[show abstract][hide abstract] ABSTRACT: High mobility group nucleosome-binding protein 5 (HMGN5) is a chromatin architectural protein that binds specifically to nucleosomes and reduces the compaction of the chromatin fiber. The protein is present in most vertebrate tissues however the physiological function of this protein is unknown. To examine the function of HMGN5 in vivo, mice lacking the nucleosome-binding domain of HMGN5 were generated and characterized. Serological analysis revealed that compared to wild-type littermates (Hmgn5(+/Y) ), mice with a targeted mutation in the HMGN5 gene (Hmgn5(tm1/Y) ), had elevated serum albumin, non-HDL cholesterol, triglycerides, and alanine transaminase, suggesting mild hepatic abnormalities. Metabolomics analysis of liver extracts and urine revealed clear differences in metabolites between Hmgn5(tm1/Y) and their Hmgn5(+/Y) littermates. Hmgn5(tm1/Y) mice had a significant increase in hepatic glutathione levels and decreased urinary concentrations of betaine, phenylacetylglycine, and creatine, all of which are metabolically related to the glutathione precursor glycine. Microarray and qPCR analysis revealed that expression of two genes affecting glutathione metabolism, glutathione peroxidase 6 (Gpx6) and hexokinase 1 (Hk1), was significantly decreased in Hmgn5(tm1/Y) mouse liver tissue. Analysis of chromatin structure by DNase I digestion revealed alterations in the chromatin structure of these genes in the livers of Hmgn5(tm1/Y) mice. Thus, functional loss of HMGN5 leads to changes in transcription of Gpx6 and Hk1 that alter glutathione metabolism.
PLoS ONE 01/2014; 9(1):e84583. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Eosinophils are major effector cells in type 2 inflammatory responses and become activated in response to IL-4 and IL-33, yet the molecular mechanisms and cooperative interaction between these cytokines remain unclear. Our objective was to investigate the molecular mechanism and cooperation of IL-4 and IL-33 in eosinophil activation. Eosinophils derived from bone marrow or isolated from Il5-transgenic mice were activated in the presence of IL-4 or IL-33 for 1 or 4 h, and the transcriptome was analyzed by RNA sequencing. The candidate genes were validated by quantitative PCR and ELISA. We demonstrated that murine-cultured eosinophils respond to IL-4 and IL-33 by phosphorylation of STAT-6 and NF-κB, respectively. RNA sequence analysis of murine-cultured eosinophils indicated that IL-33 induced 519 genes, whereas IL-4 induced only 28 genes, including 19 IL-33-regulated genes. Interestingly, IL-33 induced eosinophil activation via two distinct mechanisms, IL-4 independent and IL-4 secretion/autostimulation dependent. Anti-IL-4 or anti-IL-4Rα Ab-treated cultured and mature eosinophils, as well as Il4- or Stat6-deficient cultured eosinophils, had attenuated protein secretion of a subset of IL-33-induced genes, including Retnla and Ccl17. Additionally, IL-33 induced the rapid release of preformed IL-4 protein from eosinophils by a NF-κB-dependent mechanism. However, the induction of most IL-33-regulated transcripts (e.g., Il6 and Il13) was IL-4 independent and blocked by NF-κB inhibition. In conclusion, we have identified a novel activation pathway in murine eosinophils that is induced by IL-33 and differentially dependent upon an IL-4 auto-amplification loop.
The Journal of Immunology 09/2013; · 5.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: The interactions of nuclear lamins with the chromatin fiber play an important role in regulating nuclear architecture and chromatin function; however, the full spectrum of these interactions is not known. We report that the N-terminal domain of the nucleosome binding protein HMGN5 interacts with the C-terminal domain of the lamin binding protein LAP2α and that these proteins reciprocally alter their interaction with chromatin. Chromatin immunoprecipitation analysis of cells lacking either HMGN5 or LAP2α reveals that loss of either protein affects the genome-wide distribution of the remaining partner. Our study identifies a new functional link between chromatin-binding and lamin-binding proteins.
Journal of Biological Chemistry 05/2013; · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The nuclei of most vertebrate cells contain members of the high mobility group N (HMGN) protein family which bind specifically to nucleosome core particles and affect the structure and function of chromatin, including transcription. Here we study the biological role of this protein family by systematic analysis of phenotypes and tissue transcription profiles in mice lacking functional HMGN variants. Phenotypic analysis of Hmgn1-/-, Hmgn3-/-, and Hmgn5-/- mice and their wild type littermates with a battery of standardized tests uncovered variant-specific abnormalities. Gene expression analysis of four different tissues in each of the Hmgn-/- lines reveals very little overlap between the genes affected by the specific variants in the different tissues. Pathway analysis revels that loss of an HMGN variant affects subtly the expression of numerous genes in specific biological processes. We conclude that within the biological framework of an entire organism, HMGNs modulate the fidelity of the cellular transcriptional profile in a tissue- and HMGN variant-specific manner.
Journal of Biological Chemistry 04/2013; · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Although human papillomavirus was identified as an aetiological factor in cervical cancer, the key human gene drivers of this disease remain unknown. Here we apply an unbiased approach integrating gene expression and chromosomal aberration data. In an independent group of patients, we reconstruct and validate a gene regulatory meta-network, and identify cell cycle and antiviral genes that constitute two major subnetworks upregulated in tumour samples. These genes are located within the same regions as chromosomal amplifications, most frequently on 3q. We propose a model in which selected chromosomal gains drive activation of antiviral genes contributing to episomal virus elimination, which synergizes with cell cycle dysregulation. These findings may help to explain the paradox of episomal human papillomavirus decline in women with invasive cancer who were previously unable to clear the virus.
[show abstract][hide abstract] ABSTRACT: The HMGN family is a family of nucleosome-binding architectural proteins that affect the structure and function of chromatin in vertebrates. We report that the HMGN5 variant, encoded by a gene located on chromosome X, is a rapidly evolving protein with an acidic C-terminal domain that differs among vertebrate species. We found that the intranuclear organization and nucleosome interactions of human HMGN5 are distinct from those of mouse HMGN5 and that the C-terminal region of the protein is the main determinant of the chromatin interaction properties. Despite their apparent differences, both mouse and human HMGN5 proteins interact with histone H1, reduce its chromatin residence time, and can induce large-scale chromatin decompaction in living cells. Analysis of HMGN5 mutants suggests that distinct domains in HMGN5 affect specific steps in the interaction of H1 with chromatin. Elevated levels of either human or mouse HMGN5 affect the transcription of numerous genes, most in a variant-specific manner. Our study identifies HMGN5 as a rapidly evolving vertebrate nuclear protein with species-specific properties. HMGN5 has a highly disordered structure, binds dynamically to nucleosome core particles, modulates the binding of H1 to chromatin, reduces the compaction of the chromatin fiber, and affects transcription.
Molecular and cellular biology 07/2011; 31(13):2742-55. · 6.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: The interaction of architectural proteins such as the linker histone H1 and high-mobility-group (HMG) proteins with nucleosomes leads to changes in chromatin structure and histone modifications and alters the cellular transcription profile. The interaction of HMG proteins with chromatin is dynamic. However, it is not clear whether the proteins are constantly and randomly redistributed among all the nucleosomes or whether they preferentially associate with, and turn over at, specific regions in chromatin. To address this question, we examined the genome-wide distribution of the nucleosome binding protein HMGN1 and compared it to that of regulatory chromatin marks. We find that HMGN1 is not randomly distributed throughout the genome. Instead, the protein preferentially localizes to DNase I hypersensitive (HS) sites, promoters, functional enhancers, and transcription factor binding sites. Our results suggest that HMGN1 is part of the cellular machinery that modulates transcriptional fidelity by generating, maintaining, or preferentially interacting with specific sites in chromatin.
Molecular and cellular biology 02/2011; 31(4):700-9. · 6.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: High mobility group N (HMGN) is a family of intrinsically disordered nuclear proteins that bind to nucleosomes, alters the structure of chromatin and affects transcription. A major unresolved question is the extent of functional specificity, or redundancy, between the various members of the HMGN protein family. Here, we analyze the transcriptional profile of cells in which the expression of various HMGN proteins has been either deleted or doubled. We find that both up- and downregulation of HMGN expression altered the cellular transcription profile. Most, but not all of the changes were variant specific, suggesting limited redundancy in transcriptional regulation. Analysis of point and swap HMGN mutants revealed that the transcriptional specificity is determined by a unique combination of a functional nucleosome-binding domain and C-terminal domain. Doubling the amount of HMGN had a significantly larger effect on the transcription profile than total deletion, suggesting that the intrinsically disordered structure of HMGN proteins plays an important role in their function. The results reveal an HMGN-variant-specific effect on the fidelity of the cellular transcription profile, indicating that functionally the various HMGN subtypes are not fully redundant.
Nucleic Acids Research 02/2011; 39(10):4076-87. · 8.28 Impact Factor
[show abstract][hide abstract] ABSTRACT: The dynamic nature of the chromatin fiber provides the structural and functional flexibility required for the accurate transcriptional responses to various stimuli. In living cells, structural proteins such as the linker histone H1 and the high mobility group (HMG) proteins continuously modulate the local and global architecture of the chromatin fiber and affect the binding of regulatory factors to their nucleosomal targets. HMGN proteins specifically bind to the nucleosome core particle through a highly conserved "nucleosomal binding domain" (NBD) and reduce chromatin compaction. HMGN5 (NSBP1), a new member of the HMGN protein family, is ubiquitously expressed in mouse and human tissues. Similar to other HMGNs, HMGN5 is a nuclear protein which binds to nucleosomes via NBD, unfolds chromatin, and affects transcription. This protein remains mainly uncharacterized and its biological function is unknown. In this review, we describe the structure of the HMGN5 gene and the known properties of the HMGN5 protein. We present recent findings related to the expression pattern of the protein during development, the mechanism of HMGN5 action on chromatin, and discuss the possible role of HMGN5 in pathological and physiological processes.
Biochimica et Biophysica Acta 01/2010; 1799(1-2):86-92. · 4.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Structural changes in specific chromatin domains are essential to the orderly progression of numerous nuclear processes, including transcription. We report that the nuclear protein NSBP1 (HMGN5), a recently discovered member of the HMGN nucleosome-binding protein family, is specifically targeted by its C-terminal domain to nucleosomes in euchromatin. We find that the interaction of NSBP1 with nucleosomes alters the compaction of cellular chromatin and that in living cells, NSBP1 interacts with linker histones. We demonstrate that the negatively charged C-terminal domain of NSBP1 interacts with the positively charged C-terminal domain of H5 and that NSBP1 counteracts the linker histone-mediated compaction of a nucleosomal array. Dysregulation of the cellular levels of NSBP1 alters the transcription level of numerous genes. We suggest that mouse NSBP1 is an architectural protein that binds preferentially to euchromatin and modulates the fidelity of the cellular transcription profile by counteracting the chromatin-condensing activity of linker histones.
[show abstract][hide abstract] ABSTRACT: We report that NSBP1, a nucleosome binding protein that affects the structure of chromatin, is highly expressed in mouse placenta. In Rcho-1 cells, which recapitulate the differentiation of trophoblast giant cells of living placenta, NSBP1 expression is linked to differentiation. Disregulation of NSBP1 protein levels, by either siRNA treatment or by overexpression, alters the expression of several members of the prolactin gene family without affecting the levels of several transcription factors involved in placental differentiation. Our studies identify NSBP1 as a nucleosome binding protein that modulates the expression of prolactin gene family members most likely by inducing changes in chromatin structure.
Journal of Cellular Biochemistry 02/2009; 106(4):651-8. · 3.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: Throughout the cell cycle, the histones remain associated with DNA, but the repertoire of proteins associated with the chromatin fiber continuously changes. The chromatin interaction of HMGNs, a family of nucleosome binding proteins that modulates the structure and activity of chromatin, during the cell cycle is controversial. Immunofluorescence studies demonstrated that HMGNs are not associated with chromatin, whereas live cell imaging indicated that they are present in mitotic chromosomes. To resolve this controversy, we examined the organization of wild-type and mutated HMGN1 and HMGN2 proteins in the cell nucleus by using immunofluorescence studies, live cell imaging, gel mobility shift assays, and bimolecular fluorescence complementation (BiFC). We find that during interphase, HMGNs bind specifically to nucleosomes and form homodimeric complexes that yield distinct BiFC signals. In metaphase, the nucleosomal binding domain of the protein is inactivated, and the proteins associate with chromatin with low affinity as monomers, and they do not form specific complexes. Our studies demonstrate that the mode of binding of HMGNs to chromatin is cell cycle dependent.
Molecular biology of the cell 06/2008; 19(5):1816-24. · 5.98 Impact Factor