TRAF2 and Cellular IAPs: A Critical Link in TNFR Family Signaling

Sublethal necroptosis signaling promotes inflammation and liver cancer

It is currently not well known how necroptosis and necroptosis responses manifest in vivo. Here, we uncovered a molecular switch facilitating reprogramming between two alternative modes of necroptosis signaling in hepatocytes, fundamentally affecting immune responses and hepatocarcinogenesis. Concomitant necrosome and NF-κB activation in hepatocytes, which physiologically express low concentrations of receptor-interacting kinase 3 (RIPK3), did not lead to immediate cell death but forced them into a prolonged "sublethal" state with leaky membranes, functioning as secretory cells that released specific chemokines including CCL20 and MCP-1. This triggered hepatic cell proliferation as well as activation of procarcinogenic monocyte-derived macrophage cell clusters, contributing to hepatocarcinogenesis. In contrast, necrosome activation in hepatocytes with inactive NF-κB-signaling caused an accelerated execution of necroptosis, limiting alarmin release, and thereby preventing inflammation and hepatocarcinogenesis. Consistently, intratumoral NF-κB-necroptosis signatures were associated with poor prognosis in human hepatocarcinogenesis. Therefore, pharmacological reprogramming between these distinct forms of necroptosis may represent a promising strategy against hepatocellular carcinoma.

TWEAK/Fn14 axis is an important player in fibrosis

Fibrosis is a common pathological condition associated with abnormal repair after tissue injury. However, the etiology and molecular mechanisms of fibrosis are still not well-understood. Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) belongs to the TNF superfamily and acts by binding to its receptor, fibroblast growth factor-inducible 14 (Fn14), thereby activating a variety of intracellular signal transduction pathways in various types of cells. Besides promoting the expression of growth factors, activation of TWEAK/Fn14 signaling after tissue injury can promote the expression of pro-inflammatory cytokines, which trigger the immune response, thereby exacerbating the injury. Severe or repetitive injury leads to a dysregulated tissue repair process, in which the TWEAK/Fn14 axis promotes the activation and proliferation of myofibroblasts, induces the secretion of the extracellular matrix, and regulates profibrotic mediators to further perpetuate and sustain the fibrotic process. In this review, we summarize the available experimental evidence on the underlying molecular mechanisms by which the TWEAK/Fn14 pathway mediates the development and progression of fibrosis. In addition, we discuss the therapeutic potential of the TWEAK/Fn14 pathway in fibrosis-associated diseases based on evidence derived from multiple models and cells from injured tissue and fibrotic tissue.

Molecular characterization and functional analysis of tumor necrosis factor receptor-associated factor 2 in the Pacific oyster

Tumor necrosis factor receptor (TNFR)-associated factors (TRAFs) are a family of crucial adaptors, playing vital roles in mediating signal transduction in immune signaling pathways, including RIG-I-like receptor (RLR) signaling pathway. In the present study, a new TRAF family member (CgTRAF2) was identified in the Pacific oyster, Crassostrea gigas. Comparison and phylogenetic analysis revealed that CgTRAF2 could be a new member of the invertebrate TRAF2 family. Quantitative real-time PCR revealed that CgTRAF2 mRNA was highly expressed in the digestive gland, gills, and hemocytes, and it was significantly up-regulated after Vibrio alginolyticus and ostreid herpesvirus 1 (OsHV-1) challenge. The CgTRAF2 mRNA expression profile in different developmental stages of oyster larvae suggested that CgTRAF2 could function in early larval development. CgTRAF2 mRNA expression pattern, after the silence of CgMAVS (Mitochondrial Antiviral Signaling) -like, indicated that CgTRAF2 might function downstream of CgMAVS-like. Moreover, the subcellular localization analysis revealed that CgTRAF2 was localized in cytoplasm, and it may play predominately important roles in signal transduction. Collectively, these results demonstrated that CgTRAF2 might play important roles in the innate immunity and larval development of the Pacific oyster.

Small molecules as pro-apoptotic anticancer agents

The quest for potent and selective targeted therapies in anticancer research is taking advantage of apoptosis-related mechanisms of action to identify a number of novel clinical candidates. This review is chemically focused on small molecules and deals with five target families that influence caspase-dependent apoptosis: caspase-3, Bcl-2 and IAP protein family members, p53 and the proteasome. Each target class is briefly described at first in terms of its involvement and relevance in tumor initiation and progression. Drug candidates currently undergoing clinical trials are then presented for each target class, followed by a quick summary of target-modulating chemotypes that have appeared in patent literature since 2006. Finally, future trends likely to become significant in apoptosis-targeted cancer therapies are presented and discussed.

Functional characterization of TNF-α in grass carp head kidney leukocytes: induction and involvement in the regulation of NF-κB signaling

Tumor necrosis factor-alpha (TNF-α) is a potent regulatory cytokine, which serves as a key mediator of inflammation, immunity and apoptosis in mammals. Identification, expression and regulatory effects of TNF-α have been reported in various fish species, showing the structural and functional similarity or discrepancy between each other. In this study, TNF-α was identified from grass carp (Ctenopharyngodon idella) and the deduced grass carp TNF-α (gcTNF-α) protein possessed the TNF family signature motifs, a protease cleavage site, a transmembrane domain and two conserved cysteine residues. Further studies showed that gcTNF-α expression was induced with a rapid kinetics by immune challenge in vitro and in vivo. To characterize the function of gcTNF-α, recombinant gcTNF-α (rgcTNF-α) was prepared by using the Escherichia coli expression system. It was shown to enhance the mRNA expression of gcTNF-α and gcIL-1β in head kidney leukocytes (HKLs), confirming the biological activity of rgcTNF-α. In the same model, NF-κB inhibitor (PDTC) was able to attenuate rgcTNF-α-induced gcTNF-α mRNA expression, implying the involvement of NF-κB pathway in fish TNF-α action. This notion was reinforced by the finding that rgcTNF-α could induce the phosphorylation of IκBα in a time-dependent oscillation in HKLs, indicating a dynamical variation of NF-κB activity as seen in mammals. In addition, rgcTNF-α could up-regulate the expression of two TNF receptor-associated factors (TRAF), TRAF1 and TRAF2, in a time- and dose-dependent manner, suggesting that gcTNF-α may function as a regulator of fish NF-κB pathway. These results for the first time reveal the link of gcTNF-α to the NF-κB pathway and provide a better understanding of TNF-α signaling in teleost immunity.