HMGB1 protein and linker histone H1 have overlapping binding sites in the nucleosome. HMGB1 has been implicated in many DNA-dependent processes in chromatin involving binding of specific proteins, including transcription factors, to DNA sites pre-bent by HMGB1. HMGB1 can also act as an extracellular signaling molecule by promoting inflammation, tumor growth a metastasis. Many of the intra- and extracellular functions of HMGB1 depend on redox-sensitive cysteine residues of the protein. Here we report that mild oxidization of HMGB1 (and much less mutation of cysteines involved in disulphide bond formation) can severely compromise the functioning of the protein as a DNA chaperone by inhibiting its ability to unwind or bend DNA. Histone H1 (via the highly basic C-terminal domain) significantly inhibits DNA bending by the full-length HMGB1, and the inhibition is further enhanced upon oxidization of HMGB1. Interestingly, DNA bending by HMGB1 lacking the acidic C-tail (HMGB1ΔC) is much less affected by histone H1, but oxidization rendered DNA bending by HMGB1ΔC and HMGB1 equally prone for inhibition by histone H1. Possible consequences of histone H1-mediated inhibition of DNA bending by HMGB1 of different redox state for the functioning of chromatin are discussed.

• MeSH
• Cysteine genetics   metabolism   MeSH
• Histones chemistry   genetics   metabolism   MeSH
• Rats MeSH
• Models, Molecular MeSH
• Mutation MeSH
• Nucleosomes MeSH
• Oxidation-Reduction MeSH
• HMGB1 Protein chemistry   genetics   metabolism   MeSH
• DNA, Superhelical metabolism   MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cysteine MeSH
• Hbp1 protein, rat MeSH Browser
• Histones MeSH
• Nucleosomes MeSH
• HMGB1 Protein MeSH
• DNA, Superhelical MeSH

HMGB1 is an architectural protein in chromatin, acting also as a signaling molecule outside the cell. Recent reports from several laboratories provided evidence that a number of both the intracellular and extracellular functions of HMGB1 may depend on redox-sensitive cysteine residues of the protein. In this study we demonstrate that redox state of HMGB1 can significantly modulate the ability of the protein to bind and bend DNA, as well as to promote DNA end-joining. We also report a high affinity binding of histone H1 to hemicatenated DNA loops and DNA minicircles. Finally, we show that reduced HMGB1 can readily displace histone H1 from DNA, while oxidized HMGB1 has limited capacity for H1 displacement. Our results suggested a novel mechanism for the HMGB1-mediated modulation of histone H1 binding to DNA. Possible biological consequences of linker histones H1 replacement by HMGB1 for the functioning of chromatin are discussed.

• MeSH
• Chromatin genetics   metabolism   MeSH
• Gene Expression MeSH
• Genetic Vectors chemistry   MeSH
• Histones genetics   metabolism   MeSH
• DNA, Concatenated genetics   metabolism   MeSH
• DNA, Circular genetics   metabolism   MeSH
• Rats MeSH
• Humans MeSH
• Oxidation-Reduction MeSH
• HMGB1 Protein genetics   metabolism   MeSH
• Recombinant Proteins genetics   metabolism   MeSH
• Cattle MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Cattle MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chromatin MeSH
• Histones MeSH
• DNA, Concatenated MeSH
• DNA, Circular MeSH
• HMGB1 Protein MeSH
• Recombinant Proteins MeSH

Telomere repeats are added onto chromosome ends by telomerase, consisting of two main core components: a catalytic protein subunit (telomerase reverse trancriptase, TERT), and an RNA subunit (telomerase RNA, TR). Here, we report for the first time evidence that HMGB1 (a chromatin-associated protein in mammals, acting as a DNA chaperone in transcription, replication, recombination, and repair) can modulate cellular activity of mammalian telomerase. Knockout of the HMGB1 gene (HMGB1 KO) in mouse embryonic fibroblasts (MEFs) results in chromosomal abnormalities, enhanced colocalization of γ-H2AX foci at telomeres, and a moderate shortening of telomere lengths. HMGB1 KO MEFs also exhibit significantly (>5-fold) lower telomerase activity than the wild-type MEFs. Correspondingly, enhanced telomerase activity is observed upon overexpression of HMGB1 in MEFs. HMGB1 physically interacts with both TERT and TR, as well as with active telomerase complex in vitro. However, direct interaction of HMGB1 with telomerase is most likely not accountable for the observed higher telomerase activity in HMGB1-containing cells, as revealed from the inability of purified HMGB1 protein to stimulate telomerase activity in vitro. While no transcriptional silencing of TERT is observed in HMGB1 KO MEFs, levels of TR are diminished (~3-fold), providing possible explanation for the observed lower telomerase activity in HMGB1 KO cells. Interestingly, knockout of the HMGB2 gene elevates telomerase activity (~3-fold) in MEFs, suggesting that the two closely related proteins of the HMGB family, HMGB1 and HMGB2, have opposite effects on telomerase activity in the cell. The ability of HMGB1 to modulate cellular activity of telomerase and to maintain telomere integrity can help to understand some aspects of the protein involvement in chromosome stability and cancer.

• MeSH
• Cell Line MeSH
• Chromosome Aberrations MeSH
• Down-Regulation MeSH
• Fibroblasts cytology   metabolism   MeSH
• Microscopy, Fluorescence MeSH
• DNA Fragmentation MeSH
• Gene Knockout Techniques * MeSH
• Histones genetics   metabolism   MeSH
• In Situ Hybridization, Fluorescence MeSH
• Mice MeSH
• DNA Damage MeSH
• HMGB1 Protein genetics   metabolism   MeSH
• HMGB2 Protein genetics   metabolism   MeSH
• DNA Replication MeSH
• RNA genetics   metabolism   MeSH
• Telomerase genetics   metabolism   MeSH
• Telomere metabolism   pathology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• gamma-H2AX protein, mouse MeSH Browser
• Histones MeSH
• HMGB1 Protein MeSH
• HMGB2 Protein MeSH
• RNA MeSH
• Telomerase MeSH
• telomerase RNA MeSH Browser
• Tert protein, mouse MeSH Browser

DNA topoisomerase IIalpha (topo IIalpha) is an essential nuclear enzyme and its unique decatenation activity has been implicated in many aspects of chromosome dynamics such as chromosome replication and segregation during mitosis. Here we show that chromatin-associated protein HMGB1 (a member of the large family of HMG-box proteins with possible functions in DNA replication, transcription, recombination and DNA repair) promotes topo IIalpha-mediated catenation of circular DNA, relaxation of negatively supercoiled DNA and decatenation of kinetoplast DNA. HMGB1 interacts with topo IIalpha and this interaction, like the stimulation of the catalytic activity of the enzyme, requires both HMG-box domains of HMGB1. A mutant of HMGB1, which cannot change DNA topology stimulates DNA decatenation by topo IIalpha indistinguishably from the wild-type protein. Although HMGB1 stimulates ATP hydrolysis by topo IIalpha, the DNA cleavage is much more enhanced. The observed abilities of HMGB1 to interact with topo IIalpha and promote topo IIalpha binding to DNA suggest a mechanism by which HMGB1 stimulates the catalytic activity of the enzyme via enhancement of DNA cleavage.

• MeSH
• Adenosine Triphosphate metabolism   MeSH
• Antigens, Neoplasm metabolism   MeSH
• Diketopiperazines MeSH
• DNA-Binding Proteins metabolism   MeSH
• DNA Topoisomerases, Type II metabolism   MeSH
• DNA chemistry   metabolism   ultrastructure   MeSH
• Electrophoresis, Agar Gel MeSH
• Enzyme Inhibitors pharmacology   MeSH
• Catalysis MeSH
• DNA, Kinetoplast metabolism   MeSH
• Nucleic Acid Conformation MeSH
• DNA, Circular metabolism   MeSH
• Rats MeSH
• Humans MeSH
• Piperazines pharmacology   MeSH
• HMGB1 Protein MeSH
• High Mobility Group Proteins metabolism   MeSH
• Repressor Proteins metabolism   MeSH
• DNA, Superhelical metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione MeSH Browser
• Adenosine Triphosphate MeSH
• Antigens, Neoplasm MeSH
• Diketopiperazines MeSH
• DNA-Binding Proteins MeSH
• DNA Topoisomerases, Type II MeSH
• DNA MeSH
• Hbp1 protein, rat MeSH Browser
• Enzyme Inhibitors MeSH
• DNA, Kinetoplast MeSH
• DNA, Circular MeSH
• Piperazines MeSH
• HMGB1 Protein MeSH
• High Mobility Group Proteins MeSH
• Repressor Proteins MeSH
• DNA, Superhelical MeSH