Characterization of a novel hexameric repeat DNA sequence in the promoter of the immediate early gene, IEX-1, that mediates 1alpha,25-dihydroxyvitamin D(3)-associated IEX-1 gene repression

Localized Perivascular Therapeutic Approaches to Inhibit Venous Neointimal Hyperplasia in Arteriovenous Fistula Access for Hemodialysis Use

An arteriovenous fistula (AVF) is the preferred vascular access for chronic hemodialysis, but high failure rates restrict its use. Optimizing patients' perioperative status and the surgical technique, among other methods for preventing primary AVF failure, continue to fall short in lowering failure rates in clinical practice. One of the predominant causes of AVF failure is neointimal hyperplasia (NIH), a process that results from the synergistic effects of inflammation, hypoxia, and hemodynamic shear stress on vascular tissue. Although several systemic therapies have aimed at suppressing NIH, none has shown a clear benefit towards this goal. Localized therapeutic approaches may improve rates of AVF maturation by providing direct structural and functional support to the maturating fistula, as well as by delivering higher doses of pharmacologic agents while avoiding the adverse effects associated with systemic administration of therapeutic agents. Novel materials-such as polymeric scaffolds and nanoparticles-have enabled the development of different perivascular therapies, such as supportive mechanical devices, targeted drug delivery, and cell-based therapeutics. In this review, we summarize various perivascular therapeutic approaches, available data on their effectiveness, and the outlook for localized therapies targeting NIH in the setting of AVF for hemodialysis use. Highlights: Most systemic therapies do not improve AVF patency outcomes; therefore, localized therapeutic approaches may be beneficial. Locally delivered drugs and medical devices may improve AVF patency outcomes by providing biological and mechanical support. Cell-based therapies have shown promise in suppressing NIH by delivering a more extensive array of bioactive substances in response to the biochemical changes in the AVF microenvironment.

1α,25-Dihydroxyvitamin D3 Encapsulated in Nanoparticles Prevents Venous Neointimal Hyperplasia and Stenosis in Porcine Arteriovenous Fistulas

BACKGROUND

Few therapies prevent venous neointimal hyperplasia (VNH) and venous stenosis (VS) formation in arteriovenous fistulas (AVF). Expression of the immediate early response gene X-1 (Iex-1), also known as Ier3, is associated with VNH and stenosis in murine AVFs. The study aimed to determine if local release of Ier3 long-acting inhibitor 1α,25(OH)₂D₃ from poly(lactic-co-glycolic acid) (PLGA) nanoparticles embedded in a thermosensitive Pluronic F127 hydrogel (1,25 NP) could affect VNH/VS formation in a large animal model.

METHODS

Immediately after AVF creation in a porcine model of renal failure, 1,25 NP or vehicle control was injected into the adventitia space of AVF outflow veins. Scanning electron microscopy and dynamic light scattering characterized drug and control nanoparticles. Animals were sacrificed 3 and 28 days later for gene expression, immunohistologic, magnetic resonance imaging and angiography, and ultrasound analyses. Whole transcriptome RNA sequencing with differential gene expression analysis was performed on outflow veins of AVF.

RESULTS

Encapsulation of 1α,25(OH)₂D₃ in PLGA nanoparticles formed nanoparticles of uniform size that were similar to nanoparticles without 1α,25(OH)₂D₃. The 1,25 NP-treated AVFs exhibited lower VNH/VS, Ier3 gene expression, and IER-3, MCP-1, CD68, HIF-1α, and VEGF-A immunostaining, fibrosis, and proliferation. Blood flow and lumen area increased significantly, whereas peak systolic velocity and wall shear stress decreased. Treatment increased Young's modulus and correlated with histologic assessment of fibrosis and with no evidence of vascular calcification. RNA sequencing analysis showed changes in the expression of genes associated with inflammatory, TGFβ1, and apoptotic pathways.

CONCLUSIONS

Local release of 1,25 NP improves AVF flow and hemodynamics, and reduces stenosis in association with reduction in inflammation, apoptosis, and fibrosis in a porcine model of arteriovenous fistula.

Adventitial delivery of nanoparticles encapsulated with 1α, 25-dihydroxyvitamin D3 attenuates restenosis in a murine angioplasty model

Percutaneous transluminal angioplasty (PTA) of stenotic arteriovenous fistulas (AVFs) is performed to maintain optimal function and patency. The one-year patency rate is 60% because of venous neointimal hyperplasia (VNH) and venous stenosis (VS) formation. Immediate early response gene X-1 (Iex-1) also known as Ier3 increases in response to wall shear stress (WSS), and can cause VNH/VS formation in murine AVF. In human stenotic samples from AVFs, we demonstrated increased gene expression of Ier3. We hypothesized that 1α, 25-dihydroxyvitamin D₃, an inhibitor of IER3 delivered as 1α, 25-dihydroxyvitamin D₃ encapsulated in poly lactic-co-glycolic acid (PLGA) nanoparticles loaded in Pluronic F127 hydrogel (1,25 NP) to the adventitia of the stenotic outflow vein after PTA would decrease VNH/VS formation by reducing Ier3 and chemokine (C–C motif) ligand 2 (Ccl2) expression. In our murine model of AVF stenosis treated with PTA, increased expression of Ier3 and Ccl2 was observed. Using this model, PTA was performed and 10-μL of 1,25 NP or control vehicle (PLGA in hydrogel) was administered by adventitial delivery. Animals were sacrificed at day 3 for unbiased whole genome transcriptomic analysis and at day 21 for immunohistochemical analysis. Doppler US was performed weekly after AVF creation. At day 3, significantly lower gene expression of Ier3 and Ccl2 was noted in 1,25 NP treated vessels. Twenty-one days after PTA, 1,25 NP treated vessels had increased lumen vessel area, with decreased neointima area/media area ratio and cell density compared to vehicle controls. There was a significant increase in apoptosis, with a reduction in CD68, F4/80, CD45, pro-inflammatory macrophages, fibroblasts, Picrosirius red, Masson’s trichrome, collagen IV, and proliferation accompanied with higher wall shear stress (WSS) and average peak velocity. IER3 staining was localized to CD68 and FSP-1 (+) cells. After 1,25 NP delivery, there was a decrease in the proliferation of α-SMA (+) and CD68 (+) cells with increase in the apoptosis of FSP-1 (+) and CD68 (+) cells compared to vehicle controls. RNA sequencing revealed a decrease in inflammatory and apoptosis pathways following 1,25 NP delivery. These data suggest that adventitial delivery of 1,25 NP reduces VNH and venous stenosis formation after PTA.

The role of Iex-1 in the pathogenesis of venous neointimal hyperplasia associated with hemodialysis arteriovenous fistula

Arteriovenous fistulas (AVFs) used for hemodialysis fail because of venous neointimal hyperplasia (VNH). There are 1,500,000 patients that have end stage renal disease worldwide and the majority requires hemodialysis. In the present study, the role of the intermediate early response gene X-1 (IEX-1), also known as IER-3 in the pathogenesis of VNH was evaluated. In human samples removed from failed AVF, there was a significant increase in IEX-1 expression localized to the adventitia. In Iex-1-/- mice and wild type (WT) controls, chronic kidney disease was induced and an AVF placed 28 days later by connecting the carotid artery to jugular vein. The outflow vein was removed three days following the creation of the AVF and gene expression analysis demonstrated a significant decrease in vascular endothelial growth factor-A (Vegf-A) and monocyte chemoattractant protein-1 (Mcp-1) gene expression in Iex-1-/- mice when compared to WT mice (P<0.05). At 28 days after AVF placement, histomorphometric and immune-histochemical analyses of the outflow vein demonstrated a significant decrease in neointimal hyperplasia with an increase in average lumen vessel area associated with a decrease in fibroblast, myofibroblast, and Ly6C staining. There was a decrease in proliferation (Ki-67) and an increase in the TUNEL staining in Iex-1 KO mice compared to WT. In addition, there was a decrease in Vegf-A, Mcp-1, and matrix metalloproteiniase-9 (Mmp-9) staining. Iex-1 expression was reduced in vivo and in vitro using nanoparticles coated with calcitriol, an inhibitor of Iex-1 that demonstrated that Iex-1 reduction results in decrease in Vegf-A. In aggregate, these results indicate that the absence of IEX-1 gene results in reduced VNH accompanied with a decrease in proliferation, reduced fibroblast, myofibroblast, and Ly6C staining accompanied with increased apoptosis mediated through a reduction in Vegf-A/Mcp-1 axis and Mmp-9. Adventitial delivery of nanoparticles coated with calcitriol reduced Iex-1 and VNH.

Detection of 1α,25-dihydroxyvitamin D-regulated miRNAs in zebrafish by whole transcriptome sequencing

The sterol hormone, 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃), regulates gene expression and messenger RNA (mRNA) concentrations in zebrafish in vivo. Since mRNA concentrations and translation are influenced by micro-RNAs (miRNAs), we examined the influence of 1α,25(OH)₂D₃ on miRNA expression in zebrafish in vivo with whole transcriptome RNA sequencing, searched for miRNA binding sites in 1α,25(OH)₂D₃-sensitive genes, and performed correlation analyses between 1α,25(OH)₂D₃-sensitive miRNAs and mRNAs. In vehicle- and 1α,25(OH)₂D₃-treated, 7-day postfertilization larvae, between 282 and 295 known precursor miRNAs were expressed, and in vehicle- and 1α,25(OH)₂D₃-treated fish, between 83 and 122 novel miRNAs were detected. Following 1α,25(OH)₂D₃ treatment, 31 precursor miRNAs were differentially expressed (p<0.05). The differentially expressed miRNAs are predicted to potentially alter mRNAs for metabolic enzymes, transcription factors, growth factors, and Jak-STAT signaling. We verified the role of a 1α,25(OH)₂D₃-sensitive miRNA, miR125b, by demonstrating alterations in the concentrations of the mRNA of a 1α,25(OH)₂D₃-regulated gene, Cyp24a1, following transfection of renal cells with a miR125b miRNA mimic. Changes in the Cyp24a1 mRNA concentration by the miR125b miRNA mimic were associated with changes in the protein for Cyp24a1. Our data show that 1α,25(OH)₂D₃ regulates miRNA in zebrafish larvae in vivo and could thereby influence vitamin D-sensitive mRNA concentrations.

Vitamin D responsive elements within the HLA-DRB1 promoter region in Sardinian multiple sclerosis associated alleles

Vitamin D response elements (VDREs) have been found in the promoter region of the MS-associated allele HLA-DRB1*15:01, suggesting that with low vitamin D availability VDREs are incapable of inducing *15:01 expression allowing in early life autoreactive T-cells to escape central thymic deletion. The Italian island of Sardinia exhibits a very high frequency of MS and high solar radiation exposure. We test the contribution of VDREs analysing the promoter region of the MS-associated DRB1 *04:05, *03:01, *13:01 and *15:01 and non-MS-associated *16:01, *01, *11, *07:01 alleles in a cohort of Sardinians (44 MS patients and 112 healthy subjects). Sequencing of the DRB1 promoter region revealed a homozygous canonical VDRE in all *15:01, *16:01, *11 and in 45/73 *03:01 and in heterozygous state in 28/73 *03:01 and all *01 alleles. A new mutated homozygous VDRE was found in all *13:03, *04:05 and *07:01 alleles. Functionality of mutated and canonical VDREs was assessed for its potential to modulate levels of DRB1 gene expression using an in vitro transactivation assay after stimulation with active vitamin D metabolite. Vitamin D failed to increase promoter activity of the *04:05 and *03:01 alleles carrying the new mutated VDRE, while the *16:01 and *03:01 alleles carrying the canonical VDRE sequence showed significantly increased transcriptional activity. The ability of VDR to bind the mutant VDRE in the DRB1 promoter was evaluated by EMSA. Efficient binding of VDR to the VDRE sequence found in the *16:01 and in the *15:01 allele reduced electrophoretic mobility when either an anti-VDR or an anti-RXR monoclonal antibody was added. Conversely, the Sardinian mutated VDRE sample showed very low affinity for the RXR/VDR heterodimer. These data seem to exclude a role of VDREs in the promoter region of the DRB1 gene in susceptibility to MS carried by DRB1* alleles in Sardinian patients.

Nuclear hormone receptors enable macrophages and dendritic cells to sense their lipid environment and shape their immune response

A key issue in the immune system is to generate specific cell types, often with opposing activities. The mechanisms of differentiation and subtype specification of immune cells such as macrophages and dendritic cells are critical to understand the regulatory principles and logic of the immune system. In addition to cytokines and pathogens, it is increasingly appreciated that lipid signaling also has a key role in differentiation and subtype specification. In this review we explore how intracellular lipid signaling via a set of transcription factors regulates cellular differentiation, subtype specification, and immune as well as metabolic homeostasis. We introduce macrophages and dendritic cells and then we focus on a group of transcription factors, nuclear receptors, which regulate gene expression upon receiving lipid signals. The receptors we cover are the ones with a recognized physiological function in these cell types and ones which heterodimerize with the retinoid X receptor. These are as follows: the receptor for a metabolite of vitamin A, retinoic acid: retinoic acid receptor (RAR), the vitamin D receptor (VDR), the fatty acid receptor: peroxisome proliferator-activated receptor γ (PPARγ), the oxysterol receptor liver X receptor (LXR), and their obligate heterodimeric partner, the retinoid X receptor (RXR). We discuss how they can get activated and how ligand is generated and eliminated in these cell types. We also explore how activation of a particular target gene contributes to biological functions and how the regulation of individual target genes adds up to the coordination of gene networks. It appears that RXR heterodimeric nuclear receptors provide these cells with a coordinated and interrelated network of transcriptional regulators for interpreting the lipid milieu and the metabolic changes to bring about gene expression changes leading to subtype and functional specification. We also show that these networks are implicated in various immune diseases and are amenable to therapeutic exploitation.

Role of the immediate early response 3 (IER3) gene in cellular stress response, inflammation and tumorigenesis

The expression of the early response gene immediate early response 3 (IER3), formerly known as IEX-1, is induced by a great variety of stimuli, such as growth factors, cytokines, ionizing radiation, viral infection and other types of cellular stress. Being of a rather unique protein structure not sharing any similarity to other vertebrate proteins, IER3 plays a complex and to some extent contradictory role in cell cycle control and apoptosis. As outlined in this review, these effects of IER3 relate to an interference with certain signalling pathways, in particular NF-κB, MAPK/ERK and PI3K/Akt. In addition to numerous functional data relying on cell culture based studies, transgenic and knock-out mouse models revealed an involvement of IER3 expression in immune functions and in the physiology of the cardiovascular system. Deficiency of IER3 expression in mice results in an aberrant immune regulation and enhanced inflammation, in an alteration of blood pressure control and hypertension or in an impaired genomic stability. A number of patient related studies revealed an involvement of IER3 in tumorigenesis in a cell-type dependent but not yet understood manner. Future studies should establish the potential of IER3 as a new predictive marker and as a molecular target in human diseases such as cancer, inflammatory diseases or hypertension.

1,25-dihydroxyvitamin D3 is an autonomous regulator of the transcriptional changes leading to a tolerogenic dendritic cell phenotype

Activation of vitamin D receptor (VDR) by 1,25-dihydroxyvitamin D(3) (1,25-vitD) reprograms dendritic cells (DC) to become tolerogenic. Previous studies suggested that 1,25-vitD could inhibit the changes brought about by differentiation and maturation of DCs. Underpinning the described phenotypic and functional alterations, there must be 1,25-vitD-coordinated transcriptional events. However, this transcriptional program has not been systematically investigated, particularly not in a developmental context. Hence, it has not been explored how 1,25-vitD-regulated genes, particularly the ones bringing about the tolerogenic phenotype, are connected to differentiation. We conducted global gene expression analysis followed by comprehensive quantitative PCR validation to clarify the interrelationship between 1,25-vitD and differentiation-driven gene expression patterns in developing human monocyte-derived and blood myeloid DCs. In this study we show that 1,25-vitD regulates a large set of genes that are not affected by differentiation. Interestingly, several genes, impacted both by the ligand and by differentiation, appear to be regulated by 1,25-vitD independently of the developmental context. We have also characterized the kinetics of generation of 1,25-vitD by using three early and robustly regulated genes, the chemokine CCL22, the inhibitory receptors CD300LF and CYP24A1. We found that monocyte-derived DCs are able to turn on 1,25-vitD sensitive genes in early phases of differentiation if the precursor is present. Our data collectively suggest that exogenous or endogenously generated 1,25-vitD regulates a large set of its targets autonomously and not via inhibition of differentiation and maturation, leading to the previously characterized tolerogenic state.

Immediate early gene IEX-1 induces astrocytic differentiation of U87-MG human glioma cells

The immediate early response gene IEX-1 is involved in the regulation of apoptosis and cell growth. In order to increase the apoptotic sensitivity to chemotherapeutic drugs and gamma-ray, we attempted to establish U87-MG human glioma cell line expressing IEX-1. Unexpectedly, however, transfection of IEX-1 into U87-MG glioma cells resulted in morphological changes to astrocytic phenotype and increase in glial differentiation marker proteins, S-100 and glial fibrillary acidic protein (GFAP). Glial cell differentiation was used to examine in rat C6 glioma cell line, since this cell line express astrocytic phenotypes by increase in intracellular cAMP concentration. Stimulation of human U87-MG glioma cells by membrane-permeable dibutyryl cAMP (dbcAMP) not only elicited their morphological changes but also induced expression of IEX-1 as well as S-100 and GFAP. H89, an inhibitor of protein kinase A (PKA), blocked dbcAMP-induced morphological changes of U87-MG cells and expression of IEX-1. In contrast, morphological changes and expression of S-100 and GFAP induced by IEX-1 were not affected by H89. Morphological changes induced by dbcAMP were totally abolished by functional disruption of IEX-1 expression by anti-sense RNA. These results indicate that IEX-1 plays an important role in astrocytic differentiation of human glioma cells and that IEX-1 functions at downstream of PKA.

1,25-dihydroxyvitamin D3 transcriptionally represses p45Skp2 expression via the Sp1 sites in human prostate cancer cells

Upregulation of p27Kip1 protein in 1,25-dihydroxyvitamin D3-treated cancer cells is mediated via enhancement of gene transcription and reduction of protein degradation. 1,25-dihydroxyvitamin D3 inhibits the expression of p45Skp2, the F-box protein which is implicated in p27Kip1 degradation, to reduce turnover of p27Kip1 protein. In this study, we elucidate the underlying mechanism by which 1,25-dihydroxyvitamin D3 inhibits p45Skp2 in human LNCaP prostate cancer cells. Western blot and RT-PCR analysis suggest that 1,25-dihydroxyvitamin D3 suppresses p45Skp2 via transcriptional repression. Promoter activity assays indicate that 1,25-dihydroxyvitamin D3 directly inhibits p45Skp2 promoter activity. Deletion analysis shows that 1,25-dihydroxyvitamin D3 response element is localized at -447/-291 bp region from the translational start site of the p45Skp2 promoter. Mutation analysis suggests that two Sp1 sites localized at -386/-380 and -309/-294 bp region are required for transcriptional repression. Chromatin immunoprecipitation (CHIP) assay demonstrates that VDR indirectly binds to these Sp1 sites in vivo and this binding is increased after 1,25-dihydroxyvitamin D3 treatment. Re-CHIP assay suggests that VDR and Sp1 form a complex to bind to the Sp1 sites. DNA affinity precipitation assay (DAPA) shows that histone deacetylase 1 (HDAC1) is recruited to the Sp1 sites after 1,25-dihydroxyvitamin D3 stimulation. Re-CHIP assay verifies that binding of Sp1 and HDAC1 to p45Skp2 promoter is enhanced after 1,25-dihydroxyvitamin D3 treatment. HDAC inhibitor trichostatin A (TSA) reverses the inhibition of p45Skp2 promoter activity by 1,25-dihydroxyvitamin D3. Collectively, our results suggest that 1,25-dihydroxyvitamin D3 induces the formation of VDR/Sp1 complex and acts via a Sp1- and HDAC1-depedent pathway to inhibit p45Skp2 transcription.

Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

IEX-1 (immediate early response gene X-1) is a stress-inducible gene. Its overexpression can suppress or enhance apoptosis dependent on the nature of stress, yet the polypeptide does not possess any of the functional domains that are homologous to those present in well characterized effectors or inhibitors of apoptosis. This study using sequence-targeting mutagenesis reveals a transmembrane-like integrated region of the protein to be critical for both pro-apoptotic and anti-apoptotic functions. Substitution of the key hydrophobic residues with hydrophilic ones within this region impairs the capacity IEX-1 to positively and negatively regulate apoptosis. Mutations at N-linked glycosylation and phosphorylation sites or truncation of the C terminus of IEX-1 also abrogated its potential to promote cell survival. However, distinguished from the transmembrane-like domain, these mutants preserved pro-apoptotic activity of IEX-1 fully. On the contrary, mutation of nuclear localization sequence, despite its importance in apoptosis, did not impede IEX-1-mediated cell survival. Strikingly, all the mutants that lose their anti-apoptotic ability are unable to prevent acute increases in production of intracellular reactive oxygen species (ROS) at the initial onset of apoptosis, whereas those mutants that can sustain anti-death function also control acute ROS production as sufficiently as wild-type IEX-1. These findings suggest a critical role of IEX-1 in regulation of intracellular ROS homeostasis, providing new insight into the mechanism underlying IEX-1-mediated cell survival.

Elevated blood pressure and cardiac hypertrophy after ablation of the gly96/IEX-1 gene

gly96/IEX 1 is a growth- and apoptosis-regulating, immediate early gene that is widely expressed in epithelial and vascular tissues. In vascular tissues, expression of the gene is induced by mechanical stretch, and overexpression of the gene prevents injury-induced vascular smooth muscle hypertrophy and neointimal hyperplasia. We now show that deletion of the gly96/IEX-1 gene in mice is associated with development of elevated blood pressure, cardiac hypertrophy, and diminished fractional shortening of the left ventricle. Systolic blood pressure in conscious male gly96/IEX-1-/- mice is 20-25 mmHg higher than in gly96/IEX-1+/+ mice. Serum and/or urine concentrations of sodium, potassium, creatinine, angiotensin II, corticosterone, aldosterone, epinephrine, norepinephrine, prostaglandin E2, thromboxane B2, prostaglandin-6-keto-1alpha, nitrites and nitrates, cAMP, and cGMP are normal in gly96/IEX-1-/- mice. Alterations in dietary sodium intake do not alter blood pressure in gly96/IEX-1-/- mice. Aortic mRNAs for endothelial nitric oxide synthase, guanylate cyclase-alpha, and cGMP kinase-1 are increased in gly96/IEX-1-/- mice. Treatment with Nomega-nitro-L-arginine methyl ester or L-arginine does not alter blood pressure in gly96/IEX-1-/- mice. Gly96/IEX-1-/- mice respond to infused sodium nitroprusside with decrements in blood pressure similar to those seen in wild-type littermate mice. In contrast to gly96/IEX-1 transgenic mice that have abnormalities in immune function, gly96/IEX-1-/- mice have normal lymphoid tissue architecture and a normal complement of T and B cells in lymphoid tissues. Ablation of the gly96/IEX-1 gene results in hypertension and cardiac hypertrophy, suggesting a novel role for this gene in cardiovascular physiology.

Immediate Early Gene X1 (IEX-1) Is Organized in Subnuclear Structures and Partially Co-localizes with Promyelocytic Leukemia Protein in HeLa Cells

Immediate early gene X1 (IEX-1) represents a stress response gene involved in growth control and modulation of apoptosis. Here, we report a detailed analysis of IEX-1 with respect to its intracellular localization. By means of confocal laser scanning microscopy, a green fluorescent protein-IEX-1 fusion protein transfected into HeLa cells, as well as endogenous IEX-1, could be detected in distinct subnuclear structures. This particular subnuclear localization of IEX-1 was not observed with a green fluorescent protein-IEX-1 fusion protein lacking a putative nuclear localization sequence, along with a decreased effect on apoptosis. Double immunofluorescence staining revealed a partial co-localization of endogenous promyelocytic leukemia protein (PML) and IEX-1 in these subnuclear structures. Nuclear localization of IEX-1 is also enhanced upon treatment of cells with leptomycin B, an inhibitor of the nuclear exporter CRM1. These observations indicate that IEX-1 is specifically shuttled to and from the nucleus. Overexpression experiments using PML isoforms III and IV revealed distinct intranuclear interaction of IEX-1 and PML. Coprecipitation experiments showed physical interaction between IEX-1 and PML. The close structural relation of IEX-1-containing nuclear subdomains and PML nuclear bodies suggests a function of IEX-1 related to the multiple functions of these unique subnuclear regions, particularly during stress response and growth control.

Immediate early gene X-1 interacts with proteins that modulate apoptosis

Immediate early gene X-1 (IEX-1) modulates apoptosis, cellular growth, mechanical strain-induced cardiac hypertrophy, and vascular intimal hyperplasia. To determine how IEX-1 alters apoptosis, we performed yeast two-hybrid studies using IEX-1 as the "bait" protein, and examined interactions between IEX-1 and proteins expressed by a human kidney cDNA expression library. We found that IEX-1 interacts with several proteins of which at least four are known to play a role in the regulation of apoptosis: (1) calcium-modulating cyclophilin ligand; (2) tumor necrosis factor-related apoptosis-inducing ligand (tumor necrosis factor superfamily, member 10); (3) ML-1 myeloid cell leukemia gene encoded protein; and (4) BAT3, a gene present in the major histo-compatibility complex. Our data suggest that IEX-1 may regulate apoptosis by directly interacting with various proteins involved in the control of apoptotic pathways.

The expression of immediate early gene X-1 (IEX-1) is differentially induced by retinoic acids in NB4 and KG1 cells: possible implication in the distinct phenotype of retinoic acid-responsive and -resistant leukemic cells

In a cell-type- and stimulus-dependent fashion, the early response gene immediate early gene X-1 (IEX-1) is involved in growth control and modulation of apoptosis. The present study demonstrates that, in the two acute promyelocytic leukemia (APL) cell lines NB4 and KG1, exhibiting distinct responsiveness to retinoic acids (RAs), IEX-1 expression is rapidly (30-60 min) induced by all-trans- or cis-RA and independently of other signal transduction mediators, such as TNFalpha, NF-kappaB or MAP kinases. In NB4 cells (expressing PML-RARalpha), this increase is transient and completely reversible, along with a cell cycle arrest, ongoing differentiation and lower sensitivity to anti-cancer-drug-induced apoptosis. In contrast, the RA-induced IEX-1 expression in KG1 cells (expressing PLZF-RARalpha) persists over days, along with continued cell cycle progression and increased apoptotic sensitivity. Furthermore, two functional RA-response elements in the IEX-1 promoter were identified by gel shift and luciferase reporter gene assays. IEX-1 might be a rather unique transcriptional target of the two X-RARalpha fusion receptors exhibiting distinct responsiveness to RAs. Following a different time course of direct transcriptional induction by PML-RARalpha and PLZF-RARalpha in NB4 and KG1 cells, respectively, IEX-1 expression may be involved in the modified actions of these receptors and the distinct phenotypes of APL cells.

Modulation of X-ray-induced apoptosis in human keratinocytes (HaCaT) by 1,25-dihydroxyvitamin D3

Possible effects of 1,25-dihydoxyvitamin D3 (vitamin D) on ionizing radiation-induced cell damage have been unknown until now. The task of the present study was to analyze, in a human keratinocyte cell line (HaCaT), the effects of a preincubation with vitamin D on the X-ray-induced mRNA expression of different genes related to apoptosis (gene array). The first results show that ionizing radiation leads to a down-regulation of various apoptosis-relevant genes in HaCaT cells pretreated with vitamin D. Therefore it can be speculated that vitamin D could prove to be a promising radioprotective substance.

The early response gene IEX-1 attenuates NF-kappaB activation in 293 cells, a possible counter-regulatory process leading to enhanced cell death

The early response gene IEX-1 is involved in the regulation of cellular growth and survival, and its expression is related to stress-, growth- and death-inducing signals. Addressing the role of IEX-1 in the promotion of apoptosis, we investigated the effect of IEX-1 on nuclear factor-kappaB (NF-kappaB) activation. Stably transfected HEK-293 cells conditionally overexpressing IEX-1 exhibit decreased levels of NF-kappaB activity, either basal or TNFalpha induced, as shown by gel-shift and luciferase reporter gene assay. Furthermore, activated p65 accumulated in the nuclei of 293 cells to a lower degree, if IEX-1 expression was increased. This inhibited NF-kappaB activation was preceded by an altered turnover of IkappaBalpha and phospho-IkappaBalpha. In addition, IEX-1 expression also inhibited the activity of the 26S-proteasome, as shown by a fluorometric proteasome assay. Conversely, disruption of IEX-1 expression in 293 cells by stable transfection with specific anti-IEX-1 hammerhead ribozymes increased NF-kappaB activity, and accelerated the degradation of IkappaBalpha. Along with these opposite effects of IEX-1 expression and IEX-1 disruption on NF-kappaB activation, the sensitivity of 293 cells towards various apoptotic stimuli also changed. In contrast to ribozyme-transduced 293 cells that were significantly less sensitive to apoptosis, this sensitivity was enhanced if IEX-1 expression was increased. Our data suggest that IEX-1 - itself an NF-kappaB target gene - inhibits the activation of this transcription factor, and hereby may counteract the antiapoptotic potential of NF-kappaB.

A novel vitamin D-regulated immediate-early gene, IEX-1, alters cellular growth and apoptosis

1alpha,25-Dihydroxyvitamin D3 (1alpha,25(OH)2D3) inhibits the expression of an immediate-early gene, IEX-1, which is involved in the regulation of cellular growth and apoptosis in a variety of cells. 1alpha,25(OH)2D3 alters the subcellular localization of IEX-1 by causing an efflux of IEX-1 from the nucleus, and the sterol decreases the expression of IEX-1 messenger RNA in cells via a novel DR3 repeat-type DNA response element.