Organization, inducible-expression and chromosome localization of the human HMG-I(Y) nonhistone protein gene

Decoding high mobility group A2 protein expression regulation and implications in human cancers

High Mobility Group A2 (HMGA2) oncofetal proteins are a distinct category of Transcription Factors (TFs) known as "architectural factors" due to their lack of direct transcriptional activity. Instead, they modulate the three-dimensional structure of chromatin by binding to AT-rich regions in the minor grooves of DNA through their AT-hooks. This binding allows HMGA2 to interact with other proteins and different regions of DNA, thereby regulating the expression of numerous genes involved in carcinogenesis. Consequently, multiple mechanisms exist to finely control HMGA2 protein expression at various transcriptional levels, ensuring precise concentration adjustments to maintain cellular homeostasis. During embryonic development, HMGA2 protein is highly expressed but becomes absent in adult tissues. However, recent studies have revealed its re-elevation in various cancer types. Extensive research has demonstrated the involvement of HMGA2 protein in carcinogenesis at multiple levels. It intervenes in crucial processes such as cell cycle regulation, apoptosis, angiogenesis, epithelial-to-mesenchymal transition, cancer cell stemness, and DNA damage repair mechanisms, ultimately promoting cancer cell survival. This comprehensive review provides insights into the HMGA2 protein, spanning from the genetic regulation to functional protein behavior. It highlights the significant mechanisms governing HMGA2 gene expression and elucidates the molecular roles of HMGA2 in the carcinogenesis process.

HMGA2 promotes cancer metastasis by regulating epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is a complex physiological process that transforms polarized epithelial cells into moving mesenchymal cells. Dysfunction of EMT promotes the invasion and metastasis of cancer. The architectural transcription factor high mobility group AT-hook 2 (HMGA2) is highly overexpressed in various types of cancer (e.g., colorectal cancer, liver cancer, breast cancer, uterine leiomyomas) and significantly correlated with poor survival rates. Evidence indicated that HMGA2 overexpression markedly decreased the expression of epithelial marker E-cadherin (CDH1) and increased that of vimentin (VIM), Snail, N-cadherin (CDH2), and zinc finger E-box binding homeobox 1 (ZEB1) by targeting the transforming growth factor beta/SMAD (TGFβ/SMAD), mitogen-activated protein kinase (MAPK), and WNT/beta-catenin (WNT/β-catenin) signaling pathways. Furthermore, a new class of non-coding RNAs (miRNAs, circular RNAs, and long non-coding RNAs) plays an essential role in the process of HMGA2-induced metastasis and invasion of cancer by accelerating the EMT process. In this review, we discuss alterations in the expression of HMGA2 in various types of cancer. Furthermore, we highlight the role of HMGA2-induced EMT in promoting tumor growth, migration, and invasion. More importantly, we discuss extensively the mechanism through which HMGA2 regulates the EMT process and invasion in most cancers, including signaling pathways and the interacting RNA signaling axis. Thus, the elucidation of molecular mechanisms that underlie the effects of HMGA2 on cancer invasion and patient survival by mediating EMT may offer new therapeutic methods for preventing cancer progression.

Expression and Clinical Significance of High-Mobility Group AT-hook 2 (HMGA2) in Osteosarcoma

Objective

Although high‐mobility group AT‐hook 2 (HMGA2) has been shown to have crucial roles in the pathogenesis and metastasis of various malignancies, its expression and significance in osteosarcoma remain unknown. Here we evaluate the expression, clinical prognostic value, and overall function of HMGA2 in osteosarcoma.

Methods

Sixty‐nine osteosarcoma patient specimens within a tissue microarray (TMA) were analyzed by immunohistochemistry for HMGA2 expression. Demographics and clinicopathological information including age, gender, tumor location, metastasis, recurrence, chemotherapy response, follow‐up time, and disease status were also collected. After validation of expression, we determined whether there was a correlation between HMGA2 expression and patient clinicopathology. HMGA2 expression was also evaluated in osteosarcoma cell lines and patient tissues by Western blot, we analyzed the expression of HMGA2 in the human osteosarcoma cell lines MG63, 143B, U2OS, Saos‐2, MNNG/HOS, and KHOS. HMGA2‐specific siRNA and clonogenic assays were then used to determine the effect of HMGA2 inhibition on osteosarcoma cell proliferation, growth, and chemosensitivity.

Results

HMGA2 expression was elevated in the osteosarcoma patient specimens and human osteosarcoma cell lines. HMGA2 was differentially expressed in human osteosarcoma cell lines. Specifically, a relatively high expression of HMGA2 was present in KHOS, MNNG/HOS, 143B and a relatively low expression was in MG63, U2OS as well as Saos‐2. HMGA2 expression is correlated with metastasis and shorter overall survival. High HMGA2 expression is an independent predictor of poor osteosarcoma prognosis. There was no significant correlation between HMGA2 expression and the age, gender, or tumor site of the patient. HMGA2 expression is predominantly within the nucleus. The expression of HMGA2 also directly correlated to neoadjuvant chemoresistance. There was a significant reduction of HMGA2 expression in the siRNA transfection group. After the use of siRNA, the proliferation of osteosarcoma cells is decreased and the chemosensitivity of osteosarcoma cells is significantly increased.

Conclusion

Our study supports HMGA2 as a potential prognostic biomarker and therapeutic target in osteosarcoma.

The fellowship of the RING: BRCA1, its partner BARD1 and their liaison in DNA repair and cancer

The breast cancer type 1 susceptibility protein (BRCA1) and its partner - the BRCA1-associated RING domain protein 1 (BARD1) - are key players in a plethora of fundamental biological functions including, among others, DNA repair, replication fork protection, cell cycle progression, telomere maintenance, chromatin remodeling, apoptosis and tumor suppression. However, mutations in their encoding genes transform them into dangerous threats, and substantially increase the risk of developing cancer and other malignancies during the lifetime of the affected individuals. Understanding how BRCA1 and BARD1 perform their biological activities therefore not only provides a powerful mean to prevent such fatal occurrences but can also pave the way to the development of new targeted therapeutics. Thus, through this review work we aim at presenting the major efforts focused on the functional characterization and structural insights of BRCA1 and BARD1, per se and in combination with all their principal mediators and regulators, and on the multifaceted roles these proteins play in the maintenance of human genome integrity.

HMGA1 promotes gastric cancer growth and metastasis by transactivating SUZ12 and CCDC43 expression

HMGA1 protein is an architectural transcription factor that has been implicated in the progression of multiple malignant tumors. However, the role of HMGA1 in the growth and metastasis of gastric cancer (GC) has not yet been elucidated. Here, we show that HMGA1 is overexpressed in GC cells and the high expression of HMGA1 was correlated with worse survival in GC patients using a bioinformatics assay. Functionally, HMGA1 affected the EdU incorporation, colony formation, migration and invasion of GC cells by exogenously increasing or decreasing the expression of HMGA1. Mechanistically, HMGA1 directly bound to the SUZ12 and CCDC43 promoter and transactivated its expression in GC cells. Inhibition of SUZ12 and CCDC43 attenuated the proliferation, migration and invasiveness of HMGA1-overexpressing GC cells in vitro. Moreover, both HMGA1 and SUZ12/CCDC43 were highly expressed in cancer cells but not in normal gastric tissues, and their expressions were positively correlated. Finally, a tail vein metastatic assay showed that HMGA1 promoted SUZ12/CCDC43-mediated GC cell metastasis in vivo. Our findings suggest that HMGA1 promotes GC growth and metastasis by transactivating SUZ12 and CCDC43 expression, highlighting HMGA1 as a potential prognostic biomarker in the treatment of GC.

A novel TUBG1 mutation with neurodevelopmental disorder caused by malformations of cortical development

Neurodevelopmental disorder caused by malformations of cortical development is a rare neurological disease. Heterozygous missense variants in the TUBG1 gene lead to malformations of human cortical development, which further result in intellectual disability, developmental retardation, and epilepsy. To the best of our knowledge, only thirteen patients and a total of nine pathogenic TUBG1 variants have been described in the published literature. This study reports the case details and genetic data analysis of a girl (aged 8 years, 9 months) with developmental delay, psychomotor regression, epilepsy, and left external ear deformity. A novel TUBG1 mutation was identified by whole-exome sequencing and Sanger sequencing, confirming that this mutation may be the cause of the neurodevelopmental disorders. This case report characterizes the phenotypic spectrum, molecular genetic findings, and functional consequences of novel pathogenic TUBG1 variants in neurodevelopmental disorders caused by cortical development malformations.

Phosphorylation-regulated HMGA1a-P53 interaction unveils the function of HMGA1a acidic tail phosphorylations via synthetic proteins

As a typical member of intrinsically disordered proteins (IDPs), HMGA1a carries many post-translational modifications (PTMs). To study the undefined function of acidic tail phosphorylations, seven HMGA1a proteins with site-specific modification(s) were chemically synthesized via Ser/Thr ligation. We found that the phosphorylations significantly inhibit HMGA1a-P53 interaction and the phosphorylations can induce conformational change of HMGA1a from an "open state" to a "close state." Notably, the positively charged lysine-arginine (KR) clusters are responsible for modulating HMGA1a conformation via electrostatic interaction with the phosphorylated acidic tail. Finally, we used a synthetic protein-affinity purification mass spectrometry (SP-AP-MS) methodology to profile the specific interactors, which further supported the function of HMGA1a phosphorylation. Collectively, this study highlights a mechanism for regulating IDPs' conformation and function by phosphorylation of non-protein-binding domain and showcases that the protein chemical synthesis in combination with mass spectrometry can serve as an efficient tool to study the IDPs' PTMs.

Opposing Effects of Cohesin and Transcription on CTCF Organization Revealed by Super-resolution Imaging

CCCTC-binding factor (CTCF) and cohesin play critical roles in organizing mammalian genomes into topologically associating domains (TADs). Here, by combining genetic engineering with quantitative super-resolution stimulated emission depletion (STED) microscopy, we demonstrate that in living cells, CTCF forms clusters typically containing 2-8 molecules. A fraction of CTCF clusters, enriched for those with ≥3 molecules, are coupled with cohesin complexes with a characteristic physical distance suggestive of a defined molecular interaction. Acute degradation of the cohesin unloader WAPL or transcriptional inhibition (TI) result in increased CTCF clustering. Furthermore, the effect of TI on CTCF clusters is alleviated by the acute loss of the cohesin subunit SMC3. Our study provides quantitative characterization of CTCF clusters in living cells, uncovers the opposing effects of cohesin and transcription on CTCF clustering, and highlights the power of quantitative super-resolution microscopy as a tool to bridge the gap between biochemical and genomic methodologies in chromatin research.

Identification of HMGA2 inhibitors by AlphaScreen-based ultra-high-throughput screening assays

The mammalian high mobility group protein AT-hook 2 (HMGA2) is a multi-functional DNA-binding protein that plays important roles in tumorigenesis and adipogenesis. Previous results showed that HMGA2 is a potential therapeutic target of anticancer and anti-obesity drugs by inhibiting its DNA-binding activities. Here we report the development of a miniaturized, automated AlphaScreen ultra-high-throughput screening assay to identify inhibitors targeting HMGA2-DNA interactions. After screening the LOPAC1280 compound library, we identified several compounds that strongly inhibit HMGA2-DNA interactions including suramin, a century-old, negatively charged antiparasitic drug. Our results show that the inhibition is likely through suramin binding to the "AT-hook" DNA-binding motifs and therefore preventing HMGA2 from binding to the minor groove of AT-rich DNA sequences. Since HMGA1 proteins also carry multiple "AT-hook" DNA-binding motifs, suramin is expected to inhibit HMGA1-DNA interactions as well. Biochemical and biophysical studies show that charge-charge interactions and hydrogen bonding between the suramin sulfonated groups and Arg/Lys residues play critical roles in the binding of suramin to the "AT-hook" DNA-binding motifs. Furthermore, our results suggest that HMGA2 may be one of suramin's cellular targets.

HMGA Proteins in Hematological Malignancies

The high mobility group AT-Hook (HMGA) proteins are a family of nonhistone chromatin remodeling proteins known as "architectural transcriptional factors". By binding the minor groove of AT-rich DNA sequences, they interact with the transcription apparatus, altering the chromatin modeling and regulating gene expression by either enhancing or suppressing the binding of the more usual transcriptional activators and repressors, although they do not themselves have any transcriptional activity. Their involvement in both benign and malignant neoplasias is well-known and supported by a large volume of studies. In this review, we focus on the role of the HMGA proteins in hematological malignancies, exploring the mechanisms through which they enhance neoplastic transformation and how this knowledge could be exploited to devise tailored therapeutic strategies.

Phosphorylation orchestrates the structural ensemble of the intrinsically disordered protein HMGA1a and modulates its DNA binding to the NFκB promoter

High Mobility Group Protein A1a (HMGA1a) is a highly abundant nuclear protein, which plays a crucial role during embryogenesis, cell differentiation, and neoplasia. Here, we present the first ever NMR-based structural ensemble of full length HMGA1a. Our results show that the protein is not completely random coil but adopts a compact structure consisting of transient long-range contacts, which is regulated by post-translational phosphorylation. The CK2-, cdc2- and cdc2/CK2-phosphorylated forms of HMGA1a each exhibit a different binding affinity towards the PRD2 element of the NFκB promoter. Our study identifies connected regions between phosphorylation sites in the wildtype ensemble that change considerably upon phosphorylation, indicating that these posttranslational modifications sites are part of an electrostatic contact network that alters the structural ensemble by shifting the conformational equilibrium. Moreover, ITC data reveal that the CK2-phosphorylated HMGA1a exhibits a different DNA promoter binding affinity for the PRD2 element. Furthermore, we present the first structural model for AT-hook 1 of HMGA1a that can adopt a transient α-helical structure, which might serve as an additional regulatory mechanism in HMAG1a. Our findings will help to develop new therapeutic strategies against HMGA1a-associated cancers by taking posttranslational modifications into consideration.

HMGA and Cancer: A Review on Patent Literatures

BACKGROUND

The high mobility group A proteins modulate the transcription of numerous genes by interacting with transcription factors and/or altering the structure of chromatin. These proteins are involved in both benign and malignant neoplasias as a result of several pathways. A large amount of benign human mesenchymal tumors has rearrangements of HMGA genes. On the contrary, malignant tumors show unarranged HMGA overexpression that is frequently and causally related to neoplastic cell transformation. Here, we review the function of the HMGA proteins in human neoplastic disorders, the pathways by which they contribute to carcinogenesis and the new patents focused on targeting HMGA proteins.

OBJECTIVE

Current review was conducted to check the involvement of HMGA as a druggable target in cancer treatment.

METHODS

We reviewed the most recent patents focused on targeting HMGA in cancer treatment analyzing patent literature published during the last years, including the World Intellectual Property Organization (WIPO®), United States Patent Trademark Office (USPTO®), Espacenet®, and Google Patents.

RESULTS

HMGA proteins are intriguing targets for cancer therapy and are objects of different patents based on the use of DNA aptamers, inhibitors, oncolytic viruses, antisense molecules able to block their oncogenic functions.

CONCLUSION

Powerful strategies able to selectively interfere with HMGA expression and function could represent a helpful approach in the development of new anti-cancer therapies.

The Mammalian High Mobility Group Protein AT-Hook 2 (HMGA2): Biochemical and Biophysical Properties, and Its Association with Adipogenesis

The mammalian high-mobility-group protein AT-hook 2 (HMGA2) is a small DNA-binding protein and consists of three “AT-hook” DNA-binding motifs and a negatively charged C-terminal motif. It is a multifunctional nuclear protein directly linked to obesity, human height, stem cell youth, human intelligence, and tumorigenesis. Biochemical and biophysical studies showed that HMGA2 is an intrinsically disordered protein (IDP) and could form homodimers in aqueous buffer solution. The “AT-hook” DNA-binding motifs specifically bind to the minor groove of AT-rich DNA sequences and induce DNA-bending. HMGA2 plays an important role in adipogenesis most likely through stimulating the proliferative expansion of preadipocytes and also through regulating the expression of transcriptional factor Peroxisome proliferator-activated receptor γ (PPARγ) at the clonal expansion step from preadipocytes to adipocytes. Current evidence suggests that a main function of HMGA2 is to maintain stemness and renewal capacity of stem cells by which HMGA2 binds to chromosome and lock chromosome into a specific state, to allow the human embryonic stem cells to maintain their stem cell potency. Due to the importance of HMGA2 in adipogenesis and tumorigenesis, HMGA2 is considered a potential therapeutic target for anticancer and anti-obesity drugs. Efforts are taken to identify inhibitors targeting HMGA2.

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.

HMGA1 Modulates Gene Transcription Sustaining a Tumor Signalling Pathway Acting on the Epigenetic Status of Triple-Negative Breast Cancer Cells

Chromatin accessibility plays a critical factor in regulating gene expression in cancer cells. Several factors, including the High Mobility Group A (HMGA) family members, are known to participate directly in chromatin relaxation and transcriptional activation. The HMGA1 oncogene encodes an architectural chromatin transcription factor that alters DNA structure and interacts with transcription factors favouring their landing onto transcription regulatory sequences. Here, we provide evidence of an additional mechanism exploited by HMGA1 to modulate transcription. We demonstrate that, in a triple-negative breast cancer cellular model, HMGA1 sustains the action of epigenetic modifiers and in particular it positively influences both histone H3S10 phosphorylation by ribosomal protein S6 kinase alpha-3 (RSK2) and histone H2BK5 acetylation by CREB-binding protein (CBP). HMGA1, RSK2, and CBP control the expression of a set of genes involved in tumor progression and epithelial to mesenchymal transition. These results suggest that HMGA1 has an effect on the epigenetic status of cancer cells and that it could be exploited as a responsiveness predictor for epigenetic therapies in triple-negative breast cancers.

Tubulinopathies continued: refining the phenotypic spectrum associated with variants in TUBG1

Tubulinopathies are a heterogeneous group of conditions with a wide spectrum of clinical severity resulting from variants in genes of the tubulin superfamily. Variants in TUBG1 have been described in three patients with posterior predominant pachygyria and microcephaly. We here report eight additional patients with four novel heterozygous variants in TUBG1 identified by next-generation sequencing (NGS) analysis. All had severe motor and cognitive impairment and all except one developed seizures in early life. The core imaging features included a pachygyric cortex with posterior to anterior gradient, enlarged lateral ventricles most pronounced over the posterior horns, and variable degrees of reduced white matter volume. Basal ganglia, corpus callosum, brainstem, and cerebellum were often normal, in contrast to patients with variants in other tubulin genes where these structures are frequently malformed. The imaging phenotype associated with variants in TUBG1 is therefore more in line with the phenotype resulting from variants in LIS1 (a.k.a. PAFAH1B1). This difference may, at least in part, be explained by gamma-tubulin’s physiological function in microtubule nucleation, which differs from that of alpha and beta-tubulin.

Transcriptional Regulation of Glucose Metabolism: The Emerging Role of the HMGA1 Chromatin Factor

HMGA1 (high mobility group A1) is a nonhistone architectural chromosomal protein that functions mainly as a dynamic regulator of chromatin structure and gene transcription. As such, HMGA1 is involved in a variety of fundamental cellular processes, including gene expression, epigenetic regulation, cell differentiation and proliferation, as well as DNA repair. In the last years, many reports have demonstrated a role of HMGA1 in the transcriptional regulation of several genes implicated in glucose homeostasis. Initially, it was proved that HMGA1 is essential for normal expression of the insulin receptor (INSR), a critical link in insulin action and glucose homeostasis. Later, it was demonstrated that HMGA1 is also a downstream nuclear target of the INSR signaling pathway, representing a novel mediator of insulin action and function at this level. Moreover, other observations have indicated the role of HMGA1 as a positive modulator of the Forkhead box protein O1 (FoxO1), a master regulatory factor for gluconeogenesis and glycogenolysis, as well as a positive regulator of the expression of insulin and of a series of circulating proteins that are involved in glucose counterregulation, such as the insulin growth factor binding protein 1 (IGFBP1), and the retinol binding protein 4 (RBP4). Thus, several lines of evidence underscore the importance of HMGA1 in the regulation of glucose production and disposal. Consistently, lack of HMGA1 causes insulin resistance and diabetes in humans and mice, while variations in the HMGA1 gene are associated with the risk of type 2 diabetes and metabolic syndrome, two highly prevalent diseases that share insulin resistance as a common pathogenetic mechanism. This review intends to give an overview about our current knowledge on the role of HMGA1 in glucose metabolism. Although research in this field is ongoing, many aspects still remain elusive. Future directions to improve our insights into the pathophysiology of glucose homeostasis may include epigenetic studies and the use of "omics" strategies. We believe that a more comprehensive understanding of HMGA1 and its networks may reveal interesting molecular links between glucose metabolism and other biological processes, such as cell proliferation and differentiation.

HMGA1 amplifies Wnt signalling and expands the intestinal stem cell compartment and Paneth cell niche

High-mobility group A1 (Hmga1) chromatin remodelling proteins are enriched in intestinal stem cells (ISCs), although their function in this setting was unknown. Prior studies showed that Hmga1 drives hyperproliferation, aberrant crypt formation and polyposis in transgenic mice. Here we demonstrate that Hmga1 amplifies Wnt/β-catenin signalling to enhance self-renewal and expand the ISC compartment. Hmga1 upregulates genes encoding both Wnt agonist receptors and downstream Wnt effectors. Hmga1 also helps to 'build' an ISC niche by expanding the Paneth cell compartment and directly inducing Sox9, which is required for Paneth cell differentiation. In human intestine, HMGA1 and SOX9 are positively correlated, and both become upregulated in colorectal cancer. Our results define a unique role for Hmga1 in intestinal homeostasis by maintaining the stem cell pool and fostering terminal differentiation to establish an epithelial stem cell niche. This work also suggests that deregulated Hmga1 perturbs this equilibrium during intestinal carcinogenesis.

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.

RNA-Mediated Regulation of HMGA1 Function

The high mobility group protein A1 (HMGA1) is a master regulator of chromatin structure mediating its major gene regulatory activity by direct interactions with A/T-rich DNA sequences located in the promoter and enhancer regions of a large variety of genes. HMGA1 DNA-binding through three AT-hook motifs results in an open chromatin structure and subsequently leads to changes in gene expression. Apart from its significant expression during development, HMGA1 is over-expressed in virtually every cancer, where HMGA1 expression levels correlate with tumor malignancy. The exogenous overexpression of HMGA1 can lead to malignant cell transformation, assigning the protein a key role during cancerogenesis. Recent studies have unveiled highly specific competitive interactions of HMGA1 with cellular and viral RNAs also through an AT-hook domain of the protein, significantly impacting the HMGA1-dependent gene expression. In this review, we discuss the structure and function of HMGA1-RNA complexes during transcription and epigenomic regulation and their implications in HMGA1-related diseases.

High mobility group (HMG) proteins: Modulators of chromatin structure and DNA repair in mammalian cells

It has been almost a decade since the last review appeared comparing and contrasting the influences that the different families of High Mobility Group proteins (HMGA, HMGB and HMGN) have on the various DNA repair pathways in mammalian cells. During that time considerable progress has been made in our understanding of how these non-histone proteins modulate the efficiency of DNA repair by all of the major cellular pathways: nucleotide excision repair, base excision repair, double-stand break repair and mismatch repair. Although there are often similar and over-lapping biological activities shared by all HMG proteins, members of each of the different families appear to have a somewhat 'individualistic' impact on various DNA repair pathways. This review will focus on what is currently known about the roles that different HMG proteins play in DNA repair processes and discuss possible future research areas in this rapidly evolving field.

CRMP1 Inhibits Proliferation of Medulloblastoma and Is Regulated by HMGA1

Many facets of the tumor biology of medulloblastoma (MB) have not been fully elucidated. Collapsin response mediator protein 1 (CRMP1) is a member of cytoplasmic family of proteins that regulate the development of central nervous system. Recent studies demonstrated that CRMP1 could function as an invasion suppressor. We reported previously that high mobility group AT-hook 1 (HMGA1) contributed to development of MB and regulated its growth and migration/invasion. Transcriptional profiling and quantitative RT-PCR revealed increased expression of CRMP1 in HMGA1-depleted cells, suggesting that CRMP1 may be a downstream target of HMGA1 in MB. In this study, we showed HMGA1 can bind CRMP1 promoter by chromatin immunoprecipitation (ChIP) assay. Luciferase assay demonstrated a marked enhancement of CRMP1 transcription activity in HMGA1-depleted cells. Furthermore, quantitative RT-PCR revealed a negative correlation between HMGA1 and CRMP1 in 32 MB samples. To investigate the biological roles of CRMP1 in MB pathogenesis, we established MB clones stably expressing CRMP1. Functional analysis revealed that expression of CRMP1 significantly inhibited proliferation, migration, invasion and formation of filopodia and intense stress fiber of MB cells. Our data suggest that HMGA1 regulates CRMP1 expression and CRMP1 is implicated in MB pathogenesis.

HMGA1 silencing restores normal stem cell characteristics in colon cancer stem cells by increasing p53 levels

High-mobility group A1 (HMGA1) proteins are architectural chromatinic proteins, abundantly expressed during embryogenesis and in most cancer tissues, but expressed at low levels or absent in normal adult tissues. Several studies have demonstrated that HMGA1 proteins play a causal role in neoplastic cell transformation. The aim of this study was to investigate the role of these proteins in the control of cancer stem cells (CSCs), which have emerged as a preferred target in cancer therapy, because of their role in cancer recurrence. We observed that HMGA1 is overexpressed in colon tumour stem cell (CTSC) lines compared to normal and colon cancer tissues. We demonstrated that HMGA1 silencing in CTSCs increases stem cell quiescence and reduces self-renewal and sphere-forming efficiency (SFE). The latter, together with the upregulation and asymmetric distribution of NUMB, is indicative of the recovery of an asymmetric division pattern, typical of normal stem cells. We further found that HMGA1 transcriptionally regulates p53, which is known to control the balance between symmetric and asymmetric divisions in CSCs. Therefore, our data indicate a critical role for HMGA1 in regulating both self-renewal and the symmetric/asymmetric division ratio in CSCs, suggesting that blocking HMGA1 function may be an effective anti-cancer therapy.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Evolution of high mobility group nucleosome-binding proteins and its implications for vertebrate chromatin specialization

High mobility group (HMG)-N proteins are a family of small nonhistone proteins that bind to nucleosomes (N). Despite the amount of information available on their structure and function, there is an almost complete lack of information on the molecular evolutionary mechanisms leading to their exclusive differentiation. In the present work, we provide evidence suggesting that HMGN lineages constitute independent monophyletic groups derived from a common ancestor prior to the diversification of vertebrates. Based on observations of the functional diversification across vertebrate HMGN proteins and on the extensive silent nucleotide divergence, our results suggest that the long-term evolution of HMGNs occurs under strong purifying selection, resulting from the lineage-specific functional constraints of their different protein domains. Selection analyses on independent lineages suggest that their functional specialization was mediated by bursts of adaptive selection at specific evolutionary times, in a small subset of codons with functional relevance-most notably in HMGN1, and in the rapidly evolving HMGN5. This work provides useful information to our understanding of the specialization imparted on chromatin metabolism by HMGNs, especially on the evolutionary mechanisms underlying their functional differentiation in vertebrates.

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.

The high mobility group A1 molecular switch: turning on cancer - can we turn it off?

INTRODUCTION

Emerging evidence demonstrates that the high mobility group A1 (HMGA1) chromatin remodeling protein is a key molecular switch required by cancer cells for tumor progression and a poorly differentiated, stem-like state. Because the HMGA1 gene and proteins are expressed at high levels in all aggressive tumors studied to date, research is needed to determine how to 'turn off' this master regulatory switch in cancer.

AREAS COVERED

In this review, we describe prior studies that underscore the central role of HMGA1 in refractory cancers and we discuss approaches to target HMGA1 in cancer therapy.

EXPERT OPINION

Given the widespread overexpression of HMGA1 in diverse, aggressive tumors, further research to develop technology to target HMGA1 holds immense promise as potent anticancer therapy. Previous work in preclinical models indicates that delivery of short hairpin RNA or interfering RNA molecules to 'switch off' HMGA1 expression dramatically impairs cancer cell growth and tumor progression. The advent of nanoparticle technology to systemically deliver DNA or RNA molecules to tumors brings this approach even closer to clinical applications, although further efforts are needed to translate these advances into therapies for cancer patients.

Transcriptional regulation of the HMGA1 gene by octamer-binding proteins Oct-1 and Oct-2

The High-Mobility Group AT-Hook 1 (HMGA1) protein is an architectural transcription factor that binds to AT-rich sequences in the promoter region of DNA and functions as a specific cofactor for gene activation. Previously, we demonstrated that HMGA1 is a key regulator of the insulin receptor (INSR) gene and an important downstream target of the INSR signaling cascade. Moreover, from a pathogenic point of view, overexpression of HMGA1 has been associated with human cancer, whereas functional variants of the HMGA1 gene have been recently linked to type 2 diabetes mellitus and metabolic syndrome. However, despite of this biological and pathological relevance, the mechanisms that control HMGA1 gene expression remain unknown. In this study, to define the molecular mechanism(s) that regulate HMGA1 gene expression, the HMGA1 gene promoter was investigated by transient transfection of different cell lines, either before or after DNA and siRNA cotransfections. An octamer motif was identified as an important element of transcriptional regulation of this gene, the interaction of which with the octamer transcription factors Oct-1 and Oct-2 is crucial in modulating HMGA1 gene and protein expression. Additionally, we demonstrate that HMGA1 binds its own promoter and contributes to its transactivation by Oct-2 (but not Oct-1), supporting its role in an auto-regulatory circuit. Overall, our results provide insight into the transcriptional regulation of the HMGA1 gene, revealing a differential control exerted by both Oct-1 and Oct-2. Furthermore, they consistently support the hypothesis that a putative defect in Oct-1 and/or Oct-2, by affecting HMGA1 expression, may cause INSR dysfunction, leading to defects of the INSR signaling pathway.

Characterization of the Stoichiometry of HMGA1/DNA Complexes

High-mobility group A1 (HMGA1) non-histone chromatin architectural transcription factors regulate gene expression, embryogenesis, cell differentiation, and adaptive immune responses by binding DNA and other transcription factors. HMGA1 has also been shown to be highly over-expressed in many human cancers and is considered to be a valuable cancer biomarker. Elevated HMGA1 expression levels also make cancer cells resistant to chemotherapy. Here, HMGA1/DNA complex formation was investigated using electrophoretic mobility shift assays (EMSA). Collectively, the EMSA results indicated that full length HMGA1 mixed with DNA containing three AT-hook binding sites formed four distinct HMGA1/DNA complexes ranging in stoichiometry from 1:2 to 3:1 in HMGA1:DNA ratio. The data indicated that the distribution of complexes with different HMGA1 to DNA stoichiometries depended on the molar ratio of HMGA1 to DNA in solution, which could have significant biological implications given that HMGA1 is highly over-expressed in human cancer cells. The two naturally occurring isoforms of HMGA1, HMGA1a and HMGA1b, the latter containing an 11 amino acid deletion between the first and second AT-hooks, were observed to have slightly different DNA binding profiles. Finally, HMGA1 binding affinity to DNA was found to be influenced by the DNA A:T segment sequence context, with higher specificity be observed in HMGA1 binding to T_nA_n segments, which have two local minor groove minima on either side of the TpA step, compared to A_n:T_n segments, which have a single minor groove minimum at the 3' end of the A_n run, implying AT-hook binding favors narrow minor groove structure.

HMGA1 induces intestinal polyposis in transgenic mice and drives tumor progression and stem cell properties in colon cancer cells

BACKGROUND

Although metastatic colon cancer is a leading cause of cancer death worldwide, the molecular mechanisms that enable colon cancer cells to metastasize remain unclear. Emerging evidence suggests that metastatic cells develop by usurping transcriptional networks from embryonic stem (ES) cells to facilitate an epithelial-mesenchymal transition (EMT), invasion, and metastatic progression. Previous studies identified HMGA1 as a key transcription factor enriched in ES cells, colon cancer, and other aggressive tumors, although its role in these settings is poorly understood.

METHODS/PRINCIPAL FINDINGS

To determine how HMGA1 functions in metastatic colon cancer, we manipulated HMGA1 expression in transgenic mice and colon cancer cells. We discovered that HMGA1 drives proliferative changes, aberrant crypt formation, and intestinal polyposis in transgenic mice. In colon cancer cell lines from poorly differentiated, metastatic tumors, knock-down of HMGA1 blocks anchorage-independent cell growth, migration, invasion, xenograft tumorigenesis and three-dimensional colonosphere formation. Inhibiting HMGA1 expression blocks tumorigenesis at limiting dilutions, consistent with depletion of tumor-initiator cells in the knock-down cells. Knock-down of HMGA1 also inhibits metastatic progression to the liver in vivo. In metastatic colon cancer cells, HMGA1 induces expression of Twist1, a gene involved in embryogenesis, EMT, and tumor progression, while HMGA1 represses E-cadherin, a gene that is down-regulated during EMT and metastatic progression. In addition, HMGA1 is among the most enriched genes in colon cancer compared to normal mucosa.

CONCLUSIONS

Our findings demonstrate for the first time that HMGA1 drives proliferative changes and polyp formation in the intestines of transgenic mice and induces metastatic progression and stem-like properties in colon cancer cells. These findings indicate that HMGA1 is a key regulator, both in metastatic progression and in the maintenance of a stem-like state. Our results also suggest that HMGA1 or downstream pathways could be rational therapeutic targets in metastatic, poorly differentiated colon cancer.

Host factors mediating HIV-1 replication

Human immunodeficiency virus type 1(HIV-1) infection is the leading cause of death worldwide in adults attributable to infectious diseases. Although the majority of infections are in sub-Saharan Africa and Southeast Asia, HIV-1 is also a major health concern in most countries throughout the globe. While current antiretroviral treatments are generally effective, particularly in combination therapy, limitations exist due to drug resistance occurring among the drug classes. Traditionally, HIV-1 drugs have targeted viral proteins, which are mutable targets. As cellular genes mutate relatively infrequently, host proteins may prove to be more durable targets than viral proteins. HIV-1 replication is dependent upon cellular proteins that perform essential roles during the viral life cycle. Maraviroc is the first FDA-approved antiretroviral drug to target a cellular factor, HIV-1 coreceptor CCR5, and serves to intercept viral-host protein-protein interactions mediating entry. Recent large-scale siRNA and shRNA screens have revealed over 1000 candidate host factors that potentially support HIV-1 replication, and have implicated new pathways in the viral life cycle. These host proteins and cellular pathways may represent important targets for future therapeutic discoveries. This review discusses critical cellular factors that facilitate the successive steps in HIV-1 replication.

Phylogenetics and evolution of Su(var)3-9 SET genes in land plants: rapid diversification in structure and function

Background

Plants contain numerous Su(var)3-9 homologues (SUVH) and related (SUVR) genes, some of which await functional characterization. Although there have been studies on the evolution of plant Su(var)3-9 SET genes, a systematic evolutionary study including major land plant groups has not been reported. Large-scale phylogenetic and evolutionary analyses can help to elucidate the underlying molecular mechanisms and contribute to improve genome annotation.

Results

Putative orthologs of plant Su(var)3-9 SET protein sequences were retrieved from major representatives of land plants. A novel clustering that included most members analyzed, henceforth referred to as core Su(var)3-9 homologues and related (cSUVHR) gene clade, was identified as well as all orthologous groups previously identified. Our analysis showed that plant Su(var)3-9 SET proteins possessed a variety of domain organizations, and can be classified into five types and ten subtypes. Plant Su(var)3-9 SET genes also exhibit a wide range of gene structures among different paralogs within a family, even in the regions encoding conserved PreSET and SET domains. We also found that the majority of SUVH members were intronless and formed three subclades within the SUVH clade.

Conclusions

A detailed phylogenetic analysis of the plant Su(var)3-9 SET genes was performed. A novel deep phylogenetic relationship including most plant Su(var)3-9 SET genes was identified. Additional domains such as SAR, ZnF_C2H2 and WIYLD were early integrated into primordial PreSET/SET/PostSET domain organization. At least three classes of gene structures had been formed before the divergence of Physcomitrella patens (moss) from other land plants. One or multiple retroposition events might have occurred among SUVH genes with the donor genes leading to the V-2 orthologous group. The structural differences among evolutionary groups of plant Su(var)3-9 SET genes with different functions were described, contributing to the design of further experimental studies.

3D imaging of telomeres and nuclear architecture: An emerging tool of 3D nano-morphology-based diagnosis

Patient samples are evaluated by experienced pathologists whose diagnosis guides treating physicians. Pathological diagnoses are complex and often assisted by the application of specific tissue markers. However, cases still exist where pathologists cannot distinguish between closely related entities or determine the aggressiveness of the disease they identify under the microscope. This is due to the absence of reliable markers that define diagnostic subgroups in several cancers. Three-dimensional (3D) imaging of nuclear telomere signatures is emerging as a new tool that may change this situation offering new opportunities to the patients. This article will review current and future avenues in the assessment of diagnostic patient samples.

High-Mobility Group A (HMGA) Proteins and Breast Cancer

The high-mobility group A (HMGA) protein family includes HMGA1a, HMGA1b and HMGA1c, which are encoded by the same gene through alternative splicing, and the closely related HMGA2 protein. HMGA proteins have been found to be abundant in several malignant neoplasias, including colorectal, prostate, cervical, lung, thyroid and breast carcinoma. HMGA proteins can be ideal candidates for the identification of new prognosis and diagnosis factors with non-invasive methods. To provide some clarity regarding the abundance of articles on this topic, here we focus on the relationship between HMGA proteins and breast cancer and their clinical perspective in the development of new therapeutic strategies.

Fusion of HMGA1 to the LPP/TPRG1 intergenic region in a lipoma identified by mapping paraffin-embedded tissues

Ordinary lipoma frequently harbors rearrangement of HMGA2. LPP is the most common partner gene to HMGA2, but has not been seen fused to HMGA1. We report the fusion of HMGA1 to the intergenic region between LPP and TPRG1 in a lipoma. Conventional cytogenetic analysis of an abdominal-wall lipoma diagnosed in a 60-year-old woman showed a t(3;6)(q27;p21). Molecular cytogenetic mapping of available paraffin-embedded tissues revealed the fusion of HMGA1 to a 139-kb genomic region between the LPP and TPRG1 loci. No rearrangement of HMGA2 was found. The biological function of this novel fusion could be similar to the role of HMGA2-LPP in tumorigenesis.

Upregulation of MMP-2 by HMGA1 promotes transformation in undifferentiated, large-cell lung cancer

Although lung cancer is the leading cause of cancer death worldwide, the precise molecular mechanisms that give rise to lung cancer are incompletely understood. Here, we show that HMGA1 is an important oncogene that drives transformation in undifferentiated, large-cell carcinoma. First, we show that the HMGA1 gene is overexpressed in lung cancer cell lines and primary human lung tumors. Forced overexpression of HMGA1 induces a transformed phenotype with anchorage-independent cell growth in cultured lung cells derived from normal tissue. Conversely, inhibiting HMGA1 expression blocks anchorage-independent cell growth in the H1299 metastatic, undifferentiated, large-cell human lung carcinoma cells. We also show that the matrix metalloproteinase-2 (MMP-2) gene is a downstream target upregulated by HMGA1 in large-cell carcinoma cells. In chromatin immunoprecipitation experiments, HMGA1 binds directly to the MMP-2 promoter in vivo in large-cell lung cancer cells, but not in squamous cell carcinoma cells. In large-cell carcinoma cell lines, there is a significant, positive correlation between HMGA1 and MMP-2 mRNA. Moreover, interfering with MMP-2 expression blocks anchorage-independent cell growth in H1299 large-cell carcinoma cells, indicating that the HMGA1-MMP-2 pathway is required for this transformation phenotype in these cells. Blocking MMP-2 expression also inhibits migration and invasion in the H1299 large-cell carcinoma cells. Our findings suggest an important role for MMP-2 in transformation mediated by HMGA1 in large-cell, undifferentiated lung carcinoma and support the development of strategies to target this pathway in selected tumors.

Gene expressions of HMGI-C and HMGI(Y) are associated with stage and metastasis in colorectal cancer

PURPOSE

The high mobility group proteins (HMGs) include the HMGI family members HMGI-C and HMGI(Y), whose expressions in adult tissues generally correlate with malignant tumor phenotypes. The aim of this study was to assess the relationship of HMGI-C or HMGI(Y) gene expression and prognosis in colorectal cancer patients.

METHODS

The gene expressions of HMGI-C and HMGI(Y) in 31 paired samples of colorectal tumor and corresponding non-tumor were determined by real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The expression of HMGI(Y) in a colorectal cancer tumor was associated with Dukes staging (p = 0.044), while, in non-tumor, the expression of this gene was significant with metastasis (p = 0.003). Patients with Dukes stage A and B present high HMGI(Y) expression in non-tumor of colorectal cancer (p = 0.006). However, patients with Dukes stage C and D present high HMGI-C expression in colorectal tumor (p = 0.023). In the non-metastasis group, HMGI(Y) was highly expressed in non-tumor of colorectal cancer. However, in the metastasis group, there was no significant difference between tumor and non-tumor tissues in both HMGI-C and HMGI(Y) gene expressions.

CONCLUSIONS

The HMGI-C and HMGI(Y) quantitations by real-time RT-PCR are associated with Dukes staging and metastasis; hence, the gene expression levels may be useful in clinical practice.

Structural genomics reveals EVE as a new ASCH/PUA-related domain

We report on several proteins recently solved by structural genomics consortia, in particular by the Northeast Structural Genomics consortium (NESG). The proteins considered in this study differ substantially in their sequences but they share a similar structural core, characterized by a pseudobarrel five-stranded beta sheet. This core corresponds to the PUA domain-like architecture in the SCOP database. By connecting sequence information with structural knowledge, we characterize a new subgroup of these proteins that we propose to be distinctly different from previously described PUA domain-like domains such as PUA proper or ASCH. We refer to these newly defined domains as EVE. Although EVE may have retained the ability of PUA domains to bind RNA, the available experimental and computational data suggests that both the details of its molecular function and its cellular function differ from those of other PUA domain-like domains. This study of EVE and its relatives illustrates how the combination of structure and genomics creates new insights by connecting a cornucopia of structures that map to the same evolutionary potential. Primary sequence information alone would have not been sufficient to reveal these evolutionary links.

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.

HMGA2 participates in transformation in human lung cancer

Although previous studies have established a prominent role for HMGA1 (formerly HMG-I/Y) in aggressive human cancers, the role of HMGA2 (formerly HMGI-C) in malignant transformation has not been clearly defined. The HMGA gene family includes HMGA1, which encodes the HMGA1a and HMGA1b protein isoforms, and HMGA2, which encodes HMGA2. These chromatin-binding proteins function in transcriptional regulation and recent studies also suggest a role in cellular senescence. HMGA1 proteins also appear to participate in cell cycle regulation and malignant transformation, whereas HMGA2 has been implicated primarily in the pathogenesis of benign, mesenchymal tumors. Here, we show that overexpression of HMGA2 leads to a transformed phenotype in cultured lung cells derived from normal tissue. Conversely, inhibiting HMGA2 expression blocks the transformed phenotype in metastatic human non-small cell lung cancer cells. Moreover, we show that HMGA2 mRNA and protein are overexpressed in primary human lung cancers compared with normal tissue or indolent tumors. In addition, there is a statistically significant correlation between HMGA2 protein staining by immunohistochemical analysis and tumor grade (P < 0.001). Our results indicate that HMGA2 is an oncogene important in the pathogenesis of human lung cancer. Although additional studies with animal models are needed, these findings suggest that targeting HMGA2 could be therapeutically beneficial in lung cancer and other cancers characterized by increased HMGA2 expression.

High mobility group AT-hook 1 (HMGA1) is an independent prognostic factor and novel therapeutic target in pancreatic adenocarcinoma

BACKGROUND

High mobility group AT-hook 1 (HMGA1) proteins are architectural transcription factors that are overexpressed by pancreatic adenocarcinomas. The authors hypothesized that tumor HMGA1 status represents a novel prognostic marker in pancreatic adenocarcinoma. They also tested the hypothesis that HMGA1 promotes anchorage-independent cellular proliferation and in vivo tumorigenicity.

METHODS

Tumor HMGA1 expression was examined by immunohistochemical analysis of tissues from 89 consecutive patients who underwent resection for pancreatic adenocarcinoma. Short-hairpin RNA (shRNA)-mediated RNA interference was used to silence HMGA1 expression in MiaPaCa2 and PANC1 pancreatic cancer cells. Anchorage-independent proliferation was assessed by using soft agar assays. The roles of phosphatidylinositol 3-kinase (PI3-K)/Akt and extracellular signal-regulated kinase (ERK) signaling were investigated by using specific inhibitors and adenoviral dominant-negative/active Akt constructs. In vivo tumorigenicity was assessed by using a nude mouse xenograft model.

RESULTS

Tumor HMGA1 expression was detected in 93% of patients with pancreatic adenocarcinoma. Patients with HMGA1-negative tumors had a significantly longer median survival than patients with HMGA1-expressing cancers in univariate analysis (P = .0028) and in multivariate analysis (P<.05). shRNA-mediated HMGA1 silencing resulted in significant reductions in anchorage-independent proliferation in soft agar. Forced HMGA1 overexpression promoted proliferation in soft agar through a process that was dependent on PI3-K/Akt-activited signaling, but not on mitogen-activated protein kinase (MEK)/ERK signaling. Targeted silencing of HMGA1 reduced tumor growth in vivo through reduced proliferation (Ki-67 index) and increased apoptosis (terminal deoxynucleotidyl transferase nick-end labeling).

CONCLUSIONS

The current findings suggested that HMGA1 is an independent predictor of poor postoperative survival in patients with pancreatic adenocarcinoma. Furthermore, HMGA1 promotes tumorigenicity through a PI3-K/Akt-dependent mechanism. HMGA1 warrants further evaluation as a prognostic marker and therapeutic target in pancreatic cancer.

Genomic characterisation, chromosomal assignment and in vivo localisation of the canine high mobility group A1 (HMGA1) gene

BACKGROUND

The high mobility group A1 proteins (HMGA1a/HMGA1b) are highly conserved between mammalian species and widely described as participating in various cellular processes. By inducing DNA conformation changes the HMGA1 proteins indirectly influence the binding of various transcription factors and therefore effect the transcription regulation. In humans chromosomal aberrations affecting the HMGA1 gene locus on HSA 6p21 were described to be the cause for various benign mesenchymal tumours while high titres of HMGA1 proteins were shown to be associated with the neoplastic potential of various types of cancer. Interestingly, the absence of HMGA1 proteins was shown to cause insulin resistance and diabetes in humans and mice. Due to the various similarities in biology and presentation of human and canine cancers the dog has joined the common rodent animal model for therapeutic and preclinical studies. Accordingly, the canine genome was sequenced completely twice but unfortunately this could not solve the structure of canine HMGA1 gene.

RESULTS

Herein we report the characterisation of the genomic structure of the canine HMGA1 gene consisting of 7 exons and 6 introns spanning in total 9524 bp, the in vivo localisation of the HMGA1 protein to the nucleus, and a chromosomal assignment of the gene by FISH to CFA12q11. Additionally, we evaluated a described canine HMGA1 exon 6 SNP in 55 Dachshunds.

CONCLUSION

The performed characterisations will make comparative analyses of aberrations affecting the human and canine gene and proteins possible, thereby providing a basis for revealing mechanisms involved in HMGA1 related pathogenesis in both species.

HMGA1 is a molecular determinant of chemoresistance to gemcitabine in pancreatic adenocarcinoma

PURPOSE

HMGA1 proteins are architectural transcription factors that are overexpressed by pancreatic adenocarcinomas. We previously have shown that RNA interference targeting the HMGA1 gene may represent a potential chemosensitizing strategy in pancreatic adenocarcinoma cells. In this study, we tested the hypothesis that HMGA1 promotes chemoresistance to gemcitabine in pancreatic cancer cells.

EXPERIMENTAL DESIGN AND RESULTS

Stable short hairpin RNA-mediated HMGA1 silencing in BxPC3 and MiaPaCa2 cells promoted chemosensitivity to gemcitabine, with reductions in gemcitabine IC(50) and increases in gemcitabine-induced apoptosis and caspase-3 activation. In contrast, forced HMGA1 overexpression in MiaPaCa2 cells promoted chemoresistance to gemcitabine, with increases in gemcitabine IC(50) and reductions in gemcitabine-induced apoptosis and caspase-3 activation. Dominant negative Akt abrogated HMGA1 overexpression-induced increases in chemoresistance to gemcitabine. Finally, HMGA1 silencing promoted chemosensitivity to gemcitabine in vivo in a nude mouse xenograft model of pancreatic adenocarcinoma.

CONCLUSION

Our findings suggest that HMGA1 promotes chemoresistance to gemcitabine through an Akt-dependent mechanism. Targeted therapies directed at HMGA1 represent a potential strategy for ameliorating chemoresistance in pancreatic adenocarcinoma.

APRIN is a unique Pds5 paralog with features of a chromatin regulator in hormonal differentiation

Activation of steroid receptors results in global changes of gene expression patterns. Recent studies showed that steroid receptors control only a portion of their target genes directly, by promoter binding. The majority of the changes are indirect, through chromatin rearrangements. The mediators that relay the hormonal signals to large-scale chromatin changes are, however, unknown. We report here that APRIN, a novel hormone-induced nuclear phosphoprotein has the characteristics of a chromatin regulator and may link endocrine pathways to chromatin. We showed earlier that APRIN is involved in the hormonal regulation of proliferative arrest in cancer cells. To investigate its function we cloned and characterized APRIN orthologs and performed homology and expression studies. APRIN is a paralog of the cohesin-associated Pds5 gene lineage and arose by gene-duplication in early vertebrates. The conservation and domain differences we found suggest, however, that APRIN acquired novel chromatin-related functions (e.g. the HMG-like domains in APRIN, the hallmarks of chromatin regulators, are absent in the Pds5 family). Our results suggest that in interphase nuclei APRIN localizes in the euchromatin/heterochromatin interface and we also identified its DNA-binding and nuclear import signal domains. The results indicate that APRIN, in addition to its Pds5 similarity, has the features and localization of a hormone-induced chromatin regulator.

HMGA2 overexpression in non-small cell lung cancer

Lung cancer is still the leading cause of death from cancer worldwide primarily because of the fact that most lung cancers are diagnosed at advanced stages. Overexpression of the high mobility group protein HMGA2 has been observed in a variety of malignant tumors and often correlates with poor prognosis. Herein, HMGA2 expression levels were analyzed in matching cancerous and non-cancerous lung samples of 17 patients with adenocarcinoma (AC) and 17 patients with squamous cell carcinoma (SCC) with real-time quantitative RT-PCR (qRT-PCR). Transcript levels were compared to results obtained by immunohistochemistry (IHC). HMGA2 expression was detectable by qRT-PCR in all samples tested and varied from 5422 to 16 991 545 copies per 250 ng total RNA in the carcinoma samples and from 289 to 525 947 copies in the non-cancerous tissue samples. In 33/34 non-small cell lung cancer (NSCLC) samples tested, an overexpression of HMGA2 was revealed with statistically highly significant differences between non-neoplastic and tumor samples for both AC (P < 0.0001) as well as for SCC (P < 0.0001). Expression varies strongly and is increased up to 911-fold for AC and up to 2504-fold for SCC, respectively, with statistically significant higher increase in SCC (P < 0.05). The results presented herein indicate that HMGA2 overexpression is a common event in NSCLC and could serve as molecular marker for lung cancer.

Transcriptional Control of the HumanHigh Mobility Group A1Gene: Basal and Oncogenic Ras-Regulated Expression

Several studies have already shown that the high mobility group A1 (HMGA1) gene is up-regulated in most common types of cancer and immortalized tissue culture cell lines. HMGA1 expression is also much higher during embryonic development than in adult life. The elevated expression of HMGA1 in cancer thus likely occurs through oncofetal transcriptional mechanisms, which to date have not been well characterized. In the present study, we have cloned and functionally analyzed the TATA-less 5'-flanking regulatory region of human HMGA1. We identified two proximal regulatory regions that are important for basal transcription and in which specificity protein 1 (SP1) and activator protein 1 (AP1) transcription factors seem to be the regulating elements. In addition, we showed that the HMGA1 promoter is strongly inducible by oncogenic Ras, via a distal regulatory region. An AP1 site and three SP1-like sites are responsible for this inducible activity. An even more convincing finding for a role of oncogenic Ras in the regulation of HMGA1 in cancers is the discovery that HMGA1 up-regulation in the HCT116 colon cancer cell line is abolished when the mutated Ras allele is removed from these cells. Our data constitute the first extensive study of the regulation of basal and Ras-induced human HMGA1 gene expression and suggest that the elevated expression of HMGA1 in cancer cells requires, among others, a complex cooperation between SP1 family members and AP1 factors by the activation of Ras GTPase signaling.