adriamycin nephropathy (AN) in rats.Materials and methodsA rat AN model was induced by 2 injections of doxorubicin. The rats were randomly divided into 4 groups (n = 10 animals in each group) : normal group (N group, no treatment), control medium group (CM group, transplant medium 1.0 mL), adriamycin nephropathy group (ADR group, phosphate buffered saline 1.0 mL), or BMSCs group (BMSCs fluid 1.0 mL). Intraparenchymal injection was completed under ultrasound guidance. After 4 weeks of treatment, blood samples were collected for serum biochemical measurements and ELISAs. The kidneys were removed for histopathological examination, electron microscopy, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL), and western blot analysis.ResultsNo deaths occurred in any group after BMSCs transplantation through the renal parenchyma under ultrasound guidance. Compared with the N and CM groups, in the ADR group, blood serum creatinine (SCr), blood urea nitrogen (BUN) and urine albumin (ALb) were higher, glomerular and tubular dilatation was observed, the number of apoptotic cells was higher, and the protein levels of receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like protein (MLKL) and nucleotide leukin-rich polypeptide 3 (NLRP3), key components of pathways in rat kidney, were significantly higher. Compared with those in the ADR group, the levels of SCr, BUN, ALb and serum proinflammatory cytokines in the BMSCs group were lower, the pathological structure of the kidney was improved, the number of apoptotic cells was lower, and the levels of RIPK3/MLKL and NLRP3 were significantly lower.ConclusionUltrasound-guided intraparenchymal transplantation of BMSCs regulated the RIPK3/MLKL and NLRP3 pathways in a minimally invasive and safe manner, thereby inhibiting renal necrosis and inflammation and playing a protective role in rat AN.     

坏死性凋亡调控机制及其在肿瘤病理机制中的作用

坏死性凋亡是非caspase依赖的程序性细胞死亡形式,由受体相互作用蛋白激酶1/3(receptor interacting protein kinase 1/3,RIPK1/3)和混合连接激酶结构域样蛋白(mixed lineage kinase domain-like protein,MLKL)介导,具有与坏死相同的形态学特征。坏死性凋亡在肿瘤病理机制中具有双重作用,可以补偿性清除和杀灭凋亡耐受的肿瘤细胞,发挥抑制肿瘤效应;也可以通过激发肿瘤微环境炎症反应,促进肿瘤发生发展、侵袭转移。本文综述了坏死性凋亡的调控机制及其在肿瘤发生进展的生物学效应和病理学意义。     

Cell-specific activation of RIPK1 and MLKL after intracerebral hemorrhage in mice

Receptor-interacting protein kinase-1 (RIPK1) is a master regulator of cell death and inflammation, and mediates programmed necrosis (necroptosis) via mixed-lineage kinase like (MLKL) protein. Prior studies in experimental intracerebral hemorrhage (ICH) implicated RIPK1 in the pathogenesis of neuronal death and cognitive outcome, but the relevant cell types involved and potential role of necroptosis remain unexplored. In mice subjected to autologous blood ICH, early RIPK1 activation was observed in neurons, endothelium and pericytes, but not in astrocytes. MLKL activation was detected in astrocytes and neurons but not endothelium or pericytes. Compared with WT controls, RIPK1 kinase-dead (RIPK1^D138N/D138N) mice had reduced brain edema (24 h) and blood-brain barrier (BBB) permeability (24 h, 30 d), and improved postinjury rotarod performance. Mice deficient in MLKL (Mlkl^-/-) had reduced neuronal death (24 h) and BBB permeability at 24 h but not 30d, and improved post-injury rotarod performance vs. WT. The data support a central role for RIPK1 in the pathogenesis of ICH, including cell death, edema, BBB permeability, and motor deficits. These effects may be mediated in part through the activation of MLKL-dependent necroptosis in neurons. The data support development of RIPK1 kinase inhibitors as therapeutic agents for human ICH.     

RIP3: a molecular switch for necrosis and inflammation

The receptor-interacting protein kinase 3 (RIP3/RIPK3) has emerged as a critical regulator of programmed necrosis/necroptosis, an inflammatory form of cell death with important functions in pathogen-induced and sterile inflammation. RIP3 activation is tightly regulated by phosphorylation, ubiquitination, and caspase-mediated cleavage. These post-translational modifications coordinately regulate the assembly of a macromolecular signaling complex termed the necrosome. Recently, several reports indicate that RIP3 can promote inflammation independent of its pronecrotic activity. Here, we review our current understanding of the mechanisms that drive RIP3-dependent necrosis and its role in different inflammatory diseases.     

Direct activation of RIP3/MLKL-dependent necrosis by herpes simplex virus 1 (HSV-1) protein ICP6 triggers host antiviral defense

The receptor-interacting kinase-3 (RIP3) and its downstream substrate mixed lineage kinase domain-like protein (MLKL) have emerged as the key cellular components in programmed necrotic cell death. Receptors for the cytokines of tumor necrosis factor (TNF) family and Toll-like receptors (TLR) 3 and 4 are able to activate RIP3 through receptor-interacting kinase-1 and Toll/IL-1 receptor domain-containing adapter inducing IFN-β, respectively. This form of cell death has been implicated in the host-defense system. However, the molecular mechanisms that drive the activation of RIP3 by a variety of pathogens, other than the above-mentioned receptors, are largely unknown. Here, we report that human herpes simplex virus 1 (HSV-1) infection triggers RIP3-dependent necrosis. This process requires MLKL but is independent of TNF receptor, TLR3, cylindromatosis, and host RIP homotypic interaction motif-containing protein DNA-dependent activator of IFN regulatory factor. After HSV-1 infection, the viral ribonucleotide reductase large subunit (ICP6) interacts with RIP3. The formation of the ICP6–RIP3 complex requires the RHIM domains of both proteins. An HSV-1 ICP6 deletion mutant failed to cause effective necrosis of HSV-1–infected cells. Furthermore, ectopic expression of ICP6, but not RHIM mutant ICP6, directly activated RIP3/MLKL-mediated necrosis. Mice lacking RIP3 exhibited severely impaired control of HSV-1 replication and pathogenesis. Therefore, this study reveals a previously uncharacterized host antipathogen mechanism.Cell death triggered by pathogens is a crucial component of mammalian host-defense system. Apoptosis, a predominant programmed cell death in mammals, functions as an effective host-defense mechanism for preventing pathogen replication. Apoptosis is initiated by either mitochondria or cell-death receptors, and it is executed by a group of cysteine proteases called caspases (1). The apoptotic pathway can be subverted by pathogen-encoded apoptotic suppressors such as caspase inhibitors (2). Recent studies have revealed that caspase inhibition can lead to alternative activation of necrosis, releasing the damage-associated molecular patterns (DAMPs) signal to trigger the activation of the host immune system (3, 4).Cytokines of the TNF family are classical inducers of programmed necrosis that are morphologically characterized by the swelling of intracellular organelles and disrupted plasma membranes. Programmed necrosis triggered by death cytokines such as TNF, also known as necroptosis (5–7), is tightly regulated by receptor-interacting kinase-1 (RIP1) (8), its deubiquitin enzyme cylindromatosis (CYLD) (9), and receptor-interacting kinase-3 (RIP3) (10–12). The RIP homotypic interaction motif (RHIM) domains of RIP1 and RIP3 are required for the formation of the RIP1–RIP3 complex that is called a necrosome (13). Recently, mixed lineage kinase domain-like (MLKL) protein has been identified as a functional substrate of RIP3 kinase (14, 15). Upon phosphorylation, MLKL forms oligomers, and these oligomers translocate to both the plasma and the intracellular membranes to elicit necrosis (16–18).Additionally, Toll-like receptor (TLR) ligands activate programmed necrosis through the RHIM-dependent formation of the Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF/TICAM-1)–RIP3 complex (19). A recent study demonstrated that RIP1 is dispensable for TLR3-induced necrosis in fibroblasts (20). Furthermore, the RHIM-containing protein DAI forms a complex with RIP3 (DAI–RIP3 complex) to mediate programmed necrosis that is induced by the mutant murine cytomegalovirus (MCMV), a process that is independent of RIP1 (21, 22). Therefore, RIP3 and MLKL constitute the core biochemical executioners in necrotic cell death, which is activated by the specific recognition of a particular RHIM-containing protein.RIP3-dependent necrosis has been implicated in host defenses against invading pathogens. Vaccinia virus (VV), which encodes caspase inhibitor B13R (23, 24), has been shown to sensitize mouse embryonic fibroblasts (MEFs) to TNF-α–induced necroptosis (11). Upon VV infection, both RIP3 and TNF receptor knockout mice showed reduced inflammation and necrosis, suggesting the involvement of necroptosis in the host defenses against VV (11). In the case of MCMV infection, the virus encodes a potent RHIM-containing protein, M45/vIRA, which is capable of forming an interaction with RIP3, thus preventing RIP3 from receiving a necrotic signal mediated by a host protein named DNA-dependent activator of IFN regulatory factor (DAI) (21, 22). Although these observations suggest that programmed necrosis can function as part of host defense, the molecular mechanisms that drive the activation of RIP3-dependent necrosis by pathogens remain largely unknown.Herpes simplex virus 1 (HSV-1) is a common human pathogen that infects around 80% of adults. HSV-1 is able to establish a latent infection in sensory neurons that lasts for the entire life of the host (25). The virus uses multiple receptors for successful infection in a variety of cell types, including MEFs. Studies in animal models and in humans have shown that HSV-1 infection is not only the major cause of severe herpes infections on the mouth and lips, but also an important cause of fatal sporadic encephalitis (25, 26). In the current study, we report that HSV-1 infection triggers RIP3/MLKL-dependent necrosis via an RHIM-containing viral ribonucleotide reductase large subunit (ICP6). Ectopic expression of ICP6 directly activates RIP3/MLKL-mediated necrosis in a RHIM-dependent manner. Importantly, RIP3^−/− mice showed defective control of viral replication and pathogenesis. Thus, our work provides, to our knowledge, the first evidence that the direct activation of RIP3-dependent necrosis through a pathogen-encoded RHIM-containing protein acts as a host-defensive mechanism.     

An emerging role of neutrophils and NETosis in chronic inflammation and fibrosis in systemic lupus erythematosus (SLE) and ANCA-associated vasculitides (AAV): Implications for the pathogenesis and treatment

Neutrophils derive from hematopoietic stem cells (HSCs) with systemic inflammation driving their activation and differentiation to myeloid progenitors to ensure enhanced myelopoiesis. Epigenetic reprograming and re-education of these HSCs produces neutrophils primed towards elimination of pathogens and increased inflammatory response. Neutrophils -an important component of acute inflammation- are not present in chronic inflammatory tissues leading to the false assumption that they may not be as important for the latter. Activated neutrophils may release Neutrophil Extracellular Traps (NETs) during a distinct form of cell death, named NETosis; NETs are rich in bioactive molecules that promote thrombosis (including atherothrombosis), inflammation and fibrosis. Thus, although neutrophils may not be present in chronic inflammatory lesions, their remnants may amplify the inflammatory response beyond their short life-span in the tissues. Herein, we review current evidence supporting a role of neutrophils and NETosis in tissue injury and dysfunction in systemic autoimmunity using as disease paradigms Systemic Lupus Erythematosus (SLE) and the ANCA-associated vasculitides (AAV). We also discuss the mechanisms involved and their potential as targets for novel therapy and drug repositioning.