Induced HMGA1a expression causes aberrant splicing of Presenilin-2 pre-mRNA in sporadic Alzheimer's disease

HMGA1 Regulates IRS2 to Promote Inflammatory Responses and Oxidative Stress Injury in MPP+-Induced cells

Parkinson's disease (PD) is a prevalent neurodegenerative disorder for which novel treatment approaches are continuously sought. This study investigates the role of high-mobility group A1 (HMGA1) in modulating inflammatory responses and oxidative stress injury in PD. We utilized the murine dopaminergic neuronal cell line MN9D, treating cells with 1-methyl-4-phenylpyridinium ion (MPP+) to mimic PD conditions. The expression levels of HMGA1 and insulin receptor substrate 2 (IRS2) were measured using quantitative polymerase chain reaction and Western blot assay. Cell damage was assessed with cell counting kit-8 and lactate dehydrogenase assays. Inflammatory response and oxidative stress were evaluated by quantifying interleukin (IL)-1β, IL-6, tumor necrosis factor-α, reactive oxygen species, superoxide dismutase, and malondialdehyde (MDA) levels using enzyme-linked immunosorbent assay and commercial kits. The binding interaction between HMGA1 and IRS2 was analyzed using chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays. Our findings revealed that MPP+ treatment increased the expression of HMGA1 and IRS2. Downregulation of HMGA1 enhanced cell viability, reduced inflammation, and mitigated oxidative stress in MPP+-induced cells. Further investigation demonstrated that HMGA1 bounded to the IRS2 promoter, enhancing IRS2 expression. Overexpression of IRS2 counteracted the protective effects of HMGA1 downregulation. In conclusion, HMGA1 exacerbates MPP+-induced cell damage by activating IRS2 transcription, which in turn heightens inflammation and oxidative stress. These findings suggest that targeting HMGA1 could be a potential therapeutic strategy for PD.

Binding to the Other Side: The AT-Hook DNA-Binding Domain Allows Nuclear Factors to Exploit the DNA Minor Groove

The "AT-hook" is a peculiar DNA-binding domain that interacts with DNA in the minor groove in correspondence to AT-rich sequences. This domain has been first described in the HMGA protein family of architectural factors and later in various transcription factors and chromatin proteins, often in association with major groove DNA-binding domains. In this review, using a literature search, we identified about one hundred AT-hook-containing proteins, mainly chromatin proteins and transcription factors. After considering the prototypes of AT-hook-containing proteins, the HMGA family, we review those that have been studied in more detail and that have been involved in various pathologies with a particular focus on cancer. This review shows that the AT-hook is a domain that gives proteins not only the ability to interact with DNA but also with RNA and proteins. This domain can have enzymatic activity and can influence the activity of the major groove DNA-binding domain and chromatin docking modules when present, and its activity can be modulated by post-translational modifications. Future research on the function of AT-hook-containing proteins will allow us to better decipher their function and contribution to the different pathologies and to eventually uncover their mutual influences.

Hsa_circ_0054220 Upregulates HMGA1 by the Competitive RNA Pattern to Promote Neural Impairment in MPTP Model of Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disease. Circular RNAs (circRNAs) have been confirmed to regulate neurodegenerative diseases. This study was aimed to explore hsa_circ_0054220 functions in PD. MPP-stimulated SH-SY5Y cells were established as the PD cell model. PD mouse model was established by MPTP. Gene expression in cells and tissues was tested by RT-qPCR. Cell viability and apoptosis were evaluated through CCK-8 and TUNEL assays. The interactions of RNAs were determined by RNA pull-down assay, RIP assay, and luciferase reporter assay. Circ_0054220 expressed at a high level in MPP-treated SH-SY5Y cells. Circ_0054220 inhibition promoted viability and suppressed apoptosis in MPP-stimulated cells. Furthermore, we found that circ_0054220 can competitively bind to miR-145 and miR-625 to upregulate high mobility group A1 (HMGA1) expression. HMGA1 was positively regulated by circ_0054220 and overexpressed in MPP-treated cells as well as the striatum (STR), substantia nigra pars compacta (SNpc), and serum of MPTP-induced mouse model of PD. HMGA1 overexpression counteracted the function of circ_0054220 silencing on cell apoptosis. Furthermore, HMGA1 inhibition notably alleviated motor dysfunction and increased the quantity of neurons in mice resembling PD. Circ_0054220 upregulates HMGA1 by the competitive endogenous RNAs (ceRNA) pattern to promote neural impairment in PD.

Aging differentially alters the transcriptome and landscape of chromatin accessibility in the male and female mouse hippocampus

Aging-related memory impairment and pathological memory disorders such as Alzheimer's disease differ between males and females, and yet little is known about how aging-related changes in the transcriptome and chromatin environment differ between sexes in the hippocampus. To investigate this question, we compared the chromatin accessibility landscape and gene expression/alternative splicing pattern of young adult and aged mouse hippocampus in both males and females using ATAC-seq and RNA-seq. We detected significant aging-dependent changes in the expression of genes involved in immune response and synaptic function and aging-dependent changes in the alternative splicing of myelin sheath genes. We found significant sex-bias in the expression and alternative splicing of hundreds of genes, including aging-dependent female-biased expression of myelin sheath genes and aging-dependent male-biased expression of genes involved in synaptic function. Aging was associated with increased chromatin accessibility in both male and female hippocampus, especially in repetitive elements, and with an increase in LINE-1 transcription. We detected significant sex-bias in chromatin accessibility in both autosomes and the X chromosome, with male-biased accessibility enriched at promoters and CpG-rich regions. Sex differences in gene expression and chromatin accessibility were amplified with aging, findings that may shed light on sex differences in aging-related and pathological memory loss.

Aberrant splicing of PSEN2, but not PSEN1, in individuals with sporadic Alzheimer's disease

Alzheimer's disease is the most common neurodegenerative disease, characterized by dementia and premature death. Early-onset familial Alzheimer's disease is caused in part by pathogenic variants in presenilin 1 (PSEN1) and presenilin 2 (PSEN2), and alternative splicing of these two genes has been implicated in both familial and sporadic Alzheimer's disease. Here, we leveraged targeted isoform-sequencing to characterize thousands of complete PSEN1 and PSEN2 transcripts in the prefrontal cortex of individuals with sporadic Alzheimer's disease, familial Alzheimer's disease (carrying PSEN1 and PSEN2 variants), and controls. Our results reveal alternative splicing patterns of PSEN2 specific to sporadic Alzheimer's disease, including a human-specific cryptic exon present in intron 9 of PSEN2 as well as a 77 bp intron retention product before exon 6 that are both significantly elevated in sporadic Alzheimer's disease samples, alongside a significantly lower percentage of canonical full-length PSEN2 transcripts versus familial Alzheimer's disease samples and controls. Both alternatively spliced products are predicted to generate a prematurely truncated PSEN2 protein and were corroborated in an independent cerebellum RNA-sequencing dataset. In addition, our data in PSEN variant carriers is consistent with the hypothesis that PSEN1 and PSEN2 variants need to produce full-length but variant proteins to contribute to the onset of Alzheimer's disease, although intriguingly there were far fewer full-length transcripts carrying pathogenic alleles versus wild-type alleles in PSEN2 variant carriers. Finally, we identify frequent RNA editing at Alu elements present in an extended 3' untranslated region in PSEN2. Overall, this work expands the understanding of PSEN1 and PSEN2 variants in Alzheimer's disease, shows that transcript differences in PSEN2 may play a role in sporadic Alzheimer's disease, and suggests novel mechanisms of Alzheimer's disease pathogenesis.

An Alternative View of Familial Alzheimer's Disease Genetics

Probabilistic and parsimony-based arguments regarding available genetics data are used to propose that Hardy and Higgin's amyloid cascade hypothesis is valid but is commonly interpreted too narrowly to support, incorrectly, the primacy of the amyloid-β peptide (Aβ) in driving Alzheimer's disease pathogenesis. Instead, increased activity of the βCTF (C99) fragment of AβPP is the critical pathogenic determinant altered by mutations in the APP gene. This model is consistent with the regulation of APP mRNA translation via its 5' iron responsive element. Similar arguments support that the pathological effects of familial Alzheimer's disease mutations in the genes PSEN1 and PSEN2 are not exerted directly via changes in AβPP cleavage to produce different ratios of Aβ length. Rather, these mutations likely act through effects on presenilin holoprotein conformation and function, and possibly the formation and stability of multimers of presenilin holoprotein and/or of the γ-secretase complex. All fAD mutations in APP, PSEN1, and PSEN2 likely find unity of pathological mechanism in their actions on endolysosomal acidification and mitochondrial function, with detrimental effects on iron homeostasis and promotion of "pseudo-hypoxia" being of central importance. Aβ production is enhanced and distorted by oxidative stress and accumulates due to decreased lysosomal function. It may act as a disease-associated molecular pattern enhancing oxidative stress-driven neuroinflammation during the cognitive phase of the disease.

Relevance of a Truncated PRESENILIN 2 Transcript to Alzheimer's Disease and Neurodegeneration

BACKGROUND

The PRESENILIN genes (PSEN1, PSEN2) encoding for their respective proteins have critical roles in many aspects of Alzheimer's disease (AD) pathogenesis. The PS2V transcript of PSEN2 encodes a truncated protein and is upregulated in AD brains; however, its relevance to AD and disease progression remains to be determined.

OBJECTIVE

Assess transcript levels in postmortem AD and non-AD brain tissue and in lymphocytes collected under the Australian Imaging Biomarker and Lifestyle (AIBL) study.

METHODS

Full length PSEN2 and PS2V transcript levels were assessed by quantitative digital PCR in postmortem brain tissue (frontal cortex and hippocampus) from control, AD, frontotemporal dementia (FTD), and Lewy body dementia (LBD). Transcript levels were also assessed in lymphocytes obtained from the Perth subset of the AIBL study (n = 160). Linear regression analysis was used to assess correlations between transcript copy number and brain volume and neocortical amyloid load.

RESULTS

PS2V levels increased in AD postmortem brain but PS2V was also present at significant levels in FTD and LBD brains. PS2V transcript was detected in lymphocytes and PS2V/PSEN2 ratios were increased in mild cognitive impairment (p = 0.024) and AD (p = 0.019) groups compared to control group. Increased ratios were significantly correlated with hippocampal volumes only (n = 62, β= -0.269, p = 0.03).

CONCLUSION

Taken together, these results suggest that PS2V may be a marker of overall neurodegeneration.

Hypoxia-induced alternative splicing in human diseases: the pledge, the turn, and the prestige

Maintenance of oxygen homeostasis is an indispensable criterion for the existence of multicellular life-forms. Disruption of this homeostasis due to inadequate oxygenation of the respiring tissues leads to pathological hypoxia, which acts as a significant stressor in several pathophysiological conditions including cancer, cardiovascular defects, bacterial infections, and neurological disorders. Consequently, the hypoxic tissues develop necessary adaptations both at the tissue and cellular level. The cellular adaptations involve a dramatic alteration in gene expression, post-transcriptional and post-translational modification of gene products, bioenergetics, and metabolism. Among the key responses to oxygen-deprivation is the skewing of cellular alternative splicing program. Herein, we discuss the current concepts of oxygen tension-dependent alternative splicing relevant to various pathophysiological conditions. Following a brief description of cellular response to hypoxia and the pre-mRNA splicing mechanism, we outline the impressive number of hypoxia-elicited alternative splicing events associated with maladies like cancer, cardiovascular diseases, and neurological disorders. Furthermore, we discuss how manipulation of hypoxia-induced alternative splicing may pose promising strategies for novel translational diagnosis and therapeutic interventions.

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.

Targeting the intrinsically disordered architectural High Mobility Group A (HMGA) oncoproteins in breast cancer: learning from the past to design future strategies

INTRODUCTION

Triple-negative breast cancer (TNBC) is the most difficult breast cancer subtype to treat because of its heterogeneity and lack of specific therapeutic targets. High Mobility Group A (HMGA) proteins are chromatin architectural factors that have multiple oncogenic functions in breast cancer, and they represent promising molecular therapeutic targets for this disease.

AREAS COVERED

We offer an overview of the strategies that have been exploited to counteract HMGA oncoprotein activities at the transcriptional and post-transcriptional levels. We also present the possibility of targeting cancer-associated factors that lie downstream of HMGA proteins and discuss the contribution of HMGA proteins to chemoresistance.

EXPERT OPINION

Different strategies have been exploited to counteract HMGA protein activities; these involve interfering with their nucleic acid binding properties and the blocking of HMGA expression. Some approaches have provided promising results. However, some unique characteristics of the HMGA proteins have not been exploited; these include their extensive protein-protein interaction network and their intrinsically disordered status that present the possibility that HMGA proteins could be involved in the formation of proteinaceous membrane-less organelles (PMLO) by liquid-liquid phase separation. These unexplored characteristics could open new pharmacological avenues to counteract the oncogenic contributions of HMGA proteins.

Innate Immunity: A Common Denominator between Neurodegenerative and Neuropsychiatric Diseases

The intricate relationships between innate immunity and brain diseases raise increased interest across the wide spectrum of neurodegenerative and neuropsychiatric disorders. Barriers, such as the blood–brain barrier, and innate immunity cells such as microglia, astrocytes, macrophages, and mast cells are involved in triggering disease events in these groups, through the action of many different cytokines. Chronic inflammation can lead to dysfunctions in large-scale brain networks. Neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and frontotemporal dementia, are associated with a substrate of dysregulated immune responses that impair the central nervous system balance. Recent evidence suggests that similar phenomena are involved in psychiatric diseases, such as depression, schizophrenia, autism spectrum disorders, and post-traumatic stress disorder. The present review summarizes and discusses the main evidence linking the innate immunological response in neurodegenerative and psychiatric diseases, thus providing insights into how the responses of innate immunity represent a common denominator between diseases belonging to the neurological and psychiatric sphere. Improved knowledge of such immunological aspects could provide the framework for the future development of new diagnostic and therapeutic approaches.

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.

Alternative splicing in a presenilin 2 variant associated with Alzheimer disease

OBJECTIVE

Autosomal-dominant familial Alzheimer disease (AD) is caused by by variants in presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein (APP). Previously, we reported a rare PSEN2 frameshift variant in an early-onset AD case (PSEN2 p.K115Efs*11). In this study, we characterize a second family with the same variant and analyze cellular transcripts from both patient fibroblasts and brain lysates.

METHODS

We combined genomic, neuropathological, clinical, and molecular techniques to characterize the PSEN2 K115Efs*11 variant in two families.

RESULTS

Neuropathological and clinical evaluation confirmed the AD diagnosis in two individuals carrying the PSEN2 K115Efs*11 variant. A truncated transcript from the variant allele is detectable in patient fibroblasts while levels of wild-type PSEN2 transcript and protein are reduced compared to controls. Functional studies to assess biological consequences of the variant demonstrated that PSEN2 K115Efs*11 fibroblasts secrete less Aβ 1-40 compared to controls, indicating abnormal γ-secretase activity. Analysis of PSEN2 transcript levels in brain tissue revealed alternatively spliced PSEN2 products in patient brain as well as in sporadic AD and age-matched control brain.

INTERPRETATION

These data suggest that PSEN2 K115Efs*11 is a likely pathogenic variant associated with AD. We uncovered novel PSEN2 alternative transcripts in addition to previously reported PSEN2 splice isoforms associated with sporadic AD. In the context of a frameshift, these alternative transcripts return to the canonical reading frame with potential to generate deleterious protein products. Our findings suggest novel potential mechanisms by which PSEN variants may influence AD pathogenesis, highlighting the complexity underlying genetic contribution to disease risk.

HMGA1a induces alternative splicing of estrogen receptor alpha in MCF-7 human breast cancer cells

The high-mobility group A protein 1a (HMGA1a) protein is known as an oncogene whose expression level in cancer tissue correlates with the malignant potential, and known as a component of senescence-related structures connecting it to tumor suppressor networks in fibroblasts. HMGA1 protein binds to DNA, but recent studies have shown it exerts novel functions through RNA-binding. Our previous studies have shown that sequence-specific RNA-binding of HMGA1a induces exon-skipping of Presenilin-2 exon 5 in sporadic Alzheimer disease. Here we show that HMGA1a induced exon-skipping of the estrogen receptor alpha (ERα) gene and increased ERα46 mRNA expression in MCF-7 breast cancer cells. An RNA-decoy of HMGA1a efficiently blocked this event and reduced ERα46 protein expression. Blockage of HMGA1a RNA-binding property consequently induced cell growth through reduced ERα46 expression in MCF-7 cells and increased sensitivity to tamoxifen in the tamoxifen-resistant cell line, MCF-7/TAMR1. Stable expression of an HMGA1a RNA-decoy in MCF-7 cells exhibited decreased ERα46 protein expression and increased estrogen-dependent tumor growth when these cells were implanted in nude mice. These results show HMGA1a is involved in alternative splicing of the ERα gene and related to estrogen-related growth as well as tamoxifen sensitivity in MCF-7 breast cancer cells.

HMGA1a Induces Alternative Splicing of the Estrogen Receptor-αlpha Gene by Trapping U1 snRNP to an Upstream Pseudo-5' Splice Site

Objectives: The high-mobility group A protein 1a (HMGA1a) protein is known as a transcription factor that binds to DNA, but recent studies have shown it exerts novel functions through RNA-binding. We were prompted to decipher the mechanism of HMGA1a-induced alternative splicing of the estrogen receptor alpha (ERα) that we recently reported would alter tamoxifen sensitivity in MCF-7 TAMR1 cells.

Methods: Endogenous expression of full length ERα66 and its isoform ERα46 were evaluated in MCF-7 breast cancer cells by transient expression of HMGA1a and an RNA decoy (2′-O-methylated RNA of the HMGA1a RNA-binding site) that binds to HMGA1a. RNA-binding of HMGA1a was checked by RNA-EMSA. In vitro splicing assay was performed to check the direct involvement of HMGA1a in splicing regulation. RNA-EMSA assay in the presence of purified U1 snRNP was performed with psoralen UV crosslinking to check complex formation of HMGA1a-U1 snRNP at the upstream pseudo-5′ splice site of exon 1.

Results: HMGA1a induced exon skipping of a shortened exon 1 of ERα in in vitro splicing assays that was blocked by the HMGA1a RNA decoy and sequence-specific RNA-binding was confirmed by RNA-EMSA. RNA-EMSA combined with psoralen UV crosslinking showed that HMGA1a trapped purified U1 snRNP at the upstream pseudo-5′ splice site.

Conclusions: Regulation of ERα alternative splicing by an HMGA1a-trapped U1 snRNP complex at the upstream 5′ splice site of exon 1 offers novel insight on 5′ splice site regulation by U1 snRNP as well as a promising target in breast cancer therapy where alternative splicing of ERα is involved.

Saturation mutagenesis reveals manifold determinants of exon definition

To illuminate the extent and roles of exonic sequences in the splicing of human RNA transcripts, we conducted saturation mutagenesis of a 51-nt internal exon in a three-exon minigene. All possible single and tandem dinucleotide substitutions were surveyed. Using high-throughput genetics, 5560 minigene molecules were assayed for splicing in human HEK293 cells. Up to 70% of mutations produced substantial (greater than twofold) phenotypes of either increased or decreased splicing. Of all predicted secondary structural elements, only a single 15-nt stem–loop showed a strong correlation with splicing, acting negatively. The in vitro formation of exon-protein complexes between the mutant molecules and proteins associated with spliceosome formation (U2AF35, U2AF65, U1A, and U1-70K) correlated with splicing efficiencies, suggesting exon definition as the step affected by most mutations. The measured relative binding affinities of dozens of human RNA binding protein domains as reported in the CISBP-RNA database were found to correlate either positively or negatively with splicing efficiency, more than could fit on the 51-nt test exon simultaneously. The large number of these functional protein binding correlations point to a dynamic and heterogeneous population of pre-mRNA molecules, each responding to a particular collection of binding proteins.

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.

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.

Role of six single nucleotide polymorphisms, risk factors in coronary disease, in OLR1 alternative splicing

The OLR1 gene encodes the oxidized low-density lipoprotein receptor (LOX-1), which is responsible for the cellular uptake of oxidized LDL (Ox-LDL), foam cell formation in atheroma plaques and atherosclerotic plaque rupture. Alternative splicing (AS) of OLR1 exon 5 generates two protein isoforms with antagonistic functions in Ox-LDL uptake. Previous work identified six single nucleotide polymorphisms (SNPs) in linkage disequilibrium that influence the inclusion levels of OLR1 exon 5 and correlate with the risk of cardiovascular disease. Here we use minigenes to recapitulate the effects of two allelic series (Low- and High-Risk) on OLR1 AS and identify one SNP in intron 4 (rs3736234) as the main contributor to the differences in exon 5 inclusion, while the other SNPs in the allelic series attenuate the drastic effects of this key SNP. Bioinformatic, proteomic, mutational and functional high-throughput analyses allowed us to define regulatory sequence motifs and identify SR protein family members (SRSF1, SRSF2) and HMGA1 as factors involved in the regulation of OLR1 AS. Our results suggest that antagonism between SRSF1 and SRSF2/HMGA1, and differential recognition of their regulatory motifs depending on the identity of the rs3736234 polymorphism, influence OLR1 exon 5 inclusion and the efficiency of Ox-LDL uptake, with potential implications for atherosclerosis and coronary disease.

Alzheimer's disease-related peptide PS2V plays ancient, conserved roles in suppression of the unfolded protein response under hypoxia and stimulation of γ-secretase activity

The PRESENILIN1 and PRESENILIN2 genes encode structurally related proteases essential for γ-secretase activity. Of nearly 200 PRESENILIN mutations causing early onset, familial Alzheimer's disease (FAD) only the K115Efx10 mutation of PSEN2 causes truncation of the open reading frame. If translated, the truncated product would resemble a naturally occurring isoform of PSEN2 named PS2V that is induced by hypoxia and found at elevated levels in late onset Alzheimer's disease (AD) brains. The function of PS2V is largely unexplored. We show that zebrafish possess a PS2V-like isoform, PS1IV, produced from the fish's PSEN1 rather than PSEN2 orthologous gene. The molecular mechanism controlling formation of PS2V/PS1IV was probably present in the ancient common ancestor of the PSEN1 and PSEN2 genes. Human PS2V and zebrafish PS1IV have highly divergent structures but conserved abilities to stimulate γ-secretase activity and to suppress the unfolded protein response (UPR) under hypoxia. The putative protein truncation caused by K115Efx10 resembles PS2V in its ability to increase γ-secretase activity and suppress the UPR. This supports increased Aβ levels as a common link between K115Efx10 early onset AD and sporadic, late onset AD. The ability of mutant variants of PS2V to stimulate γ-secretase activity partially correlates with their ability to suppress the UPR. The cytosolic, transmembrane and luminal domains of PS2V are all critical to its γ-secretase and UPR-suppression activities. Our data support a model in which chronic hypoxia in aged brains promotes excessive Notch signalling and accumulation of Aβ that contribute to AD pathogenesis.

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.

The Guinea Pig as a Model for Sporadic Alzheimer's Disease (AD): The Impact of Cholesterol Intake on Expression of AD-Related Genes

We investigated the guinea pig, Cavia porcellus, as a model for Alzheimer’s disease (AD), both in terms of the conservation of genes involved in AD and the regulatory responses of these to a known AD risk factor - high cholesterol intake. Unlike rats and mice, guinea pigs possess an Aβ peptide sequence identical to human Aβ. Consistent with the commonality between cardiovascular and AD risk factors in humans, we saw that a high cholesterol diet leads to up-regulation of BACE1 (β-secretase) transcription and down-regulation of ADAM10 (α-secretase) transcription which should increase release of Aβ from APP. Significantly, guinea pigs possess isoforms of AD-related genes found in humans but not present in mice or rats. For example, we discovered that the truncated PS2V isoform of human PSEN2, that is found at raised levels in AD brains and that increases γ-secretase activity and Aβ synthesis, is not uniquely human or aberrant as previously believed. We show that PS2V formation is up-regulated by hypoxia and a high-cholesterol diet while, consistent with observations in humans, Aβ concentrations are raised in some brain regions but not others. Also like humans, but unlike mice, the guinea pig gene encoding tau, MAPT, encodes isoforms with both three and four microtubule binding domains, and cholesterol alters the ratio of these isoforms. We conclude that AD-related genes are highly conserved and more similar to human than the rat or mouse. Guinea pigs represent a superior rodent model for analysis of the impact of dietary factors such as cholesterol on the regulation of AD-related genes.

Tailoring of membrane proteins by alternative splicing of pre-mRNA

Alternative splicing (AS) of RNA is a key mechanism for diversification of the eukaryotic proteome. In this process, different mRNA transcripts can be produced through altered excision and/or inclusion of exons during processing of the pre-mRNA molecule. Since its discovery, AS has been shown to play roles in protein structure, function, and localization. Dysregulation of this process can result in disease phenotypes. Moreover, AS pathways are promising therapeutic targets for a number of diseases. Integral membrane proteins (MPs) represent a class of proteins that may be particularly amenable to regulation by alternative splicing because of the distinctive topological restraints associated with their folding, structure, trafficking, and function. Here, we review the impact of AS on MP form and function and the roles of AS in MP-related disorders such as Alzheimer's disease.

The response of HMGA1 to changes in oxygen availability is evolutionarily conserved

Zebrafish embryos have evolved to cope with hypoxia during development. This includes the ability to completely suspend embryo development for extended periods until normoxia is restored. However, only a limited number of studies have examined the gene regulatory responses of zebrafish embryos to hypoxia. The High Mobility Group A1 protein encoded by the mammalian gene HMGA1 is widely expressed during embryo development but not in adults. Its expression can be induced in adult neurons by hypoxia/oxidative stress and it is commonly reactivated in many types of cancer. We report the identification by phylogenetic and conserved synteny analyses of an HMGA1 orthologue in zebrafish, hmga1 (hmg-i/y) and analysis of sodium azide as a chemical agent for inducing hypoxia-like responses in zebrafish embryos including temporary suspension of development ("suspended animation"). Evidence was only found for the existence of the "a" isoform of HMGA1 in fish. The "b" and "c" isoforms were not detected. We show that zebrafish hmga1 is expressed in a manner similar to in mammals including its induction by hypoxia during hatching stage and in adult zebrafish brain. However, earlier during development, hypoxia causes a decrease in hmga1 transcript levels. By analysis of conservation of the HMGA1a isoform binding site in zebrafish psen2 gene transcripts, we predict that a zebrafish equivalent of the PS2V isoform of human PSEN2 is not formed and we support this by RT-PCR analyses. Thus, analysis of hmga1 function in zebrafish embryogenesis may be valuable for understanding its wider role in vertebrate development, cancer and cellular responses to hypoxia but not for analysis of the action of HMGA1 in PS2V formation.

HMGA1a is involved in specific splice site regulation of human immunodeficiency virus type 1

Human immunodeficiency virus type 1 (HIV-1) utilizes a highly complex splice site regulation system, taking advantage of host proteins, to express its own viral protein in an orderly way. We show here that one of the host proteins, high mobility group A protein 1a (HMGA1a), is involved in splice site regulation of 3' splice site 2 (A2) and 5'splice site 3 (D3) of HIV-1 genomic RNA. shRNA knockdown of HMGA1 in HeLa cells resulting in a decrease of HMGA1 showed a significant decrease of Vpr mRNA. RNA electrophoretic mobility shift assays showed HMGA1a specifically binds to a sequence adjacently upstream D3. In vitro splicing using heterologous pre-mRNA with A2 and D3, showed HMGA1a induced a splicing intermediate which decreased when an RNA decoy of the HMGA1a binding site was added. RT-PCR of in vitro splicing products revealed that HMGA1a induced an incomplete splicing product resulting from usage of A2 but inhibition of D3, which is reminiscent of the splicing pattern necessary for Vpr mRNA formation. HMGA1a interacted with hnRNPA1 shown by coimmunoprecipitation and supershifted U1 snRNP in an RNA electrophoretic mobility shift assay. We conclude that HMGA1a anchors U1 snRNP to inhibit D3 function, and that HMGA1a inhibits hnRNPA1 function on exon splicing silencer of Vpr (ESSV) to activate A2 function. We show here for the first time that HMGA1a is involved in specific splice site regulation of HIV-1.

Yokukansan inhibits neuronal death during ER stress by regulating the unfolded protein response

BACKGROUND

Recently, several studies have reported Yokukansan (Tsumura TJ-54), a traditional Japanese medicine, as a potential new drug for the treatment of Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress is known to play an important role in the pathogenesis of AD, particularly in neuronal death. Therefore, we examined the effect of Yokukansan on ER stress-induced neurotoxicity and on familial AD-linked presenilin-1 mutation-associated cell death.

METHODS

We employed the WST-1 assay and monitored morphological changes to evaluate cell viability following Yokukansan treatment or treatment with its components. Western blotting and PCR were used to observe the expression levels of GRP78/BiP, caspase-4 and C/EBP homologous protein.

RESULTS

Yokukansan inhibited neuronal death during ER stress, with Cnidii Rhizoma (Senkyu), a component of Yokukansan, being particularly effective. We also showed that Yokukansan and Senkyu affect the unfolded protein response following ER stress and that these drugs inhibit the activation of caspase-4, resulting in the inhibition of ER stress-induced neuronal death. Furthermore, we found that the protective effect of Yokukansan and Senkyu against ER stress could be attributed to the ferulic acid content of these two drugs.

CONCLUSIONS

Our results indicate that Yokukansan, Senkyu and ferulic acid are protective against ER stress-induced neuronal cell death and may provide a possible new treatment for AD.

Phenotyping of an in vitro model of ischemic penumbra by iTRAQ-based shotgun quantitative proteomics

Cerebral ischemia is a major cause of death and long-term disability worldwide. Ischemic penumbra, the electrically silent but metabolically viable perifocal brain tissue, is the target for the much elusive stroke therapy. To characterize the molecular events of the dynamic penumbra, we applied an iTRAQ-based shotgun proteomic approach in an in vitro neuronal model, using the rat B104 neuroblastoma cell line. Various functional and cytometric assays were performed to establish the relevant time-point and conditions for ischemia to recapitulate the pathology of the penumbra. Two replicate iTRAQ experiments identified 1796 and 1566 proteins, respectively (<or=1.0% false discovery rate). Mining of proteomic data indicated the up-regulation of proteins involved in ammoniagenesis, antiapoptotic, anti-inflammatory and mitochondrial heat shock response and down-regulation of proteins pertaining to antioxidative defense and protein metabolism. Additionally, many proteins (for instance, park7 and VAP-A) involved in the chronic neurological disorders (such as Alzheimer's disease, Parkinson's disease or Bipolar disorder) were also regulated in this model of acute neuronal injury. Our results also provide preliminary evidence about the presence of a relative glucose paradox under in vitro conditions indicating possible application of this cell system to study the mechanisms of transient protection induced by concomitant glucose deprivation under hypoxia. In conclusion, our study shows the potential application of iTRAQ-based quantitative proteomics for the elucidation of pathophysiology and the discovery of novel therapeutic targets in the field of neuroproteomics.

HMGA1a trapping of U1 snRNP at an authentic 5' splice site induces aberrant exon skipping in sporadic Alzheimer's disease

Overexpression of high-mobility group A protein 1a (HMGA1a) causes aberrant exon 5 skipping of the Presenilin-2 (PS2) pre-mRNA, which is almost exclusively detected in patients with sporadic Alzheimer's disease. An electrophoretic mobility shift assay confirmed aberrant U1 small nuclear ribonucleoprotein particle (snRNP)-HMGA1a complex formation (via the U1-70K component), with RNA containing a specific HMGA1a-binding site and an adjacent 5' splice site. Psoralen cross-linking analysis demonstrated that the binding of HMGA1a adjacent to the 5' splice site induces unusually extended association of U1 snRNP to the 5' splice site. As a result, spliceosome assembly across either the intron or the exon is arrested at an early ATP-independent stage. We conclude that the HMGA1a-induced aberrant exon skipping is caused by impaired dissociation of U1 snRNP from the 5' splice site, leading to a defect in exon definition. The proposed molecular mechanism has profound implications for other known posttranscriptional modulation strategies in various organisms, all of which are triggered by aberrant U1 snRNP binding.

Identification and analysis of two splice variants of human G2A generated by alternative splicing

G2A is a G protein-coupled receptor that can be induced by various stressors. G2A is reported to have proton-sensing activity that mediates intracellular inositol phosphate (IP) accumulation with decreasing pH. We previously showed that G2A is also activated by some oxidized free fatty acids such as 9-hydroxyoctadecadienoic acid (9-HODE). In this study, we identified a novel alternative splice variant of G2A (G2A-b) that has a partially different N terminus compared with the G2A originally reported (G2A-a). The two splice variants of G2A show similar tissue distributions, but G2A-b is expressed more abundantly. There was no difference between the two variants in 9-HODE-induced cellular responses, such as intracellular calcium mobilization and GDP/GTP exchange of Galpha protein, and in proton-sensitive IP accumulation. However, G2A-b showed a higher basal activity in terms of IP accumulation. Mutagenesis study revealed that the difference in the basal activity is attributable to the K7 residue that exists only in G2A-a. We further demonstrated that an R42A mutation largely impaired both the basal and proton-sensing activities, but did not affect the 9-HODE-induced intracellular calcium increase. Taken together, we found an additional novel G2A variant (G2A-b) that is the major transcript with functional response to ligand stimulation as well as G2A-a, and succeeded in discriminating proton-sensing and oxidized fatty acid-sensing activities of G2A.

An Alu-derived intronic splicing enhancer facilitates intronic processing and modulates aberrant splicing in ATM

We have previously reported a natural GTAA deletion within an intronic splicing processing element (ISPE) of the ataxia telangiectasia mutated (ATM) gene that disrupts a non-canonical U1 snRNP interaction and activates the excision of the upstream portion of the intron. The resulting pre-mRNA splicing intermediate is then processed to a cryptic exon, whose aberrant inclusion in the final mRNA is responsible for ataxia telangiectasia. We show here that the last 40 bases of a downstream intronic antisense Alu repeat are required for the activation of the cryptic exon by the ISPE deletion. Evaluation of the pre-mRNA splicing intermediate by a hybrid minigene assay indicates that the identified intronic splicing enhancer represents a novel class of enhancers that facilitates processing of splicing intermediates possibly by recruiting U1 snRNP to defective donor sites. In the absence of this element, the splicing intermediate accumulates and is not further processed to generate the cryptic exon. Our results indicate that Alu-derived sequences can provide intronic splicing regulatory elements that facilitate pre-mRNA processing and potentially affect the severity of disease-causing splicing mutations.

HMGA1a recognition candidate DNA sequences in humans

High mobility group protein A1a (HMGA1a) acts as an architectural transcription factor and influences a diverse array of normal biological processes. It binds AT-rich sequences, and previous reports have demonstrated HMGA1a binding to the authentic promoters of various genes. However, the precise sequences that HMGA1a binds to remain to be clarified. Therefore, in this study, we searched for the sequences with the highest affinity for human HMGA1a using an existing SELEX method, and then compared the identified sequences with known human promoter sequences. Based on our results, we propose the sequences “-(G/A)-G-(A/T)-(A/T)-A-T-T-T-” as HMGA1a-binding candidate sequences. Furthermore, these candidate sequences bound native human HMGA1a from SK-N-SH cells. When candidate sequences were analyzed by performing FASTAs against all known human promoter sequences, 500–900 sequences were hit by each one. Some of the extracted genes have already been proven or suggested as HMGA1a-binding promoters. The candidate sequences presented here represent important information for research into the various roles of HMGA1a, including cell differentiation, death, growth, proliferation, and the pathogenesis of cancer.

Altered splicing in exon 8 of the DNA replication factor CIZ1 affects subnuclear distribution and is associated with Alzheimer's disease

In order to understand the gene-mediated processes underlying sporadic Alzheimer's disease (AD), we carried out a subtractive cloning screen for novel AD candidate genes. We identified the gene encoding the DNA replication factor CIZ1 (CDKN1A interacting zinc finger protein 1) as being more highly expressed in Alzheimer tissue than in healthy brains. We show here that an isoform of CIZ1 which lacks a glutamine-rich region, due to alternative splicing in exon 8, is upregulated in AD brains relative to the full-length CIZ1 protein. We demonstrate for the first time that a minimal 28 amino acid sequence within this region is required for CIZ1 to associate with the nuclear matrix and to form nuclear foci.

Knockdown of the L3/Lhx8 gene suppresses cholinergic differentiation of murine embryonic stem cell-derived spheres

L3/Lhx8, a member of the Lim-homeobox gene family, is selectively and specifically expressed in the murine embryonic medial ganglionic eminence (MGE). Our previous study demonstrated that L3/Lhx8-deficient mice specifically lack cholinergic neurons in the basal forebrain. In this manuscript, we report the in vitro effects of reduced L3/Lhx8 gene expression on cholinergic differentiation in murine embryonic stem (ES) cell-derived spheres without dissociation. The knockdown of L3/Lhx8 gene expression dramatically decreased the cholinergic phenotype of spheres without altering other known phenotypes (TuJ1, GABA and GFAP). These results strongly suggest that L3/Lhx8 is a key factor for cholinergic differentiation of murine ES cell-derived spheres and is involved in basal forebrain development.

Pioneer round of translation mediated by nuclear cap-binding proteins CBP80/20 occurs during prolonged hypoxia

Nonsense-mediated mRNA decay (NMD) is one of the mRNA surveillance mechanisms, which eliminates aberrant mRNAs harboring premature termination codons. NMD targets only mRNAs bound by the nuclear cap-binding protein complex CBP80/20 which directs the pioneer round of translation. Here we demonstrate that NMD occurs efficiently during prolonged hypoxia in which steady-state translation is drastically inhibited. Accordingly, CBP80 remains in the nucleus, and processing bodies are unaffected with regard to their abundance and number under prolonged hypoxic conditions. These results indicate that mRNAs enter the pioneer round of translation during prolonged hypoxia.

HMGA1a: sequence-specific RNA-binding factor causing sporadic Alzheimer's disease-linked exon skipping of presenilin-2 pre-mRNA

Aberrant exon 5 skipping of presenilin-2 (PS2) pre-mRNA produces a deleterious protein isoform PS2V, which is almost exclusively observed in the brains of sporadic Alzheimer's disease patients. PS2V over-expression in vivo enhances susceptibility to various endoplasmic reticulum (ER) stresses and increases production of amyloid-beta peptides. We previously purified and identified high mobility group A protein 1a (HMGA1a) as a trans-acting factor responsible for aberrant exon 5 skipping. Using heterologous pre-mRNAs, here we demonstrate that a specific HMGA1a-binding sequence in exon 5 adjacent to the 5' splice site is necessary for HMGA1a to inactivate the 5' splice site. An aberrant HMGA1a-U1 snRNP complex was detected on the HMGA1a-binding site adjacent to the 5' splice site during the early splicing reaction. A competitor 2'-O-methyl RNA (2'-O-Me RNA) consisting of the HMGA1a-binding sequence markedly repressed exon 5 skipping of PS2 pre-mRNA in vitro and in vivo. Finally, HMGA1a-induced cell death under ER stress was prevented by transfection of the competitor 2'-O-Me RNA. These results provide insights into the molecular basis for PS2V-associated neurodegenerative diseases that are initiated by specific RNA binding of HMGA1a.

High-mobility group A1 proteins inhibit expression of nucleotide excision repair factor xeroderma pigmentosum group A

Cells that overexpress high-mobility group A1 (HMGA1) proteins exhibit deficient nucleotide excision repair (NER) after exposure to DNA-damaging agents, a condition ameliorated by artificially lowering intracellular levels of these nonhistone proteins. One possible mechanism for this NER inhibition is down-regulation of proteins involved in NER, such as xeroderma pigmentosum complimentation group A (XPA). Microarray and reverse transcription-PCR data indicate a 2.6-fold decrease in intracellular XPA mRNA in transgenic MCF-7 cells overexpressing HMGA1 proteins compared with non-HMGA1-expressing cells. XPA protein levels are also approximately 3-fold lower in HMGA1-expressing MCF-7 cells. Moreover, whereas a >2-fold induction of XPA proteins is observed in normal MCF-7 cells 30 min after UV exposure, no apparent induction of XPA protein is observed in MCF-7 cells expressing HMGA1. Mechanistically, we present both chromatin immunoprecipitation and promoter site-specific mutagenesis evidence linking HMGA1 to repression of XPA transcription via binding to a negative regulatory element in the endogenous XPA gene promoter. Phenotypically, HMGA1-expressing cells exhibit compromised removal of cyclobutane pyrimidine dimer lesions, a characteristic of cells that express low levels of XPA. Importantly, we show that restoring expression of wild-type XPA in HMGA1-expressing cells rescues UV resistance comparable with that of normal MCF-7 cells. Together, these data provide strong experimental evidence that HMGA1 proteins are involved in inhibiting XPA expression, resulting in increased UV sensitivity in cells that overexpress these proteins. Because HMGA1 proteins are overexpressed in most naturally occurring cancers, with increasing cellular concentrations correlating with increasing metastatic potential and poor patient prognosis, the current findings provide new insights into previously unsuspected mechanisms contributing to tumor progression.

A novel role for Fyn: Change in sphere formation ability in murine embryonic stem cells

Fyn, a member of the Src-family protein tyrosine kinase (PTK), is an essential factor in myelination in the CNS and is involved in murine embryonic stem (ES) cell growth and differentiation. Although dysfunctions of Fyn have been comparatively studied, the gain of function by ectopic expression, especially using ES cells, has seldom been investigated. In this article, we give the first report of the involvement of Fyn alteration in the sphere formation ability of murine ES cells. First, transient transfection of Fyn hardly affected multiplication and specialization. Then, we investigated Fyn overexpression using ES cells, which stably express Fyn. As a result, altered sphere formation capability was observed in all clones stably expressing Fyn. These results may provide important information for reproduction medical treatment using ES cells.

L3/Lhx8 is a pivotal factor for cholinergic differentiation of murine embryonic stem cells

L3/Lhx8 is a member of the LIM-homeobox gene family. Previously, we demonstrated that L3/Lhx8-null mice specifically lacked cholinergic neurons in the basal forebrain. In the present study, we conditionally suppressed L3/Lhx8 function during retinoic acid-induced neural differentiation of a murine embryonic stem (ES) cell line using an L3/Lhx8-targeted small interfering RNA (siRNA) produced by an H1.2 promoter-driven vector. Our culture conditions induced efficient differentiation of the ES cells into neurons and astrocytes, but far less efficient differentiation into oligodendrocytes. Suppression of L3/Lhx8 expression by siRNA led to a dramatic decrease in the number of cells positive for the cholinergic marker ChAT, and overexpression of L3/Lhx8 recovered this effect. However, no significant changes were observed in the number of Tuj1+ neurons and GABA+ cells. These results strongly suggest that L3/Lhx8 is a key factor in the cholinergic differentiation of murine ES cells and is involved in basal forebrain development.

Novel interaction between HMGA1a and StIP1 in murine terminally differentiated retina

High mobility group protein A1a (HMGA1a) is expressed at high levels in embryonic cells and has been implicated in their transcriptional regulation. However, it has been reported that high levels of HMGA1a expression are normally detected in the photoreceptor of adult (terminally differentiated cells) murine retina. We showed that biochemical purification of the recombinant HMGA1a binding activity in nuclear fractions from murine retina, but not from hippocampus, resulted in STAT3 interacting protein 1 (StIP1) that formed a novel complex with HMGA1a, STAT3 and homeodomain-interacting protein kinase 2 (HIPK2). While StIP1 expressions in brain, liver, lung, heart, skeletal muscle, spleen and thymus have previously been demonstrated, this is the first report that StIP1 was expressed in nuclear fractions from murine retina, and that in murine retina there are several novel complexes of transcriptional regulators consisting of HMGA1a, StIP1, STAT3 and HIPK2.

Structural genomics analysis of alternative splicing and application to isoform structure modeling

Alternative splicing is a sophisticated nuclear process that regulates gene expression. It represents an important mechanism for enhancing the functional diversity of proteins. Our current knowledge of alternatively spliced variants is derived mainly from mRNA transcripts, and very little is known about their protein tertiary structures. We carried out a large-scale analysis of known alternatively spliced variants at both protein sequence and structure levels and have shown that threading is, in general, a viable approach for modeling structures of alternatively spliced variants. An examination of alternative splicing at the protein sequence level revealed that the size of splicing events follows the power law distribution and the majority of splicing isoforms harbor only one or two alternations. We examined alternative splicing in the context of protein 3D structures and found that the boundaries of alternative splicing events generally happen in coil regions of secondary structures and exposed residues and the majority of the sequences involved in splicing are located on the surface of proteins. In light of these findings, we then proceeded to demonstrate that threading represents a useful tool for structure prediction of alternative splicing isoforms and addressed the fold stability issue of threading-based structure prediction by molecular dynamics simulation. Our analysis and the insights gained have helped to establish a viable method for structure prediction of alternatively spliced isoforms at the genome scale.

Cellular abnormalities linked to endoplasmic reticulum dysfunction in cerebrovascular disease—therapeutic potential

Unfolded proteins accumulate in the lumen of the endoplasmic reticulum (ER) as part of the cellular response to cerebral hypoxia/ischemia and also to the overexpression of the mutant genes responsible for familial forms of degenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyothrophic lateral sclerosis, and Huntington's disease, as well as other disorders that are caused by an expanded CAG repeat. This accumulation arises from an imbalance between the load of proteins that need to be folded and processed in the ER lumen and the ER folding/processing capacity. To withstand such potentially lethal conditions, stress responses are activated that includes the shutdown of translation to reduce the ER work load and the activation of the expression of genes coding for proteins involved in the folding and processing reactions, to increase folding/processing capacity. In transient cerebral ischemia, ER stress-induced suppression of protein synthesis is believed to be too severe to permit sufficient activation of the genetic arm of the ER stress response. Mutations associated with Alzheimer's disease down-regulate the ER stress response and make cells more vulnerable to conditions associated with ER stress. When the functioning of the ER is severely impaired and affected cells can no longer withstand these stressful conditions, programmed cell death is induced, including a mitochondria-driven apoptotic pathway. Raising the resistance of cells to conditions that interfere with ER functions and activating the degradation and refolding of unfolded proteins accumulated in the ER lumen are possible strategies for blocking the pathological process leading to cell death at an early stage.

Molecular mechanism of HMGA1 deregulation in human neuroblastoma

Very soon after their original identification in HeLa cells in 1983, HMGA proteins appeared as interesting cancer-related molecules. Indeed, they were immediately noted as a sub-class of High Mobility Group proteins induced in fibroblast or epithelial cells transformed with sarcoma viruses. After more than 20 years, the association between HMGA protein expressions and cellular transformation has been largely confirmed and HMGA are among the most widely expressed cancer-associated proteins. Nevertheless, their functional contribution to tumour development and progression is far from being completely understood. Furthermore, although HMGA1 expression has been reported to be inducible by a number of factors and circumstances, the question of how their expression is deregulated in cancer is even less clear and somehow has been ignored from most researchers. An active AP1 site is the only characterized element of the HMGA1 human promoter, that remains a rather complicated and unexplored source of information to answer this question. Following the indication that c-Myc might bind and activate the mouse HMGA1 gene promoter, we have demonstrated that HMGA1 is a new target for MYCN in human neuroblastomas. In this report, we overview part of the current information on HMGA1 and focus our attention on the analysis of its human promoter.