Epigenetic Regulation of Ameloblast Differentiation by HMGN Proteins.

Dental enamel formation is coordinated by ameloblast differentiation, production of enamel matrix proteins, and crystal growth. The factors regulating ameloblast differentiation are not fully understood. Here we show that the high mobility group N (HMGN) nucleosomal binding proteins modulate the rate of ameloblast differentiation and enamel formation. We found that HMGN1 and HMGN2 proteins are downregulated during mouse ameloblast differentiation. Genetically altered mice lacking HMGN1 and HMGN2 proteins show faster ameloblast differentiation and a higher rate of enamel deposition in mice molars and incisors. In vitro differentiation of induced pluripotent stem cells to dental epithelium cells showed that HMGN proteins modulate the expression and chromatin accessibility of ameloblast-specific genes and affect the binding of transcription factors epiprofin and PITX2 to ameloblast-specific genes. Our results suggest that HMGN proteins regulate ameloblast differentiation and enamel mineralization by modulating lineage-specific chromatin accessibility and transcription factor binding to ameloblast regulatory sites.

HMGN2 represses gene transcription via interaction with transcription factors Lef-1 and Pitx2 during amelogenesis.

The chromatin-associated high mobility group protein N2 (HMGN2) cofactor regulates transcription factor activity through both chromatin and protein interactions. Hmgn2 expression is known to be developmentally regulated, but the post-transcriptional mechanisms that regulate Hmgn2 expression and its precise roles in tooth development remain unclear. Here, we demonstrate that HMGN2 inhibits the activity of multiple transcription factors as a general mechanism to regulate early development. Bimolecular fluorescence complementation, pull-down, and coimmunoprecipitation assays show that HMGN2 interacts with the transcription factor Lef-1 through its HMG-box domain as well as with other early development transcription factors, Dlx2, FoxJ1, and Pitx2. Furthermore, EMSAs demonstrate that HMGN2 binding to Lef-1 inhibits its DNA-binding activity. We found that Pitx2 and Hmgn2 associate with H4K5ac and H3K4me2 chromatin marks in the proximal Dlx2 promoter, demonstrating Hmgn2 association with open chromatin. In addition, we demonstrate that microRNAs (miRs) mir-23a and miR-23b directly target Hmgn2, promoting transcriptional activation at several gene promoters, including the amelogenin promoter. In vivo, we found that decreased Hmgn2 expression correlates with increased miR-23 expression in craniofacial tissues as the murine embryo develops. Finally, we show that ablation of Hmgn2 in mice results in increased amelogenin expression because of increased Pitx2, Dlx2, Lef-1, and FoxJ1 transcriptional activity. Taken together, our results demonstrate both post-transcriptional regulation of Hmgn2 by miR-23a/b and post-translational regulation of gene expression by Hmgn2-transcription factor interactions. We conclude that HMGN2 regulates tooth development through its interaction with multiple transcription factors.

Recombinant jurkat cells (HMGN2-T cells) secrete cytokines and inhibit the growth of tumor cells.

High Mobility Group Chromosomal Protein N2 (HMGN2) can recognize tumor cells and enhance the anti-tumor effect of immune cells. This study aimed to establish a lentiviral vector of recombinant HMGN2 gene, establish recombinant T cells (HMGN2-T cells), and observe their anti-tumor effects. Total RNA was isolated from peripheral blood mononuclear cells. HMGN2, cluster of differentiation (CD) 8 A, CD28, CD137, and CD3ζ genes were amplified and connected. Jurkat cells were transfected with the recombinant lentivirus vector. The viability, apoptosis, and cell cycle of HMGN2-T cells were detected using Cell Counting Kit-8 assay and flow cytometry. The co-culture was performed by adding HMGN2-T cells to tumor cells with different effect-to-target (E:T) ratios. The cytotoxic activity was measured by lactate dehydrogenase (LDH) releasing assay. The sequences of HMGN2, CD8A, CD28, CD137, and CD3ζ gene plasmids were confirmed using gene sequencing. After the lentiviral transfection for 72 h, green fluorescence cells (HMGN2-T cells) could be seen. Cell viability and apoptosis were increased in HMGN2-T cells. The cytokine levels of interleukin 2 (IL-2) and tumor necrosis factor α (TNF-α) increased in cell supernatants of HMGN2-T cells. The percentage of G0/G1 phase cells was lower, the rate of S phase cells was higher in HMGN2-T cells than control cells. The co-culture of HMGN2-T cells and tumor cells could promote the cytokines' release. The LDH level was increased with the elevation of E:T ratios. In conclusion, the HMGN2-T cells were well-established and have the effect of secreting cytokines and killing tumor cells.

Novel biomarkers predict prognosis and drug-induced neuroendocrine differentiation in patients with prostate cancer.

Background: A huge focus is being placed on the development of novel signatures in the form of new combinatorial regimens to distinguish the neuroendocrine (NE) characteristics from castration resistant prostate cancer (CRPC) timely and accurately, as well as predict the disease-free survival (DFS) and progression-free survival (PFS) of prostate cancer (PCa) patients. Methods: Single cell data of 4 normal samples, 3 CRPC samples and 3 CRPC-NE samples were obtained from GEO database, and CellChatDB was used for potential intercellular communication, Secondly, using the "limma" package (v3.52.0), we obtained the differential expressed genes between CRPC and CRPC-NE both in single-cell RNA seq and bulk RNA seq samples, and discovered 12 differential genes characterized by CRPC-NE. Then, on the one hand, the diagnosis model of CRPC-NE is developed by random forest algorithm and artificial neural network (ANN) through Cbioportal database; On the other hand, using the data in Cbioportal and GEO database, the DFS and PFS prognostic model of PCa was established and verified through univariate Cox analysis, least absolute shrinkage and selection operator (Lasso) regression and multivariate Cox regression in R software. Finally, somatic mutation and immune infiltration were also discussed. Results: Our research shows that there exists specific intercellular communication in classified clusters. Secondly, a CRPC-NE diagnostic model of six genes (HMGN2, MLLT11, SOX4, PCSK1N, RGS16 and PTMA) has been established and verified, the area under the ROC curve (AUC) is as high as 0.952 (95% CI: 0.882-0.994). The mutation landscape shows that these six genes are rarely mutated in the CRPC and NEPC samples. In addition, NE-DFS signature (STMN1 and PCSK1N) and NE-PFS signature (STMN1, UBE2S and HMGN2) are good predictors of DFS and PFS in PCa patients and better than other clinical features. Lastly, the infiltration levels of plasma cells, T cells CD4 naive, Eosinophils and Monocytes were significantly different between the CRPC and NEPC groups. Conclusions: This study revealed the heterogeneity between CRPC and CRPC-NE from different perspectives, and developed a reliable diagnostic model of CRPC-NE and robust prognostic models for PCa.

Spatial and Temporal Expression of High-Mobility-Group Nucleosome-Binding (HMGN) Genes in Brain Areas Associated with Cognition in Individuals with Down Syndrome.

DNA methylation and histone posttranslational modifications are epigenetics processes that contribute to neurophenotype of Down Syndrome (DS). Previous reports present strong evidence that nonhistone high-mobility-group N proteins (HMGN) are epigenetic regulators. They play important functions in various process to maintain homeostasis in the brain. We aimed to analyze the differential expression of five human HMGN genes in some brain structures and age ranks from DS postmortem brain samples. Methodology: We performed a computational analysis of the expression of human HMGN from the data of a DNA microarray experiment (GEO database ID GSE59630). Using the transformed log2 data, we analyzed the differential expression of five HMGN genes in several brain areas associated with cognition in patients with DS. Moreover, using information from different genome databases, we explored the co-expression and protein interactions of HMNGs with the histones of nucleosome core particle and linker H1 histone. Results: We registered that HMGN1 and HMGN5 were significantly overexpressed in the hippocampus and areas of prefrontal cortex including DFC, OFC, and VFC of DS patients. Age-rank comparisons between euploid control and DS individuals showed that HMGN2 and HMGN4 were overexpressed in the DS brain at 16 to 22 gestation weeks. From the BioGRID database, we registered high interaction scores of HMGN2 and HMGN4 with Hist1H1A and Hist1H3A. Conclusions: Overall, our results give strong evidence to propose that DS would be an epigenetics-based aneuploidy. Remodeling brain chromatin by HMGN1 and HMGN5 would be an essential pathway in the modification of brain homeostasis in DS.

The regulatory effect of acetylation of HMGN2 and H3K27 on pyocyanin-induced autophagy in macrophages by affecting Ulk1 transcription.

Pyocyanin (PYO) is a major virulence factor secreted by Pseudomonas aeruginosa, and autophagy is a crucial homeostatic mechanism for the interaction between the pathogens and the host. It remains unknown whether PYO leads to autophagy in macrophages by regulating histone acetylation. The high mobility group nucleosomal binding domain 2 (HMGN2) has been reported to regulate the PYO-induced autophagy and oxidative stress in the epithelial cells; however, the underlying molecular mechanism has not been fully elucidated. In this study, PYO was found to induce autophagy in macrophages, and the mechanism might be correlated with the up-regulation of HMGN2 acetylation (HMGN2ac) and the down-regulation of H3K27 acetylation (H3K27ac) by modulation of the activities of acetyltransferases and deacetylases. Moreover, we further demonstrated that the up-regulated HMGN2ac enhances its recruitment to the Ulk1 promoter, while the down-regulation of H3K27ac reduces its recruitment to the Ulk1 promoter, thereby promoting or inhibiting the transcription of Ulk1. In conclusion, HMGN2ac and H3K27ac play regulatory roles in the PYO-induced autophagy in macrophages.

Prolactin Drives a Dynamic STAT5A/HDAC6/HMGN2 Cis-Regulatory Landscape Exploitable in ER+ Breast Cancer.

The hormone prolactin has been implicated in breast cancer pathogenesis and regulates chromatin engagement by the transcription factor, STAT5A. STAT5A is known to inducibly bind promoters and cis-regulatory elements genome-wide, though the mechanisms by which it exerts specificity and regulation of target gene expression remain enigmatic. We previously identified HDAC6 and HMGN2 as cofactors that facilitate prolactin-induced, STAT5A-mediated gene expression. Here, multicondition STAT5A, HDAC6, and HMGN2 chromatin immunoprecipitation and sequencing with parallel condition RNA-seq are utilized to reveal the cis-regulatory landscape and cofactor dynamics underlying prolactin-stimulated gene expression in breast cancer. We find that prolactin-regulated genes are significantly enriched for cis-regulatory elements bound by HDAC6 and HMGN2, and that inducible STAT5A binding at enhancers, rather than promoters, conveys specificity for prolactin-regulated genes. The selective HDAC6 inhibitor, ACY-241, blocks prolactin-induced STAT5A chromatin engagement at cis-regulatory elements as well as a significant proportion of prolactin-stimulated gene expression. We identify functional pathways known to contribute to the development and/or progression of breast cancer that are activated by prolactin and inhibited by ACY-241. Additionally, we find that the DNA sequences underlying shared STAT5A and HDAC6 binding sites at enhancers are differentially enriched for estrogen response elements (ESR1 and ESR2 motifs) relative to enhancers bound by STAT5A alone. Gene set enrichment analysis identifies significant overlap of ERα-regulated genes with genes regulated by prolactin, particularly prolactin-regulated genes with promoters or enhancers co-occupied by both STAT5A and HDAC6. Lastly, the therapeutic efficacy of ACY-241 is demonstrated in in vitro and in vivo breast cancer models, where we identify synergistic ACY-241 drug combinations and observe differential sensitivity of ER+ models relative to ER- models.

Prognostic value of HMGN family expression in acute myeloid leukemia.

Aim: The objective of this work was to investigate the prognostic role of the HMGN family in acute myeloid leukemia (AML). Methods: A total of 155 AML patients with HMGN1-5 expression data from the Cancer Genome Atlas database were enrolled in this study. Results: In the chemotherapy-only group, patients with high HMGN2 expression had significantly longer event-free survival (EFS) and overall survival (OS) than those with low expression (all p < 0.05), whereas high HMGN5 expressers had shorter EFS and OS than the low expressers (all p < 0.05). Multivariate analysis identified that high HMGN2 expression was an independent favorable prognostic factor for patients who only received chemotherapy (all p < 0.05). HMGN family expression had no impact on EFS and OS in AML patients receiving allogeneic hematopoietic stem cell transplantation. Conclusion: High HMGN2/5 expression is a potential prognostic indicator for AML.

Transcriptomic analysis of peripheral blood mononuclear cells in head and neck squamous cell carcinoma patients.

OBJECTIVES: To investigate the gene expression profile of peripheral blood mononuclear cells (PBMCs) from head and neck squamous cell carcinoma (HNSCC), including oral cancer (OC) and oropharyngeal cancer (OPC) patients, and compare them with healthy controls (HC). MATERIALS AND METHODS: Transcriptomic analysis of PBMCs was performed by RNA-sequencing. The upregulated candidate genes were selected for validation by quantitative real-time polymerase chain reaction (qPCR). In addition, related plasma protein levels were determined by enzyme-linked immunosorbent assay (ELISA). RESULTS: Three significantly upregulated genes, including high mobility group nucleosomal binding domain 2 (HMGN2), folate receptor gamma (FOLR3), and amphiregulin (AREG), were selected. In the first cohort, the results showed that only HMGN2 expression was significantly increased in OC patients. In the larger sample size, the overall results demonstrated that HMGN2 expression had a tendency to increase in both OC and OPC patients compared with HC. Interestingly, the plasma HMGN2 (HMG-17) protein level exhibited the same trend as that observed at the transcriptional level. CONCLUSION: HMGN2 expression and plasma HMG-17 (HMGN2 protein) were increased in both cancer patients compared with HC. This gene may be important for further functional studies in the PBMCs of HNSCC patients.

High mobility group nucleosomal binding 2 reduces integrin α5/ß1-mediated adhesion of Klebsiella pneumoniae on human pulmonary epithelial cells via nuclear factor I.

It has been reported that high mobility group nucleosomal binding domain 2 (HMGN2) is a nucleus-related protein that regulates gene transcription and plays a critical role in bacterial clearance. An elevated level of HMGN2 reduced integrin α5/ß1 expression of human pulmonary epithelial A549 cells was demonstrated during Klebsiella pneumoniae infection, thus weakening bacterial adhesion and invasion. However, the mechanism by which HMGN2 regulates integrin expression remains unclear. This study found that a transcription factor-nuclear factor I (NFI), which serves as the potential target of HMGN2 regulated integrin expression. The results showed that HMGN2 was able to promote NFIA and NFIB expression by increasing H3K27 acetylation of NFIA/B promoter regions. The integrin α5/ß1 expression was significantly enhanced by knockdown of NFIA/B via a siRNA approach. Meanwhile, NFIA/B silence could also compromise the inhibition effect of HMGN2 on the integrin α5/ß1 expression. Mechanistically, it was demonstrated that HMGN2 facilitated the recruitment of NFI on the promoter regions of integrin α5/ß1 according to the chromatin immunoprecipitation assay. In addition, it was further demonstrated that the knockdown of NFIA/B induced more adhesion of Klebsiella pneumoniae on pulmonary epithelial A549 cells, which could be reversed by the application of an integrin inhibitor RGD. The results revealed a regulatory role of HMGN2 on the transcription level of integrin α5/ß1, indicating a potential treatment strategy against Klebsiella pneumoniae-induced infectious lung diseases.

Human HMGN1 and HMGN2 are not required for transcription-coupled DNA repair.

Transcription-coupled repair (TCR) removes DNA lesions from the transcribed strand of active genes. Stalling of RNA polymerase II (RNAPII) at DNA lesions initiates TCR through the recruitment of the CSB and CSA proteins. The full repertoire of proteins required for human TCR - particularly in a chromatin context - remains to be determined. Studies in mice have revealed that the nucleosome-binding protein HMGN1 is required to enhance the repair of UV-induced lesions in transcribed genes. However, whether HMGN1 is required for human TCR remains unaddressed. Here, we show that knockout or knockdown of HMGN1, either alone or in combination with HMGN2, does not render human cells sensitive to UV light or Illudin S-induced transcription-blocking DNA lesions. Moreover, transcription restart after UV irradiation was not impaired in HMGN-deficient cells. In contrast, TCR-deficient cells were highly sensitive to DNA damage and failed to restart transcription. Furthermore, GFP-tagged HMGN1 was not recruited to sites of UV-induced DNA damage under conditions where GFP-CSB readily accumulated. In line with this, HMGN1 did not associate with the TCR complex, nor did TCR proteins require HMGN1 to associate with DNA damage-stalled RNAPII. Together, our findings suggest that HMGN1 and HMGN2 are not required for human TCR.

High-mobility group nucleosomal binding domain 2 protects against microcephaly by maintaining global chromatin accessibility during corticogenesis.

The surface area of the human cerebral cortex undergoes dramatic expansion during late fetal development, leading to cortical folding, an evolutionary feature not present in rodents. Microcephaly is a neurodevelopmental disorder defined by an abnormally small brain, and many gene mutations have been found to be associated with primary microcephaly. However, mouse models generated by ablating primary microcephaly-associated genes often fail to recapitulate the severe loss of cortical surface area observed in individuals with this pathology. Here, we show that a mouse model with deficient expression of high-mobility group nucleosomal binding domain 2 (HMGN2) manifests microcephaly with reduced cortical surface area and almost normal radial corticogenesis, with a pattern of incomplete penetrance. We revealed that altered cleavage plane and mitotic delay of ventricular radial glia may explain the rising ratio of intermediate progenitor cells to radial glia and the displacement of neural progenitor cells in microcephalic mutant mice. These led to decreased self-renewal of the radial glia and reduction in lateral expansion. Furthermore, we found that HMGN2 protected corticogenesis by maintaining global chromatin accessibility mainly at promoter regions, thereby ensuring the correct regulation of the transcriptome. Our findings underscore the importance of the regulation of chromatin structure in cortical development and highlight a mouse model with critical insights into the etiology of microcephaly.

Maintenance of active chromatin states by HMGN2 is required for stem cell identity in a pluripotent stem cell model.

BACKGROUND: Members of the HMGN protein family modulate chromatin structure and influence epigenetic modifications. HMGN1 and HMGN2 are highly expressed during early development and in the neural stem/progenitor cells of the developing and adult brain. Here, we investigate whether HMGN proteins contribute to the chromatin plasticity and epigenetic regulation that is essential for maintaining pluripotency in stem cells. RESULTS: We show that loss of Hmgn1 or Hmgn2 in pluripotent embryonal carcinoma cells leads to increased levels of spontaneous neuronal differentiation. This is accompanied by the loss of pluripotency markers Nanog and Ssea1, and increased expression of the pro-neural transcription factors Neurog1 and Ascl1. Neural stem cells derived from these Hmgn-knockout lines also show increased spontaneous neuronal differentiation and Neurog1 expression. The loss of HMGN2 leads to a global reduction in H3K9 acetylation, and disrupts the profile of H3K4me3, H3K9ac, H3K27ac and H3K122ac at the Nanog and Oct4 loci. At endodermal/mesodermal genes, Hmgn2-knockout cells show a switch from a bivalent to a repressive chromatin configuration. However, at neuronal lineage genes whose expression is increased, no epigenetic changes are observed and their bivalent states are retained following the loss of HMGN2. CONCLUSIONS: We conclude that HMGN1 and HMGN2 maintain the identity of pluripotent embryonal carcinoma cells by optimising the pluripotency transcription factor network and protecting the cells from precocious differentiation. Our evidence suggests that HMGN2 regulates active and bivalent genes by promoting an epigenetic landscape of active histone modifications at promoters and enhancers.

HMGN2 regulates non-tuberculous mycobacteria survival via modulation of M1 macrophage polarization.

Non-tuberculous mycobacteria (NTM), also known as an environmental and atypical mycobacteria, can cause the chronic pulmonary infectious diseases. Macrophages have been suggested as the main host cell to initiate the innate immune responses to NTM infection. However, the molecular mechanism to regulate the antimicrobial immune responses to NTM is still largely unknown. Current study showed that the NTM clinical groups, Mycobacterium abscessus and Mycobacterium smegmatis, significantly induced the M1 macrophage polarization with the characteristic production of nitric oxide (NO) and marker gene expression of iNOS, IFNγ, TNF-α, IL1-ß and IL-6. Interestingly, a non-histone nuclear protein, HMGN2 (high-mobility group N2), was found to be spontaneously induced during NTM-activated M1 macrophage polarization. Functional studies revealed that HMGN2 deficiency in NTM-infected macrophage promotes the expression of M1 markers and the production of NO via the enhanced activation of NF-κB and MAPK signalling. Further studies exhibited that HMGN2 knock-down also enhanced IFNγ-induced M1 macrophage polarization. Finally, we observed that silencing HMGN2 affected the survival of NTM in macrophage, which might largely relevant to enhanced macrophage polarization into M1 phenotype under the NTM infection. Collectively, current studies thus suggested a novel function of HMGN2 in regulating the anti-non-tuberculous mycobacteria innate immunity of macrophage.

High-mobility group protein N2 induces autophagy by activating AMPK/ULK1 pathway and thereby boosts UPEC proliferation within bladder epithelial cells.

Urinary tract infection is one of the most common bacterial infections which is mainly caused by Escherichia coli (UPEC). Autophagy plays a key role in immune response to eliminate invading pathogens. Exploring the effect of autophagy on UPEC infection and the molecular mechanisms will be benefit for the treatment of urinary tract infection. High-mobility group protein N2 (HMGN2), a highly conserved nuclear protein and an antibacterial peptide, has been associated with bacterial infection induced immune response; however, whether this function is due to the regulation of autophagy remains unclear. In this study, we demonstrate for the first time that HMGN2 is upregulated in UPEC infection of bladder epithelial cell line 5637 (BEC 5637). Furthermore, HMGN2 enhances autophagy in BEC 5637 via activation of AMPK and ULK1, whereas UPEC suppresses autophagy. In addition, the enhanced autophagy activity by HMGN2 overexpression or rapamycin boosts the proliferation of UPEC J96 in BEC 5637. In summary, our data indicate that HMGN2 activates autophagy via AMPK/ULK1 pathway which can be utilized by UPEC J96 for their proliferation within bladder epithelial cells.

Binding of HMGN proteins to cell specific enhancers stabilizes cell identity.

The dynamic nature of the chromatin epigenetic landscape plays a key role in the establishment and maintenance of cell identity, yet the factors that affect the dynamics of the epigenome are not fully known. Here we find that the ubiquitous nucleosome binding proteins HMGN1 and HMGN2 preferentially colocalize with epigenetic marks of active chromatin, and with cell-type specific enhancers. Loss of HMGNs enhances the rate of OSKM induced reprogramming of mouse embryonic fibroblasts (MEFs) into induced pluripotent stem cells (iPSCs), and the ASCL1 induced conversion of fibroblast into neurons. During transcription factor induced reprogramming to pluripotency, loss of HMGNs accelerates the erasure of the MEF-specific epigenetic landscape and the establishment of an iPSCs-specific chromatin landscape, without affecting the pluripotency potential and the differentiation potential of the reprogrammed cells. Thus, HMGN proteins modulate the plasticity of the chromatin epigenetic landscape thereby stabilizing, rather than determining cell identity.

Non-histone nuclear protein HMGN2 differently regulates the urothelium barrier function by altering expression of antimicrobial peptides and tight junction protein genes in UPEC J96-infected bladder epithelial cell monolayer.

The urinary tract is vulnerable to frequent challenges from environmental microflora. Uropathogenic Escherichia coli (UPEC) makes a major contribution to urinary tract infection (UTI). Previous studies have characterized positive roles of non-histone nuclear protein HMGN2 in lung epithelial innate immune response. In the study presented here, we found HMGN2 expression was up-regulated in UPEC J96-infected urothelium. Surprisingly, over-expression of HMGN2 promoted disruption of BECs 5637 cells' intercellular junctions by down-regulating tight junction (TJs) components' expression and physical structure under J96 infection. Further investigation showed that BECs 5637 monolayer, in which HMGN2 was over-expressed, had significantly increased permeability to J96. Our study systemically explored the regulatory roles of HMGN2 in BECs barrier function during UPEC infection and suggested different modulations of intracellular and paracellular routes through which UPEC invades the bladder epithelium.

HMGN2: An Antitumor Effector Molecule of γδT Cells.

γδT cells function in the regulation of T-cell activation in cancer and have been identified as a novel target for cancer immunotherapy. Activated γδT cells release a series of cytotoxic molecules-including granulysin, perforin, Fas/Fas ligand (Fas-L), and granzymes A and B-to kill target cells. Our previous research has shown that high mobility group nucleosomal-binding domain 2 (HMGN2), which is expressed at a high level in activated CD8T cells, is an antitumor effector molecule of CD8T cells. In the present study, we examined the expression and antitumor effects of HMGN2 in γδT cells. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy donors with a PBMC separation column. PMBCs were stimulated with isopentenyl pyrophosphate (IPP) and interleukin-2 (IL-2) for 10 days for activation and expansion. Activated γδT cells were isolated from IPP-pretreated PBMCs with a Moflo XDP flow cytometry sorter. The expression of HMGN2 in γδT cells was detected by flow cytometry and enzyme-linked immunosorbent assay. The cytotoxic effects of γδT cells and HMGN2 were analyzed by carboxyfluorescein succinimidyl ester labeling. IPP combined with IL-2 induced significant activation and expansion of γδT cells in vitro. HMGN2 was constitutively expressed in γδT cells. IPP-activated γδT cells expressed a high level of HMGN2 that could be detected intracellularly and in the supernatant. Moreover, supernatants of purified γδT cells were sufficient to kill tumor cells and could be blocked with anti-human HMGN2 antibody. This study suggests that HMGN2 is an antitumor effector molecule of γδT cells.

Evidence For Hmgn2 Involvement in Mouse Embryo Implantation and Decidualization.

BACKGROUND/AIMS: Hmgn2 is involved in regulating embryonic development, but its physiological function during embryo implantation and decidualization remains unknown. METHODS: In situ hybridization, real-time PCR, RNA interference, gene overexpression and MTS assay were used to examine the expression of Hmgn2 in mouse uterus during the pre-implantation period and explore its function and regulatory mechanisms in epithelial adhesion junction and stromal cell proliferation and differentiation. RESULTS: Hmgn2 was primarily accumulated in uterine luminal epithelia on day 4 of pregnancy and subluminal stromal cells around the implanting blastocyst at implantation sites on day 5. Similar results were observed during delayed implantation and activation. Meanwhile, Hmgn2 expression was visualized in the decidua. In uterine epithelial cells, silencing of Hmgn2 by specific siRNA reduced the expression of adhesion molecules Cdh1, Cdh2 and Ctnnb1 and enhanced the expression of Muc1, whereas constitutive activation of Hmgn2 exhibited the opposite effects, suggesting a role for Hmgn2 in attachment reaction during embryo implantation. Estrogen stimulated the expression of Hmgn2 in uterine epithelia, but the stimulation was abrogated by ER antagonist ICI 182,780. Further analysis evidenced that attenuation of Hmgn2 might eliminate the regulation of estrogen on the expression of Cdh1, Cdh2 and Ctnnb1. In uterine stromal cells, progesterone induced the accumulation of Hmgn2 which advanced the expression of Prl8a2 and Prl3c1, two well-known differentiation markers for decidualization, but did not affect the proliferation of stromal cells. Knockdown of Hmgn2 blocked the progesterone-induced differentiation of uterine stromal cells. Moreover, Hmgn2 might serve as an intermediate to mediate the regulation of progesterone on Hand2. CONCLUSION: Hmgn2 may play an important role during embryo implantation and decidualization.

HMGN1 and 2 remodel core and linker histone tail domains within chromatin.

The structure of the nucleosome, the basic building block of the chromatin fiber, plays a key role in epigenetic regulatory processes that affect DNA-dependent processes in the context of chromatin. Members of the HMGN family of proteins bind specifically to nucleosomes and affect chromatin structure and function, including transcription and DNA repair. To better understand the mechanisms by which HMGN 1 and 2 alter chromatin, we analyzed their effect on the organization of histone tails and linker histone H1 in nucleosomes. We find that HMGNs counteract linker histone (H1)-dependent stabilization of higher order 'tertiary' chromatin structures but do not alter the intrinsic ability of nucleosome arrays to undergo salt-induced compaction and self-association. Surprisingly, HMGNs do not displace H1s from nucleosomes; rather these proteins bind nucleosomes simultaneously with H1s without disturbing specific contacts between the H1 globular domain and nucleosomal DNA. However, HMGNs do alter the nucleosome-dependent condensation of the linker histone C-terminal domain, which is critical for stabilizing higher-order chromatin structures. Moreover, HMGNs affect the interactions of the core histone tail domains with nucleosomal DNA, redirecting the tails to more interior positions within the nucleosome. Our studies provide new insights into the molecular mechanisms whereby HMGNs affect chromatin structure.