MFAP4-Mediated Effects in Elastic Fiber Homeostasis, Integrin Signaling and Cancer, and Its Role in Teleost Fish.
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ABSTRACT: Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix (ECM) protein belonging to the fibrinogen-related domain superfamily. MFAP4 is highly expressed in elastin-rich tissues such as lung, blood vessels and skin. MFAP4 is involved in organization of the ECM, regulating proper elastic fiber assembly. On the other hand, during pathology MFAP4 actively contributes to disease development and progression due to its interactions with RGD-dependent integrin receptors. Both tissue expression and circulating MFAP4 levels are associated with various disorders, including liver fibrosis and cancer. In other experimental models, such as teleost fish, MFAP4 appears to participate in host defense as a macrophage-specific innate immune molecule. The aim of this review is to summarize the accumulating evidence that indicates the importance of MFAP4 in homeostasis as well as pathological conditions, discuss its known biological functions with special focus on elastic fiber assembly, integrin signaling and cancer, as well as describe the reported functions of non-mammalian MFAP4 in fish. Overall, our work provides a comprehensive overview on the role of MFAP4 in health and disease.
Project description:Muscle regeneration is mediated by the activity of resident muscle satellite cells (muSCs) that express Pax7. In mouse Notch signaling regulates muSCs during quiescence and promotes muSC proliferation in regeneration. It is unclear if these roles of Notch in regulating muSC biology are conserved across vertebrates or are a mammalian specific feature. We have therefore investigated the role of Notch in regulating muSC homeostasis and regeneration in a teleost fish, the zebrafish. We have also tested whether muSCs show differential sensitivity to Notch during myotome development. In an absence of injury Notch is important for preventing muSC proliferation at the vertical myoseptum. In contrast, Notch signaling promotes proliferation and prevents differentiation in the context of injury. Notch is required for the proliferative response to injury at early and later larval stages, suggesting it plays a similar role in regulating muSCs at developing and adult stages. Our results reveal a conserved role for Notch signaling in regulating muSCs under homeostasis and for promoting proliferation during regeneration in teleost fish.
Project description:MFAP4 (microfibrillar-associated protein 4) is an extracellular glycoprotein found in elastic fibers without a clearly defined role in elastic fiber assembly. In the present study, we characterized molecular interactions between MFAP4 and elastic fiber components. We established that MFAP4 primarily assembles into trimeric and hexameric structures of homodimers. Binding analysis revealed that MFAP4 specifically binds tropoelastin and fibrillin-1 and -2, as well as the elastin cross-linking amino acid desmosine, and that it co-localizes with fibrillin-1-positive fibers in vivo. Site-directed mutagenesis disclosed residues Phe(241) and Ser(203) in MFAP4 as being crucial for type I collagen, elastin, and tropoelastin binding. Furthermore, we found that MFAP4 actively promotes tropoelastin self-assembly. In conclusion, our data identify MFAP4 as a new ligand of microfibrils and tropoelastin involved in proper elastic fiber organization.
Project description:Symbiotic bacteria and mucosal immunoglobulins have co-evolved for millions of years in vertebrate animals. Symbiotic bacteria products are known to modulate different aspects of the host immune system. We recently reported that Flectobacillus major is a predominant species that lives in the gill and skin mucosal surfaces of rainbow trout (Oncorhynchus mykiss). F. major is known to produce sphingolipids of a unique molecular structure. Here we propose a role for F. major and its sphingolipids in the regulation of B cell populations in rainbow trout, as well as an essential role for sphingolipids in trout mucosal homeostasis. We found that F. major-specific IgT titers are confined to the gill and skin mucus, whereas F. major-specific IgM titers are only detected in serum. Live F. major cells are able to stimulate sustained IgT expression and secretion in gills. F. major sphingolipids modulate the growth of trout total skin and gill symbiotic bacteria. In vivo systemic administration of F. major sphingolipids changes the proportion of IgT+ to IgM+ B cells in trout HK. These results demonstrate the key role of the symbiont F. major and its sphingolipids in mucosal homeostasis via the modulation of mucosal and systemic Igs and B cells.
Project description:Optimal activation of NF-κB signaling is crucial for the initiation of inflammatory responses and eliminating invading bacteria. Bacteria have likewise evolved the ability to evade immunity; however, mechanisms by which bacteria dysregulate host NF-κB signaling are unclear. In this study, we identify eukaryotic translation initiation factor eIF3k, a nonessential member of the eIF3 translation initiation complex, as a suppressor of the NF-κB pathway. Mechanistically, we show that eIF3k expression induced by Vibrio harveyi enhances E3 ligase Nrdp1-mediated K27-linked ubiquitination of MyD88, an upstream regulator of NF-κB pathway activation. Furthermore, we show that eIF3k acts as a bridge linking ubiquitin-tagged MyD88 and ATG5, an important mediator of autophagy. We demonstrate that the MyD88-eIF3k-ATG5 complex is transported to the autophagosome for degradation, and that innate immune signaling is subsequently terminated and does not attack invading V. harveyi. Therefore, our study identifies eIF3k as a specific inhibitor of the MyD88-dependent NF-κB pathway and suggests that eIF3k may act as a selective autophagic receptor that synergizes with ATG5 to promote the autophagic degradation of MyD88, which helps V. harveyi to evade innate immunity. We conclude that V. harveyi can manipulate a host's autophagy process to evade immunity in fish and also provide a new perspective on mammalian resistance to bacterial invasion.
Project description:Long noncoding RNAs (lncRNAs) function as microregulatory factors that influence gene expression after a variety of pathogenic infections, and they have been extensively studied in the past few years. Although less attention has been paid to lncRNAs in lower vertebrates than in mammals, current studies reveals that lncRNAs play a vital role in fish stimulated by pathogens. Here, we discovered a new lncRNA, termed MIR2187HG, which can function as a precursor of a small RNA, miR-2187-3p, with regulatory functions in the miiuy croaker (Miichthys miiuy). Upon Siniperca chuatsi rhabdovirus (SCRV) virus infection, the expression levels of MIR2187HG were remarkably enhanced. Elevated MIR2187HG expression can act as a pivotally negative regulator that participates in the innate immune response of teleost fish to inhibit the intracellular TANK-binding kinase 1 (TBK1)-mediated antiviral signaling pathways, which can effectively avoid excessive immunity. In addition, we found that SCRV could also utilize MIR2187HG to enhance its own numbers. Our results not only provide evidence regarding the involvement of the lncRNAs in response to viruses in fish but also broaden our understanding of the function of lncRNAs as precursor microRNAs (miRNAs) in teleost fish for the first time. IMPORTANCE SCRV infection upregulates MIR2187HG levels, which in turn suppresses SCRV-triggered type I interferon production, thus promoting viral replication in miiuy croaker. Notably, MIR2187HG regulates the release of miR-2187-3p, and TBK1 is a target of miR-2187-3p. MIR2187HG could acquire from miR-2187-3p the function of inhibiting TBK1 expression and subsequently modulate TBK1-mediated NF-κB and IRF3 signaling. The collective results suggest that the novel regulation mechanism of TBK1-mediated antiviral response during RNA viral infection was regulated by MIR2187HG. Therefore, a new regulation mechanism for lncRNAs to regulate antiviral immune responses in fish is proposed.
Project description:In mammals, Toll-like receptors (TLR) recognize ligands, including pathogen-associated molecular patterns (PAMPs), and respond with ligand-specific induction of genes. In this study, we establish evolutionary conservation in teleost fish of key components of the TLR-signaling pathway that act as switches for differential gene induction, including MYD88, TIRAP, TRIF, TRAF6, IRF3, and IRF7. We further explore this conservation with a molecular phylogenetic analysis of MYD88. To the extent that current genomic analysis can establish, each vertebrate has one ortholog to each of these genes. For molecular tree construction and phylogeny inference, we demonstrate a methodology for including genes with only partial primary sequences without disrupting the topology provided by the high-confidence full-length sequences. Conservation of the TLR-signaling molecules suggests that the basic program of gene regulation by the TLR-signaling pathway is conserved across vertebrates. To test this hypothesis, leukocytes from a model fish, rainbow trout (Oncorhynchus mykiss), were stimulated with known mammalian TLR agonists including: diacylated and triacylated forms of lipoprotein, flagellin, two forms of LPS, synthetic double-stranded RNA, and two imidazoquinoline compounds (loxoribine and R848). Trout leukocytes responded in vitro to a number of these agonists with distinct patterns of cytokine expression that correspond to mammalian responses. Our results support the key prediction from our phylogenetic analyses that strong selective pressure of pathogenic microbes has preserved both TLR recognition and signaling functions during vertebrate evolution.
Project description:Mediator of IRF3 activation (MITA) is a significant signal adaptor in the retinoic acid-inducible gene-I like receptor (RLR) signaling pathway and plays an important role in the innate immune system. As a transcription factor, nuclear factor kappa B (NF-κB) can be available in many signaling pathways including the RLR signaling pathway and relative to biological processes like immune responses. In this study, it is determined that IRF4b and IRF8 can have a negative effect on NF-κB signaling pathway mediated by MITA in fish. Firstly, it is found that IRF4b and IRF8 have an inhibitory function on MITA-mediated NF-κB signaling pathway. It is interesting that IRF4b and IRF8 have similar functions to achieve precise downregulated and the degradation of MITA through the ubiquitin-proteasome pathway. IRF is taken as the core domain of IRF4b or IRF8 for the downregulation to MITA. This study provides data on MITA-mediated NF-κB signaling pathway in teleost fish and provides new insights into the regulatory mechanism in fish immune system.