RIP1 Kinase Is an Oncogenic Driver in Melanoma

Necroptosis in human cancers with special emphasis on oral squamous cell carcinoma

Necroptosis is a type of caspase independent 'programmed or regulated' necrotic cell death that has a morphological resemblance to necrosis and mechanistic analogy to apoptosis. This type of cell death requires RIPK1, RIPK3, MLKL, death receptors, toll like receptors, interferons, and various other proteins. Necroptosis is implicated in plethora of diseases like rheumatoid arthritis, Alzheimer's disease, Crohn's disease, and head and neck cancers including oral squamous cell carcinoma. Oral carcinomas show dysregulation or mutation of necroptotic proteins, mediate antitumoral immunity, activate immune response and control tumor progression. Necroptosis is known to play a dual role (pro tumorigenic and anti-tumorigenic) in cancer progression and targeting this pathway could be an effective approach in cancer therapy. Necroptosis based chemotherapy has been proposed in malignancies, highlighting the importance of necroptotic pathway to overcome apoptosis resistance and serve as a "fail-safe" pathway to modulate cancer initiation, progression, and metastasis. However, there is dearth of information regarding the use of necroptotic cell death mechanism in the treatment of oral squamous cell carcinoma. In this review, we summarise molecular mechanism of necroptosis, and its protumorigenic and antitumorigenic role in cancers to shed light on the possible therapeutic significance of necroptosis in oral squamous cell carcinoma.

Identification and validation of a novel necroptosis-related molecular signature to evaluate prognosis and immune features in breast cancer

Necroptosis has been shown to play an important role in the development of tumors. However, the characteristics of the necroptosis-related subtypes and the associated immune cell infiltration in the tumor microenvironment (TME) of breast cancer (BRCA) remain unclear. In this study, we identified three clusters related to necroptosis using the expression patterns of necroptosis-relevant genes (NRGs), and found that these three clusters had different clinicopathological features, prognosis and immune cell infiltration in the TME. Cluster 2 was characterized by less infiltration of immune cells in the TME and was associated with a worse prognosis. Then, a necroptosis risk score (NRS) composed of 14 NRGs was constructed using the least absolute shrinkage and selection operator regression (LASSO) Cox regression method. Based on NRS, all BRCA patients in the TCGA datasets were classified into a low-risk group and a high-risk group. Patients in the low-risk group were characterized by longer overall survival (OS), lower mutation burden, and higher infiltration level of immune cells in the TME. Moreover, the NRS was significantly associated with chemotherapeutic drug sensitivity. Finally, the knockdown of VDAC1 reduced the proliferation and migration of BRCA cells, and promoted cell death induced by necroptosis inducer. This study identified a novel necroptosis-related subtype of BRCA, and a comprehensive analysis of NRGs in BRCA revealed its potential roles in prognosis, clinicopathological features, TME, chemotherapy, tumor proliferation, and tumor necroptosis. These results may improve our understanding of NRGs in BRCA and provide a reference for developing individualized therapeutic strategies.

Roles of RIPK1 as a stress sentinel coordinating cell survival and immunogenic cell death

Cell death and inflammation are closely linked arms of the innate immune response to combat infection and tissue malfunction. Recent advancements in our understanding of the intricate signals originating from dying cells have revealed that cell death serves as more than just an end point. It facilitates the exchange of information between the dying cell and cells of the tissue microenvironment, particularly immune cells, alerting and recruiting them to the site of disturbance. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is emerging as a critical stress sentinel that functions as a molecular switch, governing cellular survival, inflammatory responses and immunogenic cell death signalling. Its tight regulation involves multiple layers of post-translational modifications. In this Review, we discuss the molecular mechanisms that regulate RIPK1 to maintain homeostasis and cellular survival in healthy cells, yet drive cell death in a context-dependent manner. We address how RIPK1 mutations or aberrant regulation is associated with inflammatory and autoimmune disorders and cancer. Moreover, we tease apart what is known about catalytic and non-catalytic roles of RIPK1 and discuss the successes and pitfalls of current strategies that aim to target RIPK1 in the clinic.

A novel RIP1-mediated canonical WNT signaling pathway that promotes colorectal cancer metastasis via β -catenin stabilization-induced EMT

RIP1 (receptor-interacting protein kinase 1) is an important component of TNF-α signaling that contributes to various pathological effects. Here, we revealed new potential roles of RIP1 in controlling WNT/β-catenin canonical signaling to enhance metastasis of colorectal cancer (CRC). First, we showed that WNT3A treatment sequentially increased the expression of RIP1 and β-catenin. Immunohistochemical analyses of human CRC tissue arrays consisting of normal, primary, and metastatic cancers indicated that elevated RIP1 expression might be related to β-catenin expression, carcinogenesis, and metastasis. Intravenous injection of RIP1 over-expressed CRC cells into mice has demonstrated that RIP1 may promote metastasis. Immunoprecipitation (IP) results indicated that WNT3A treatment induces direct binding between RIP1 and β-catenin, and that this stabilizes the β-catenin protein in a manner that depends on the regulation of RIP1 ubiquitination via downregulation of the E3 ligase, cIAP1/2. Elimination of cIAP1/2 expression and inhibition of its ubiquitinase activity enhance WNT3A-induced RIP1 and β-catenin protein expression and binding, which stimulates endothelial-mesenchymal transition (EMT) induction to enhance the migration and invasion of CRC cells in vitro. The results of the in vitro binding assay and IP of exogenous RIP1-containing CRC cells additionally verified the direct binding of RIP1 and β-catenin. RIP1 expression can destroy the β-catenin-β-TrCP complex. Taken together, these results suggest a novel EMT-enhancing role of RIP1 in the WNT pathway and suggest a new canonical WNT3A-RIP1-β-catenin pathway that contributes to CRC malignancy by promoting EMT.

Role of Receptor Interacting Protein (RIP) kinases in cancer

The Receptor Interacting Protein (RIP) kinase family consists of seven Serine/Threonine kinases, which plays a key signaling role in cell survival and cell death. Each RIP family member contains a conserved kinase domain and other domains that determine the specific kinase function through protein-protein interactions. RIP1 and RIP3 are best known for their critical roles in necroptosis, programmed necrosis and a non-apoptotic inflammatory cell death process. Dysregulation of RIP kinases contributes to a variety of pathogenic conditions such as inflammatory diseases, neurological diseases, and cancer. In cancer cells, alterations of RIP kinases at genetic, epigenetic and expression levels are frequently found, and suggested to promote tumor progression and metastasis, escape of antitumor immune response, and therapeutic resistance. However, RIP kinases can be either pro-tumor or anti-tumor depending on specific tumor types and cellular contexts. Therapeutic agents for targeting RIP kinases have been tested in clinical trials mainly for inflammatory diseases. Deregulated expression of these kinases in different types of cancer suggests that they represent attractive therapeutic targets. The focus of this review is to outline the role of RIP kinases in cancer, highlighting potential opportunities to manipulate these proteins in cancer treatment.

Bacterial-agglutinating and opsonic activities of RIPK1 in zebrafish

Many studies have demonstrated that receptor interacting protein kinase-1 acts as a crucial mediator in the regulation of immune response, but evidence remains lacking for its direct interaction with bacteria. In this study, we found that challenge with lipopolysaccharide and lipoteichoic acid resulted in a significantly increased transcriptional expression of receptor interacting protein kinase-1 in zebrafish, suggesting the receptor interacting protein kinase-1 is implicated in anti-infectious responses. In accordance, we found that recombinant receptor interacting protein kinase-1 was not only able to bind to Gram-negative and -positive bacteria via interaction with lipopolysaccharide and lipoteichoic acid, but also agglutinate both Gram-negative and -positive bacteria in a Ca²⁺-dependent manner.

Necroptosis: A Pathogenic Negotiator in Human Diseases

Over the past few decades, mechanisms of programmed cell death have attracted the scientific community because they are involved in diverse human diseases. Initially, apoptosis was considered as a crucial mechanistic pathway for programmed cell death; recently, an alternative regulated mode of cell death was identified, mimicking the features of both apoptosis and necrosis. Several lines of evidence have revealed that dysregulation of necroptosis leads to pathological diseases such as cancer, cardiovascular, lung, renal, hepatic, neurodegenerative, and inflammatory diseases. Regulated forms of necrosis are executed by death receptor ligands through the activation of receptor-interacting protein kinase (RIPK)-1/3 and mixed-lineage kinase domain-like (MLKL), resulting in the formation of a necrosome complex. Many papers based on genetic and pharmacological studies have shown that RIPKs and MLKL are the key regulatory effectors during the progression of multiple pathological diseases. This review focused on illuminating the mechanisms underlying necroptosis, the functions of necroptosis-associated proteins, and their influences on disease progression. We also discuss numerous natural and chemical compounds and novel targeted therapies that elicit beneficial roles of necroptotic cell death in malignant cells to bypass apoptosis and drug resistance and to provide suggestions for further research in this field.

Advances in RIPK1 kinase inhibitors

Programmed necrosis is a new modulated cell death mode with necrotizing morphological characteristics. Receptor interacting protein 1 (RIPK1) is a critical mediator of the programmed necrosis pathway that is involved in stroke, myocardial infarction, fatal systemic inflammatory response syndrome, Alzheimer's disease, and malignancy. At present, the reported inhibitors are divided into four categories. The first category is the type I ATP-competitive kinase inhibitors that targets the area occupied by the ATP adenylate ring; The second category is type Ⅱ ATP competitive kinase inhibitors targeting the DLG-out conformation of RIPK1; The third category is type Ⅲ kinase inhibitors that compete for binding to allosteric sites near ATP pockets; The last category is others. This paper reviews the structure, biological function, and recent research progress of receptor interaction protein-1 kinase inhibitors.

Emerging Role of Deubiquitinating Enzymes (DUBs) in Melanoma Pathogenesis

Metastatic melanoma is the leading cause of death from skin cancer. Therapies targeting the BRAF oncogenic pathway and immunotherapies show remarkable clinical efficacy. However, these treatments are limited to subgroups of patients and relapse is common. Overall, the majority of patients require additional treatments, justifying the development of new therapeutic strategies. Non-genetic and genetic alterations are considered to be important drivers of cellular adaptation mechanisms to current therapies and disease relapse. Importantly, modification of the overall proteome in response to non-genetic and genetic events supports major cellular changes that are required for the survival, proliferation, and migration of melanoma cells. However, the mechanisms underlying these adaptive responses remain to be investigated. The major contributor to proteome remodeling involves the ubiquitin pathway, ubiquitinating enzymes, and ubiquitin-specific proteases also known as DeUBiquitinases (DUBs). In this review, we summarize the current knowledge regarding the nature and roles of the DUBs recently identified in melanoma progression and therapeutic resistance and discuss their potential as novel sources of vulnerability for melanoma therapy.

[Autoinflammatory diseases associated with RIPK1 mutations: A review of the literature]

Autoinflammatory diseases related to RIPK1 mutations have been recently described. Two distinct clinical phenotypes have been reported and depend on the type and location of the mutation. When the mutation is recessive with loss of function, patients develop a combined phenotype of immune deficiency with recurrent bacterial and fungal infections and signs of early inflammatory bowel disease, non-erosive polyarthritis and growth retardation. On the other hand, when the mutation is dominant, gain of function, the manifestations are only auto-inflammatory with extensive lymphoproliferation, oral lesions such as aphthosis or ulcers, abdominal pain and hepatosplenomegaly. The mutations described for the dominant form affect only the cleavage site of caspase 8 and the clinical phenotype is called CRIA for Cleavage-Resistant RIPK1-Induced Autoinflammatory syndrome. The recessive form is severe and life-threatening requiring hematopoietic stem cell transplantation while the dominant form responds well to interleukin-6 receptor antagonists. Thus, RIPK1 mutations can induce various clinical manifestations with two distinct phenotypes. Although still rare, because of their recent description, these diseases can be suspected by an internist, in front of recurrent digestive features and will be increasingly diagnosed in the future through the integration of this gene in the diagnostic chips dedicated to autoinflammatory diseases and early inflammatory bowel diseases, using next generation sequencing.

Translational Value of Tumor-Associated Lymphangiogenesis in Cholangiocarcinoma

The prognosis of cholangiocarcinoma remains poor in spite of the advances in immunotherapy and molecular profiling, which has led to the identification of several targetable genetic alterations. Surgical procedures, including both liver resection and liver transplantation, still represent the treatment with the best curative potential, though the outcomes are significantly compromised by the early development of lymph node metastases. Progression of lymphatic metastasis from the primary tumor to tumor-draining lymph nodes is mediated by tumor-associated lymphangiogenesis, a topic largely overlooked until recently. Recent findings highlight tumor-associated lymphangiogenesis as paradigmatic of the role played by the tumor microenvironment in sustaining cholangiocarcinoma invasiveness and progression. This study reviews the current knowledge about the intercellular signaling and molecular mechanism of tumor-associated lymphangiogenesis in cholangiocarcinoma in the hope of identifying novel therapeutic targets to halt a process that often limits the success of the few available treatments.

MLKL deficiency in BrafV600EPten−/− melanoma model results in a modest delay of nevi development and reduced lymph node dissemination in male mice

Cancers acquire several capabilities to survive the multistep process in carcinogenesis. Resisting cell death is one of them. Silencing of the necroptosis initiator Ripk3 occurs in a wide variety of cancer types including melanoma. Little is known about the role of the necroptosis executioner MLKL in tumor development. Studies often indicate opposing roles for MLKL as a tumor-suppressing or a tumor-promoting protein. This study investigates the role of MLKL during melanoma initiation and progression using a tamoxifen-inducible melanoma mouse model driven by melanocyte-specific overexpression of mutated Braf and simultaneous deletion of Pten (Braf^V600EPten^−/−). In this model we observed a clear sex difference: melanoma initiation and progression were faster in females mice. Mlkl deficiency in male mice resulted in a modest but significant reduction of nevi growth rate compared to the littermate control. In these mice, infiltration and expansion of melanoma cells in the inguinal lymph node were also modestly decreased. This is likely to be a consequence of the delay in nevi development. No significant difference was observed in the Mlkl-deficient condition in female mice in which melanoma development was faster. Overall, our results indicate that in this genetic model MLKL has a minor role during melanoma initiation and progression.

Evaluation of the expression of necroptosis pathway mediators and its association with tumor characteristics in functional and non-functional pituitary adenomas

BACKGROUND

Pituitary adenomas impose a burden of morbidity on patients and characterizing the molecular mechanisms underlying its pathogenesis received remarkable attention. Despite the appealing role of necroptosis as an alternative cell death pathway in cancer pathogenesis, its relevance to pituitary adenoma pathogenesis has yet to be determined that is perused in the current study.

METHODS

The total number of 109 specimens including pituitary adenomas and cadaveric healthy pituitary tissues were enrolled in the current study. Tumor and healthy pituitary tissues were subjected to RNA extraction and gene analysis using Real-Time PCR. The expression levels of necroptosis markers (RIP1K, RIP3K and, MLKL) and their association with the patient's demographic features were evaluated, also the protein level of MLKL was assessed using immunohistochemistry in tissues.

RESULTS

Based on our data, the remarkable reduction in RIP3K and MLKL expression were detected in nonfunctional and GH-secreting pituitary tumors compared to pituitary normal tissues. Invasive tumors revealed lower expression of RIP3K and MLKL compared to non-invasive tumors, also the attenuated level of MLKL was associated with the tumor size in invasive NFPA. The simultaneous down-regulation of MLKL protein in pituitary adenoma tissues was observed which was in line with its gene expression. While, RIP1K over-expressed significantly in both types of pituitary tumors which showed no significant correlation with patient's age, gender and tumor size in GHPPA and NFPA group. Notably, MLKL and RIP3K gene expression was significantly correlated in the GHPPA group.

CONCLUSIONS

According to our data, the reduced expression of necroptosis mediators (RIP3K, MLKL) in pituitary adenoma reinforces the hypothesis that the necroptosis pathway can be effective in regulating the proliferation and growth of pituitary tumor cells and tumor recurrence.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

RIPK1 regulates cell function and death mediated by UVB radiation and TNF-α

The RIP family plays a key role in mediating cell inflammation, oxidative stress and death. Among them, RIPK1, as an important regulatory factor in the upstream of the NF-κB pathway, is involved in multiple pathways of cell inflammation and death. Epidermal cells constitute the outermost barrier of the human body. Radiation can induce epidermal cell death, inflammation and oxidative stress to cause damage. Therefore, this paper selected HaCaT cell and used CRISPR/Cas technology to construct a cell model of stable knockout of RIPK1 gene, to analyze the effect and regulation of RIPK1 knockout on the function and death of HaCaT cells induced by UVB or TNF-α. The results showed that knockout of RIPK1 had no significant effect on the morphology of HaCaT cells at rest, but it led to slowing cell proliferation and blocking the G2M phase of cell cycle. Compared with HaCaT^WT, HaCaT^RIP1KO was abnormally sensitive to TNF-α-induced cell death and apoptosis, and may be associated with inhibition of NF-κB pathway. Knocking out RIPK1 led to a more significant inhibition of cell growth by UVB, and up-regulation of the expression of the inflammatory factor IL-1α. P38 MAPK and NF-κB pathways may be involved this process. This study further found that RIPK1 in epidermal cell has a regulatory function on pro-survival signals.

RIP1 Perturbation Induces Chondrocyte Necroptosis and Promotes Osteoarthritis Pathogenesis via Targeting BMP7

Osteoarthritis (OA) is a highly prevalent and debilitating joint disorder that characterized by progressive destruction of articular cartilage. There is no effective disease-modifying therapy for the condition due to limited understanding of the molecular mechanisms on cartilage maintenance and destruction. Receptor-interacting protein kinase 1 (RIP1)-mediated necroptosis plays a vital role in various diseases, but the involvement of RIP1 in OA pathogenesis remains largely unknown. Here we show that typical necrotic cell morphology is observed within human OA cartilage samples in situ, and that RIP1 is significantly upregulated in cartilage from both OA patients and experimental OA rat models. Intra-articular RIP1 overexpression is sufficient to induce structural and functional defects of cartilage in rats, highlighting the crucial role of RIP1 during OA onset and progression by mediating chondrocyte necroptosis and disrupting extracellular matrix (ECM) metabolism homeostasis. Inhibition of RIP1 activity by its inhibitor necrostatin-1 protects the rats from trauma-induced cartilage degradation as well as limb pain. More importantly, we identify bone morphogenetic protein 7 (BMP7) as a novel downstream target that mediates RIP1-induced chondrocyte necroptosis and OA manifestations, thereby representing a non-canonical regulation mode of necroptosis. Our study supports a model whereby the activation of RIP1-BMP7 functional axis promotes chondrocyte necroptosis and subsequent OA pathogenesis, thus providing a new therapeutic target for OA.

RIPK1 contributes to cisplatin-induced apoptosis of esophageal squamous cell carcinoma cells via activation of JNK pathway

AIMS

Previous studies have uncovered the function of receptor-interacting protein kinase 1 (RIPK1) to mediate both cell survival and death. Moreover, RIPK1 modulates apoptosis and necroptosis depending on its activity, phosphorylation or ubiquitylation status. Many studies have explained the role or mechanism of RIPK1 in necroptosis. However, the role of RIPK1 has not been elucidated fully in human esophageal squamous cell carcinoma (ESCC) cells.

MATERIALS AND METHODS

The protein and mRNA expression levels of RIPK1 in a panel of ESCC cell lines by Western blot and real-time quantitative reverse transcription PCR (qRT-PCR) were analyzed. MTS assay was used to examine cellular proliferation, flow cytometric analysis to detect apoptosis, mitochondrial membrane potential and reactive oxygen species production. ESCC cells with either inhibitor or overexpressed RIPK1were analyzed to determine cell proliferation, colony formation and apoptosis. Flow cytometry and western blotting assays were used to explore the underlying mechanism.

KEY FINDINGS

In our study, RIPK1 expression was found to contribute significantly to cisplatin-induced apoptosis in the human ESCC cells. The reduced RIPK1 expression promoted cells proliferation and overexpressed RIPK1 facilitated cell apoptosis. Mechanistic investigations have revealed that the inhibition of proliferation for RIPK1 in ESCC cells was regulated via activation of c-Jun NH2-terminal kinase signaling. Additionally, damages were observed in the mitochondrial membrane, depletion of ATP and increased generation in reactive oxygen species.

SIGNIFICANCE

Our findings verified the evidence that RIPK1 can promote cell death in ESCC cells, with potential implications for activating c-Jun NH2-terminal kinase pathway as a novel approach to the disease.

Receptor-interacting protein kinase 1 is a key mediator in TLR3 ligand and Smac mimetic-induced cell death and suppresses TLR3 ligand-promoted invasion in cholangiocarcinoma

BACKGROUND

Toll-like receptor 3 (TLR3) ligand which activates TLR3 signaling induces both cancer cell death and activates anti-tumor immunity. However, TLR3 signaling can also harbor pro-tumorigenic consequences. Therefore, we examined the status of TLR3 in cholangiocarcinoma (CCA) cases to better understand TLR3 signaling and explore the potential therapeutic target in CCA.

METHODS

The expression of TLR3 and receptor-interacting protein kinase 1 (RIPK1) in primary CCA tissues was assayed by Immunohistochemical staining and their associations with clinicopathological characteristics and survival data were evaluated. The effects of TLR3 ligand, Poly(I:C) and Smac mimetic, an IAP antagonist on CCA cell death and invasion were determined by cell death detection methods and Transwell invasion assay, respectively. Both genetic and pharmacological inhibition of RIPK1, RIPK3 and MLKL and inhibitors targeting NF-κB and MAPK signaling were used to investigate the underlying mechanisms.

RESULTS

TLR3 was significantly higher expressed in tumor than adjacent normal tissues. We demonstrated in a panel of CCA cell lines that TLR3 was frequently expressed in CCA cell lines, but was not detected in a nontumor cholangiocyte. Subsequent in vitro study demonstrated that Poly(I:C) specifically induced CCA cell death, but only when cIAPs were removed by Smac mimetic. Cell death was also switched from apoptosis to necroptosis when caspases were inhibited in CCA cells-expressing RIPK3. In addition, RIPK1 was required for Poly(I:C) and Smac mimetic-induced apoptosis and necroptosis. Of particular interest, high TLR3 or low RIPK1 status in CCA patients was associated with more invasiveness. In vitro invasion demonstrated that Poly(I:C)-induced invasion through NF-κB and MAPK signaling. Furthermore, the loss of RIPK1 enhanced Poly(I:C)-induced invasion and ERK activation in vitro. Smac mimetic also reversed Poly(I:C)-induced invasion, partly mediated by RIPK1. Finally, a subgroup of patients with high TLR3 and high RIPK1 had a trend toward longer disease-free survival (p = 0.078, 28.0 months and 10.9 months).

CONCLUSION

RIPK1 plays a pivotal role in TLR3 ligand, Poly(I:C)-induced cell death when cIAPs activity was inhibited and loss of RIPK1 enhanced Poly(I:C)-induced invasion which was partially reversed by Smac mimetic. Our results suggested that TLR3 ligand in combination with Smac mimetic could provide therapeutic benefits to the patients with CCA. Video abstract.

A20 promotes melanoma progression via the activation of Akt pathway

Melanoma is the most life-threatening skin cancer with increasing incidence around the world. Although recent advances in targeted therapy and immunotherapy have brought revolutionary progress of the treatment outcome, the survival of patients with advanced melanoma remains unoptimistic, and metastatic melanoma is still an incurable disease. Therefore, to further understand the mechanism underlying melanoma pathogenesis could be helpful for developing novel therapeutic strategy. A20 is a crucial ubiquitin-editing enzyme implicated immunity regulation, inflammatory responses and cancer pathogenesis. Herein, we report that A20 played an oncogenic role in melanoma. We first found that the expression of A20 was significantly up-regulated in melanoma cell lines. Then, we showed that knockdown of A20 suppressed melanoma cell proliferation in vitro and melanoma growth in vivo through the regulation of cell-cycle progression. Moreover, A20 could potentiate the invasive and migratory capacities of melanoma cell in vitro and melanoma metastasis in vivo by promoting epithelial–mesenchymal transition (EMT). Mechanistically, we found that Akt activation mediated the oncogenic effect of A20 on melanoma development, with the involvement of glycolysis. What’s more, the up-regulation of A20 conferred the acquired resistance to Vemurafenib in BRAF-mutant melanoma. Taken together, we demonstrated that up-regulated A20 promoted melanoma progression via the activation of Akt pathway, and that A20 could be exploited as a potential therapeutic target for melanoma treatment.

RIP1 promotes proliferation through G2/M checkpoint progression and mediates cisplatin-induced apoptosis and necroptosis in human ovarian cancer cells

Receptor-interacting protein 1 (RIP1, also known as RIPK1) is not only a tumor-promoting factor in several cancers but also mediates either apoptosis or necroptosis in certain circumstances. In this study we investigated what role RIP1 plays in human ovarian cancer cells. We showed that knockout (KO) of RIP1 substantially suppressed cell proliferation, accompanied by the G2/M checkpoint arrest in two human ovarian cancer cell lines SKOV3 and A2780. On the other hand, RIP1 KO remarkably attenuated cisplatin-induced cytotoxicity, which was associated with reduction of the apoptosis markers PARP cleavage and the necroptosis marker phospho-MLKL. We found that RIP1 KO suppressed cisplatin-induced ROS accumulation in both SKOV3 and A2780 cells. ROS scavenger BHA, apoptosis inhibitor Z-VAD or necroptosis inhibitor NSA could effectively suppress cisplatin’s cytotoxicity in the control cells, suggesting that ROS-mediated apoptosis and necroptosis were involved in cisplatin-induced cell death. In addition, blocking necroptosis with MLKL siRNA effectively attenuated cisplatin-induced cytotoxicity. In human ovarian cancer A2780 cell line xenograft nude mice, RIP1 KO not only significantly suppressed the tumor growth but also greatly attenuated cisplatin’s anticancer activity. Our results demonstrate a dual role of RIP1 in human ovarian cancer: it acts as either a tumor-promoting factor to promote cancer cell proliferation or a tumor-suppressing factor to facilitate anticancer effects of chemotherapeutics such as cisplatin.

The Role of Necroptosis in ROS-Mediated Cancer Therapies and Its Promising Applications

Over the past decades, promising therapies targeting different signaling pathways have emerged. Among these pathways, apoptosis has been well investigated and targeted to design diverse chemotherapies. However, some patients are chemoresistant to these therapies due to compromised apoptotic cell death. Hence, exploring alternative treatments aimed at different mechanisms of cell death seems to be a potential strategy for bypassing impaired apoptotic cell death. Emerging evidence has shown that necroptosis, a caspase-independent form of cell death with features between apoptosis and necrosis, can overcome the predicament of drug resistance. Furthermore, previous studies have also indicated that there is a close correlation between necroptosis and reactive oxygen species (ROS); both necroptosis and ROS play significant roles both under human physiological conditions such as the regulation of inflammation and in cancer biology. Several small molecules used in experiments and clinical practice eliminate cancer cells via the modulation of ROS and necroptosis. The molecular mechanisms of these promising therapies are discussed in detail in this review.

Necroptosis in Immuno-Oncology and Cancer Immunotherapy

Immune-checkpoint blockers (ICBs) have revolutionized oncology and firmly established the subfield of immuno-oncology. Despite this renaissance, a subset of cancer patients remain unresponsive to ICBs due to widespread immuno-resistance. To "break" cancer cell-driven immuno-resistance, researchers have long floated the idea of therapeutically facilitating the immunogenicity of cancer cells by disrupting tumor-associated immuno-tolerance via conventional anticancer therapies. It is well appreciated that anticancer therapies causing immunogenic or inflammatory cell death are best positioned to productively activate anticancer immunity. A large proportion of studies have emphasized the importance of immunogenic apoptosis (i.e., immunogenic cell death or ICD); yet, it has also emerged that necroptosis, a programmed necrotic cell death pathway, can also be immunogenic. Emergence of a proficient immune profile for necroptosis has important implications for cancer because resistance to apoptosis is one of the major hallmarks of tumors. Putative immunogenic or inflammatory characteristics driven by necroptosis can be of great impact in immuno-oncology. However, as is typical for a highly complex and multi-factorial disease like cancer, a clear cause versus consensus relationship on the immunobiology of necroptosis in cancer cells has been tough to establish. In this review, we discuss the various aspects of necroptosis immunobiology with specific focus on immuno-oncology and cancer immunotherapy.

Smac mimetic promotes TNF-α to induce apoptosis of gallbladder carcinoma cells

Gallbladder carcinoma has a high degree of malignancy. No effective treatment exists for patients with advanced tumors. The second mitochondria-derived activator of caspases (Smac) is the antagonist of the inhibitors of apoptosis protein. Smac mimetics are a class of effective tumor-targeted drugs undergoing clinical trials. However, studies on the effect of Smac mimetics on gallbladder cancer are unavailable. In this study, Smac mimetics can promote tumor necrosis factor-α (TNF-α) to inhibit the proliferation of gallbladder cancer cells and activate the apoptotic pathway, thereby promoting the ubiquitination of Lys48 on Receptor interacting protein kinase-1 (RIPK1) and leading to proteasomal degradation that causes damage to RIPK1 protein integrity. The formation of complex I (RIPK1, tumor necrosis factor 1-associated death domain protein, and TNF receptor-associated factor 2) is inhibited. Then, nonubiquitinated RIPK1 binds with the Fas-associated death domain and caspase-8 to form complex II and promotes the death receptor pathway of apoptosis. Animal experiments further verify that TNF-α combined with Smac mimetics can inhibit the growth of transplanted tumors and induce the apoptosis of transplanted tumor cells. This research provides a new direction for the targeted therapy of gallbladder cancer.

Insight into the role of p62 in the cisplatin resistant mechanisms of ovarian cancer

Cisplatin is a platinum-based first-line drug for treating ovarian cancer. However, chemotherapy tolerance has limited the efficacy of cisplatin for ovarian cancer patients. Research has demonstrated that cisplatin causes changes in cell survival and death signaling pathways through its interaction with macromolecules and organelles, which indicates that investigation into the DNA off-target effects of cisplatin may provide critical insights into the mechanisms underlying drug resistance. The multifunctional protein p62 works as a signaling hub in the regulation of pro-survival transcriptional factors NF-κB and Nrf2 and connects autophagy and apoptotic signals, which play important roles in maintaining cell homeostasis. In this review, we discuss the role of p62 in cisplatin resistance by exploring p62-associated signaling pathways based on current studies and our work. Insights into these resistance mechanisms may lead to more effective therapeutic strategies for ovarian cancer by targeting p62.

TWEAK Promotes the Proliferation of Squamous Cell Carcinoma Cells Through Activating cIAP1 Signals

Recent studies showed that tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) induces the proliferation of squamous cell carcinoma (SCC) cells. However, the precise mechanism underlying such effect of TWEAK remains unclear. This study was designed to elucidate the role of cellular inhibitor of apoptosis 1 (cIAP1) in TWEAK-induced proliferation of SCC cells. Human SCC cells (SCC-13, A431, and SCC-9) were cultured in vitro, receiving the stimulation of TWEAK or TNF-related apoptosis-inducing ligand (TRAIL). We found that TWEAK induced cytoplasmic cIAP1 importation and RIP1 ubiquitination in cells, followed by the activation of canonical nuclear factor kappa B signals. MV1, a cIAP1 inhibitor, abrogated TWEAK-induced proliferation of these cells. Moreover, the interaction between TWEAK and its receptor, fibroblast growth factor-inducible 14 (Fn14), enhanced the expression of TRAIL receptor types 3 and 4 (TRAIL-R3/4). Furthermore, the transfection of TRAIL-R3/4 siRNA abrogated the promotion effect of TWEAK on SCC-13 cell proliferation and cIAP1 expression. Therefore, TWEAK/Fn14 interaction promotes the proliferation of SCC cells through activating cIAP1 signals. Targeting the downstream cIAP1 signals might attenuate the effect of TWEAK on SCC cells.

Cylindromatosis Is Required for Survival of a Subset of Melanoma Cells

The deubiquitinase cylindromatosis (CYLD) functions as a tumor suppressor inhibiting cell proliferation in many cancer types including melanoma. Here we present evidence that a proportion of melanoma cells are nonetheless addicted to CYLD for survival. The expression levels of CYLD varied widely in melanoma cell lines and melanomas in vivo, with a subset of melanoma cell lines and melanomas displaying even higher levels of CYLD than melanocyte lines and nevi, respectively. Strikingly, although short hairpin RNA (shRNA) knockdown of CYLD promoted, as anticipated, cell proliferation in some melanoma cell lines, it reduced cell viability in a fraction of melanoma cell lines with relatively high levels of CYLD expression and did not impinge on survival and proliferation in a third type of melanoma cell lines. The decrease in cell viability caused by CYLD knockdown was due to induction of apoptosis, as it was associated with activation of the caspase cascade and was abolished by treatment with a general caspase inhibitor. Mechanistic investigations demonstrated that induction of apoptosis by CYLD knockdown was caused by upregulation of receptor-interacting protein kinase 1 (RIPK1) that was associated with elevated K63-linked polyubiquitination of the protein, indicating that CYLD is critical for controlling RIPK1 expression in these cells. Of note, microRNA (miR) profiling showed that miR-99b-3p that was predicted to target the 3′-untranslated region (3′-UTR) of the CYLD mRNA was reduced in melanoma cell lines with high levels of CYLD compared with melanocyte lines. Further functional studies confirmed that the reduction in miR-99b-3p expression was responsible for the increased expression of CYLD in a highly cell line-specific manner. Taken together, these results reveal an unexpected role of CYLD in promoting survival of a subset of melanoma cells and uncover the heterogeneity of CYLD expression and its biological significance in melanoma.

Necroptosis regulates tumor repopulation after radiotherapy via RIP1/RIP3/MLKL/JNK/IL8 pathway

Background

Tumor cell repopulation after radiotherapy is a major cause for the tumor radioresistance and recurrence. This study aims to investigate the underlying mechanism of tumor repopulation after radiotherapy, with focus on whether and how necroptosis takes part in this process.

Methods

Necroptosis after irradiation were examined in vitro and in vivo. And the growth-promoting effect of necroptotic cells was investigated by chemical inhibitors or shRNA against necroptosis associated proteins and genes in in vitro and in vivo tumor repopulation models. Downstream relevance factors of necroptosis were identified by western blot and chemiluminescent immunoassays. Finally, the immunohistochemistry staining of identified necroptosis association growth stimulation factor was conducted in human colorectal tumor specimens to verify the relationship with clinical outcome.

Results

Radiation-induced necroptosis depended on activation of RIP1/RIP3/MLKL pathway, and the evidence in vitro and in vivo demonstrated that the inhibition of necroptosis attenuated growth-stimulating effects of irradiated tumor cells on living tumor reporter cells. The JNK/IL-8 were identified as downstream molecules of pMLKL during necroptosis, and inhibition of JNK, IL-8 or IL-8 receptor significantly reduced tumor repopulation after radiotherapy. Moreover, the high expression of IL-8 was associated with poor clinical prognosis in colorectal cancer patients.

Conclusions

Necroptosis associated tumor repopulation after radiotherapy depended on activation of RIP1/RIP3/MLKL/JNK/IL-8 pathway. This novel pathway provided new insight into understanding the mechanism of tumor radioresistance and repopulation, and MLKL/JNK/IL-8 could be developed as promising targets for blocking tumor repopulation to enhance the efficacy of colorectal cancer radiotherapy.

Receptor-Interacting Protein Kinase 1 Promotes Cholangiocarcinoma Proliferation And Lymphangiogenesis Through The Activation Protein 1 Pathway

PURPOSE

Receptor-interacting protein kinase 1 (RIPK1) is an important upstream regulator of multiple cell signaling pathways including inflammatory signals. RIPK1 is reported to be closely associated with the prognostic implications of cancer, especially epithelial tumors. But its role in proliferation and lymphangiogenesis in cholangiocarcinoma (CCA) remains unclear and requires further investigation.

PATIENTS AND METHODS

Expression of RIPK1 in human CCA tissues and CCA cell lines (QBC939, HUH28 and CCPL-1) was measured using qPCR, immunoblotting and immunohistochemistry. Silencing of RIPK1 was achieved by transduction of CCA cells via lentiviral plasmids (LV3-H1/GFP&Puro) encapsulating RIPK1 shRNA (LV-shRIPK1) or negative control shRNA (LV-shNC), and puromycin was used to select stable colonies. Proliferation and lymphangiogenesis were assessed in vitro by CCK-8 and matrigel-based tube formation assays, respectively. Activity of the activation protein-1 (AP-1) was evaluated by double-luciferase reporter gene assay. Protein expression of JNK, P38MAPK, ERK1/2, AP-1, P-AP-1, E-cadherin, N-cadherin and vascular endothelial growth factor-C (VEGF-C) was measured by immunoblotting or ELISA. An orthotopic CCA model in null mice was generated by transplanting QBC939 LV-shRIPK1, LV-shNC and control cells to further evaluate the role of RIPK1 on lymphangiogenesis in vivo. Immunohistochemistry was utilized to evaluate the expression of RIPK1 and VEGF-C, and tumor lymphatic vessels in the CCA model mice.

RESULTS

Upregulated expression of RIPK1 in CCA tissues was closely related to tumor size, lymph node metastasis and poor prognosis. RIPK1 promoted proliferation and lymphangiogenesis in CCA cells, and regulated the activation of JNK and P38MAPK-mediated AP-1/VEGF-C pathway. Finally, in vivo animal experiments in the orthotopic CCA mouse model further confirmed the function of RIPK1 in lymphangiogenesis.

CONCLUSION

This is the first report demonstrating the role of RIPK1 in proliferation and lymphangiogenesis through the MAPK (JNK and P38MAPK)- AP-1 pathway in CCA.

The role of necroptosis in cancer: A double-edged sword?

Necroptosis is a programmed, caspase-independent cell death that is morphologically similar to necrosis. Unlike apoptosis, necroptosis evokes inflammatory responses by releasing damage-associated molecular patterns. Recent studies suggest that tumor undergoes necroptosis in vivo and necroptosis has pro- or anti-tumoral effects in cancer development and progression. Furthermore, triggering necroptosis in tumor cells has been explored as a potential therapeutic strategy against cancer. Here, we will review the recent research progress of necroptosis in conferring anti- or pro-tumoral effects and its potential application in cancer therapy.

Human RIPK1 deficiency causes combined immunodeficiency and inflammatory bowel diseases

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is a critical regulator of cell death and inflammation, but its relevance for human disease pathogenesis remains elusive. Studies of monogenic disorders might provide critical insights into disease mechanisms and therapeutic targeting of RIPK1 for common diseases. Here, we report on eight patients from six unrelated pedigrees with biallelic loss-of-function mutations in RIPK1 presenting with primary immunodeficiency and/or intestinal inflammation. Mutations in RIPK1 were associated with reduced NF-κB activity, defective differentiation of T and B cells, increased inflammasome activity, and impaired response to TNFR1-mediated cell death in intestinal epithelial cells. The characterization of RIPK1-deficient patients highlights the essential role of RIPK1 in controlling human immune and intestinal homeostasis, and might have critical implications for therapies targeting RIPK1.

RIP Kinases in Liver Cell Death, Inflammation and Cancer

Cell death is intrinsically linked to inflammatory liver disease and cancer development. Recent genetic studies have suggested that receptor-interacting protein kinase (RIPK)1 is implicated in liver disease pathogenesis by regulating caspase-dependent hepatocyte apoptosis induced by tumor necrosis factor (TNF) or other stimuli. In contrast, the contribution of caspase-independent RIPK3/mixed lineage kinase like (MLKL)-mediated hepatocyte necroptosis remains debatable. Hepatocyte apoptosis depends on the balance between RIPK1 prosurvival scaffolding functions and its kinase-activity-mediated proapoptotic function. Several regulatory steps promote the prosurvival role of RIPK1, including phosphorylation and ubiquitination of RIPK1 itself and other molecules involved in RIPK1 signaling. Pharmacological inhibition of liver damage by targeting RIPK1 signaling emerges as a potential therapeutic strategy to prevent chronic liver inflammation and hepatocarcinogenesis.

Progress in studies of necroptosis and its relationship to disease processes

This review briefly introduces the mechanism and detection methods of necroptosis in recent years. The most significant points of this review focus on the involvement of necroptotic proteins in disease progression. The following aspects are summarized: 1) RIPs, MLKL, and the upstream and downstream molecules that mediate necroptosis; 2) The development of detection methods for necroptosis; 3) The involvement of related necroptotic proteins in diverse diseases etiology; and 4) The application of necroptotic proteins in disease diagnosis.

Azithromycin enhances anticancer activity of TRAIL by inhibiting autophagy and up-regulating the protein levels of DR4/5 in colon cancer cells in vitro and in vivo

Background

Azithromycin is a member of macrolide antibiotics, and has been reported to inhibit the proliferation of cancer cells. However, the underlying mechanisms are not been fully elucidated. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively targets tumor cells without damaging healthy cells. In the present study, we examined whether azithromycin is synergistic with TRAIL, and if so, the underlying mechanisms in colon cancers.

Methods

HCT-116, SW480, SW620 and DiFi cells were treated with azithromycin, purified TRAIL, or their combination. A sulforhoddamine B assay was used to examine cell survival. Apoptosis was examined using annexin V-FITC/PI staining, and autophagy was observed by acridine orange staining. Western blot analysis was used to detect protein expression levels. In mechanistic experiments, siRNAs were used to knockdown death receptors (DR4, DR5) and LC-3B. The anticancer effect of azithromycin and TRAIL was also examined in BALB/c nude mice carrying HCT-116 xenografts.

Results

Azithromycin decreased the proliferation of HCT-116 and SW480 cells in a dose-dependent manner. Combination of azithromycin and TRAIL inhibited tumor growth in a manner that could not be explained by additive effects. Azithromycin increased the expressions of DR4, DR5, p62 and LC-3B proteins and potentiated induction of apoptosis by TRAIL. Knockdown of DR4 and DR5 with siRNAs increased cell survival rate and decreased the expression of cleaved-PARP induced by the combination of azithromycin and TRAIL. LC-3B siRNA and CQ potentiated the anti-proliferation activity of TRAIL alone, and increased the expressions of DR4 and DR5.

Conclusion

The synergistic antitumor effect of azithromycin and TRAIL mainly relies on the up-regulations of DR4 and DR5, which in turn result from LC-3B-involved autophagy inhibition.

Electronic supplementary material

The online version of this article (10.1186/s40880-018-0309-9) contains supplementary material, which is available to authorized users.

RIP1 protects melanoma cells from apoptosis induced by BRAF/MEK inhibitors

Many recent studies have uncovered the necessary role for the receptor-interacting protein kinase 1 (RIP1) in regulating apoptosis and necrosis that cells undergo in response to various cellular stresses. However, the functional significance of RIP1 in promoting cancer cells survival remains poorly understood. Here, we report that RIP1 was upregulated and contributed to both intrinsic and acquired resistance of melanoma cells to BRAF/MEK inhibitors through activation of NF-κB. Strikingly, Snail1-mediated suppression of CYLD played a crucial role in promoting RIP1 expression upon ERK activation, particularly, in melanoma cells with acquired resistance to BRAF inhibitors. In addition, RIP1 kinase activity was not required for melanoma cells to survive BRAF/MEK inhibition as RIP1 mediated NF-κB activation through its intermediate domain. Collectively, our findings reveal that targeting RIP1 in combination with BRAF/MEK inhibitors is a potential approach in the treatment of the disease.

RIP1 regulates TNF-α-mediated lymphangiogenesis and lymphatic metastasis in gallbladder cancer by modulating the NF-κB-VEGF-C pathway

Background

Tumor necrosis factor alpha (TNF-α) enhances lymphangiogenesis in gallbladder carcinoma (GBC) via activation of nuclear factor (NF-κB)-dependent vascular endothelial growth factor-C (VEGF-C). Receptor-interacting protein 1 (RIP1) is a multifunctional protein in the TNF-α signaling pathway and is highly expressed in GBC. However, whether RIP1 participates in the signaling pathway of TNF-α-mediated VEGF-C expression that enhances lymphangiogenesis in GBC remains unclear.

Methods

The RIP1 protein levels in the GBC-SD and NOZ cells upon stimulation with increasing concentrations of TNF-α as indicated was examined using Western blot. Lentiviral RIP1 shRNA and siIκBα were constructed and transduced respectively them into NOZ and GBC-SD cells, and then PcDNA3.1-RIP1 vectors was transduced into siRIP1 cell lines to reverse RIP1 expression. The protein expression of RIP1, inhibitor of NF-κB alpha (IκBα), p-IκBα, TAK1, NF-κB essential modulator were examined through immunoblotting or immunoprecipitation. Moreover, VEGF-C mRNA levels were measured by quantitative real-time polymerase chain reaction, VEGF-C protein levels were measured by immunoblotting and enzyme-linked immunosorbent assay, and VEGF-C promoter and NF-κB activities were quantified using a dual luciferase reporter assay. The association of NF-κB with the VEGF-C promoter was analysed by chromatin immunoprecipitation assay. A three-dimensional coculture method and orthotopic transplantation nude mice model were used to evaluate lymphatic tube-forming and metastasis ability in GBC cells. The expression of RIP1 protein, TNF-α protein and lymphatic vessels in human GBC tissues was examined by immunohistochemistry, and the dependence between RIP1 protein with TNF-α protein and lymphatic vessel density was analysed.

Results

TNF-α dose- and time-dependently increased RIP1 protein expression in the GBC-SD and NOZ cells of GBC, and the strongest effect was observed with a concentration of 50 ng/ml. RIP1 is fundamental for TNF-α-mediated NF-κB activation in GBC cells and can regulate TNF-α-mediated VEGF-C expression at the protein and transcriptional levels through the NF-κB pathway. RIP1 can regulate TNF-α-mediated lymphatic tube formation and metastasis in GBC cells both in vitro and vivo. The average optical density of RIP1 was linearly related to that of TNF-α protein and the lymphatic vessel density in GBC tissues.

Conclusion

We conclude that RIP1 regulates TNF-α-mediated lymphangiogenesis and lymph node metastasis in GBC by modulating the NF-κB-VEGF-C pathway.

ACTN4 regulates the stability of RIPK1 in melanoma

The actin crosslinking protein α-actinin-4 (ACTN4) is emerging as an important contributor to the pathogenesis of cancer. This has largely been attributed to its role in regulating cytoskeleton organization and its involvement in transcriptional regulation of gene expression. Here we report a novel function of ACTN4 as a scaffold necessary for stabilization of receptor-interacting protein kinase 1 (RIPK1) that we have recently found to be an oncogenic driver in melanoma. ACTN4 bound to RIPK1 and cellular inhibitor of apoptosis protein 1 (cIAP1) with its actin-binding domain at the N-terminus and the CaM-like domain at the C-terminus, respectively. This facilitated the physical association between RIPK1 and cIAP1 and was critical for stabilization of RIPK1 that in turn activated NF-κB. Functional investigations showed that silencing of ACTN4 suppressed melanoma cell proliferation and retarded melanoma xenograft growth. In contrast, overexpression of ACTN4 promoted melanocyte and melanoma cell proliferation and moreover, prompted melanocyte anchorage-independent growth. Of note, the expression of ACTN4 was transcriptionally activated by NF-κB. Taken together, our findings identify ACTN4 as an oncogenic regulator through driving a feedforward signaling axis of ACTN4-RIPK1-NF-κB, with potential implications for targeting ACTN4 in the treatment of melanoma.

RIPK1 downregulation in keratinocyte enhances TRAIL signaling in psoriasis

BACKGROUND

Psoriasis, a common inflammatory skin disorder characterized by scaly erythema and plaques, is induced by dysregulation of dendritic cell- and T cell-mediated immune reaction. Receptor-interacting protein kinase 1 (RIPK1) regulates inflammatory signaling in response to stimuli such as TNF-α, TRAIL, and TLRs, resulting in apoptosis, necroptosis and NF-κB activation. However, the physiological relevance in human epidermis remains elusive.

OBJECTIVE

In this study, we examined whether RIPK1 is involved in the pathogenesis of psoriasis vulgaris.

METHODS

Skin samples of eight patients with psoriasis vulgaris were investigated by western blotting and immunohistochemistry. The functions of RIPK1 in keratinocytes were examined by RT-PCR and ELISA in vitro. TRAIL-neutralization-experiment was employed in an imiquimod-induced murine psoriasis model.

RESULTS

In lesional psoriatic epidermis, RIPK1-expression was decreased compared with that in normal epidermis. Cytokines involved in the pathomechanism of psoriasis, such as IL-1β, IL-17A, IL-22 and TRAIL, reduced RIPK1-expression in normal human epidermal keratinocytes (HEK) in vitro. In addition, RIPK1-knockdown enhanced TRAIL-mediated expression of psoriasis-relating cytokines, such as IL-1β, IL-6, IL-8, TNF-α, in HEK. Numerous TRAIL-positive cells were detected in the dermis of lesional psoriatic skin, and TRAIL receptors were expressed in psoriatic epidermis and HEK in conventional cultures. Moreover, TRAIL-neutralization in an imiquimod-induced murine psoriasis model remarkably improved skin phenotypes, such as ear thickness, and TNF-α expression in lesional skin.

CONCLUSIONS

These results lead us to conclude that RIPK1-downregulation in keratinocytes increases their susceptibility to TRAIL stimulation, and plays a role in the pathogenesis of psoriasis vulgaris.

RIPK1 Binds MCU to Mediate Induction of Mitochondrial Ca2+ Uptake and Promotes Colorectal Oncogenesis

The receptor-interacting protein kinase 1 (RIPK1) is an essential signaling molecule in pathways for cell survival, apoptosis, and necroptosis. We report here that RIPK1 is upregulated in human colorectal cancer and promotes cell proliferation when overexpressed in a colon cancer cell line. RIPK1 interacts with mitochondrial Ca²⁺ uniporter (MCU) to promote proliferation by increasing mitochondrial Ca²⁺ uptake and energy metabolism. The ubiquitination site of RIPK1 (RIPK1-K377) was critical for this interaction with MCU and function in promoting cell proliferation. These findings identify the RIPK1-MCU pathway as a promising target to treat colorectal cancer.Significance: RIPK1-mediated cell proliferation through MCU is a central mechanism underlying colorectal cancer progression and may prove to be an important therapeutic target for colorectal cancer treatment. Cancer Res; 78(11); 2876-85. ©2018 AACR.

Novel smac mimetic APG-1387 elicits ovarian cancer cell killing through TNF-alpha, Ripoptosome and autophagy mediated cell death pathway

Background

Ovarian cancer is a deadly disease. Inhibitors of apoptosis proteins (IAPs) are key regulators of apoptosis and are frequently dysregulated in ovarian cancer. Overexpression of IAPs proteins has been correlated with tumorigenesis, treatment resistance and poor prognosis. Reinstalling functional cell death machinery by pharmacological inhibition of IAPs proteins may represent an attractive therapeutic strategy for treatment of ovarian cancer.

Methods

CCK-8 and colony formation assay was performed to examine cytotoxic activity. Apoptosis was analyzed by fluorescence microscopy, flow cytometry and TUNEL assay. Elisa assay was used to determine TNFα protein. Caspase activity assay was used for caspase activation evaluation. Immunoprecipitation and siRNA interference were carried out for functional analysis. Western blotting analysis were carried out to test protein expression. Ovarian cancer cell xenograft nude mice model was used for in vivo efficacy evaluation.

Results

APG-1387 demonstrated potent inhibitory effect on ovarian cancer cell growth and clonogenic cell survival. APG-1387 induced RIP1- and TNFα-dependent apoptotic cell death in ovarian cancer through downregulation of IAPs proteins and induction of caspase-8/FADD/RIP1 complex, which drives caspase-8 activation. NF-κB signaling pathway was activated upon APG-1387 treatment and RIP1 contributed to NF-κB activation. APG-1387 induced cytoprotective autophagy while triggering apoptosis in ovarian cancer cells and inhibition of autophagy enhanced APG-1387-induced apoptotic cell death. APG-1387 exhibited potent antitumor activity against established human ovarian cancer xenografts.

Conclusions

Our results demonstrate that APG-1387 targets IAPs proteins to potently elicit apoptotic cell death in vitro and in vivo, and provide mechanistic and applicable rationale for future clinical evaluation of APG-1387 in ovarian cancer.

RIPK1-dependent cell death: a novel target of the Aurora kinase inhibitor Tozasertib (VX-680)

The Aurora kinase family (Aurora A, B and C) are crucial regulators of several mitotic events, including cytokinesis. Increased expression of these kinases is associated with tumorigenesis and several compounds targeting Aurora kinase are under evaluation in clinical trials (a.o. AT9283, AZD1152, Danusertib, MLN8054). Here, we demonstrate that the pan-Aurora kinase inhibitor Tozasertib (VX-680 and MK-0457) not only causes cytokinesis defects through Aurora kinase inhibition, but is also a potent inhibitor of necroptosis, a cell death process regulated and executed by the RIPK1, RIPK3 and MLKL signalling axis. Tozasertib’s potency to inhibit RIPK1-dependent necroptosis and to block cytokinesis in cells is in the same concentration range, with an IC50 of 1.06 µM and 0.554 µM, respectively. A structure activity relationship (SAR) analysis of 67 Tozasertib analogues, modified at 4 different positions, allowed the identification of analogues that showed increased specificity for either cytokinesis inhibition or for necroptosis inhibition, reflecting more specific inhibition of Aurora kinase or RIPK1, respectively. These results also suggested that RIPK1 and Aurora kinases are functionally non-interacting targets of Tozasertib and its analogues. Indeed, more specific Aurora kinase inhibitors did not show any effect in necroptosis and Necrostatin-1s treatment did not result in cytokinesis defects, demonstrating that both cellular processes are not interrelated. Finally, Tozasertib inhibited recombinant human RIPK1, human Aurora A and human Aurora B kinase activity, but not RIPK3. The potency ranking of the newly derived Tozasertib analogues and their specificity profile, as observed in cellular assays, coincide with ADP-Glo recombinant kinase activity assays. Overall, we show that Tozasertib not only targets Aurora kinases but also RIPK1 independently, and that we could generate analogues with increased selectivity to RIPK1 or Aurora kinases, respectively.

The STAT3/NFIL3 signaling axis-mediated chemotherapy resistance is reversed by Raddeanin A via inducing apoptosis in choriocarcinoma cells

Chemotherapy resistance is the major issue of choriocarcinoma. Apoptosis always is the ultimate outcome of chemotherapeutic drugs, which considered one of the reasons of resistance. We investigated the role of STAT3/NFIL3 signaling‐inhibited apoptosis in chemotherapy resistance and whether Raddeanin A (RA) could be a new drug to reverse resistance. Established three drug‐resistant cell lines as JEG‐3/MTX, JEG‐3/5‐FU, and JEG‐3/VP16. NFIL3 and STAT3 expression was evaluated in the cells. The IC₅₀ value, apoptosis rate and apoptins were observed with transfection of siNFIL3, Lenti‐OE™‐NFIL3, shSTAT3, and Lenti‐OE™‐STAT3 or RA treatment. In addition, the luciferase reporter analysis and co‐immunoprecipitation assays were used to investigate the relation of STAT3 and NFIL3. Hyper‐activation of STAT3 and NFIL3 expression were observed in three drug‐resistant cell lines. STAT3 enhanced NFIL3 transcriptional activity by binding the relative promoter region. Activated STAT3/NFIL3 pathway caused low rate of apoptosis which resulted in chemotherapy resistance. RA reduced the resistance index of resistant cells and induced caspase 3 dependent apoptosis, meanwhile it repressed the STAT3/NFIL3 activation. STAT3/NFIL3 axis‐inhibited apoptosis is a novel mechanism of chemotherapy resistance in choriocarcinoma. With the suppression of STAT3/NFIL3 axis and apoptosis induction, RA is a potential agent or lead candidate for improving chemotherapy.

MELK Promotes Melanoma Growth by Stimulating the NF-κB Pathway

Melanoma accounts for more than 80% of skin cancer-related deaths, and current therapies provide only short-term benefit to patients. Here, we show in melanoma cells that maternal embryonic leucine zipper kinase (MELK) is transcriptionally upregulated by the MAPK pathway via transcription factor E2F1. MELK knockdown or pharmacological inhibition blocked melanoma growth and enhanced the effectiveness of BRAFV600E inhibitor against melanoma cells. To identify mediators of MELK function, we performed stable isotope labeling with amino acids in cell culture (SILAC) and identified 469 proteins that had downregulated phosphorylation after MELK inhibition. Of these proteins, 139 were previously reported as substrates of BRAF or MEK, demonstrating that MELK is an important downstream mediator of the MAPK pathway. Furthermore, we show that MELK promotes melanoma growth by activating NF-κB pathway activity via Sequestosome 1 (SQSTM1/p62). Altogether, these results underpin an important role for MELK in melanoma growth downstream of the MAPK pathway.

Key roles of necroptotic factors in promoting tumor growth

Necroptotic factors are generally assumed to play a positive role in tumor therapy by eliminating damaged tumor cells. Here we show that, contrary to expectation, necroptotic factors RIPK1, RIPK3, and MLKL promote tumor growth. We demonstrate that genetic knockout of necroptotic genes RIPK1, RIPK3, or MLKL in cancer cells significantly attenuated their abilities to grow in an anchorage-independent manner. In addition, they exhibited significantly enhanced radiosensitivity. The knockout cells also showed greatly reduced ability to form tumors in mice. Moreover, necrosulfonamide (NSA), a previously identified chemical inhibitor of necroptosis, could significantly delay tumor growth in a xenograft model. Mechanistically, we show that necroptoic factors play a significant role in maintaining the activity of NF-κB. Finally, we found that high levels of phosphorylated MLKL in human esophageal and colon cancers are associated with poor overall survival. Taken together, we conclude that pro-necroptic factors such as RIPK1, RIPK3, and MLKL may play a role in supporting tumor growth, and MLKL may be a promising target for cancer treatment.

RIPK1 binds to vitamin D receptor and decreases vitamin D-induced growth suppression

Receptor interacting protein kinase 1 (RIPK1) is an enzyme acting downstream of tumor necrosis factor alpha to control cell survival and death. RIPK1 expression has been reported to cause drug resistance in cancer cells, but so far, no published studies have investigated the role of RIPK1 in vitamin D signaling. In the present study, we investigated whether RIPK1 plays any roles in 1,25-dihydroxyvitamin D3 (1,25D3)-induced growth suppression. In our studies, RIPK1 decreased the transcriptional activity of vitamin D receptor (VDR) in luciferase reporter assays independent of its kinase activity, suggesting a negative role of RIPK1 in 1,25D3 action. RIPK1 also formed a complex with VDR, and deletion analyses mapped the RIPK1 binding region to the C-terminal ligand-binding domain of the VDR. Subcellular fractionation analyses indicated that RIPK1 increased VDR retention in the cytoplasm, which may account for its inhibition of VDR transcriptional activity. Consistent with the reporter analyses, 1,25D3-induced growth suppression was more pronounced in RIPK1-null MEFs and RIPK1-knockdown ovarian cancer cells than in control cells. Our studies have defined RIPK1 as a VDR repressor, projecting RIPK1 depletion as a potential strategy to increase the potency of 1,25D3 and its analogs for cancer intervention.

Skp2-Mediated Stabilization of MTH1 Promotes Survival of Melanoma Cells upon Oxidative Stress

MTH1 helps prevent misincorporation of ROS-damaged dNTPs into genomic DNA; however, there is little understanding of how MTH1 itself is regulated. Here, we report that MTH1 is regulated by polyubiquitination mediated by the E3 ligase Skp2. In melanoma cells, MTH1 was upregulated commonly mainly due to its improved stability caused by K63-linked polyubiquitination. Although Skp2 along with other components of the Skp1-Cullin-F-box (SCF) ubiquitin ligase complex was physically associated with MTH1, blocking the SCF function ablated MTH1 ubiquitination and expression. Conversely, overexpressing Skp2-elevated levels of MTH1 associated with an increase in its K63-linked ubiquitination. In melanoma cell lines and patient specimens, we observed a positive correlation of Skp2 and MTH1 expression. Mechanistic investigations showed that Skp2 limited DNA damage and apoptosis triggered by oxidative stress and that MAPK upregulated Skp2 and MTH1 to render cells more resistant to such stress. Collectively, our findings identify Skp2-mediated K63-linked polyubiquitination as a critical regulatory mechanism responsible for MTH1 upregulation in melanoma, with potential implications to target the MAPK/Skp2/MTH1 pathway to improve its treatment. Cancer Res; 77(22); 6226-39. ©2017 AACR.