Table 1.

Interactions of HmgB1 with other proteins.

Localization of Protein	Partner	Functions
Nuclear HmgB1	Linker histone H1	C-terminal sequence of HmgB1 binds N-terminal region of H1, disrupting its interactions with DNA and leading to the displacement of H1 [29,30] to facilitate the sliding of nucleosome along the DNA, which is essential for the binding of transcription factors [12,72,83].
	Transcription factors	The interaction of transcription factors with DNA might occur via the formation of an intermediate complex TF1–DNA–HmgB1, whose formation induces attachment of other regulatory chromatin proteins [11].
	Hsp70, MSH2, MLH1	HmgB1 works during the initial stages of recognition/damage of the DNA and interacts with MMR proteins, [113,114,115].
	Enzymes which take part in BER and NER	Base excision repair (BER) and nucleotide excision repair (NER) are also associated with the interaction between HmgB1 and various enzymes [67,68,69,70,116,117,118].
	DNA-dependent protein kinase RAG1 and RAG2 proteins T4 DNA ligase	Repair of double-strand breaks (DSBR) involves DNA-dependent protein kinase (DNA-PKcs) [119]: in vitro HmgB1 protein stimulates activity of DNA-Pkcs [119], RAG1, and RAG2 proteins [120] and increases the activity of T4 DNA ligase [121]. The complex between RAG1, RAG2, and HmgB1 proteins induces the formation of hairpin on DNA [122].
	Tumor suppressor p53 protein	Interaction of p53 with the A-domain of HmgB1 is regulated by C-terminal tail of HmgB1 [131]. HmgB1/p53 complex regulates apoptosis and autophagy [135,136].
	Nuclear factor (NF)-κB Steroid hormone receptors Glucocorticoid receptors	HmgB1 regulates the transcriptional activity of these proteins [133,160].
	Nuclear export protein CRM1	N-glycosylation of HmgB1 is important for binding with CRM1 [85].
	LPS (lipopolysaccharide)	N-glycosylation of HmgB1 is mediated by phorbol 12-myristate 13-acetate (PMA), trichostatin A (TSA) and lipopolysaccharide (LPS) and can lead to the secretion of the protein into the extracellular space as a result of decreasing HmgB1-DNA binding affinity and increasing association with nuclear export protein CRM1 [85].
	cPKC (calcium/phospholipid-dependent protein kinase C)	In vertebrates, phosphorylation of HmgB1 involves calcium/phospholipid-dependent protein kinase C (cPKC) by the PI3K-PKC signaling pathway [77].
	Phosphatase inhibitors (TNF-α or okadaic acid)	HmgB1 can be phosphorylated in mouse macrophage cells RAW264.7 and human monocytes after their treatment with these phosphatase inhibitors, leading to HmgB1 translocation to cytoplasm with possible subsequent secretion into the extracellular space [75].
	PARP1 (poly-ADP-ribose polymerase 1)	PARP1 promotes repair of damaged bases and single-stranded DNA breaks by modulating the structure of chromatin and binding DNA repair factors [89]. Thus, there is a cross-link between ADP-ribosylation of HmgB1 and PARP1 in regulating cell death.
Extranuclear HmgB1	RAGE (receptor for advanced glycation end products)	ADP-ribosylation affects the binding of HmgB1 to RAGE [88]. fr-HmgB1 can bind to RAGE and promote autophagy by inhibiting mTOR kinase and promoting Beclin1–Ptdlns3KC3 complex formation [171]. RAGE binding to fr-HmgB1 stimulates production of CXCL12. ds-HmgB1–RAGE interaction leads to activation of neutrophils and the formation of their extracellular traps [164,165].
	Toll-like receptor TLR9	HmgB1 interacts with TLR9, increasing cytokine production [168].
	Toll-like receptors TLR2 and TLR4	ds-HmgB1/TLR4-MD2 complex stimulates release of inflammatory and angiogenic factors by activation of transcription nuclear factor NF-κB. The interaction of HmgB1 with TLR2 or TLR4 regulates inflammation process when lungs or liver are damaged due to epilepsy, heart disease, or cancer [52].
	Toll-like receptor TLR5	The HmgB1–TLR5 complex activates the NF-κB signaling pathway through the adapter protein MyD88, involved in signal transmission from toll-like receptors, which leads to increased synthesis of pro-inflammatory cytokines [152].
	TIM-3 (T cell immunoglobulin mucin-3)	The interaction of HmgB1 with TIM-3 inhibits the activity of dendritic cells [152].
	Rap1 (Ras-associated protein-1)	HmgB1 activates signal pathway of Rap1 [185].
	TLR9	HmgB1 interacts with TLR9 of endoplasmic reticulum and Golgi complex [152].
	Illexin IL-6	The oxidized form of the HMGB1 protein stimulates the secretion of pro-inflammatory cytokines, including IL-6 by activation of the TLR-4 receptor [152].