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

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 cruciforms play an important role in the regulation of natural processes involving DNA. These structures are formed by inverted repeats, and their stability is enhanced by DNA supercoiling. Cruciform structures are fundamentally important for a wide range of biological processes, including replication, regulation of gene expression, nucleosome structure and recombination. They also have been implicated in the evolution and development of diseases including cancer, Werner's syndrome and others.Cruciform structures are targets for many architectural and regulatory proteins, such as histones H1 and H5, topoisomerase IIβ, HMG proteins, HU, p53, the proto-oncogene protein DEK and others. A number of DNA-binding proteins, such as the HMGB-box family members, Rad54, BRCA1 protein, as well as PARP-1 polymerase, possess weak sequence specific DNA binding yet bind preferentially to cruciform structures. Some of these proteins are, in fact, capable of inducing the formation of cruciform structures upon DNA binding. In this article, we review the protein families that are involved in interacting with and regulating cruciform structures, including (a) the junction-resolving enzymes, (b) DNA repair proteins and transcription factors, (c) proteins involved in replication and (d) chromatin-associated proteins. The prevalence of cruciform structures and their roles in protein interactions, epigenetic regulation and the maintenance of cell homeostasis are also discussed.

• MeSH
• DNA-Binding Proteins chemistry   metabolism   MeSH
• DNA chemistry   metabolism   ultrastructure   MeSH
• Nucleic Acid Conformation * MeSH
• Protein Conformation MeSH
• Molecular Sequence Data MeSH
• Gene Expression Regulation * MeSH
• DNA Replication * MeSH
• Base Sequence MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• DNA-Binding Proteins MeSH
• DNA MeSH

Topoisomerase IIalpha (topo IIalpha) is a nuclear enzyme involved in several critical processes, including chromosome replication, segregation and recombination. Previously we have shown that chromosomal protein HMGB1 interacts with topo IIalpha, and stimulates its catalytic activity. Here we show the effect of HMGB1 on the activity of the human topo IIalpha gene promoter in different cell lines. We demonstrate that HMGB1, but not a mutant of HMGB1 incapable of DNA bending, up-regulates the activity of the topo IIalpha promoter in human cells that lack functional retinoblastoma protein pRb. Transient over-expression of pRb in pRb-negative Saos-2 cells inhibits the ability of HMGB1 to activate the topo IIalpha promoter. The involvement of HMGB1 and its close relative, HMGB2, in modulation of activity of the topo IIalpha gene is further supported by knock-down of HMGB1/2, as evidenced by significantly decreased levels of topo IIalpha mRNA and protein. Our experiments suggest a mechanism of up-regulation of cellular expression of topo IIalpha by HMGB1/2 in pRb-negative cells by modulation of binding of transcription factor NF-Y to the topo IIalpha promoter, and the results are discussed in the framework of previously observed pRb-inactivation, and increased levels of HMGB1/2 and topo IIalpha in tumors.

• MeSH
• Transcriptional Activation MeSH
• Antigens, Neoplasm biosynthesis   genetics   MeSH
• DNA-Binding Proteins biosynthesis   genetics   MeSH
• DNA Topoisomerases, Type II biosynthesis   genetics   MeSH
• DNA chemistry   metabolism   MeSH
• CCAAT-Binding Factor metabolism   MeSH
• Humans MeSH
• Mutagenesis MeSH
• Cell Line, Tumor MeSH
• Promoter Regions, Genetic MeSH
• HMGB1 Protein chemistry   genetics   metabolism   MeSH
• HMGB2 Protein metabolism   MeSH
• Retinoblastoma Protein metabolism   MeSH
• Aged MeSH
• Up-Regulation * MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Aged MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antigens, Neoplasm MeSH
• DNA-Binding Proteins MeSH
• DNA Topoisomerases, Type II MeSH
• DNA MeSH
• CCAAT-Binding Factor MeSH
• HMGB1 Protein MeSH
• HMGB2 Protein MeSH
• Retinoblastoma Protein MeSH