The role of high-mobility group I(Y) proteins in expression of IL-2 and T cell proliferation

HMGA1 induces FGF19 to drive pancreatic carcinogenesis and stroma formation

High mobility group A1 (HMGA1) chromatin regulators are upregulated in diverse tumors where they portend adverse outcomes, although how they function in cancer remains unclear. Pancreatic ductal adenocarcinomas (PDACs) are highly lethal tumors characterized by dense desmoplastic stroma composed predominantly of cancer-associated fibroblasts and fibrotic tissue. Here, we uncover an epigenetic program whereby HMGA1 upregulates FGF19 during tumor progression and stroma formation. HMGA1 deficiency disrupts oncogenic properties in vitro while impairing tumor inception and progression in KPC mice and subcutaneous or orthotopic models of PDAC. RNA sequencing revealed HMGA1 transcriptional networks governing proliferation and tumor-stroma interactions, including the FGF19 gene. HMGA1 directly induces FGF19 expression and increases its protein secretion by recruiting active histone marks (H3K4me3, H3K27Ac). Surprisingly, disrupting FGF19 via gene silencing or the FGFR4 inhibitor BLU9931 recapitulates most phenotypes observed with HMGA1 deficiency, decreasing tumor growth and formation of a desmoplastic stroma in mouse models of PDAC. In human PDAC, overexpression of HMGA1 and FGF19 defines a subset of tumors with extremely poor outcomes. Our results reveal what we believe is a new paradigm whereby HMGA1 and FGF19 drive tumor progression and stroma formation, thus illuminating FGF19 as a rational therapeutic target for a molecularly defined PDAC subtype.

The Chromatin Regulator HMGA1a Undergoes Phase Separation in the Nucleus

The protein high mobility group A1 (HMGA1) is an important regulator of chromatin organization and function. However, the mechanisms by which it exerts its biological function are not fully understood. Here, we report that the HMGA isoform, HMGA1a, nucleates into foci that display liquid-like properties in the nucleus, and that the protein readily undergoes phase separation to form liquid condensates in vitro. By bringing together machine-leaning modelling, cellular and biophysical experiments and multiscale simulations, we demonstrate that phase separation of HMGA1a is promoted by protein-DNA interactions, and has the potential to be modulated by post-transcriptional effects such as phosphorylation. We further show that the intrinsically disordered C-terminal tail of HMGA1a significantly contributes to its phase separation through electrostatic interactions via AT hooks 2 and 3. Our work sheds light on HMGA1 phase separation as an emergent biophysical factor in regulating chromatin structure.

Putative regulatory functions of SNPs associated with bronchial asthma, arterial hypertension and their comorbid phenotype

Linkage disequilibrium (LD) of single nucleotide polymorphisms (SNPs) of TLR4/AL160272.2 (rs1927914, rs1928298, rs7038716, rs7026297, rs7025144) was estimated in the Slavs of West Siberia. We further investigated an association of SNPs in TLR4/AL160272.2 (rs1927914, rs7038716, rs7025144), SERPINA1 (rs1980616), ATXN2/BRAP (rs11065987), IL2RB (rs2284033), NT5C2 (rs11191582), CARD8 (rs11669386), ANG/RNASE4 (rs1010461), and ABTB2/ САТ (rs2022318) genes with bronchial asthma (BA), arterial hypertension (AH) and their comorbidity. Then, the disease-associated SNPs were annotated in silico in relation to their potential regulatory functions. Strong LD was detected between rs1928298 and rs1927914, as well as rs7026297 and rs7038716 in the Slavs of West Siberia. It was found that the rs1927914 G allele of the TLR4 gene and the rs1980616 C allele of the SERPINA1 gene are associated with the predisposition to BA. These SNPs can affect binding affinity of transcription factors of the Pou and Klf4 families, as well as the expression levels of the TLR4 and SERPINA1 genes. The rs11065987 allele A of the ATXN2/BRAP genes, the rs11669386 A allele of the CARD8 gene, the rs2284033 allele G of the IL2RB gene, and the rs11191582 allele G of the NT5C2 gene were associated with the risk of AH. These variants can alter binding affinity of the Hoxa9, Irf, RORalpha1 and HMG-IY transcription factors, as well as the expression levels of the ALDH2, CARD8, NT5C2, ARL3, and SFXN2 genes in blood cells/vessels/heart, respectively. The risk of developing a comorbid phenotype of AD and AH is associated with the A allele of rs7038716 and the T allele of rs7025144 of the TLR4/AL160272.2 genes, the A allele of rs1010461 of the ANG gene and the C allele of rs2022318 of the ABTB2/CAT genes. Variants rs7038716 and rs7025144 can change the expression levels of the TLR4 gene in blood cells, while rs1010461 and rs2022318 influence the expression levels of the ANG and RNASE4 genes as well as the CAT and ABTB2 genes in blood cells, lungs/vessels/heart.

Mesenchymal stromal cells expressing a dominant-negative high mobility group A1 transgene exhibit improved function during sepsis

High mobility group (HMG)A proteins are nonhistone chromatin proteins that bind to the minor groove of DNA, interact with transcriptional machinery, and facilitate DNA-directed nuclear processes. HMGA1 has been shown to regulate genes involved with systemic inflammatory processes. We hypothesized that HMGA1 is important in the function of mesenchymal stromal cells (MSCs), which are known to modulate inflammatory responses due to sepsis. To study this process, we harvested MSCs from transgenic (Tg) mice expressing a dominant-negative (dn) form of HMGA1 in mesenchymal cells. MSCs harvested from Tg mice contained the dnHMGA1 transgene, and transgene expression did not change endogenous HMGA1 levels. Immunophenotyping of the cells, along with trilineage differentiation revealed no striking differences between Tg and wild-type (WT) MSCs. However, Tg MSCs growth was decreased compared with WT MSCs, although Tg MSCs were more resistant to oxidative stress-induced death and expressed less IL-6. Tg MSCs administered after the onset of Escherichia coli-induced sepsis maintained their ability to improve survival when given in a single dose, in contrast with WT MSCs. This survival benefit of Tg MSCs was associated with less tissue cell death, and also a reduction in tissue neutrophil infiltration and expression of neutrophil chemokines. Finally, Tg MSCs promoted bacterial clearance and enhanced neutrophil phagocytosis, in part through their increased expression of stromal cell-derived factor-1 compared with WT MSCs. Taken together, these data demonstrate that expression of dnHMGA1 in MSCs provides a functional advantage of the cells when administered during bacterial sepsis.

An Arabidopsis AT-hook motif nuclear protein mediates somatic embryogenesis and coinciding genome duplication

Plant somatic cells can be reprogrammed into totipotent embryonic cells that are able to form differentiated embryos in a process called somatic embryogenesis (SE), by hormone treatment or through overexpression of certain transcription factor genes, such as BABY BOOM (BBM). Here we show that overexpression of the AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) gene induces formation of somatic embryos on Arabidopsis thaliana seedlings in the absence of hormone treatment. During zygotic embryogenesis, AHL15 expression starts early in embryo development, and AH15 and other AHL genes are required for proper embryo patterning and development beyond the globular stage. Moreover, AHL15 and several of its homologs are upregulated and required for SE induction upon hormone treatment, and they are required for efficient BBM-induced SE as downstream targets of BBM. A significant number of plants derived from AHL15 overexpression-induced somatic embryos are polyploid. Polyploidisation occurs by endomitosis specifically during the initiation of SE, and is caused by strong heterochromatin decondensation induced by AHL15 overexpression.

Overexpression of AtAHL20 causes delayed flowering in Arabidopsis via repression of FT expression

BACKGROUND

The 29-member Arabidopsis AHL gene family is classified into three main classes based on nucleotide and protein sequence evolutionary differences. These differences include the presence or absence of introns, type and/or number of conserved AT-hook and PPC domains. AHL gene family members are divided into two phylogenetic clades, Clade-A and Clade-B. A majority of the 29 members remain functionally uncharacterized. Furthermore, the biological significance of the DNA and peptide sequence diversity, observed in the conserved motifs and domains found in the different AHL types, is a subject area that remains largely unexplored.

RESULTS

Transgenic plants overexpressing AtAHL20 flowered later than the wild type under both short and long days. Transcript accumulation analyses showed that 35S:AtAHL20 plants contained reduced FT, TSF, AGL8 and SPL3 mRNA levels. Similarly, overexpression of AtAHL20's orthologue in Camelina sativa, Arabidopsis' closely related Brassicaceae family member species, conferred a late-flowering phenotype via suppression of CsFT expression. However, overexpression of an aberrant AtAHL20 gene harboring a missense mutation in the AT-hook domain's highly conserved R-G-R core motif abolished the late-flowering phenotype. Data from targeted yeast-two-hybrid assays showed that AtAHL20 interacted with itself and several other Clade-A Type-I AHLs which have been previously implicated in flowering-time regulation: AtAHL19, AtAHL22 and AtAHL29.

CONCLUSION

We showed via gain-of-function analysis that AtAHL20 is a negative regulator of FT expression, as well as other downstream flowering time regulating genes. A similar outcome in Camelina sativa transgenic plants overexpressing CsAHL20 suggest that this is a conserved function. Our results demonstrate that AtAHL20 acts as a photoperiod-independent negative regulator of transition to flowering.

High Mobility Group A (HMGA): Chromatin Nodes Controlled by a Knotty miRNA Network

High mobility group A (HMGA) proteins are oncofoetal chromatin architectural factors that are widely involved in regulating gene expression. These proteins are unique, because they are highly expressed in embryonic and cancer cells, where they play a relevant role in cell proliferation, stemness, and the acquisition of aggressive tumour traits, i.e., motility, invasiveness, and metastatic properties. The HMGA protein expression levels and activities are controlled by a connected set of events at the transcriptional, post-transcriptional, and post-translational levels. In fact, microRNA (miRNA)-mediated RNA stability is the most-studied mechanism of HMGA protein expression modulation. In this review, we contribute to a comprehensive overview of HMGA-targeting miRNAs; we provide detailed information regarding HMGA gene structural organization and a comprehensive evaluation and description of HMGA-targeting miRNAs, while focusing on those that are widely involved in HMGA regulation; and, we aim to offer insights into HMGA-miRNA mutual cross-talk from a functional and cancer-related perspective, highlighting possible clinical implications.

HMGA Genes and Proteins in Development and Evolution

HMGA (high mobility group A) (HMGA1 and HMGA2) are small non-histone proteins that can bind DNA and modify chromatin state, thus modulating the accessibility of regulatory factors to the DNA and contributing to the overall panorama of gene expression tuning. In general, they are abundantly expressed during embryogenesis, but are downregulated in the adult differentiated tissues. In the present review, we summarize some aspects of their role during development, also dealing with relevant studies that have shed light on their functioning in cell biology and with emerging possible involvement of HMGA1 and HMGA2 in evolutionary biology.

Expression and regulation of high mobility group AT-hook 1 (HMGA1) during ovulation and luteinisation in rat ovary

High mobility group AT-hook 1 (HMGA1) is able to regulate gene expression and function as a tumour suppressor. The spatiotemporal expression pattern of HMGA1 was investigated in this study. Immature female rats (22–23 days old) were treated with 10IU, s.c., pregnant mare’s serum gonadotrophin to stimulate follicular development, followed 48h later by injection with 5IU, s.c., human chorionic gonadotrophin (hCG). Whole ovaries or granulosa cells were collected at various times after hCG administration (n=3 per time point). Real-time polymerase chain reaction and western blot analysis revealed that HMGA1 was highly stimulated in the ovary by 4–12h after hCG treatment. In situ hybridisation analysis demonstrated that Hmga1 mRNA expression was induced in granulosa cells between 8 and 12h after hCG treatment. There was negligible Hmga1 mRNA signal observed in newly forming corpora lutea. In addition, the data indicated that both the protein kinase (PK) A and PKC pathways regulated Hmga1 expression in rat granulosa cells. In rat granulosa cell cultures, upregulation of Hmga1 was dependent on new protein synthesis because Hmga1 was inhibited by cycloheximide. Furthermore, Hmga1 mRNA expression in rat granulosa cell cultures was inhibited by AG1478, whereas NS398 and RU486 had no effect, suggesting that Hmga1 expression was regulated, in part, by the epidermal growth factor pathway. In summary, the findings of this study suggest that induction of Hmga1 may be important for theca and granulosa cell differentiation into luteal cells.

Frontline Science: Targeted expression of a dominant-negative high mobility group A1 transgene improves outcome in sepsis

High mobility group (HMG) proteins are a family of architectural transcription factors, with HMGA1 playing a role in the regulation of genes involved in promoting systemic inflammatory responses. We speculated that blocking HMGA1-mediated pathways might improve outcomes from sepsis. To investigate HMGA1 further, we developed genetically modified mice expressing a dominant negative (dn) form of HMGA1 targeted to the vasculature. In dnHMGA1 transgenic (Tg) mice, endogenous HMGA1 is present, but its function is decreased due to the mutant transgene. These mice allowed us to specifically study the importance of HMGA1 not only during a purely pro-inflammatory insult of endotoxemia, but also during microbial sepsis induced by implantation of a bacterial-laden fibrin clot into the peritoneum. We found that the dnHMGA1 transgene was only present in Tg and not wild-type (WT) littermate mice, and the mutant transgene was able to interact with transcription factors (such as NF-κB), but was not able to bind DNA. Tg mice exhibited a blunted hypotensive response to endotoxemia, and less mortality in microbial sepsis. Moreover, Tg mice had a reduced inflammatory response during sepsis, with decreased macrophage and neutrophil infiltration into tissues, which was associated with reduced expression of monocyte chemotactic protein-1 and macrophage inflammatory protein-2. Collectively, these data suggest that targeted expression of a dnHMGA1 transgene is able to improve outcomes in models of endotoxin exposure and microbial sepsis, in part by modulating the immune response and suggest a novel modifiable pathway to target therapeutics in sepsis.

The High Mobility Group A1 (HMGA1) Transcriptome in Cancer and Development

BACKGROUND & OBJECTIVES

Chromatin structure is the single most important feature that distinguishes a cancer cell from a normal cell histologically. Chromatin remodeling proteins regulate chromatin structure and high mobility group A (HMGA1) proteins are among the most abundant, nonhistone chromatin remodeling proteins found in cancer cells. These proteins include HMGA1a/HMGA1b isoforms, which result from alternatively spliced mRNA. The HMGA1 gene is overexpressed in cancer and high levels portend a poor prognosis in diverse tumors. HMGA1 is also highly expressed during embryogenesis and postnatally in adult stem cells. Overexpression of HMGA1 drives neoplastic transformation in cultured cells, while inhibiting HMGA1 blocks oncogenic and cancer stem cell properties. Hmga1 transgenic mice succumb to aggressive tumors, demonstrating that dysregulated expression of HMGA1 causes cancer in vivo. HMGA1 is also required for reprogramming somatic cells into induced pluripotent stem cells. HMGA1 proteins function as ancillary transcription factors that bend chromatin and recruit other transcription factors to DNA. They induce oncogenic transformation by activating or repressing specific genes involved in this process and an HMGA1 "transcriptome" is emerging. Although prior studies reveal potent oncogenic properties of HMGA1, we are only beginning to understand the molecular mechanisms through which HMGA1 functions. In this review, we summarize the list of putative downstream transcriptional targets regulated by HMGA1. We also briefly discuss studies linking HMGA1 to Alzheimer's disease and type-2 diabetes.

CONCLUSION

Further elucidation of HMGA1 function should lead to novel therapeutic strategies for cancer and possibly for other diseases associated with aberrant HMGA1 expression.

Hitting the bull's eye: targeting HMGA1 in cancer stem cells

Emerging evidence suggests that when cancer cells hijack normal stem cell properties, they acquire the ability to invade, metastasize to distant sites and evade therapy. Thus, eliminating cancer cells with stem cell properties, or cancer stem cells, is of prime importance for the successful treatment of cancer, regardless of the tissue of origin. Previous efforts to target cancer stem cells (CSCs), however, have been largely unsuccessful. Recent studies led to the discovery of a novel role for the high mobility group A1 (HMGA1) protein as a master regulator in both CSCs and normal embryonic stem cells. Here, we present exciting new work unveiling HMGA1 as a promising target for therapies directed at eradicating CSCs.

HMGA1 recruits CTIP2-repressed P-TEFb to the HIV-1 and cellular target promoters

Active positive transcription elongation factor b (P-TEFb) is essential for cellular and human immunodeficiency virus type 1 (HIV-1) transcription elongation. CTIP2 represses P-TEFb activity in a complex containing 7SK RNA and HEXIM1. Recently, the inactive 7SK/P-TEFb small nuclear RNP (snRNP) has been detected at the HIV-1 core promoter as well as at the promoters of cellular genes, but a recruiting mechanism still remains unknown to date. Here we show global synergy between CTIP2 and the 7SK-binding chromatin master-regulator HMGA1 in terms of P-TEFb–dependent endogenous and HIV-1 gene expression regulation. While CTIP2 and HMGA1 concordingly repress the expression of cellular 7SK-dependent P-TEFb targets, the simultaneous knock-down of CTIP2 and HMGA1 also results in a boost in Tat-dependent and independent HIV-1 promoter activity. Chromatin immunoprecipitation experiments reveal a significant loss of CTIP2/7SK/P-TEFb snRNP recruitment to cellular gene promoters and the HIV-1 promoter on HMGA1 knock-down. Our findings not only provide insights into a recruiting mechanism for the inactive 7SK/P-TEFb snRNP, but may also contribute to a better understanding of viral latency.

Arabidopsis thaliana AHL family modulates hypocotyl growth redundantly by interacting with each other via the PPC/DUF296 domain

The Arabidopsis thaliana genome encodes 29 AT-hook motif containing nuclear localized (AHL) genes, which evolved into two phylogenic clades. The AHL proteins contain one or two AT-hook motif(s) and one plant and prokaryote conserved (PPC)/domain of unknown function #296 (DUF296) domain. Seedlings lacking both SOB3/AHL29 and ESC/AHL27 confer a subtle long-hypocotyl phenotype compared with the WT or either single-null mutant. In contrast, the missense allele sob3-6 confers a dramatic long-hypocotyl phenotype in the light. In this study, we examined the dominant-negative feature of sob3-6 and found that it encodes a protein with a disrupted AT-hook motif that abolishes binding to AT-rich DNA. A loss-of-function approach demonstrated different, yet redundant, contributions of additional AHL genes in suppressing hypocotyl elongation in the light. We showed that AHL proteins interact with each other and themselves via the PPC/DUF296 domain. AHLs also share interactions with other nuclear proteins, such as transcription factors, suggesting that these interactions also contribute to the functional redundancy within this gene family. The coordinated action of AHLs requires an AT-hook motif capable of binding AT-rich DNA, as well as a PPC/DUF296 domain containing a conserved Gly-Arg-Phe-Glu-Ile-Leu region. Alteration of this region abolished SOB3/AHL29's physical interaction with transcription factors and resulted in a dominant-negative allele in planta that was phenotypically similar to sob3-6. We propose a molecular model where AHLs interact with each other and themselves, as well as other nuclear proteins, to form complexes which modulate plant growth and development.

WhiB7, an Fe-S-dependent transcription factor that activates species-specific repertoires of drug resistance determinants in actinobacteria

WhiB-like (Wbl) proteins are well known for their diverse roles in actinobacterial morphogenesis, cell division, virulence, primary and secondary metabolism, and intrinsic antibiotic resistance. Gene disruption experiments showed that three different Actinobacteria (Mycobacterium smegmatis, Streptomyces lividans, and Rhodococcus jostii) each exhibited a different whiB7-dependent resistance profile. Heterologous expression of whiB7 genes showed these resistance profiles reflected the host's repertoire of endogenous whiB7-dependent genes. Transcriptional activation of two resistance genes in the whiB7 regulon, tap (a multidrug transporter) and erm(37) (a ribosomal methyltransferase), required interaction of WhiB7 with their promoters. Furthermore, heterologous expression of tap genes isolated from Mycobacterium species demonstrated that divergencies in drug specificity of homologous structural proteins contribute to the variation of WhiB7-dependent drug resistance. WhiB7 has a specific tryptophan/glycine-rich region and four conserved cysteine residues; it also has a peptide sequence (AT-hook) at its C terminus that binds AT-rich DNA sequence motifs upstream of the promoters it activates. Targeted mutagenesis showed that these motifs were required to provide antibiotic resistance in vivo. Anaerobically purified WhiB7 from S. lividans was dimeric and contained 2.1 ± 0.3 and 2.2 ± 0.3 mol of iron and sulfur, respectively, per protomer (consistent with the presence of a 2Fe-2S cluster). However, the properties of the dimer's absorption spectrum were most consistent with the presence of an oxygen-labile 4Fe-4S cluster, suggesting 50% occupancy. These data provide the first insights into WhiB7 iron-sulfur clusters as they exist in vivo, a major unresolved issue in studies of Wbl proteins.

Human height genes and cancer

Body development requires the ability to control cell proliferation and metabolism, together with selective 'invasive' cell migration for organogenesis. These requirements are shared with cancer. Human height-associated loci have been recently identified by genome-wide SNP-association studies. Strikingly, most of the more than 100 genes found associated to height appear linked to neoplastic growth, and impose a higher risk for cancer. Height-associated genes drive the HH/PTCH and BMP/TGFβ pathways, with p53, c-Myc, ERα, HNF4A and SMADs as central network nodes. Genetic analysis of body-size-affecting diseases and evidence from genetically-modified animals support this model. The finding that cancer is deeply linked to normal, body-plan master genes may profoundly affect current paradigms on tumor development.

HMGA1 reprograms somatic cells into pluripotent stem cells by inducing stem cell transcriptional networks

BACKGROUND

Although recent studies have identified genes expressed in human embryonic stem cells (hESCs) that induce pluripotency, the molecular underpinnings of normal stem cell function remain poorly understood. The high mobility group A1 (HMGA1) gene is highly expressed in hESCs and poorly differentiated, stem-like cancers; however, its role in these settings has been unclear.

METHODS/PRINCIPAL FINDINGS

We show that HMGA1 is highly expressed in fully reprogrammed iPSCs and hESCs, with intermediate levels in ECCs and low levels in fibroblasts. When hESCs are induced to differentiate, HMGA1 decreases and parallels that of other pluripotency factors. Conversely, forced expression of HMGA1 blocks differentiation of hESCs. We also discovered that HMGA1 enhances cellular reprogramming of somatic cells to iPSCs together with the Yamanaka factors (OCT4, SOX2, KLF4, cMYC - OSKM). HMGA1 increases the number and size of iPSC colonies compared to OSKM controls. Surprisingly, there was normal differentiation in vitro and benign teratoma formation in vivo of the HMGA1-derived iPSCs. During the reprogramming process, HMGA1 induces the expression of pluripotency genes, including SOX2, LIN28, and cMYC, while knockdown of HMGA1 in hESCs results in the repression of these genes. Chromatin immunoprecipitation shows that HMGA1 binds to the promoters of these pluripotency genes in vivo. In addition, interfering with HMGA1 function using a short hairpin RNA or a dominant-negative construct blocks cellular reprogramming to a pluripotent state.

CONCLUSIONS

Our findings demonstrate for the first time that HMGA1 enhances cellular reprogramming from a somatic cell to a fully pluripotent stem cell. These findings identify a novel role for HMGA1 as a key regulator of the stem cell state by inducing transcriptional networks that drive pluripotency. Although further studies are needed, these HMGA1 pathways could be exploited in regenerative medicine or as novel therapeutic targets for poorly differentiated, stem-like cancers.

Distamycin A inhibits HMGA1-binding to the P-selectin promoter and attenuates lung and liver inflammation during murine endotoxemia

BACKGROUND

The architectural transcription factor High Mobility Group-A1 (HMGA1) binds to the minor groove of AT-rich DNA and forms transcription factor complexes ("enhanceosomes") that upregulate expression of select genes within the inflammatory cascade during critical illness syndromes such as acute lung injury (ALI). AT-rich regions of DNA surround transcription factor binding sites in genes critical for the inflammatory response. Minor groove binding drugs (MGBs), such as Distamycin A (Dist A), interfere with AT-rich region DNA binding in a sequence and conformation-specific manner, and HMGA1 is one of the few transcription factors whose binding is inhibited by MGBs.

OBJECTIVES

To determine whether MGBs exert beneficial effects during endotoxemia through attenuating tissue inflammation via interfering with HMGA1-DNA binding and modulating expression of adhesion molecules.

METHODOLOGY/PRINCIPAL FINDINGS

Administration of Dist A significantly decreased lung and liver inflammation during murine endotoxemia. In intravital microscopy studies, Dist A attenuated neutrophil-endothelial interactions in vivo following an inflammatory stimulus. Endotoxin induction of P-selectin expression in lung and liver tissue and promoter activity in endothelial cells was significantly reduced by Dist A, while E-selectin induction was not significantly affected. Moreover, Dist A disrupted formation of an inducible complex containing NF-kappaB that binds an AT-rich region of the P-selectin promoter. Transfection studies demonstrated a critical role for HMGA1 in facilitating cytokine and NF-kappaB induction of P-selectin promoter activity, and Dist A inhibited binding of HMGA1 to this AT-rich region of the P-selectin promoter in vivo.

CONCLUSIONS/SIGNIFICANCE

We describe a novel targeted approach in modulating lung and liver inflammation in vivo during murine endotoxemia through decreasing binding of HMGA1 to a distinct AT-rich region of the P-selectin promoter. These studies highlight the ability of MGBs to function as molecular tools for dissecting transcriptional mechanisms in vivo and suggest alternative treatment approaches for critical illness.

HMGA1 is induced by Wnt/beta-catenin pathway and maintains cell proliferation in gastric cancer

The development of stomach cancer is closely associated with chronic inflammation, and the Wnt/beta-catenin signaling pathway is activated in most cases of this cancer. High-mobility group A (HMGA) proteins are oncogenic chromatin factors that are primarily expressed not only in undifferentiated tissues but also in various tumors. Here we report that HMGA1 is induced by the Wnt/beta-catenin pathway and maintains proliferation of gastric cancer cells. Specific knockdown of HMGA1 resulted in marked reduction of cell growth. The loss of beta-catenin or its downstream c-myc decreased HMGA1 expression, whereas Wnt3a treatment increased HMGA1 and c-myc transcripts. Furthermore, Wnt3a-induced expression of HMGA1 was inhibited by c-myc knockdown, suggesting that HMGA1 is a downstream target of the Wnt/beta-catenin pathway. Enhanced expression of HMGA1 coexisted with the nuclear accumulation of beta-catenin in about 30% of gastric cancer tissues. To visualize the expression of HMGA1 in vivo, transgenic mice expressing endogenous HMGA1 fused to enhanced green fluorescent protein were generated and then crossed with K19-Wnt1/C2mE mice, which develop gastric tumors through activation of both the Wnt and prostaglandin E2 pathways. Expression of HMGA1-enhanced green fluorescent protein was normally detected in the forestomach, along the upper border of the glandular stomach, but its expression was also up-regulated in cancerous glandular stomach. These data suggest that HMGA1 is involved in proliferation and gastric tumor formation via the Wnt/beta-catenin pathway.

Nuclear functions of the HMG proteins

Although the three families of mammalian HMG proteins (HMGA, HMGB and HMGN) participate in many of the same nuclear processes, each family plays its own unique role in modulating chromatin structure and regulating genomic function. This review focuses on the similarities and differences in the mechanisms by which the different HMG families impact chromatin structure and influence cellular phenotype. The biological implications of having three architectural transcription factor families with complementary, but partially overlapping, nuclear functions are discussed.

Interaction proteomics of the HMGA chromatin architectural factors

The high mobility group A (HMGA) chromatin architectural transcription factors are a group of proteins involved in development and neoplastic transformation. They take part in an articulated interaction network, both with DNA and other nuclear proteins, organizing multimolecular complexes at chromatin level. Here, we report the development of a novel in vitro strategy for the identification of HMGA molecular partners based on the combination of an RP-HPLC prefractionation procedure, 2-DE gels, blot-overlay and MS. To demonstrate that our approach could be a reliable screening method we confirmed a representative number of interactions in vitro by GST pull-down and far-Western and in vivo by co-affinity purification. This approach allowed us to enlarge the HMGA molecular network confirming their involvement also in non-transcriptional-related processes such as RNA processing and DNA repair.

Biphasic regulation of Il2 transcription in CD4+ T cells: roles for TNF-alpha receptor signaling and chromatin structure

We describe a novel biphasic regulation of Il2 transcription in naive CD4(+) T cells. Few ( approximately 5%) CD4(+) T cells transcribe Il2 within 6 h of anti-TCR-beta plus anti-CD28 stimulation (early phase). Most naive CD4(+) T cells do not initiate Il2 transcription until after an additional approximately 12 h of T cell stimulation (late phase). In comparison, essentially all previously activated (Pre-Ac) CD4(+) T cells that transcribe Il2 do so with an early-phase response. Late-phase Il2 expression mostly requires c-Rel, CD28, and TNFR signaling. In contrast, early-phase transcription is only partly c-Rel and CD28 dependent and TNFR independent. There was also increased stable DNA accessibility at the Il2 locus and elevated c-Rel expression in resting Pre-Ac CD4(+) cells. Upon T cell activation, a faster and greater increase in DNA accessibility as well as c-Rel nuclear expression were observed in Pre-Ac CD4(+) cells relative to naive CD4(+) T cells. In addition, both acetylated histone H3 and total H3 decreased at the Il2 locus upon rechallenge of Pre-Ac CD4(+) T cells, whereas increased acetylated histone H3 with no change in total H3 was observed following activation of naive CD4(+) T cells. We propose a model in which nucleosome disassembly facilitates rapid initiation of Il2 transcription in CD4(+) T cells, and suggest that a threshold level of c-Rel must be reached for Il2 promoter activity in both naive and Pre-Ac CD4(+) T cells. This is provided, at least partially, by TNFR signaling during priming, but not during recall.

SUMOylation of HMGA2: selective destabilization of promyelocytic leukemia protein via proteasome

The HMGA2 architectural protein functions in a variety of cellular processes, such as cell growth, transcription regulation, neoplastic transformation, and progression. Up-regulation of HMGA2 protein is observed in many tumors and is associated with advanced cancers with poor prognoses. Although the expression and biochemical properties of HMGA2 protein are regulated by microRNA and phosphorylation, it is unknown whether HMGA2 activity can also be regulated by SUMOylation, and that is what is investigated in this report. We identified HMGA2 as a SUMOylation target and showed that the expression of wild-type HMGA2, but not SUMOylation-defective HMGA2(2K/R), selectively lowered the steady-state level of PML protein. Consequently, the HMGA2-elicited PML down-regulation rendered a reduction in the average number of PML nuclear bodies per cell and the volume of PML assembled per PML nuclear body. Using small interfering RNA to suppress endogenous ubiquitin expression and proteasome inhibitor to repress ubiquitin-mediated protein degradation, we showed that HMGA2 confers PML down-regulation through ubiquitin-proteasome-dependent protein degradation. Importantly, arsenic trioxide treatment stimulated HMGA2 SUMOylation, leading to the formation of HMGA2 nuclear foci surrounding PML nuclear bodies and the stimulation of PML degradation. Collectively, our results unveil a previously unrecognized effect by HMGA2 on the modulation of PML protein level, providing a novel mechanism underlying HMGA2 function and underscoring the molecular basis for oncogenic progression by HMGA2.

High mobility group A1 protein mediates human nitric oxide synthase 2 gene expression

Nitric oxide synthase (NOS)2, an inducible enzyme that produces NO during inflammation, is transcriptionally regulated. Our goal was to determine whether high mobility group (HMG)A1 contributes to human (h)NOS2 gene regulation. Using a small molecule inhibitor of HMGA1 binding to DNA, or a dominant-negative form of HMGA1, we blunted the induction of hNOS2 by pro-inflammatory stimuli. Binding of HMGA1 in the region -3506 to -3375 of the hNOS2 promoter, a region not previously known to be involved in hNOS2 regulation, contributed to the induction of hNOS2 promoter in conjunction with upstream enhancer regions. We demonstrate a previously unknown role for HMGA1 in the regulation of hNOS2.

Functional Role for IκBNS in T Cell Cytokine Regulation As Revealed by Targeted Gene Disruption

Triggering of the TCR by cognate peptide/MHC ligands induces expression of I kappa BNS, a member of the I kappa B family of NF-kappaB inhibitors whose expression is associated with apoptosis of immature thymocytes. To understand the role of I kappa BNS in TCR triggering, we created a targeted disruption of the I kappa BNS gene. Surprisingly, mice lacking I kappa BNS show normal thymic progression but both thymocytes and T cells manifest reduced TCR-stimulated proliferation. Moreover, I kappa BNS knockout thymocytes and T cells produce significantly less IL-2 and IFN-gamma than wild-type cells. Transfection analysis demonstrates that I kappa BNS and c-Rel individually increase IL-2 promoter activity. The effect of I kappa BNS on the IL-2 promoter, unlike c-Rel, is dependent on the NF-kappaB rather than the CD28RE site; mutation of the NF-kappaB site extinguishes the induction of transcription by I kappa BNS in transfectants and prevents association of I kappa BNS with IL-2 promoter DNA. Microarray analyses confirm the reduction in IL-2 production and some IFN-gamma-linked transcripts in I kappa BNS knockout T cells. Collectively, our findings demonstrate that I kappa BNS regulates production of IL-2 and other cytokines induced via "strong" TCR ligation.

Characterization of the sequence and architectural constraints of the regulatory and core regions of the human interleukin-2 promoter

The cytokine interleukin-2 (IL-2) is produced by T cells when they recognize a foreign antigen. Transcription of the IL-2 gene is tightly controlled by the combined actions of multiple transcriptional activators. However, the contribution of sequences in the IL-2 core promoter and the architecture of the IL-2 regulatory region to setting levels of IL-2 transcription are not understood. We have probed these properties of the human IL-2 promoter to understand how the regulatory and core promoter regions cooperate in response to T cell stimulation, thereby setting high levels of inducible transcription. We found that the IL-2 core promoter contains a TATA box that is critical for inducible expression. Moreover, the spacing and orientation between the IL-2 regulatory and core promoter regions is important for setting the level of transcription. The regulatory region of the IL-2 promoter is capable of mediating high levels of expression even when the helical phasing between transcription factor binding sites is perturbed. Although long considered an enhancer, our studies indicate that the regulatory region in the IL-2 promoter is better considered as a proximal regulatory element, since it lacks multiple properties associated with enhancer elements.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and T-cell responses: what we do and don't know

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important hematopoietic growth factor and immune modulator. GM-CSF also has profound effects on the functional activities of various circulating leukocytes. It is produced by a variety of cell types including T cells, macrophages, endothelial cells and fibroblasts upon receiving immune stimuli. Although GM-CSF is produced locally, it can act in a paracrine fashion to recruit circulating neutrophils, monocytes and lymphocytes to enhance their functions in host defense. Recent intensive investigations are centered on the application of GM-CSF as an immune adjuvant for its ability to increase dendritic cell (DC) maturation and function as well as macrophage activity. It is used clinically to treat neutropenia in cancer patients undergoing chemotherapy, in AIDS patients during therapy, and in patients after bone marrow transplantation. Interestingly, the hematopoietic system of GM-CSF-deficient mice appears to be normal; the most significant changes are in some specific T cell responses. Although molecular cloning of GM-CSF was carried out using cDNA library of T cells and it is well known that the T cells produce GM-CSF after activation, there is a lack of systematic investigation of this cytokine in production by T cells and its effect on T cell function. In this article, we will focus mainly on the immunobiology of GM-CSF in T cells.

New high mobility group box 1 assay system

BACKGROUND

High-sensitivity sandwich ELISA methods have been developed using chemiluminescent substrates. HMGB1 (high mobility group box 1) protein has been shown to play a critical role in several inflammatory diseases and it may be involved in the development of atherosclerosis.

METHODS

Anti-human HMGB1 monoclonal antibodies and anti-peptide polyclonal antibodies against the peptide sequence (KPDAAKKGVVKAEK) with high antigenicity and different from the sequence of HMGB2 were developed, and the antibodies were used to construct sandwich ELISA methods with a chromogenic substrate (TMBZ) and a chemiluminescent substrate (PS-atto). Highly purified human HMGB1 was used as a standard material and high-sensitivity CRP was measured to compare with HMGB1.

RESULTS

The analytical characteristics of the ELISA method we developed were validated inter-assay and intra-assay CVs were <10%, and the detection limit was 0.3 microg/l by the chemiluminescent method and 1 microg/l with the chromogenic substrates. HMGB1 was detected in the serum of patients with acute coronary syndrome (ACS). When a cut-off of 0.6 microg/l HMGB1 upon admission to the intensive care unit (ICU) was used, the risk of developing an acute cardiac event within 1 month after discharge of ACS patients with an abnormal HMGB1 was significantly higher than for the patients with normal values (P<0.0001). The usefulness of HMGB1 as an acute prognostic marker was suggested.

CONCLUSIONS

The assay is easy to perform and suitable for use in the hospital laboratory and for screening large populations. HMGB1 is detectable in the serum of ACS patients and that the serum concentration of HMGB1 may be a prognostic indicator in ACS patients.

Haploinsufficiency of theHmga1Gene Causes Cardiac Hypertrophy and Myelo-Lymphoproliferative Disorders in Mice

The HMGA1 protein is a major factor in chromatin architecture and gene control. It plays a critical role in neoplastic transformation. In fact, blockage of HMGA1 synthesis prevents rat thyroid cell transformation by murine transforming retroviruses, and an adenovirus carrying the HMGA1 gene in the antisense orientation induces apoptotic cell death in anaplastic human thyroid carcinoma cell lines, but not in normal thyroid cells. Moreover, both in vitro and in vivo studies have established the oncogenic role of the HMGA1 gene. In this study, to define HMGA1 function in vivo, we examined the consequences of disrupting the Hmga1 gene in mice. Both heterozygous and homozygous mice for the Hmga1-null allele show cardiac hypertrophy due to the direct role of HMGA1 on cardiomyocytic cell growth regulation. These mice also developed hematologic malignancies, including B cell lymphoma and myeloid granuloerythroblastic leukemia. The B cell expansion and the increased expression of the RAG1/2 endonuclease, observed in HMGA1-knockout spleen tissues, might be responsible for the high rate of abnormal IgH rearrangements observed in these neoplasias. Therefore, the data reported here indicate the critical role of HMGA1 in heart development and growth, and reveal an unsuspected antioncogenic potential for this gene in hematologic malignancies.

c-Rel-dependent priming of naive T cells by inflammatory cytokines

The intrinsic refractoriness of naive T cells for cytokine production is counteracted by cells of the innate immune system. Upon sensing danger via Toll-like receptors, these cells upregulate T cell costimulatory molecules and secrete cytokines that enhance T cell activation. We show that cytokine-mediated priming of naive T cells requires the NF-kappaB family member c-Rel. In resting naive cells c-Rel is associated primarily with IkappaBbeta, an inhibitory molecule that is not effectively degraded by TCR signals. Exposure of T cells to proinflammatory cytokines, TNF-alpha and IL-1beta, shifts c-Rel to IkappaBalpha-associated complexes that are readily targeted by the TCR. As a consequence, IL-2 and IFN-gamma mRNA are produced more quickly, and at higher levels, in cytokine-primed T cells. This mechanism does not operate in effector T cells where cytokine gene expression is c-Rel-independent. We propose that c-Rel plays a crucial role as a target of innate signals in T cells.

The Herpesvirus saimiri replication and transcription activator acts synergistically with CCAAT enhancer binding protein alpha to activate the DNA polymerase promoter

The open reading frame (ORF) 50 gene product, also known as the replication and transcription activator (Rta), is an immediate-early gene which is well conserved among all gamma-2 herpesviruses and plays a pivotal role in regulating the latent-lytic switch. Herpesvirus saimiri (HVS) ORF 50a functions as a sequence-specific transactivator capable of activating delayed-early (DE) gene expression via binding directly to an ORF 50 response element (RE) within the respective promoter. Analysis of the ORF 50 REs have identified two distinct types within HVS gene promoters. The first comprises a consensus sequence motif, CCN(9)GG, the second an AT-rich sequence. Here we demonstrate that ORF 50a is capable of transactivating the DE ORF 9 promoter which encodes the DNA polymerase. Deletion analysis of the ORF 9 promoter mapped the ORF 50 RE to a 95-bp region situated 126 bp upstream of the initiation codon. Gel retardation analysis further mapped the RE to a 28-bp fragment, which was able to confer ORF 50 responsiveness on an enhancerless simian virus 40 minimal promoter. Furthermore, sequence analysis identified multiple CCAAT enhancer binding protein alpha (C/EBPalpha) binding sites within the ORF 9 promoter and specifically two within the close vicinity of the AT-rich ORF 50 RE. Analysis demonstrated that the HVS ORF 50a and C/EBPalpha proteins associate with the ORF 9 promoter in vivo, interact directly, and synergistically activate the ORF 9 promoter by binding to adjacent binding motifs. Overall, these data suggest a cooperative interaction between HVS ORF 50a and C/EBPalpha proteins to activate the DNA polymerase promoter during early stages of the lytic replication cycle.

Discovering high mobility group A molecular partners in tumour cells

DNA-based activities rely on an extremely coordinated sequence of events performed by several chromatin-associated proteins which act in concert. High Mobility Group A (HMGA) proteins are non-histone architectural nuclear factors that participate in the regulation of specific genes but they are also believed to have a more general role in chromatin dynamics. The peculiarity of these proteins is their flexibility, both in terms of DNA-binding and in protein-protein interactions. Since these proteins act as core elements in the assembly of multiprotein complexes called enhanceosomes, and have already displayed the ability to interact with several different proteins, we started a proteomic approach for the systematic identification of their molecular partners. By a combination of affinity chromatography, two-dimensional gel electrophoresis and mass spectrometry we have identified about twenty putative HMGA interactors which could be roughly assigned to three different classes: mRNA processing proteins, chromatin remodelling related factors and structural proteins. Direct HMGA interaction with some of these proteins was confirmed by glutathione-S-transferase pull-down assays and the HMGA domain involved was mapped. Blot-overlay experiments reveal that members of the HMGA family share most of their molecular partners but, interestingly, it seems that there are some cell-type specific partners. Taken together, these experimental data indicate that HMGA proteins are highly connected nodes in the chromatin protein network. Since these proteins are strongly implicated with cancer development, the identification of molecules able to perturb the HMGA molecular network could be a possible tool to interfere with their oncogenic activity.

Signals from CD28 induce stable epigenetic modification of the IL-2 promoter

CD28 costimulation controls multiple aspects of T cell function, including the expression of proinflammatory cytokine genes. One of these genes encodes IL-2, a growth factor that influences T cell proliferation, survival, and differentiation. Antigenic signaling in the absence of CD28 costimulation leads to anergy, a mechanism of tolerance that renders CD4+ T cells unable to produce IL-2. The molecular mechanisms by which CD28 costimulatory signals induce gene expression are not fully understood. In eukaryotic cells, the expression of many genes is influenced by their physical structure at the level of DNA methylation and local chromatin remodeling. To address whether these epigenetic mechanisms are operative during CD28-dependent gene expression in CD4+ T cells, we compared cytosine methylation and chromatin structure at the IL-2 locus in fully activated CD4+ effector T cells and CD4+ T cells rendered anergic by TCR ligation in the absence of CD28 costimulation. Costimulation through CD28 led to marked, stable histone acetylation and loss of cytosine methylation at the IL-2 promoter/enhancer. This was accompanied by extensive remodeling of the chromatin in this region to a structure highly accessible to DNA binding proteins. Conversely, TCR activation in the absence of CD28 costimulation was not sufficient to promote histone acetylation or cytosine demethylation, and the IL-2 promoter/enhancer in anergic cells remained completely inaccessible. These data suggest that CD28 may function through epigenetic mechanisms to promote CD4+ T cell responses.

The herpesvirus saimiri Rta gene autostimulates via binding to a non-consensus response element

Herpesvirus saimiri ORF 50a protein expression is sufficient to reactivate the entire lytic-replication cycle. ORF 50a functions as a sequence-specific transactivator that is capable of activating delayed-early gene expression via direct binding to an ORF 50 response element (RE) within the respective promoter. Here, it is shown that ORF 50a is capable of transactivating its own promoter. Deletion analysis of the ORF 50a promoter showed that the ORF 50-responsive element is contained within an 80 bp fragment, situated 293–373 bp from the transcription initiation site. Gel-retardation analysis further mapped the RE to a 34 bp fragment that was able to confer ORF 50 responsiveness to an enhancerless SV40 minimal promoter. Sequence analysis showed that this RE has no direct similarity to previously identified ORF 50 REs. Therefore, it is concluded that ORF 50a is capable of stimulating its own promoter via a novel RE.

HMGI(Y) gene expression in colorectal cancer: comparison with some histological typing, grading, and clinical staging

We investigated HMGI(Y) gene expression in 81 pairs of frozen samples obtained from colorectal carcinomas and adjacent normal colorectal mucosas and in four samples from colorectal mucosa from patients without neoplastic diseases. In this group, HMGI(Y)-positive/-negative expression was compared with some histological features, grading, and clinical staging of neoplasms investigated to assess its potential role as a prognostic marker for colorectal cancer. Expression of HMGI(Y) gene was found in 51 of 81 cases of colorectal cancers, while, in normal mucosa, expression of this gene was not observed. HMGI(Y) gene expression was associated with more advanced tumors (T3, T4) and metastases to lymph nodes (N1, N2). The most interesting finding was that expression of this gene correlated with distant metastases. HMGI(Y) gene expression was detected in all cases classified as M1 (n = 19, p = 0.0008). We did not find any association between age, gender, tumor localization, histological type and this gene expression.

Dominant-negative c-Jun (TAM67) target genes: HMGA1 is required for tumor promoter-induced transformation

Activation of the transcription factor AP-1 (activator protein-1) is required for tumor promotion and maintenance of malignant phenotype. A number of AP-1-regulated genes that play a role in tumor progression have been identified. However, AP-1-regulated genes driving tumor induction are yet to be defined. Previous studies have established that expression of a dominant-negative c-Jun (TAM67) inhibits phorbol 12-tetradecanoyl-13-acetate (TPA)-induced AP-1 transactivation as well as transformation in mouse epidermal JB6/P+ cells and tumor promotion in mouse skin carcinogenesis. In this study, we utilized the tumor promotion-sensitive JB6/P+ cells to identify AP-1-regulated TAM67 target genes and to establish causal significance in transformation for one target gene. A 2700 cDNA microarray was queried with RNA from TPA-treated P+ cells with or without TAM67 expression. Under conditions in which TAM expression inhibited TPA-induced transformation, microarray analysis identified a subset of six genes induced by TPA and suppressed by TAM67. One of the identified genes, the high-mobility group protein A1 (Hmga1) is induced by TPA in P+, but not in transformation-resistant P cells. We show that TPA induction of the architectural transcription factor HMGA1 is inhibited by TAM67, is extracellular-signal-regulated kinase (ERK)-activation dependent, and is mediated by AP-1. HMGA1 antisense construct transfected into P+ cells blocked HMGA1 protein expression and inhibited TPA-induced transformation indicating that HMGA1 is required for transformation. HMGA1 is not however sufficient as HMGA1a or HMGA1b overexpression did not confer transformation sensitivity on P- cells. Although HMGA1 expression is ERK dependent, it is not the only ERK-dependent event required for transformation because it does not suffice to rescue ERK-deficient P- cells. Our study shows (a) TAM 67 when it inhibits AP-1 and transformation, targets a relatively small number of genes; (b) HMGA1, a TAM67 target gene, is causally related to transformation and therefore a potentially important target for cancer prevention.

HMG-I/Y Is a c-Jun/Activator Protein-1 Target Gene and Is Necessary for c-Jun–Induced Anchorage-Independent Growth in Rat1a Cells

The transcription complex activator protein-1 (AP-1) plays a role in a diverse number of cellular processes including proliferation, differentiation, and apoptosis. To identify AP-1–responsive target genes, we used a doxycycline-inducible c-Jun system in Rat1a cells. The HMG-I/Y chromatin binding protein was found to be up-regulated by c-Jun. Following induction of c-Jun expression, Rat1a cells under nonadherent growth conditions have sustained HMG-I/Y mRNA expression and 2-fold higher protein than uninduced cells. HMG-I/Y promoter reporter assays show that HMG-I/Y promoter activity increases in the presence of c-Jun expression, and gel mobility shift assays demonstrate that induced c-Jun binds to an AP-1 consensus site at position −1,091 in the HMG-I/Y promoter. Suppression of HMG-I/Y expression by its antisense sequence significantly reduces the ability of c-Jun–overexpressing Rat1a cells to grow in an anchorage-independent fashion. HMG-I/Y transforms Rat1a cells (although the colonies are smaller than that observed for the cells overexpressing c-Jun). Taken together, these results suggest that HMG-I/Y is a direct transcriptional target of c-Jun necessary for c-Jun–induced anchorage-independent growth in Rat1a cells.

HMGA1 co-activates transcription in B cells through indirect association with DNA

The immunoglobulin heavy chain enhancer, or mu enhancer, is required for B cell development. Only the appropriate combination of transcription factors results in B cell-specific enhancer activation. HMGA1 (formerly (HMG-I(Y)) is a proposed co-activator of the ETS transcription factors required for mu enhancer activity. HMGA1 associates with the ETS factor PU.1, resulting in changes in PU.1 structure, and enhanced transcriptional synergy with Ets-1 on the mu enhancer in nonlymphoid cells. New data show HMGA1 directly interacts with Ets-1 in addition to PU.1. In vitro HMGA1/Ets-1 interaction facilitates Ets-1/mu enhancer binding in the absence of an HMGA1.Ets-1.DNA complex. To address whether HMGA1 is present in the transcriptionally active mu nucleoprotein complex, we completed DNA pull-down assays to detect protein tethering in the context of protein/DNA interaction. Results show that HMGA1 is not tightly associated with mu enhancer DNA through PU.1 or Ets-1, despite strong associations between these proteins in solution. However, chromatin immunoprecipitation assays show HMGA1 associates with the endogenous enhancer in B cells. Furthermore, antisense HMGA1 substantially decreases mu enhancer activity in B cells. Taken together, these data suggest that HMGA1 functions as a transcriptional mu enhancer co-activator in B cells through indirect association with DNA.

Expression of the stress-associated protein p8 is a requisite for tumor development

We identified a new gene, called p8, because its expression was strongly induced during the acute phase of pancreatitis. Further experiments have shown that p8 mRNA is activated in response to several stresses and that its activation is not restricted to pancreatic cells. p8 is a nuclear protein and biochemical and biophysical studies have shown that p8 was very similar in many structural aspects to the HMG proteins, although sharing only low amino acid sequence homology. Also, p8 was found overexpressed in many human cancers. Therefore, we wondered whether the p8-mediated response to cellular stress was necessary for tumor establishment. Subcutaneous or intraperitoneal injections of transformed p8-expressing fibroblasts led to tumor formation in nude mice, but no tumor was observed with transformed p8-deficient cells. Restoring p8 expression in transformed p8-deficient fibroblasts led to tumor formation, demonstrating that p8 expression is crucial for tumor development and suggesting that the stress-response mechanisms governed by p8 are required for tumor establishment.

Construction and analysis of cells lacking the HMGA gene family

The high mobility group A (HMGA) family of non-histone chromosomal proteins is encoded by two related genes, HMGA1 and HMGA2. HMGA proteins are architectural transcription factors that have been found to regulate the transcription of a large number of genes. They are also some of the most commonly dysregulated genes in human neoplasias, highlighting a role in growth control. HMGA1 and HMGA2 have also been found to stimulate retroviral integration in vitro. In this study, we have cloned chicken HMGA1, and used the chicken DT40 B-cell lymphoma line to generate cells lacking HMGA1, HMGA2 and both in combination. We tested these lines for effects on cellular growth, gene control and retroviral integration. Surprisingly, we found that the HMGA gene family is dispensable for growth in DT40 cells, and that there is no apparent defect in retroviral integration in the absence of HMGA1 or HMGA2. We also analyzed the activity of approximately 4000 chicken genes, but found no significant changes. We conclude that HMGA proteins are not strictly required for growth control or retroviral integration in DT40 cells and may well be redundant with other factors.

Loss of Hmga1 gene function affects embryonic stem cell lympho-hematopoietic differentiation

By interacting with transcription machinery, high-mobility group A 1 (HMGA1) proteins alter the chromatin structure and thereby regulate the transcriptional activity of several genes. To assess their role in development, we studied the in vitro differentiation of embryonic stem (ES) cells that bear one or both disrupted Hmga1 alleles. Here, we report that Hmga1 null ES cells generate fewer T-cell precursors than do wild-type ES cells. Indeed, they preferentially differentiate to B cells, probably consequent to decreased interleukin 2 expression and increased interleukin 6 expression. Moreover, a lack of HMGA1 expression induces changes in hemopoietic differentiation, i.e., a reduced monocyte/macrophage population and an increase in megakaryocyte precursor numbers, erythropoiesis, and globin gene expression. Re-expression of the Hmga1 gene in Hmga1 null ES cells restores the wild-type phenotype. The effect on megakaryocyte/erythrocyte lineages seems, at least in part, mediated by the GATA-1 transcription factor, a key regulator of red blood cell differentiation. In fact, we found that Hmga1-/- ES cells overexpress GATA-1 and that HMGA1 proteins directly control GATA-1 transcription. Taken together, these data indicate that HMGA1 proteins play a prime role in lymphohematopoietic differentiation.

HMGA proteins: flexibility finds a nuclear niche?

The mammalian HMGA family of chromatin proteins possesses an unusual constellation of physical, biochemical, and biological characteristics that distinguish them from other nuclear proteins. Principal among these is the fact that, unlike other proteins, they possess little detectable secondary structure prior to interactions with other macromolecules (DNA, RNA, proteins). Upon binding to substrates, however, the HMGA proteins undergo specific disordered-to-ordered structural transitions and also induce alterations in the structure of the substrates themselves. Their intrinsic structural flexibility, combined with other features such as the control of their substrate interactions via complex patterns of in vivo biochemical modifications, allows the HMGA proteins to actively participate in a wide variety of nuclear activities including DNA replication, DNA repair, chromatin remodeling, control of gene transcription, and regulation of mRNA processing

SS-A/Ro52, an autoantigen involved in CD28-mediated IL-2 production

An autoantibody against SS-A/Ro52 (Ro52) is most frequently found in the sera of patients with Sjögren's syndrome, systemic lupus erythematosus, and congenital heart block from anti-Ro52 Ab-positive mother. However, the physiological function of the autoantigen SS-A/Ro52 has not yet been elucidated. In this study, we describe the role of Ro52 protein in T cell activation. Overexpression of SS-A/Ro52 in Jurkat T cell resulted in enhanced IL-2 production following CD28 stimulation. Furthermore, transfection of anti-Ro52-specific small RNA duplexes partially blocked the expression of native and overexpressed Ro52 in Jurkat T cell, resulting in decreased IL-2 production via CD28 pathway in these cells. Finally, intracellular localization of Ro52 dramatically changed following CD28 stimulation. Our data reveal a novel function of Ro52 in CD28-mediated pathway, which eventually contributes to cytokine production and expression of the T cell biological programs.

The human IL-2 gene promoter can assemble a positioned nucleosome that becomes remodeled upon T cell activation

Controlled production of the cytokine IL-2 plays a key role in the mammalian immune system. Expression from the gene is tightly regulated with no detectable expression in resting T cells and a strong induction following T cell activation. The IL-2 proximal promoter (+1 to -300) contains many well-defined transcriptional activation elements that respond to T cell stimulation. To determine the role of chromatin structure in the regulation of interleukin-2 gene transcription, nucleosome assembly across the IL-2 promoter region was examined using in vitro chromatin reconstitution assays. The IL-2 promoter assembles a nucleosome that is both translationally and rotationally positioned, spanning some of the major functional control elements. The binding of transcription factors to these elements, with the exception of the architectural protein HMGA1, was occluded by the presence of the nucleosome. Analysis of the chromatin architecture of the IL-2 gene in Jurkat T cells provided evidence for the presence of a similarly positioned nucleosome in vivo. The region encompassed by this nucleosome becomes remodeled following activation of Jurkat T cells. These observations suggest that the presence of a positioned nucleosome across the IL-2 proximal promoter may play an important role in maintaining an inactive gene in resting T cells and that remodeling of this nucleosome is important for gene activation.

It's all Rel-ative: NF-kappaB and CD28 costimulation of T-cell activation

Costimulatory signals complement or modify the signals provided to a lymphocyte through antigen receptors. For productive T-cell activation, the CD28 molecule is apparently the most important, although not the only, costimulatory receptor. CD28 can provide a signal that is at least partially distinct from that delivered by the T cell receptor (TCR)-CD3 complex. Several lines of evidence indicate that the nuclear factor (NF)-kappaB pathway is perhaps the most relevant biochemical or transcriptional target for the costimulatory activity of CD28. Although many questions remain, recent years have witnessed significant progress in understanding the signal transduction pathways leading from the TCR and CD28 to Rel/NF-kappaB-dependent transcription.

Immunomodulation by parasites: high mobility group 2 (HMG-2) protein is a putative intracellular mediator for fucosylated sugars of Schistosoma mansoni

Fucosylated sugars in Schistosoma mansoni possess immunomodulatory properties. In order to gain insights to the mechanisms involved, attempts were made to identify host immune cell molecules that specifically recognize these sugars. On Western blots, specific binding of synthetic biotinylated fucose sugars to proteins of approximately 25-27kDa was observed. Three proteins were isolated by affinity chromatography and subjected to protein sequencing. The determined N-terminal sequences and that of tryptic peptides of two proteins did not show homology to known sequences in the NCBI database. The third was identified as a member of the high mobility group 2 (HMG-2) proteins. In vitro stimulation of mouse spleen cells with Lewis(x) sugars up-regulated the expression of HMG-2 mRNA. These data suggest that HMG-2 protein may function as a putative intracellular receptor/mediator for fucosylated sugars of parasites.

Dominant-negative HMGA1 blocks mu enhancer activation through a novel mechanism

The immunoglobulin mu intronic enhancer is a potent B cell-specific transcriptional activator. The enhancer is activated by the appropriate combination of transcription factors, amongst which are ets and bHLH proteins. HMGA1 (formerly HMG-I(Y)) is a demonstrated co-activator of the mu enhancer. HMGA1 functions through direct interaction with PU.1, one of the ets proteins critical for enhancer activation. New data demonstrates dominant negative HMGA1 dramatically decreases enhancer activity in B cells. EMSA analysis demonstrated that DN HMGA1 disrupts established PU.1/mu enhancer binding. Similarly, DN HMGA1 blocks mu enhancer binding by Ets-1. In sharp contrast, DN HMGA1 had no effect on binding activity of the ETS DNA binding domains of either PU.1 or Ets-1, or the bHLH-zip protein TFE3, suggesting specificity. Taken together, the data suggest that DN HMGA1 utilizes a novel mechanism to specifically block interaction between ets proteins and mu enhancer DNA, suggesting DN HMGA1 represents a new, highly specific means of regulating mu enhancer activity.

HMGA1 enhances the transcriptional activity and binding of the estrogen receptor to its responsive element

The estrogen receptor (ER) plays a critical role in the development of hormone-dependent cancer. Since HMGA1, a member of the "high mobility group" proteins, is overexpressed in certain malignant cells, we investigated the interaction between these nuclear proteins. Transfection of the HMGA1 expression vector increased 2-fold the transcriptional activation of ERE containing promoter by E(2). Furthermore, the HMGA1 protein stimulated severalfold the binding of purified ER to the consensus ERE oligonucleotides in gel mobility shift assays and saturation assays. However, HMGA1 could not bind alone either to consensus or to modified EREs, and the minor groove binding drug distamycin A failed to prevent the synergism between ER and HMGA1. This could suggest that the binding of HMGA1 to DNA was not required for its stimulatory effect. Antibody supershift assays showed that HMGA1 was required for increased binding and suggest a protein-protein interaction between those factors. This was confirmed by pull down assay. These data show that HMGA1 acts in concert with the ER to regulate the expression of estrogen responsive genes through a mechanism that does not require direct binding to DNA. These observations may be relevant in malignant cells expressing both proteins.