High mobility group box 1 protein, also known as high-mobility group protein 1 (HMG-1) and amphoterin, is a protein that in humans is encoded by the HMGB1 gene. [3] [4]
HMG-1 belongs to the high mobility group and contains a HMG-box domain.
High mobility group box 1 protein, also known as high-mobility group protein 1 (HMG-1) and amphoterin, is a protein that in humans is encoded by the HMGB1 gene. [3] [4]
HMG-1 belongs to the high mobility group and contains a HMG-box domain.
Like the histones, HMGB1 is among the most important chromatin proteins. In the nucleus HMGB1 interacts with nucleosomes, transcription factors, and histones. [5] This nuclear protein organizes the DNA and regulates transcription. [6] After binding, HMGB1 bends [7] DNA, which facilitates the binding of other proteins. HMGB1 supports transcription of many genes in interactions with many transcription factors. It also interacts with nucleosomes to loosen packed DNA and remodel the chromatin. Contact with core histones changes the structure of nucleosomes.
The presence of HMGB1 in the nucleus depends on posttranslational modifications. When the protein is not acetylated, it stays in the nucleus, but hyperacetylation on lysine residues causes it to translocate into the cytosol. [6]
HMGB1 has been shown to play an important role in helping the RAG endonuclease form a paired complex during V(D)J recombination. [8]
HMGB1 is secreted by immune cells (like macrophages, monocytes and dendritic cells) through leaderless secretory pathway. [6] Activated macrophages and monocytes secrete HMGB1 as a cytokine mediator of Inflammation. [9] Antibodies that neutralize HMGB1 confer protection against damage and tissue injury during arthritis, colitis, ischemia, sepsis, endotoxemia, and systemic lupus erythematosus.[ citation needed ] The mechanism of inflammation and damage consists of binding to toll-like receptor TLR2 and TLR4, which mediates HMGB1-dependent activation of macrophage cytokine release. This positions HMGB1 at the intersection of sterile and infectious inflammatory responses. [10] [11]
ADP-ribosylation of HMGB1 by PARP1 inhibits removal of apoptotic cells, thereby sustaining inflammation. [12] TLR4 binding by HMGB1 or LPS (lipopolysaccharide) sustains ADP-ribosylation of HMGB1 by PARP1 thereby serving as an amplification loop for inflammation. [12]
HMGB1 has been proposed as a DNA vaccine adjuvant. [13] HMGB1 released from tumour cells was demonstrated to mediate anti-tumour immune responses by activating Toll-like receptor 2 (TLR2) signaling on bone marrow-derived GBM-infiltrating DCs. [14]
HMGB1 has to interact with p53. [15] [16]
HMGB1 is a nuclear protein that binds to DNA and acts as an architectural chromatin-binding factor. It can also be released from cells, in which extracellular form it can bind the inflammatory receptor RAGE (Receptor for Advanced Glycation End-products) and Toll-like receptors (TLRs). Release from cells seems to involve two distinct processes: necrosis, in which case cell membranes are permeabilized and intracellular constituents may diffuse out of the cell; and some form of active or facilitated secretion induced by signaling through the NF-κB. HMGB1 also translocates to the cytosol under stressful conditions such as increased ROS inside the cells. Under such conditions, HMGB1 promotes cell survival by sustaining autophagy through interactions with beclin-1. It is largely considered as an antiapoptotic protein.
HMGB1 can interact with TLR ligands and cytokines, and activates cells through the multiple surface receptors including TLR2, TLR4, and RAGE. [17]
Some actions of HMGB1 are mediated through the toll-like receptors (TLRs). [18] Interaction between HMGB1 and TLR4 results in upregulation of NF-κB, which leads to increased production and release of cytokines. HMGB1 is also able to interact with TLR4 on neutrophils to stimulate the production of reactive oxygen species by NADPH oxidase. [6] [19] HMGB1-LPS complex activates TLR4, and causes the binding of adapter proteins (MyD88 and others), leading to signal transduction and the activation of various signaling cascades. The downstream effect of this signaling is to activate MAPK and NF-κB, and thus cause the production of inflammatory molecules such as cytokines. [20] [21]
HMGB1 has been proposed as a target for cancer therapy, [22] as well as a vector for reducing inflammation from SARS-CoV-2 infection. [23] It also serves as a biomarker for post-COVID-19 condition. [24]
The neurodegenerative disease spinocerebellar ataxia type 1 (SCA1) is caused by mutation in the ataxin 1 gene. In a mouse model of SCA1, mutant ataxin 1 protein mediated the reduction or inhibition of HMGB1 in the mitochondria of neurons. [25] HMGB1 regulates DNA architectural changes essential for repair of DNA damage. In the SCA1 mouse model, over-expression of the HMGB1 protein by means of an introduced virus vector bearing the HMGB1 gene facilitated repair of the mitochondrial DNA damage, ameliorated the neuropathology and the motor defects of the SCA1 mice, and also extended their lifespan. [25] Thus impairment of HMGB1 function appears to have a key role in the pathogenesis of SCA1.
Recently, a study provided evidence of an association between raised levels of HMGB1 and attention to detail and systemizing in unmedicated children with high-functioning Autism spectrum disorder (ASD), suggesting that inflammatory processes mediated by HMGB1 may play a role in the disruption of neurobiological mechanisms regulating cognitive processes in ASD. [26] In this study, HMGB1 serum concentrations in children with ASD were found significantly higher than those of typically developing children. Additionally, HMGB1 serum concentrations were positively correlated with the Autistic quotient (AQ) attention to detail score and the Systemizing Quotient (SQ) total score in the ASD group. [27] However, comprehensive evidence in children is limited, highlighting the need for in-depth research towards understanding possible mechanisms linking HMGB1 with the core features of ASD. Nevertheless, it has been suggested that HMGB1 could be a reliable inflammatory marker, explaining the link between inflammatory processes and several autistic traits, and therefore a possible therapeutic target in this neurodevelopmental disorder.
The JAK-STAT signaling pathway is a chain of interactions between proteins in a cell, and is involved in processes such as immunity, cell division, cell death, and tumor formation. The pathway communicates information from chemical signals outside of a cell to the cell nucleus, resulting in the activation of genes through the process of transcription. There are three key parts of JAK-STAT signalling: Janus kinases (JAKs), signal transducer and activator of transcription proteins (STATs), and receptors. Disrupted JAK-STAT signalling may lead to a variety of diseases, such as skin conditions, cancers, and disorders affecting the immune system.
The innate immune system or nonspecific immune system is one of the two main immunity strategies in vertebrates. The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants, fungi, prokaryotes, and invertebrates.
RAGE, also called AGER, is a 35 kilodalton transmembrane receptor of the immunoglobulin super family which was first characterized in 1992 by Neeper et al. Its name comes from its ability to bind advanced glycation endproducts (AGE), which include chiefly glycoproteins, the glycans of which have been modified non-enzymatically through the Maillard reaction. In view of its inflammatory function in innate immunity and its ability to detect a class of ligands through a common structural motif, RAGE is often referred to as a pattern recognition receptor. RAGE also has at least one other agonistic ligand: high mobility group protein B1 (HMGB1). HMGB1 is an intracellular DNA-binding protein important in chromatin remodeling which can be released by necrotic cells passively, and by active secretion from macrophages, natural killer cells, and dendritic cells.
Mothers against decapentaplegic homolog 3 also known as SMAD family member 3 or SMAD3 is a protein that in humans is encoded by the SMAD3 gene.
High-Mobility Group or HMG is a group of chromosomal proteins that are involved in the regulation of DNA-dependent processes such as transcription, replication, recombination, and DNA repair.
Ataxin-1 is a DNA-binding protein which in humans is encoded by the ATXN1 gene.
Toll-like receptor 4 (TLR4), also designated as CD284, is a key activator of the innate immune response and plays a central role in the fight against bacterial infections. TLR4 is a transmembrane protein of approximately 95 kDa that is encoded by the TLR4 gene.
GRB2-associated-binding protein 2 also known as GAB2 is a protein that in humans is encoded by the GAB2 gene.
Signal transducer and activator of transcription 6 (STAT6) is a transcription factor that belongs to the Signal Transducer and Activator of Transcription (STAT) family of proteins. The proteins of STAT family transmit signals from a receptor complex to the nucleus and activate gene expression. Similarly as other STAT family proteins, STAT6 is also activated by growth factors and cytokines. STAT6 is mainly activated by cytokines interleukin-4 and interleukin-13.
Signal transducer and activator of transcription 4 (STAT4) is a transcription factor belonging to the STAT protein family, composed of STAT1, STAT2, STAT3, STAT4, STAT5A, STAT5B, STAT6. STAT proteins are key activators of gene transcription which bind to DNA in response to cytokine gradient. STAT proteins are a common part of Janus kinase (JAK)- signalling pathways, activated by cytokines.STAT4 is required for the development of Th1 cells from naive CD4+ T cells and IFN-γ production in response to IL-12. There are two known STAT4 transcripts, STAT4α and STAT4β, differing in the levels of interferon-gamma production downstream.
The nuclear receptor 4A1 also known as Nur77, TR3, and NGFI-B is a protein that in humans is encoded by the NR4A1 gene.
Toll-like receptor 9 is a protein that in humans is encoded by the TLR9 gene. TLR9 has also been designated as CD289. It is a member of the toll-like receptor (TLR) family. TLR9 is an important receptor expressed in immune system cells including dendritic cells, macrophages, natural killer cells, and other antigen presenting cells. TLR9 is expressed on endosomes internalized from the plasma membrane, binds DNA, and triggers signaling cascades that lead to a pro-inflammatory cytokine response. Cancer, infection, and tissue damage can all modulate TLR9 expression and activation. TLR9 is also an important factor in autoimmune diseases, and there is active research into synthetic TLR9 agonists and antagonists that help regulate autoimmune inflammation.
High-mobility group protein HMG-I/HMG-Y is a protein that in humans is encoded by the HMGA1 gene.
Lymphoid enhancer-binding factor 1 (LEF1) is a protein that in humans is encoded by the LEF1 gene. It is a member of T cell factor/lymphoid enhancer factor (TCF/LEF) family.
High-mobility group protein B2 also known as high-mobility group protein 2 (HMG-2) is a protein that in humans is encoded by the HMGB2 gene.
Hepatitis A virus cellular receptor 2 (HAVCR2), also known as T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), is a protein that in humans is encoded by the HAVCR2 (TIM-3) gene. HAVCR2 was first described in 2002 as a cell surface molecule expressed on IFNγ producing CD4+ Th1 and CD8+ Tc1 cells. Later, the expression was detected in Th17 cells, regulatory T-cells, and innate immune cells. HAVCR2 receptor is a regulator of the immune response.
Single Ig IL-1-related receptor (SIGIRR), also called Toll/Interleukin-1 receptor 8 (TIR8) or Interleukin-1 receptor 8 (IL-1R8), is transmembrane protein encoded by gene SIGIRR, which modulate inflammation, immune response, and tumorigenesis of colonic epithelial cells.
Thymocyte selection-associated high mobility group box protein TOX is a protein that in humans is encoded by the TOX gene. TOX drives T-cell exhaustion and plays a role in innate lymphoid cell development.
Damage-associated molecular patterns (DAMPs) are molecules within cells that are a component of the innate immune response released from damaged or dying cells due to trauma or an infection by a pathogen. They are also known as danger signals, and alarmins because they serve as warning signs to alert the organism to any damage or infection to its cells. DAMPs are endogenous danger signals that are discharged to the extracellular space in response to damage to the cell from mechanical trauma or a pathogen. Once a DAMP is released from the cell, it promotes a noninfectious inflammatory response by binding to a pattern recognition receptor (PRR). Inflammation is a key aspect of the innate immune response; it is used to help mitigate future damage to the organism by removing harmful invaders from the affected area and start the healing process. As an example, the cytokine IL-1α is a DAMP that originates within the nucleus of the cell which, once released to the extracellular space, binds to the PRR IL-1R, which in turn initiates an inflammatory response to the trauma or pathogen that initiated the release of IL-1α. In contrast to the noninfectious inflammatory response produced by DAMPs, pathogen-associated molecular patterns (PAMPs) initiate and perpetuate the infectious pathogen-induced inflammatory response. Many DAMPs are nuclear or cytosolic proteins with defined intracellular function that are released outside the cell following tissue injury. This displacement from the intracellular space to the extracellular space moves the DAMPs from a reducing to an oxidizing environment, causing their functional denaturation, resulting in their loss of function. Outside of the aforementioned nuclear and cytosolic DAMPs, there are other DAMPs originated from different sources, such as mitochondria, granules, the extracellular matrix, the endoplasmic reticulum, and the plasma membrane.
Murine caspase-11, and its human homologs caspase-4 and caspase-5, are mammalian intracellular receptor proteases activated by TLR4 and TLR3 signaling during the innate immune response. Caspase-11, also termed the non-canonical inflammasome, is activated by TLR3/TLR4-TRIF signaling and directly binds cytosolic lipopolysaccharide (LPS), a major structural element of Gram-negative bacterial cell walls. Activation of caspase-11 by LPS is known to cause the activation of other caspase proteins, leading to septic shock, pyroptosis, and often organismal death.
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