RIPK4 activates an IRF6-mediated proinflammatory cytokine response in keratinocytes

Exploring the prognostic significance of arm-level copy number alterations in triple-negative breast cancer

Somatic copy number alterations (SCNAs) are prevalent in cancer and play a significant role in both tumorigenesis and therapeutic resistance. While focal SCNAs have been extensively studied, the impact of larger arm-level SCNAs remains poorly understood. Here, we investigated the association between arm-level SCNAs and overall survival in triple-negative breast cancer (TNBC), an aggressive subtype of breast cancer lacking targeted therapies. We identified frequent arm-level SCNAs, including 21q gain and 7p gain, which correlated with poor overall survival in TNBC patients. Further, we identified the expression of specific genes within these SCNAs associated with survival. Notably, we found that the expression of RIPK4, a gene located on 21q, exhibited a strong correlation with poor overall survival. In functional assays, we demonstrated that targeting Ripk4 in a murine lung metastatic TNBC model significantly reduced tumor burden, improved survival, and increased CD4+ and CD8+ T cell infiltration. RIPK4 enhanced the survival of triple-negative breast cancer cells at secondary sites, thereby facilitating the formation of metastatic lesions. Our findings highlight the significance of arm-level SCNAs in breast cancer progression and identify RIPK4 as a putative driver of TNBC metastasis and immunosuppression.

The involvement of RIPK4 in TNF-α-stimulated IL-6 and IL-8 production by melanoma cells

PURPOSE

The receptor-interacting protein kinase (RIPK4) has an oncogenic function in melanoma, regulates NF-κB and Wnt/β-catenin pathways, and is sensitive to the BRAF inhibitors: vemurafenib and dabrafenib which lead to its decreased level. As its role in melanoma remains not fully understood, we examined the effects of its downregulation on the transcriptomic profile of melanoma.

METHODS

Applying RNA-seq, we revealed global alterations in the transcriptome of WM266.4 cells with RIPK4 silencing. Functional partners of RIPK4 were evaluated using STRING and GeneMANIA databases. Cells with transient knockdown (via siRNA) and stable knockout (via CRISPR/Cas9) of RIPK4 were stimulated with TNF-α. The expression levels of selected proteins were assessed using Western blot, ELISA, and qPCR.

RESULTS

Global analysis of gene expression changes indicates a complex role for RIPK4 in regulating adhesion, migration, proliferation, and inflammatory processes in melanoma cells. Our study highlights potential functional partners of RIPK4 such as BIRC3, TNF-α receptors, and MAP2K6. Data from RIPK4 knockout cells suggest a putative role for RIPK4 in modulating TNF-α-induced production of IL-8 and IL-6 through two distinct signaling pathways-BIRC3/NF-κB and p38/MAPK. Furthermore, increased serum TNF-α levels and the correlation of RIPK4 with NF-κB were revealed in melanoma patients.

CONCLUSION

These data reveal a complex role for RIPK4 in regulating the immune signaling network in melanoma cells and suggest that this kinase may represent an alternative target for melanoma-targeted adjuvant therapy.

Functions of the RIP kinase family members in the skin

The receptor interacting protein kinases (RIPK) are a family of serine/threonine kinases that are involved in the integration of various stress signals. In response to several extracellular and/or intracellular stimuli, RIP kinases engage signaling cascades leading to the activation of NF-κB and mitogen-activated protein kinases, cell death, inflammation, differentiation and Wnt signaling and can have kinase-dependent and kinase-independent functions. Although it was previously suggested that seven RIPKs are part of the RIPK family, phylogenetic analysis indicates that there are only five genuine RIPKs. RIPK1 and RIPK3 are mainly involved in controlling and executing necroptosis in keratinocytes, while RIPK4 controls proliferation and differentiation of keratinocytes and thereby can act as a tumor suppressor in skin. Therefore, in this review we summarize and discuss the functions of RIPKs in skin homeostasis as well as the signaling pathways involved.

Targeting transcription factors for therapeutic benefit in rheumatoid arthritis

Rheumatoid arthritis (RA) is a destructive inflammatory autoimmune disease that causes pain and disability. Many of the currently available drugs for treating RA patients are aimed at halting the progression of the disease and alleviating inflammation. Further, some of these treatment options have drawbacks, including disease recurrence and adverse effects due to long-term use. These inefficiencies have created a need for a different approach to treating RA. Recently, the focus has shifted to direct targeting of transcription factors (TFs), as they play a vital role in the pathogenesis of RA, activating key cytokines, chemokines, adhesion molecules, and enzymes. In light of this, synthetic drugs and natural compounds are being explored to target key TFs or their signaling pathways in RA. This review discusses the role of four key TFs in inflammation, namely NF-κB, STATs, AP-1 and IRFs, and their potential for being targeted to treat RA.

Comparative and evolutionary analysis of RIP kinases in immune responses

The group of receptor-interacting protein (RIP) kinases has seven members (RIPK1–7), with one homologous kinase domain but distinct non-kinase regions. Although RIPK1–3 have emerged as key modulators of inflammation and cell death, few studies have connected RIPK4–7 to immune responses. The divergence in domain structures and paralogue information in the Ensembl database have raised question about the phylogeny of RIPK1–7. In this study, phylogenetic trees of RIPK1–7 and paralogues constructed using full-length amino acid sequences or Kinase domain demonstrate that RIPK6 and RIPK7 are distinct from RIPK1–5 and paralogues shown in the Ensembl database are inaccurate. Comparative and evolutionary analyses were subsequently performed to gain new clues about the potential functions of RIPK3–7. RIPK3 gene loss in birds and animals that undergo torpor, a common physiological phenomenon in cold environments, implies that RIPK3 may be involved in ischemia-reperfusion injury and/or high metabolic rate. The negligible expression of RIPK4 and RIPK5 in immune cells is likely responsible for the lack of studies on the direct role of these members in immunity; RIPK6 and RIPK7 are conserved among plants, invertebrates and vertebrates, and dominantly expressed in innate immune cells, indicating their roles in innate immunity. Overall, our results provide insights into the multifaceted and conserved biochemical functions of RIP kinases.

Irf6 participates in sevoflurane-induced perioperative neurocognitive disorder via modulating M2, but not M1 polarization of microglia

Perioperative neurocognitive disorder (PND) frequently occurs in elderly patients following anesthesia, and is associated with pro-inflammatory activation of microglia in hippocampus. In this study, sevoflurane, a commonly used inhaled anesthetic in clinic, was used to induce PND-like symptoms in aged SD rats (18-20 months). Data from novel object recognition and Y-maze tests first confirmed that aged SD rats exposed to 2% sevoflurane for 5 h developed cognitive impairment. Microglia preferred to polarizing towards pro-inflammatory M1 subtype (iNOS+Iba-1 +) in rat hippocampus post sevoflurane exposure, but not anti-inflammatory M2 subtype (Arg-1 +Iba-1 +). Microarray data identified interferon regulatory factor 6 (Irf6) as one (Fold change = -2.52, p = 0.006) of the 15 downregulated genes in hippocampus of the rats exposed to sevoflurane. Co-immunofluorescence data further illustrated that sevoflurane decreased Irf6 expression in hippocampal microglia. In vitro, sevoflurane enhanced lipopolysaccharide-induced M1 polarization of BV-2 cells and inhibited interleukin-4 induced M2 polarization. Interestingly, manipulation of Irf6 expression hardly affected M1 polarization. However, Irf6 overexpression further augmented the inhibitory effects on M2 polarization, and its silencing showed opposite effects. In addition, such M2 polarization-promoting effects of Irf6 knockdown may be associated with induction of peroxisome proliferator activated receptor gamma expression. Collectively, these findings suggest that Irf6 downregulation in hippocampal microglia may be a compensatory mechanism against sevoflurane-induced PND in the elderly.

Advances in scarless foetal wound healing and prospects for scar reduction in adults

Healing after mammalian skin injury involves the interaction between numerous cellular constituents and regulatory factors, which together form three overlapping phases: an inflammatory response, a proliferation phase and a remodelling phase. Any slight variation in these three stages can substantially alter the healing process and resultant production of scars. Of particular significance are the mechanisms responsible for the scar‐free phenomenon observed in the foetus. Uncovering such mechanisms would offer great expectations in the treatment of scars and therefore represents an important area of investigation. In this review, we provide a comprehensive summary of studies on injury‐induced skin regeneration within the foetus. The information contained in these studies provides an opportunity for new insights into the treatment of clinical scars based on the cellular and molecular processes involved.

The diverse roles of RIP kinases in host-pathogen interactions

Receptor Interacting Protein Kinases (RIPKs) are cellular signaling molecules that are critical for homeostatic signaling in both communicable and non-communicable disease processes. In particular, RIPK1, RIPK2, RIPK3 and RIPK7 have emerged as key mediators of intracellular signal transduction including inflammation, autophagy and programmed cell death, and are thus essential for the early control of many diverse pathogenic organisms. In this review, we discuss the role of each RIPK in host responses to bacterial and viral pathogens, with a focus on studies that have used pathogen infection models rather than artificial stimulation with purified pathogen associated molecular patterns. We also discuss the intricate mechanisms of host evasion by pathogens that specifically target RIPKs for inactivation, and finally, we will touch on the controversial issue of drug development for kinase inhibitors to treat chronic inflammatory and neurological disorders, and the implications this may have on the outcome of pathogen infections.

Insight Into the Function of RIPK4 in Keratinocyte Differentiation and Carcinogenesis

The receptor-interacting protein kinase 4 (RIPK4), a member of the RIPK family, was originally described as an interaction partner of protein kinase C (PKC) β and PKCδ. RIPK4 is identified as a key regulator of keratinocyte differentiation, cutaneous inflammation, and cutaneous wound repair. The mechanism by which RIPK4 integrates upstream signals to initiate specific responses remains elusive. Previous studies have indicated that RIPK4 can regulate several signaling pathways, including the NF-κB, Wnt/β-catenin, and RAF/MEK/ERK pathways. Furthermore, RIPK4-related biological signaling pathways interact with each other to form a complex network. Mounting evidence suggests that RIPK4 is aberrantly expressed in various kinds of cancers. In several types of squamous cell carcinoma (SCC), the mutations that drive aggressive SCC have been found in RIPK4. In addition, the function of RIPK4 in carcinogenesis is probably tissue-specific, since RIPK4 can play a dual role as both a tumor promoter and a tumor suppressor in different tumor types. Therefore, RIPK4 may represent as an independent prognostic factor and a promising novel therapeutic target, which can be used to identify the risks of patients and guide personalized treatments. In future, RIPK4-interacting pathways and precise molecular targets need to be investigated in order to further elucidate the mechanisms underlying epidermal differentiation and carcinogenesis.

RIPK protein kinase family: Atypical lives of typical kinases

Receptor Interacting Protein Kinases (RIPKs) are a family of Ser/Thr/Tyr kinases whose functions, regulation and pathophysiologic roles have remained an enigma for a long time. In recent years, these proteins garnered significant interest due to their roles in regulating a variety of host defense functions including control of inflammatory gene expression, different forms of cell death, and cutaneous and intestinal barrier functions. In addition, there is accumulating evidence that while these kinases seemingly follow typical kinase blueprints, their functioning in cells can take forms that are atypical for protein kinases. Lastly, while these kinases generally belong to distinct areas of innate immune regulation, there are emerging overarching themes that may unify the functions of this kinase family. Our review seeks to discuss the biology of RIPKs, and how typical and atypical features of this family informs the activity of a rapidly growing repertoire of RIPK inhibitors.

Immune Control by TRAF6-Mediated Pathways of Epithelial Cells in the EIME (Epithelial Immune Microenvironment)

In the protective responses of epithelial tissues, not only immune cells but also non-immune cells directly respond to external agents. Epithelial cells can be involved in the organization of immune responses through two phases. First, the exogenous harmful agents trigger the primary responses of the epithelial cells leading to various types of immune cell activation. Second, cytokines produced by the immune cells that are activated directly by the external agents and indirectly by the epithelial cell products elicit the secondary responses giving rise to further propagation of immune responses. TRAF6 is a ubiquitin E3 ligase, which intermediates between various types of receptors for exogenous agents or endogenous mediators and activation of subsequent transcriptional responses via NF-kappaB and MAPK pathways. TRAF6 ubiquitously participates in many protective responses in immune and non-immune cells. Particularly, epithelial TRAF6 has an essential role in the primary and secondary responses via driving type 17 response in psoriatic inflammation of the skin. Consistently, many psoriasis susceptibility genes encode the TRAF6 signaling players, such as ACT1 (TRAF3IP2), A20 (TNFAIP3), ABIN1 (TNIP1), IL-36Ra (IL36RN), IkappaBzeta (NFKBIZ), and CARD14. Herein, we describe the principal functions of TRAF6, especially in terms of positive and regulatory immune controls by interaction between immune cells and epithelial cells. In addition, we discuss how TRAF6 in the epithelial cells can organize the differentiation of immune responses and drive inflammatory loops in the epithelial immune microenvironment, which is termed EIME.

Integrative Analysis Identified IRF6 and NDST1 as Potential Causal Genes for Ischemic Stroke

Objective: To highlight potential functional variants and causal genes for ischemic stroke (IS) in genomic loci identified by genome-wide association studies (GWAS).

Methods: We examined the association between m⁶A-SNPs and IS in large scale GWAS. Furthermore, eQTL analysis was performed to evaluate the effect of m⁶A-SNPs on gene expression. The top associations between m⁶A-SNPs and gene expressions were validated in 40 individuals from the Chinese Han population. Besides, we applied differential expression analysis and Mendelian randomization (MR) analysis to detect potential causal genes for IS.

Results: We found 310 (7.39%) m⁶A-SNPs which were nominally associated with IS. The proportion of m⁶A-SNPs with P < 0.05 for IS was significantly higher than the non-m⁶A-SNPs (95%CI: [5.84%, 7.36%], P = 0.02). We found that the IS-associated m⁶A-SNP rs2013162 was associated with IRF6 expression (P = 6.30 × 10⁻²³), meanwhile IRF6 was differentially expressed between IS cases and controls (P = 6.15 × 10⁻³) and showed a causal association with IS (P = 3.64 × 10⁻⁴). Similar results were found for m⁶A-SNP rs2273235 in the NDST1 gene which was associated with cardioembolic stroke (P = 8.47 × 10⁻³). The associations of rs2013162 and rs2273235 with the expression of IRF6 and NDST1 were validated in blood cells (P = 0.0247 and 0.0007), respectively.

Conclusions: This study showed that m⁶A-SNPs may affect IS risk through altering gene expressions. The results suggested that m⁶A might play a role in IS etiology and gene expressions that affected by m⁶A may be causal factors for IS.

Dietary Fatty Acids and Other Nutrients in Relation to Inflammation and Particularly to Oral Mucosa Inflammation. A Literature Review

Oral mucosa is site of inflammatory process development. When they are chronic, they provide a microenvironment based on cytokines and inflammatory mediators that contribute to cancer initiation, progression, invasion, and metastasis. Certain dietary fatty acids (FAs) have immunomodulatory, inflammatory, and antiinflammatory effects. This review examined the literature on inflammation, mainly referred to the oral mucosa, and its association with dietary FAs and other nutrients. A Pubmed search of studies published in English until June 2018 was carried out. N-3 FAs have shown immunomodulatory and antiinflammatory activity in certain human diseases. These FAs and their mediators may inhibit inflammation, angiogenesis, and cancer via multiple mechanisms. Studies on cellular models of murine and human intestinal mucosa indicate association between dietary n-3 FA intake and the inflammatory state of mucosa membranes. Nevertheless scarce information on the association between dietary FAs and oral inflammation could be found. Based on the evidence, we hypothesize that n-3 FAs reduce the oral mucosa inflammation thus decreasing the risk of developing precancerous lesions and cancer. Molecular and clinical studies referred to this topic should be carried out as a contribution to the oral cancer prevention.

Crystal Structure of Ripk4 Reveals Dimerization-Dependent Kinase Activity

Receptor-interacting protein kinase 4 (RIPK4) is a highly conserved regulator of epidermal differentiation. Members of the RIPK family possess a common kinase domain as well as unique accessory domains that likely dictate subcellular localization and substrate preferences. Mutations in human RIPK4 manifest as Bartsocas-Papas syndrome (BPS), a genetic disorder characterized by severe craniofacial and limb abnormalities. We describe the structure of the murine Ripk4 (MmRipk4) kinase domain, in ATP- and inhibitor-bound forms. The crystallographic dimer of MmRipk4 is similar to those of RIPK2 and BRAF, and we show that the intact dimeric entity is required for MmRipk4 catalytic activity through a series of engineered mutations and cell-based assays. We also assess the impact of BPS mutations on protein structure and activity to elucidate the molecular origins of the disease.

Influence of protein kinase RIPK4 expression on the apoptosis and proliferation of chondrocytes in osteoarthritis

The present study aimed to investigate the expression of receptor‑interacting protein kinase 4 (RIPK4) and its effect on the apoptosis and proliferation of chondrocytes in osteoarthritis (OA). A total of 28 OA cartilage tissues and 20 normal cartilage tissues were collected to detect the expression of RIPK4 by using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Chondrocytes were isolated from OA cartilage tissues and divided into OA, NC, si‑RIPK4, Wnt3a, and si‑RIPK4+Wnt3a groups, and those isolated from normal cartilage tissues were considered the Normal group. Chondrocytes proliferation was detected by MTT assay, cell apoptosis was indicated using flow cytometry and Wnt/β‑catenin signaling pathway related‑proteins were investigated using western blot analysis. RIPK4 mRNA and protein expression levels in OA cartilage tissues and OA chondrocytes were increased compared with normal controls (all P<0.05). Additionally, OA chondrocytes showed reduced cell proliferation, increased cell apoptosis and upregulated expression levels of Wnt/β‑catenin signaling pathway related‑proteins (all P<0.05). Once transfected with si‑RIPK4, the proliferation ability of chondrocytes was enhanced, but apoptosis was notably decreased. Furthermore, the expression levels of Wnt/β‑catenin signaling pathway related‑proteins were significantly downregulated (all P<0.05). Results indicated that Wnt3a reversed the effect of si‑RIPK4 on chondrocyte proliferation and apoptosis (all P<0.05). Thus, silencing RIPK4 promoted the proliferation and inhibited the apoptosis of chondrocytes. In addition, silencing RIPK4 blocked the Wnt/β‑catenin signaling pathway, thus contributing to alleviating the OA pathogenesis.

Interferon Regulatory Factor 6 Promotes Keratinocyte Differentiation in Response to Porphyromonas gingivalis

We recently demonstrated that the expression of the interferon regulatory factor 6 (IRF6) transcription factor in oral keratinocytes was stimulated by the periodontal pathogen Porphyromonas gingivalis Here, we have established that IRF6 promotes the differentiation of oral keratinocytes in response to P. gingivalis This was evidenced by the IRF6-dependent upregulation of specific markers of keratinocyte terminal differentiation (e.g., involucrin [IVL] and keratin 13 [KRT13]), together with additional transcriptional regulators of keratinocyte differentiation, including Grainyhead-like 3 (GRHL3) and Ovo-like zinc finger 1 (OVOL1). We have previously established that the transactivator function of IRF6 is activated by receptor-interacting protein kinase 4 (RIPK4). Consistently, the silencing of RIPK4 inhibited the stimulation of IVL, KRT13, GRHL3, and OVOL1 gene expression. IRF6 was shown to also regulate the stimulation of transglutaminase-1 (TGM1) gene expression by P. gingivalis, as well as that of small proline-rich proteins (e.g., SPRR1), which are covalently cross-linked by TGM1 to other proteins, including IVL, during cornification. The expression of the tight junction protein occludin (OCLN) was found to also be upregulated in an IRF6-dependent manner. IRF6 was demonstrated to be important for the barrier function of oral keratinocytes; specifically, silencing of IRF6 increased P. gingivalis-induced intercellular permeability and cell invasion. Taken together, our findings potentially position IRF6 as an important mediator of barrier defense against P. gingivalis.

A novel regulatory relationship between RIPK4 and ELF3 in keratinocytes

Keratinocytes are central to the barrier functions of surface epithelia, such as the gingiva and epidermis. RIPK4 is a key regulator of keratinocyte differentiation; however, the signalling pathways in which it functions remain poorly defined. In this study, we identified a regulatory relationship between RIPK4 and ELF3, an ETS family transcription factor. RIPK4 was shown to be important for the upregulation of ELF3 gene expression by the PKC agonist PMA in both oral and epidermal keratinocytes. RIPK4 promotes keratinocyte differentiation in part by phosphorylating and thereby activating the IRF6 transcription factor. Significantly, silencing of IRF6 inhibited the PMA-inducible expression of ELF3. A role for the GRHL3 transcription factor, a downstream target gene of IRF6, in the regulation of ELF3 expression was similarly demonstrated. ELF3 has previously been shown to regulate the expression of SPPR1A and SPRR1B, small proline-rich proteins that contribute to the cornification of keratinocytes. Consistently, RIPK4 and IRF6 were important for the PMA-inducible expression of SPRR1A and SPRR1B. They were also important for the upregulation of TGM1, a transglutaminase that catalyses the cross-linking of proteins, including small proline-rich proteins, during keratinocyte cornification. RIPK4 was also shown to upregulate the expression of TGM2 independently of IRF6. Collectively, our findings position RIPK4 upstream of a hierarchal IRF6-GRHL3-ELF3 transcription factor pathway in keratinocytes, as well as provide insight into a potential role for RIPK4 in the regulation of keratinocyte cornification.