HMGB1, High mobility group protein B1
Also Known as
HMGB1_HUMAN, HMGB1, HMG1
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)., Nuclear functions are attributed to fully reduced HGMB1. Associates with chromatin and binds DNA with a preference to non-canonical DNA structures such as single-stranded DNA, DNA-containing cruciforms or bent structures, supercoiled DNA and ZDNA. Can bent DNA and enhance DNA flexibility by looping thus providing a mechanism to promote activities on various gene promoters by enhancing transcription factor binding and/or bringing distant regulatory sequences into close proximity (PubMed:20123072). May have an enhancing role in nucleotide excision repair (NER) (By similarity). However, effects in NER using in vitro systems have been reported conflictingly (PubMed:19446504, PubMed:19360789). May be involved in mismatch repair (MMR) and base excision repair (BER) pathways (PubMed:15014079, PubMed:16143102, PubMed:17803946). May be involved in double strand break repair such as non-homologous end joining (NHEJ) (By similarity). Involved in V(D)J recombination by acting as a cofactor of the RAG complex: acts by stimulating cleavage and RAG protein binding at the 23 bp spacer of conserved recombination signal sequences (RSS) (By similarity). In vitro can displace histone H1 from highly bent DNA (By similarity). Can restructure the canonical nucleosome leading to relaxation of structural constraints for transcription factor-binding (By similarity). Enhances binding of sterol regulatory element-binding proteins (SREBPs) such as SREBF1 to their cognate DNA sequences and increases their transcriptional activities (By similarity). Facilitates binding of TP53 to DNA (PubMed:23063560). Proposed to be involved in mitochondrial quality control and autophagy in a transcription-dependent fashion implicating HSPB1; however, this function has been questioned (By similarity). Can modulate the activity of the telomerase complex and may be involved in telomere maintenance., In the cytoplasm proposed to dissociate the BECN1:BCL2 complex via competitive interaction with BECN1 leading to autophagy activation (PubMed:20819940). Involved in oxidative stress-mediated autophagy (PubMed:21395369). Can protect BECN1 and ATG5 from calpain-mediated cleavage and thus proposed to control their proautophagic and proapoptotic functi 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).