Nucleosome structural changes induced by binding of non-histone chromosomal proteins HMGN1 and HMGN2

Exploring the role of estrogen and progestins in breast cancer: A genomic approach to diagnosis

Breast cancer (BC) is the most common cancer among women and a major cause of death from cancer. The role of estrogen and progestins, including synthetic hormones like R5020, in the development of BC has been highlighted in numerous studies. In our study, we employed machine learning and advanced bioinformatics to identify genes that could serve as diagnostic markers for BC. We thoroughly analyzed the transcriptomic data of two BC cell lines, T47D and UDC4, and performed differential gene expression analysis. We also conducted functional enrichment analysis to understand the biological functions influenced by these genes. Our study identified several diagnostic genes strongly associated with BC, including MIR6728, ENO1-IT1, ENO1-AS1, RNU6-304P, HMGN2P17, RP3-477M7.5, RP3-477M7.6, and CA6. The genes MIR6728, ENO1-IT1, ENO1-AS1, and HMGN2P17 are involved in cancer control, glycolysis, and DNA-related processes, while CA6 is associated with apoptosis and cancer development. These genes could potentially serve as predictors for BC, paving the way for more precise diagnostic methods and personalized treatment plans. This research enhances our understanding of BC and offers promising avenues for improving patient care in the future.

Site-specific modification and segmental isotope labelling of HMGN1 reveals long-range conformational perturbations caused by posttranslational modifications

Interactions between histones, which package DNA in eukaryotes, and nuclear proteins such as the high mobility group nucleosome-binding protein HMGN1 are important for regulating access to DNA. HMGN1 is a highly charged and intrinsically disordered protein (IDP) that is modified at several sites by posttranslational modifications (PTMs) - acetylation, phosphorylation and ADP-ribosylation. These PTMs are thought to affect cellular localisation of HMGN1 and its ability to bind nucleosomes; however, little is known about how these PTMs regulate the structure and function of HMGN1 at a molecular level. Here, we combine the chemical biology tools of protein semi-synthesis and site-specific modification to generate a series of unique HMGN1 variants bearing precise PTMs at their N- or C-termini with segmental isotope labelling for NMR spectroscopy. With access to these precisely-defined variants, we show that PTMs in both the N- and C-termini cause changes in the chemical shifts and conformational populations in regions distant from the PTM sites; up to 50-60 residues upstream of the PTM site. The PTMs investigated had only minor effects on binding of HMGN1 to nucleosome core particles, suggesting that they have other regulatory roles. This study demonstrates the power of combining protein semi-synthesis for introduction of site-specific PTMs with segmental isotope labelling for structural biology, allowing us to understand the role of PTMs with atomic precision, from both structural and functional perspectives.

Optimized Cross-Linking Mass Spectrometry for in Situ Interaction Proteomics

Recent development of mass spectrometer cleavable protein cross-linkers and algorithms for their spectral identification now permits large-scale cross-linking mass spectrometry (XL-MS). Here, we optimized the use of cleavable disuccinimidyl sulfoxide (DSSO) cross-linker for labeling native protein complexes in live human cells. We applied a generalized linear mixture model to calibrate cross-link peptide-spectra matching (CSM) scores to control the sensitivity and specificity of large-scale XL-MS. Using specific CSM score thresholds to control the false discovery rate, we found that higher-energy collisional dissociation (HCD) and electron transfer dissociation (ETD) can both be effective for large-scale XL-MS protein interaction mapping. We found that the coverage of protein-protein interaction maps is significantly improved through the use of multiple proteases. In addition, the use of focused sample-specific search databases can be used to improve the specificity of cross-linked peptide spectral matching. Application of this approach to human chromatin labeled in live cells recapitulated known and revealed new protein interactions of nucleosomes and other chromatin-associated complexes in situ. This optimized approach for mapping native protein interactions should be useful for a wide range of biological problems.

Effect of HMGN2 on proliferation and apoptosis of MCF-7 breast cancer cells

We investigated the effect of high mobility group protein N2 (HMGN2) on the proliferation and apoptosis of the human MCF-7 breast cancer cell line, and its effect on tumor growth in a subcutaneous heterotopic transplantation tumor model of breast cancer. The cell viability assay was used to verify the effect of the recombinant human HMGN2 on MCF-7 cell proliferation. The Transwell chamber assay was used to verify the effect of HMGN2 on MCF-7 cell migration. Flow cytometry and Hoechst staining were used to detect the effect of HMGN2 on MCF-7 cell apoptosis. MCF-7 was injected to establish a subcutaneous heterotopic transplantation tumor model of breast cancer in nude mice. The size, weight and volume of tumor in each group were compared after the administration of different concentrations of HMGN2 solution around the tumor tissue at day 1, 3, 5 and 7. The tumor tissue was removed and cut into sections, and the apoptotic cells in tumors of nude mice were detected by a TUNEL kit. The CCK-8 assay showed that HMGN2 at different concentrations inhibited the proliferation of the MCF-7 breast cancer cells, and the proliferation of MCF-7 cells were significantly inhibited when the concentration of HMGN2 reached 3 µg/ml (P<0.01). The Transwell chamber assay showed that 3 µg/ml of HMGN2 significantly decreased the migration capacity of MCF-7 cells (P<0.01). Flow cytometry and Hoechst staining showed that 3 µg/ml of HMGN2 significantly increased apoptosis of MCF-7 cells (P<0.01). After the nude mouse model of breast cancer was established, HMGN2 at different concentrations was injected around the tumor tissue at day 1, 3, 5 and 7. We demonstrated that the growth of breast cancer was significantly inhibited when the concentration of HMGN2 reached 15 µg/ml. TUNEL staining showed that the number of apoptotic cells in the 15 µg/ml dose group was significantly higher than that in the control group (P<0.01). Therefore, in vitro and in vivo experiments proved that recombinant human HMGN2 could significantly inhibit the proliferation and migration of breast cancer cells, which increased the apoptosis of breast cancer cells and exerted anti-breast cancer effects, which enriched our understanding of the biological roles of HMGN2.

Spermatid-specific linker histone HILS1 is a poor condenser of DNA and chromatin and preferentially associates with LINE-1 elements

BACKGROUND

Linker histones establish and maintain higher-order chromatin structure. Eleven linker histone subtypes have been reported in mammals. HILS1 is a spermatid-specific linker histone, and its expression overlaps with the histone-protamine exchange process during mammalian spermiogenesis. However, the role of HILS1 in spermatid chromatin remodeling is largely unknown.

RESULTS

In this study, we demonstrate using circular dichroism spectroscopy that HILS1 is a poor condenser of DNA and chromatin compared to somatic linker histone H1d. Genome-wide occupancy study in elongating/condensing spermatids revealed the preferential binding of HILS1 to the LINE-1 (L1) elements within the intergenic and intronic regions of rat spermatid genome. We observed specific enrichment of the histone PTMs like H3K9me3, H4K20me3 and H4 acetylation marks (H4K5ac and H4K12ac) in the HILS1-bound chromatin complex, whereas H3K4me3 and H3K27me3 marks were absent.

CONCLUSIONS

HILS1 possesses significantly lower α-helicity compared to other linker histones such as H1t and H1d. Interestingly, in contrast to the somatic histone variant H1d, HILS1 is a poor condenser of chromatin which demonstrate the idea that this particular linker histone variant may have distinct role in histone to protamine replacement. Based on HILS1 ChIP-seq analysis of elongating/condensing spermatids, we speculate that HILS1 may provide a platform for the structural transitions and forms the higher-order chromatin structures encompassing LINE-1 elements during spermiogenesis.

Increased expression of high-mobility group nucleosomal-binding domain 2 protein in various tumor cell lines

High mobility group nucleosomal-binding domain 2 (HMGN2) is an abundant non-histone nuclear protein of vertebrates and invertebrates. The aim of the present study was to characterize the endogenous expression of HMGN2 in various types of tumor cell. Western blotting was performed to analyze HMGN2 expression in the following tumor cell lines: H1975, HSC-4, MDA-MB-468, MDA-MB-231, SCC-25 and THP-1. Periodontal ligament cells (PDLCs) were included as a noncancerous control. HMGN2 was detected in human oral squamous cell carcinoma tissues by immunohistochemical analysis. The results demonstrated that the expression of HMGN2 was increased in the majority of tumor cell lines, particularly MDA-MB-468 and THP-1 cells, compared with PDLCs. The expression of HMGN2 in oral squamous cell carcinoma tissue was significantly increased compared with the expression in normal tissue. Furthermore, the expression of HMGN2 in metastatic oral squamous cell carcinoma tissues was increased compared with that in its non-metastatic counterpart. These results indicated that HMGN2 may serve an important function in the growth and metastasis of tumor cells.

Understanding nucleosomal histone and DNA interactions: a biophysical study

Histones are associated with DNA to form nucleosome essential for chromatin structure and major nuclear processes like gene regulation and expression. Histones consist of H1, H2A, H2B and H3, H4 type proteins. In the present study, combined histones from calf thymus were complexed with ct DNA and their binding affinities were measured fluorimetrically. All the five histones were resolved on SDS page and their binding with DNA was visualized. The values of biding affinities varied with pH and salt concentration. Highest affinity (4.0 × 10⁵ M^-1) was recorded at pH 6.5 in 50 mM phosphate buffer and 1.5 × 10⁴ M^-1 in 2 M NaCl at pH 7.0. The CD spectra support the highest binding affinity with maximum conformational changes at pH 7.0. The time-resolved fluorescence data recorded two life times for histone tyrosine residues at 300 nm emission in phosphate buffer pH 6.5. These life times did not show much change upon binding with DNA in buffer as well as in 2 M NaCl. The isothermal calorimetric studies yielded thermodynamic parameters ΔG, ΔH and ΔS as -1.6 × 10⁵ cal/mol, -1.13 × 10³ cal/mol and -3.80 cal/mol/deg, respectively, evidencing a spontaneous exothermic reaction. The dominant binding forces in building the nucleosome are electrostatic interactions.

Recognition of chromatin by the plant alkaloid, ellipticine as a dual binder

Recognition of core histone components of chromatin along with chromosomal DNA by a class of small molecule modulators is worth examining to evaluate their intracellular mode of action. A plant alkaloid ellipticine (ELP) which is a putative anticancer agent has so far been reported to function via DNA intercalation, association with topoisomerase II and binding to telomere region. However, its effect upon the potential intracellular target, chromatin is hitherto unreported. Here we have characterized the biomolecular recognition between ELP and different hierarchical levels of chromatin. The significant result is that in addition to DNA, it binds to core histone(s) and can be categorized as a 'dual binder'. As a sequel to binding with histone(s) and core octamer, it alters post-translational histone acetylation marks. We have further demonstrated that it has the potential to modulate gene expression thereby regulating several key biological processes such as nuclear organization, transcription, translation and histone modifications.

Non-coding RNAs as direct and indirect modulators of epigenetic mechanism regulation of cardiac fibrosis

INTRODUCTION

Cardiac fibroblast activation is a pivotal cellular event in cardiac fibrosis. Numerous studies have indicated that epigenetic modifications control cardiac fibroblast activation. Greater knowledge of the role of epigenetic modifications could improve understanding of the cardiac fibrosis pathogenesis.

AREAS COVERED

The aim of this review is to describe the present knowledge about the important role of non-coding RNA (ncRNA) transcripts in epigenetic gene regulation in cardiac fibrosis and looks ahead on new perspectives of epigenetic modification research. Furthermore, we will discuss examples of ncRNAs that interact with histone modification or DNA methylation to regulate gene expression.

EXPERT OPINION

MicroRNAs (miRNAs) and long ncRNAs (lncRNAs) modulate several important aspects of function. Recently, some studies continue to find novel pathways, including the important role of ncRNA transcripts in epigenetic gene regulation. Targeting the miRNAs and lncRNAs can be a promising direction in cardiac fibrosis treatment. We discuss new perspectives of ncRNAs that interact with histone modification or DNA methylation to regulate gene expression, others that are targets of these epigenetic mechanisms. The emerging recognition of the diverse functions of ncRNAs in regulating gene expression by epigenetic mechanisms suggests that they may represent new targets for therapeutic intervention.