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Oncogenic intercellular signaling is regulated by extracellular vesicles (EVs), but the underlying mechanisms remain mostly unclear. Since TCTP (translationally controlled tumor protein) is an EV component, we investigated whether it has a role in genotoxic stress signaling and malignant transformation. By generating a Tctp-inducible knockout mouse model (Tctp–/f–), we report that Tctp is required for genotoxic stress-induced apoptosis signaling via small EVs (sEVs). Human breast cancer cells knocked-down for TCTP show impaired spontaneous EV secretion, thereby reducing sEV-dependent malignant growth. Since Trp53–/– mice are prone to tumor formation, we derived tumor cells from Trp53–/–;Tctp–/f– double mutant mice and describe a drastic decrease in tumori-genicity with concomitant decrease in sEV secretion and content. Remarkably, Trp53–/–;Tctp–/f– mice show highly prolonged survival. Treatment of Trp53–/– mice with sertraline, which inhibits TCTP function, increases their survival. Mechanistically, TCTP binds DDX3, recruiting RNAs, including miRNAs, to sEVs. Our findings establish TCTP as an essential protagonist in the regulation of sEV-signaling in the context of apoptosis and tumorigenicity. Synopsis: Signaling via small extracellular vesicles (sEVs) is crucial for the regulation of cell fate. This study shows that TCTP is an essential component of sEVs, regulating their secretion, protein and RNA content, affecting thereby both apoptosis and cancer. Tctp–/f– sEVs have impaired cell death signaling capacity upon genotoxic stress. Deletion of Tctp reprograms/reverts Trp53–/–-driven tumorigenesis. Tumor-derived sEVs promote malignant transformation in a TCTP-dependent manner. TCTP binds DDX3 to regulate the transport of microRNAs into sEVs. Signaling via small extracellular vesicles (sEVs) is crucial for the regulation of cell fate. This study shows that TCTP is an essential component of sEVs, regulating their secretion, protein and RNA content, affecting thereby both apoptosis and cancer. [ABSTRACT FROM AUTHOR]

SARS‐CoV‐2 infects cells by attachment to its receptor—the angiotensin converting enzyme 2 (ACE2). Regardless of the wealth of structural data, little is known about the physicochemical mechanism of interactions of the viral spike (S) protein with ACE2 and how this mechanism has evolved during the pandemic. Here, we applied experimental and computational approaches to characterize the molecular interaction of S proteins from SARS‐CoV‐2 variants of concern (VOC). Data on kinetics, activation‐, and equilibrium thermodynamics of binding of the receptor binding domain (RBD) from VOC with ACE2 as well as data from computational protein electrostatics revealed a profound remodeling of the physicochemical characteristics of the interaction during the evolution. Thus, as compared to RBDs from Wuhan strain and other VOC, Omicron RBD presented as a unique protein in terms of conformational dynamics and types of non‐covalent forces driving the complex formation with ACE2. Viral evolution resulted in a restriction of the RBD structural dynamics, and a shift to a major role of polar forces for ACE2 binding. Further, we investigated how the reshaping of the physicochemical characteristics of interaction affects the binding specificity of S proteins. Data from various binding assays revealed that SARS‐CoV‐2 Wuhan and Omicron RBDs manifest capacity for promiscuous recognition of unrelated human proteins, but they harbor distinct reactivity patterns. These findings might contribute for mechanistic understanding of the viral tropism and capacity to evade immune responses during evolution. [ABSTRACT FROM AUTHOR]

Heme's interaction with Toll‐like receptor 4 (TLR4) does not fully explain the proinflammatory properties of this hemoglobin‐derived molecule during intravascular hemolysis. The receptor for advanced glycation end products (RAGE) shares many features with TLR4 such as common ligands and proinflammatory, prothrombotic, and pro‐oxidative signaling pathways, prompting us to study its involvement as a heme sensor. Stable RAGE‐heme complexes with micromolar affinity were detected as heme‐mediated RAGE oligomerization. The heme‐binding site was located in the V domain of RAGE. This interaction was Fe3+‐dependent and competitive with carboxymethyllysine, another RAGE ligand. We confirmed a strong basal gene expression of RAGE in mouse lungs. After intraperitoneal heme injection, pulmonary TNF‐α, IL1β, and tissue factor gene expression levels increased in WT mice but were significantly lower in their RAGE−/− littermates. This may be related to the lower activation of ERK1/2 and Akt observed in the lungs of heme‐treated, RAGE−/− mice. Overall, heme binds to RAGE with micromolar affinity and could promote proinflammatory and prothrombotic signaling in vivo, suggesting that this interaction could be implicated in heme‐overload conditions. [ABSTRACT FROM AUTHOR]

B cells producing IgG antibodies specific to a variety of self- or foreign antigens are a normal constituent of the immune system of all healthy individuals. These naturally occurring IgG antibodies are found in the serum, external secretions, and pooled human immunoglobulin preparations. They bind with low affinity to antigens, which can also be targets for pathologic autoantibodies. An enhancement of naturally occurring IgG autoantibody activity was observed after treatment of human IgG molecules with protein-destabilizing agents. We have investigated the interactions of human immunoglobulins that were obtained from serum or from breast milk of healthy individuals or IVIg with human liver antigens. Proteins from an individual serum or milk were isolated by two methods, one of which included exposure to low pH and the other did not. Purified serum, mucosal IgM, IgA, and the fraction containing immunoglobulin G F(ab')2 fragments each inhibited the binding of a single donor or pooled IgG to human liver antigens. Our study presents findings regarding the role of the breast milk or serum antibodies in blocking the self-reactivity of IgG antibodies. It supports the suggestion that not IVIg only, but also the pooled human IgM and IgA might possess a potent beneficial immunomodulatory activity in autoimmune patients. [ABSTRACT FROM AUTHOR]

IgG molecules are exposed on a regular basis to acidic conditions during immunoaffinity purification procedures, as well as during the production of some therapeutic immunoglobulin preparations. This exposure is known to induce in them an antigen-binding polyreactivity. The molecular mechanisms and the possible biological significance of this phenomenon remain, however, poorly understood. In addition to the previously reported ability of these modified IgG antibodies to interact with a large panel of self-antigens, enhanced binding to non-self-antigens (bacterial), an increased ability to engage in F(ab′)2/F(ab′)2 (idiotype/anti-idiotype) interactions and an increased functional antigen-binding affinity are reported here. The newly acquired ‘induced polyreactivity’ of low-pH buffer-exposed IgG is related to structural changes in the immunoglobulin molecules, and is at least partly attributable to the enhanced role of the hydrophobic effect in their interactions with antigen. Our results suggest that data from many previous studies on monoclonal and polyclonal IgG antibodies purified by low-pH buffer elution from protein A or protein G immunoaffinity columns should be reconsidered, as the procedure itself may have dramatically affected their antigen-binding behavior and biological activity. Low-pH buffer-treated pooled therapeutic immunoglobulins acquire novel beneficial properties, as passive immunotherapy with the pH 4.0 buffer-exposed, but not with the native therapeutic intravenous immunoglobulin preparation, improves the survival of mice with bacterial lipopolysaccharide-induced septic shock. [ABSTRACT FROM AUTHOR]

Abstract: Anti-factor VIII (FVIII) inhibitory IgG may arise as alloantibodies to therapeutic FVIII in patients with congenital hemophilia A, or as autoantibodies to endogenous FVIII in individuals with acquired hemophilia. We have described FVIII-hydrolyzing IgG both in hemophilia A patients with anti-FVIII IgG and in acquired hemophilia patients. Here, we compared the properties of proteolytic auto- and allo-antibodies. Rates of FVIII hydrolysis differed significantly between the two groups of antibodies. Proline-phenylalanine-arginine-methylcoumarinamide was a surrogate substrate for FVIII-hydrolyzing autoantibodies. Our data suggest that populations of proteolytic anti-FVIII IgG in acquired hemophilia patients are different from that of inhibitor-positive hemophilia A patients. [Copyright &y& Elsevier]