HMGB1 Antibody

Description: High mobility group protein B1 (HMGB1) belongs to a family of highly conserved proteins that contain HMG box domains (1, 2). All three family members (HMGB1, HMGB2, and HMGB3) contain two HMG box domains and a C-terminal acidic domain. HMGB1 is a widely expressed and highly abundant protein (2). HMGB2 is widely expressed during embryonic development, but is restricted to lymphoid organs and testis in adult animals (3). HMGB3 is only expressed during embryogenesis (4). While expression varies, the biochemical properties of the different family members may be indistinguishable. The HMG box domains facilitate the binding of HMGB proteins to the minor groove of DNA, which results in local bending of the DNA double helix (1, 2). HMGB proteins are recruited by and help facilitate the assembly of site-specific DNA binding proteins to their cognate binding sites in chromatin. For example, HMGB1 facilitates the binding of Hox proteins, Oct-1, p53, Rel proteins, and steroid hormone receptor proteins to their target gene promoters (1, 2). In addition to their functions in the nucleus, HMGB proteins play a significant role in extracellular signaling associated with inflammation (5, 6). HMGB1 is massively released into the extracellular environment during cell necrosis, but not apoptosis. Extracellular HMGB1 alarms the innate immune system by acting as a chemoattractant for inflammatory leukocytes, smooth muscle cells, and stem cells, functioning as an immune adjuvant for soluble and particulate antigens, and triggering activation of T cells and dendritic cells. In addition, activated monocytes, macrophages and, dendritic cells also secrete HMGB1, forming a positive feedback loop that results in the release of additional cytokines and neutrophils. Hypoxia has also been shown to cause the release of HMGB1 in the liver, and some studies suggest a role for extracellular HMGB1 in tumor homeostasis (5, 6).
Function: Multifunctional redox sensitive protein with various roles in different cellular compartments. In the nucleus is one of the major chromatin-associated non-histone proteins and acts as a DNA chaperone involved in replication, transcription, chromatin remodeling, V(D)J recombination, DNA repair and genome stability. Proposed to be an universal biosensor for nucleic acids. Promotes host inflammatory response to sterile and infectious signals and is involved in the coordination and integration of innate and adaptive immune responses. In the cytoplasm functions as sensor and/or chaperone for immunogenic nucleic acids implicating the activation of TLR9-mediated immune responses, and mediates autophagy. Acts as danger associated molecular pattern (DAMP) molecule that amplifies immune responses during tissue injury (PubMed:27362237). Released to the extracellular environment can bind DNA, nucleosomes, IL-1 beta, CXCL12, AGER isoform 2/sRAGE, lipopolysaccharide (LPS) and lipoteichoic acid (LTA), and activates cells through engagement of multiple surface receptors. In the extracellular compartment fully reduced HMGB1 (released by necrosis) acts as a chemokine, disulfide HMGB1 (actively secreted) as a cytokine, and sulfonyl HMGB1 (released from apoptotic cells) promotes immunological tolerance (PubMed:23519706, PubMed:23446148, PubMed:23994764, PubMed:25048472). Has proangiogdenic activity (By similarity). May be involved in platelet activation (By similarity). Binds to phosphatidylserine and phosphatidylethanolamide (By similarity). Bound to RAGE mediates signaling for neuronal outgrowth (By similarity). May play a role in accumulation of expanded polyglutamine (polyQ) proteins such as huntingtin (HTT) or TBP (PubMed:23303669, PubMed:25549101).
Subunit Structure: Interacts (fully reduced HMGB1) with CXCL12; probably in a 1:2 ratio involving two molecules of CXCL12, each interacting with one HMG box of HMGB1; inhibited by glycyrrhizin (PubMed:22370717). Associates with the TLR4:LY96 receptor complex (PubMed:20547845). Component of the RAG complex composed of core components RAG1 and RAG2, and associated component HMGB1 or HMGB2 (By similarity). Interacts (in cytoplasm upon starvation) with BECN1; inhibits the interaction of BECN1 and BCL2 leading to promotion of autophagy (PubMed:20819940). Interacts with KPNA1; involved in nuclear import (PubMed:17114460). Interacts with SREBF1, TLR2, TLR4, TLR9, PTPRZ1, APEX1, FEN1, POLB, TERT (By similarity). Interacts with IL1B, AGER, MSH2, XPA, XPC, HNF1A, TP53 (PubMed:15014079, PubMed:18250463, PubMed:18160415, PubMed:19446504, PubMed:24474694, PubMed:23063560). Interacts with CD24; the probable CD24:SIGLEC10 complex is proposed to inhibit HGMB1-mediated tissue damage immune response (PubMed:19264983). Interacts with THBD; prevents HGMB1 interaction with ACER/RAGE and inhibits HGMB1 proinflammatory activity (PubMed:15841214). Interacts with HAVCR2; impairs HMGB1 binding to B-DNA and likely HMGB1-mediated innate immume response (By similarity). Interacts with XPO1; mediating nuclear export (By similarity). Interacts with HTT (wild-type and mutant HTT with expanded polyglutamine repeat) (PubMed:23303669).
Post-translational Modifications: Phosphorylated at serine residues. Phosphorylation in both NLS regions is required for cytoplasmic translocation followed by secretion (PubMed:17114460). Acetylated on multiple sites upon stimulation with LPS (PubMed:22801494). Acetylation on lysine residues in the nuclear localization signals (NLS 1 and NLS 2) leads to cytoplasmic localization and subsequent secretion (By similarity). Acetylation on Lys-3 results in preferential binding to DNA ends and impairs DNA bending activity (By similarity). Reduction/oxidation of cysteine residues Cys-23, Cys-45 and Cys-106 and a possible intramolecular disulfide bond involving Cys-23 and Cys-45 give rise to different redox forms with specific functional activities in various cellular compartments: 1-fully reduced HMGB1 (HMGB1C23hC45hC106h), 2-disulfide HMGB1 (HMGB1C23-C45C106h) and 3-sulfonyl HMGB1 (HMGB1C23soC45soC106so). Poly-ADP-ribosylated by PARP1 when secreted following stimulation with LPS (By similarity). In vitro cleavage by CASP1 is liberating a HMG box 1-containing peptide which may mediate immunogenic activity; the peptide antagonizes apoptosis-induced immune tolerance (PubMed:24474694). Can be proteolytically cleaved by a thrombin:thrombomodulin complex; reduces binding to heparin and proinflammatory activities (By similarity).
Similarity: HMG box 2 mediates proinflammatory cytokine-stimulating activity and binding to TLR4 (PubMed:12765338, PubMed:20547845). However, not involved in mediating immunogenic activity in the context of apoptosis-induced immune tolerance (PubMed:24474694).The acidic C-terminal domain forms a flexible structure which can reversibly interact intramolecularily with the HMG boxes and modulate binding to DNA and other proteins (PubMed:23063560). Belongs to the HMGB family.