An Sp1-binding silencer element is a critical negative regulator of the megakaryocyte-specific alphaIIb gene

Role and mechanism of miR-335-5p in the pathogenesis and treatment of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder of unknown etiology that occurs in women of reproductive age. Despite being considered to affect up to one-fifth of women in this cohort, the condition lacks generally accepted diagnostic biomarkers and options for targeted therapy. Hereby, we analyzed the diagnostic, therapeutic, and functional potential of a recently discovered miR-335-5p that was observed to be reduced in the follicular fluid (FF) of PCOS patients as compared with healthy women. We found miR-335-5p to be significantly decreased in the serum and FF samples of PCOS patients (n = 40) vs healthy women (n = 30), as well as in primary human granulosa cells (hGCs), and in 3 different hormonally induced PCOS-like murine models vs. wild-type (WT) mice. The level of circulating miR-335-5p was found to significantly correlate with the impaired endocrine and clinical features associated with PCOS in human patients. Ovarian intrabursal injection of the miR-335-5p antagomir in WT mice ovaries induced a PCOS-like reproductive phenotype. Treatment with the miR-335-5p agomir rescued the dihydrotestosterone-induced PCOS-phenotype in mice, thereby providing a functional link between miR-335-5p and PCOS. We identified SP1 as a miR-335-5p target gene by using the dual-luciferase reporter assay. Both the luciferase reporter assay and chromatin immunoprecipitation assay showed that SP1 bound to the promoter region of human CYP19A1 and inhibited its transcription. miR-335-5p increased the production of estradiol via the SP1/CYP19A1 axis in hGCs, thereby suggesting its mechanistic pathway of action. In conclusion, these results provide evidence that miR-335-5p may function as a mediator in the etiopathogenesis of PCOS, as well as has the potential as both a novel diagnostic biomarker and therapeutic target for PCOS.

Effect of CREB1 promoter non-CpG island methylation on its differential expression profile on sheep ovaries associated with prolificacy

This study aimed to investigate the effect of different methylated regions of cyclic-AMP response element binding protein 1 (CREB1) by comparing the high prolificacy (HP) group and low prolificacy (LP) group, which was detected in our previous study. The expression level of CREB1 mRNA in the ovaries of the HP group was higher than in the LP group (P <  0.05). The differential methylated region (DMR) had 4 methylated CG dinucleotides(CGs): -1546, -1544, -1494 and -1464. The DNA methylation levels of -1546 CGs and -1464 CGs were significantly higher in the HP group than in the LP group (P <  0.05). The activity from -1296 to +26 (without DMR) was significantly higher than the activity from -1598 to +26 (with DMR) (P <  0.05). The result of 5-aza-2'-deoxycytidine treatment indicated that the inhibition DNA methylation of DMR reduced the transcription of CREB1. The bioinformatics predictive analysis were found that the -1546 CG site was located in the CCAAT/enhancer-binding protein alpha (CEBPA) binding site and the -1464 CG site was located in the Sp1 binding site. Finally, this study revealed the relationship between the methylation of non-CpG sites of the promoter and transcription of CREB1. This study will provide a theoretical basis of the Hu sheep ovaries associated with DNA methylation.

Elevated histone H3 acetylation and loss of the Sp1-HDAC1 complex de-repress the GM2-synthase gene in renal cell carcinoma

GM2-synthase produces sialic acid-containing glycosphingolipids called gangliosides, and its mRNA overexpression and the gangliosides it generates are linked to tumor progression, migration, and suppression of tumor-specific host immune responses. However, the mechanism underlying GM2-synthase de-repression in renal cell carcinoma (RCC) is poorly understood. Here, we demonstrate that higher GM2-synthase mRNA expression levels in various cancer cells and in human RCC tumors correlate with higher histone acetylation levels (H3K9, H3K14, or both) at region +38/+187 relative to the transcription start site (TSS) of the GM2-synthase gene than in normal kidney epithelial (NKE) cells or healthy adjacent tissues. An increase in GM2-synthase mRNA expression in cells treated with a histone deacetylase (HDAC) inhibitor was accompanied by increased histone acetylation levels at this promoter region. DNA methylation around the TSS was absent in both RCC cell lines and NKE cells. Of note, both the transcription factor Sp1 and corepressor HDAC1 associated with the +38/+187 region when the GM2-synthase gene was repressed in NKE and tumor-adjacent tissues, indicating plausible site-specific repressive roles of HDAC1 and Sp1 in GM2-synthase mRNA expression. Site-directed mutagenesis of the Sp1-binding site within the +38/+187 region relieved repressed luciferase activity of this region by limiting HDAC1 recruitment. Moreover, Sp1 or HDAC1 knock down increased GM2-synthase transcription, and butyrate-mediated activation of GM2-synthase mRNA expression in SK-RC-45 cells was accompanied by Sp1 and HDAC1 loss from the +38/+187 region. Taken together, we have identified an epigenetic mechanism for the de-repression of the GM2-synthase gene in RCC.

Silencing of Transcription Factor Sp1 Promotes SN1 Transporter Regulation by Ammonia in Mouse Cortical Astrocytes

The involvement of the astrocytic SN1 (SNAT3) transporter in ammonia-induced l-glutamine retention was recently documented in mouse-cultured astrocytes. Here we investigated the involvement of specificity protein 1 (Sp1) transcription factor in SN1 regulation in ammonium chloride (“ammonia”)-treated astrocytes. Sp1 expression and its cellular localization were determined using real-time qPCR, Western blot, and confocal microscopy. Sp1 binding to Snat3 promoter was analyzed by chromatin immunoprecipitation. The role of Sp1 in SN1 expression and SN1-mediated [³H]glutamine uptake in ammonia-treated astrocytes was verified using siRNA and mithramycin A. The involvement of protein kinase C (PKC) isoforms in Sp1 level/phosphorylation status was verified using siRNA technology. Sp1 translocation to the nuclei and its enhanced binding to the Snat3 promoter, along with Sp1 dependence of system N-mediated [³H]glutamine uptake, were observed in astrocytes upon ammonia exposure. Ammonia decreased the level of phosphorylated Sp1, and the effect was reinforced by long-term incubation with PKC modulator, phorbol 12-myristate 13-acetate, which is a treatment likely to dephosphorylate Sp1. Furthermore, silencing of the PKCδ isoform appears to enhance the ammonia effect on the Sp1 level. Collectively, the results demonstrate the regulatory role of Sp1 in regulation of SN1 expression and activity in ammonia-treated astrocytes and implicate altered Sp1 phosphorylation status in this capacity.

Repression of Human T-lymphotropic virus type 1 Long Terminal Repeat sense transcription by Sp1 recruitment to novel Sp1 binding sites

Human T-lymphotropic Virus type 1 (HTLV-1) infection is characterized by viral latency in the majority of infected cells and by the absence of viremia. These features are thought to be due to the repression of viral sense transcription in vivo. Here, our in silico analysis of the HTLV-1 Long Terminal Repeat (LTR) promoter nucleotide sequence revealed, in addition to the four Sp1 binding sites previously identified, the presence of two additional potential Sp1 sites within the R region. We demonstrated that the Sp1 and Sp3 transcription factors bound in vitro to these two sites and compared the binding affinity for Sp1 of all six different HTLV-1 Sp1 sites. By chromatin immunoprecipitation experiments, we showed Sp1 recruitment in vivo to the newly identified Sp1 sites. We demonstrated in the nucleosomal context of an episomal reporter vector that the Sp1 sites interfered with both the sense and antisense LTR promoter activities. Interestingly, the Sp1 sites exhibited together a repressor effect on the LTR sense transcriptional activity but had no effect on the LTR antisense activity. Thus, our results demonstrate the presence of two new functional Sp1 binding sites in the HTLV-1 LTR, which act as negative cis-regulatory elements of sense viral transcription.

A position effect on TRPS1 is associated with Ambras syndrome in humans and the Koala phenotype in mice

Ambras syndrome (AS) is a rare form of congenital hypertrichosis with excessive hair on the shoulders, face and ears. Cytogenetic studies have previously implicated an association with rearrangements of chromosome 8. Here we define an 11.5 Mb candidate interval for AS on chromosome 8q based on cytogenetic breakpoints in three patients. TRPS1, a gene within this interval, was deleted in a patient with an 8q23 chromosomal rearrangement, while its expression was significantly downregulated in another patient with an inversion breakpoint 7.3 Mb downstream of TRPS1. Here, we describe the first potential long-range position effect on the expression of TRPS1. To gain insight into the mechanisms by which Trps1 affects the hair follicle, we performed a detailed analysis of the hair abnormalities in Koa mice, a mouse model of hypertrichosis. We found that the proximal breakpoint of the Koa inversion is located 791 kb upstream of Trps1. Quantitative real-time polymerase chain reaction, in situ hybridization and immunofluorescence analysis revealed that Trps1 expression levels are reduced in Koa mutant mice at the sites of pathology for the phenotype. We determined that the Koa inversion creates a new Sp1 binding site and translocates additional Sp1 binding sites within a highly conserved stretch spanning the proximal breakpoint, providing a potential mechanism for the position effect. Collectively, these results describe a position effect that downregulates TRPS1 expression as the probable cause of hypertrichosis in AS in humans and the Koa phenotype in mice.

Keep your fingers off my DNA: protein-protein interactions mediated by C2H2 zinc finger domains

Cys2-His2 (C2H2) zinc finger domains (ZFs) were originally identified as DNA-binding domains, and uncharacterized domains are typically assumed to function in DNA binding. However, a growing body of evidence suggests an important and widespread role for these domains in protein binding. There are even examples of zinc fingers that support both DNA and protein interactions, which can be found in well-known DNA-binding proteins such as Sp1, Zif268, and Ying Yang 1 (YY1). C2H2 protein-protein interactions (PPIs) are proving to be more abundant than previously appreciated, more plastic than their DNA-binding counterparts, and more variable and complex in their interactions surfaces. Here we review the current knowledge of over 100 C2H2 zinc finger-mediated PPIs, focusing on what is known about the binding surface, contributions of individual fingers to the interaction, and function. An accurate understanding of zinc finger biology will likely require greater insights into the potential protein interaction capabilities of C2H2 ZFs.

A novel variable number of tandem repeats (VNTR) polymorphism containing Sp1 binding elements in the promoter of XRCC5 is a risk factor for human bladder cancer

X-ray repair cross-complementing 5 (XRCC5) is a gene involved in repair of DNA double-strand breaks. Abnormal expression of the XRCC5 protein is associated with genomic instability and an increased incidence of cancers. In our study, a polymorphism with a variable number of tandem repeats (21-bp repeat elements at position -201 to -160 relative to the initiation of transcription) in the promoter of XRCC5 was identified. As determined with gel-shift and super-shift assays, the binding affinity of the transcription factor Sp1 to the allele with two 21-bp repeats was greater than that for the allele with one 21-bp repeat. As established with a reporter assay, plasmids containing zero or one repeat element had higher transcriptional activities than plasmids containing two repeat elements. Furthermore, fewer tandem repeats in the promoter of XRCC5 was associated with enhanced levels of the XRCC5 protein in bladder cancer patients. Although, in a case-control study, the different genotypes were not associated with the risk of bladder cancer, individuals not carrying the two tandem repeats allele had an increased risk of bladder cancer compared with those carrying the allele with two repeats. These results indicated that, at least in a population in southeastern China, this polymorphism in the promoter of XRCC5 could regulate the expression of XRCC5 and thereby contribute to susceptibility to bladder cancer.

Hydroxyurea and interleukin-6 synergistically reactivate HIV-1 replication in a latently infected promonocytic cell line via SP1/SP3 transcription factors

The existence of viral latency limits the success of highly active antiretroviral therapy. With the therapeutic intention of reactivating latent virus to induce a cure, in this study we assessed the impact of cell synchronizers on HIV gene activation in latently infected U1 cells and investigated the molecular mechanisms responsible for such effect. Latently infected U1 cells were treated with 10 drugs including hydroxyurea (HU) and HIV-1 replication monitored using a p24 antigen capture assay. We found that HU was able to induce HIV-1 replication by 5-fold. HU has been used in the clinical treatment of HIV-1-infected patients in combination with didanosine; therefore, we investigated the impact of HU on HIV-1 activation in the presence of the proinflammatory cytokines, interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha). IL-6 or TNF-alpha alone induced HIV replication by 18- and approximately 500-fold, respectively. Of interest, in the presence of HU, IL-6-mediated HIV-1 activation was enhanced by >90-fold, whereas TNF-alpha-mediated activation was inhibited by >30%. A reporter gene assay showed that HU and IL-6 synergized to activate HIV promoter activity via the Sp1 binding site. Electrophoretic mobility shift and supershift assays revealed increased binding of the Sp1 and Sp3 transcription factors to this region. Western blot analysis showed that HU and IL-6 co-stimulation resulted in increased levels of Sp1 and Sp3 proteins. In contrast, treatment with HU plus TNF-alpha down-regulated the expression of NF-kappaB. These findings suggest that Sp1/Sp3 is involved in controlling the HU/IL-6-induced reactivation of HIV-1 in latently infected cells.

The C/A(-18) polymorphism in the surfactant protein B gene influences transcription and protein levels of surfactant protein B

Surfactant protein B (SP-B) is an essential component of surfactant that promotes adsorption and spreading of surfactant phospholipids and stabilizes the phospholipid monolayer. SP-B is essential for respiratory function in newborn humans and mice; adult mice with levels of SP-B below 25% of wild-type develop fatal respiratory distress syndrome. A potential regulatory function of the C/A(-18) single nucleotide polymorphism (SNP) in the promoter of the SP-B gene was examined. Transcriptional analysis and ELISA on bronchoalveolar lavage fluid revealed that the presence of the C allele correlated with more SP-B promoter activity and protein. There was approximately threefold difference in amounts of SP-B in bronchoalveolar lavage fluid from CA(-18) and AA(-18) individuals. By EMSA, Sp1 bound more tightly to the C allele sequence than to the A allele sequence, perhaps accounting for the differences in transcription. Genotyping of a normal volunteer population showed approximately 31% of the population were AA homozygotes, suggesting that these individuals produce less SP-B. Differences in amounts of SP-B resulting from the promoter SNP could affect the clinical presentation of pulmonary disease.

A novel T-77C polymorphism in DNA repair gene XRCC1 contributes to diminished promoter activity and increased risk of non-small cell lung cancer

X-ray repair cross-complementing 1 (XRCC1) plays a key role in DNA base excision repair and cells lacking its activity are hypersensitive to DNA damage. Recently, we reported a SNP (rs3213245, -77T>C) in the XRCC1 gene 5' untranslated region (UTR) was significantly associated with the risk of developing esophageal squamous-cell carcinoma. Computer analysis predicted that this SNP was in the core of Sp1-binding motif, which suggested its functional significance. Gel shift and super shift assays confirmed that -77T>C polymorphic site in the XRCC1 promoter was within the Sp1-binding motif and the T>C substitution greatly enhanced the binding affinity of Sp1 to this region. Luciferase assays indicated that the Sp1-high-affinity C-allelic XRCC1 promoter was associated with a reduced transcriptional activity. The association between -77T>C and three other amino-acid substitution-causing polymorphisms in XRCC1 and risk of lung cancer was examined in 1024 patients and 1118 controls and the results showed that only the -77T>C polymorphism was significantly associated with an increased risk of developing lung cancer. Multivariate logistic regression analysis found that an increased risk of lung cancer was associated with the variant XRCC1 -77 genotypes (TC and CC) compared with the TT genotype (OR=1.46, 95% CI=1.18-1.82; P=0.001) and the increased risk was more pronounced in smokers (OR=1.63, 95% CI=1.20-2.21) than in non-smokers (OR=1.28, 95% CI=0.94-1.76). Taken together, these results showed that the functional SNP -77T>C in XRCC1 5'UTR was associated with cancer development owing to the decreased transcriptional activity of C-allele-containing promoter with higher affinity to Sp1 binding.

Transcriptional Activity of Sp1 Is Regulated by Molecular Interactions between the Zinc Finger DNA Binding Domain and the Inhibitory Domain with Corepressors, and This Interaction Is Modulated by MEK

Sp1 activates the transcription of many cellular and viral genes with the GC-box in either the proximal promoter or the enhancer. Sp1 is composed of several functional domains, such as the inhibitory domain (ID), two serine/threonine-rich domains, two glutamine-rich domains, three C2H2-type zinc finger DNA binding domains (ZFDBD), and a C-terminal D domain. The ZDDBD is the most highly conserved domain among the Sp-family transcription factors and plays a critical role in GC-box recognition. In this study, we investigated the protein-protein interactions occurring at the Sp1ZFDBD and the Sp1ID, and the molecular mechanisms controlling the interaction. Our results found that Sp1ZFDBD and Sp1ID repressed transcription once they were targeted to the proximal promoter of the pGal4 UAS reporter fusion gene system, suggesting molecular interaction with the repressor molecules. Indeed, mammalian two-hybrid assays, GST fusion protein pull-down assays, and co-immunoprecipitation assays showed that Sp1ZFDBD and Sp1ID are able to interact with corepressor proteins such as SMRT, NcoR, and BCoR. The molecular interactions appear to be regulated by MAP kinase/Erk kinase kinase (MEK). The molecular interactions between Sp1ID and the corepressor might explain the role of Sp1 as a repressor under certain circumstances. The siRNA-induced degradation of the corepressors resulted in an up-regulation of Sp1-dependent transcription. The cellular context of the corepressors and the regulation of molecular interaction between corepressors and Sp1ZFDBD or Sp1ID might be important in controlling Sp1 activity.

Arsenic suppresses gene expression in promyelocytic leukemia cells partly through Sp1 oxidation

The mechanism by which arsenic dramatically affects gene expression remains poorly understood. Here we report that prolonged exposure of acute promyelocytic leukemia NB4 cells to low levels of arsenic trioxide increased the expression of a set of genes responsible for reactive oxygen species (ROS) production. We hypothesize that arsenic-induced ROS in turn contribute partially to altered gene expression. To identify genes responsive to arsenic-induced ROS, we used microarray gene expression analysis and identified genes that responded to arsenic and hydrogen peroxide but whose response to arsenic was reversed by an ROS scavenger, N-acetyl-L-cysteine. We found that 26% of the genes significantly responsive to arsenic might have been directly altered by ROS. We further explored the mechanisms by which ROS affects gene regulation and found that the Sp1 transcription factor was oxidized by arsenic treatment, with a corresponding decrease in its in situ binding on the promoters of 3 genes, hTERT, C17, and c-Myc, whose expressions were significantly suppressed. We conclude that ROS contributed partly to arsenic-mediated gene regulation and that Sp1 oxidation contributed to gene suppression by arsenic-induced ROS.

Characterization of the human P-type 6-phosphofructo-1-kinase gene promoter in neural cell lines

In humans three isoforms of 6-phosphofructo-1-kinase (PFK) exist. Among them platelet-type PFK (PFKP) is highly abundant in the brain. With its distinct allosteric properties PFKP is regarded to be the key enzyme for the regulation of glycolysis in this organ. We cloned 1.7 kb of the 5' upstream promoter of the human PFKP gene and analyzed the promoter activity by deletion and mutation analysis using a luciferase reporter. The transcription start point was determined at 48 bp upstream of the start codon. In deletion studies the region -65 to +48 turned out to be sufficient for promoter activity while fragment -153 to +48 showed the highest promoter activity. Sequence analysis of the region from -153 to +48 revealed a stretch of eight adjacent putative transcription factor binding sites, seven of which are Sp-family specific sites. Sp1 and Sp3 were shown to bind to most if not all of them. Additionally, an NF-Y binding site was identified. Results of deletion and mutation analysis suggest that all of these transcription factors contribute positively to promoter activity. The methylation status of the promoter region was analyzed in different neural tumor cell lines and compared with that in human leukocytes and muscle.

Vascular smooth muscle cell-specific regulation of cyclin-dependent kinase inhibitor p21WAF1/Cip1 transcription by Sp1 is mediated via distinctcis-acting positive and negative regulatory elements in the proximal p21WAF1/Cip1 promoter

Smooth muscle cells (SMC) play a central role in common vascular pathologies such as atherosclerosis and restenosis. Understanding the molecular regulation of SMC proliferation at a transcriptional level may provide important clues for the targeted control of vascular hyperplasia. We recently reported the capacity of the transcription factor Sp1 to down-regulate p21(WAF1/Cip1) production thereby reducing p21(WAF1/Cip1)-cyclin D1-Cdk4 complex formation and inhibiting vascular SMC proliferation (Kavurma and Khachigian [2003] J. Biol. Chem. 278, 32537-32543). We have now localized the Sp1-response elements in the p21(WAF1/Cip1) promoter responsible for p21(WAF1/Cip1) repression in WKY12-22 SMCs. The proximal region of the p21(WAF1/Cip1) promoter contains five distinct Sp1-binding elements that we have termed A, B, C, D, and E. Electrophoretic mobility shift analysis revealed that SMC nuclear Sp1 interacts with all five Sp1-binding sites, and each of these sites is critical for Sp1 repression of the p21(WAF1/Cip1) promoter, since mutation in any one element ablates repression, and in some cases results in activation. In contrast, only elements C, D, and E are bound by Sp1 in endothelial cells. Sp1 overexpression activates the p21(WAF1/Cip1) promoter in this cell type. Furthermore, mutation in any of these five elements is not sufficient to prevent activation of the p21(WAF1/Cip1) promoter by Sp1 in endothelial cells. Surprisingly, double mutations of elements C and E facilitates superactivation by Sp1 in both cell types, whereas triple mutations of C, D, and E inactivate the promoter. These findings demonstrate cell type-specific regulation of p21(WAF1/Cip1) transcription by Sp1 via distinct cis-acting positive and negative regulatory elements in the proximal p21(WAF1/Cip1) promoter.

Ets-dependent regulation of target gene expression during megakaryopoiesis

Megakaryopoiesis is the process by which hematopoietic stem cells in the bone marrow differentiate into mature megakaryocytes. The expression of megakaryocytic genes during megakaryopoiesis is controlled by specific transcription factors. Fli-1 and GATA-1 transcription factors are required for development of megakaryocytes and promoter analysis has defined in vitro functional binding sites for these factors in several megakaryocytic genes, including GPIIb, GPIX, and C-MPL. Herein, we utilize chromatin immunoprecipitation to examine the presence of Ets-1, Fli-1, and GATA-1 on these promoters in vivo. Fli-1 and Ets-1 occupy the promoters of GPIIb, GPIX, and C-MPL genes in both Meg-01 and CMK11-5 cells. Whereas GPIIb is expressed in both Meg-01 and CMK11-5 cells, GPIX and C-MPL are only expressed in the more differentiated CMK11-5 cells. Thus, in vivo occupancy by an Ets factor is not sufficient to promote transcription of some megakaryocytic genes. GATA-1 and Fli-1 are both expressed in CMK11-5 cells and co-occupy the GPIX and C-MPL promoters. Transcription of all three megakaryocytic genes is correlated with the presence of acetylated histone H3 and phosphorylated RNA polymerase II on their promoters. We also show that exogenous expression of GATA-1 in Meg-01 cells leads to the expression of endogenous c-mpl and gpIX mRNA. Whereas GPIIb, GPIX, and C-MPL are direct target genes for Fli-1, both Fli-1 and GATA-1 are required for formation of an active transcriptional complex on the C-MPL and GPIX promoters in vivo. In contrast, GPIIb expression appears to be independent of GATA-1 in Meg-01 cells.

Gelsolin gene silencing involving unusual hypersensitivities to dimethylsulfate and KMnO4 in vivo footprinting on its promoter region

We previously reported that gelsolin gene expression is reduced in various tumors. In an effort to gain further insights into the mechanism of gelsolin downregulation in tumors, we examined the in vivo properties of the gelsolin promoter in urinary bladder cancer cell lines. Neither mutation nor hypermethylation was responsible for gene silencing at the promoter. After exposure to trichostatin A (TSA), a histone deacetylase inhibitor, gelsolin promoter activity was markedly enhanced in the cancer cells, not in cells derived from normal tissue. Chromatin immunoprecipitation assays revealed that both histones H3 and H4 were hypoacetylated in the promoter region of the cancer cells, and the accumulation of acetylated histones was detected by TSA treatment. In vivo footprinting analysis revealed the presence of dimethylsulfate (DMS) hypersensitive site in the untranslated region around nucleotide--35 only in the cancer cells but not in cells derived from normal tissue, and analysis of KMnO4 reactive nucleotides showed that the stem loop structure could be formed in vivo of the cancer cells. This novel stem loop structure may play a part in regulating the transcription of the gelsolin gene in the cancer cells. These results suggest that nucleosome accessibility through histone deacetylation and structural changes (DMS hypersensitivity and stem loop structure) in the promoter region form the basis of the mechanism leading to the silencing of gelsolin gene in human bladder cancer.

Gene regulation by Sp1 and Sp3

The Sp family of transcription factors is united by a particular combination of three conserved Cys2His2 zinc fingers that form the sequence-specific DNA-binding domain. Within the Sp family of transcription factors, Sp1 and Sp3 are ubiquitously expressed in mammalian cells. They can bind and act through GC boxes to regulate gene expression of multiple target genes. Although Sp1 and Sp3 have similar structures and high homology in their DNA binding domains, in vitro and in vivo studies reveal that these transcription factors have strikingly different functions. Sp1 and Sp3 are able to enhance or repress promoter activity. Regulation of the transcriptional activity of Sp1 and Sp3 occurs largely at the post-translational level. In this review, we focus on the roles of Sp1 and Sp3 in the regulation of gene expression.Key words: Sp1, Sp3, gene regulation, sub-cellular localization.

An evolutionary and molecular analysis of Bmp2 expression

The coding regions of many metazoan genes are highly similar. For example, homologs to the key developmental factor bone morphogenetic protein (BMP) 2 have been cloned by sequence identity from arthropods, mollusks, cnidarians, and nematodes. Wide conservation of protein sequences suggests that differential gene expression explains many of the vast morphological differences between species. To test the hypothesis that the regulatory mechanisms controlling this evolutionarily ancient and critical gene are conserved, we compared sequences flanking Bmp2 genes of several species. We identified numerous conserved noncoding sequences including some retained because the fish lineage separated 450 million years ago. We tested the function of some of these sequences in the F9 cell model system of Bmp2 expression. We demonstrated that both mouse and primate Bmp2 promoters drive a reporter gene in an expression pattern resembling that of the endogenous transcript in F9 cells. A conserved Sp1 site contributes to the retinoic acid responsiveness of the Bmp2 promoter, which lacks a classical retinoic acid response element. We have also discovered a sequence downstream of the stop codon whose conservation between humans, rodents, deer, chickens, frogs, and fish is striking. A fragment containing this region influences reporter gene expression in F9 cells. The conserved region contains elements that may mediate the half-life of the Bmp2 transcript. Together, our molecular and evolutionary analysis has identified new regulatory elements controlling Bmp2 expression.

Identification and characterization of a novel progesterone receptor-binding element in the mouse prostaglandin E receptor subtype EP2 gene

BACKGROUND

Gene expression of prostaglandin E receptor EP2 is induced in the luminal epithelium of the mouse uterus during peri-implantation period (day-5 of pseudopregnancy), suggesting the involvement of progesterone and its receptor (PR) in this expression. However it remains unclear whether PR affects EP2 gene expression through its binding.

RESULTS

We investigated transcriptional regulation of EP2 gene expression with reporter gene analysis using HeLa cells with or without expression of the PR. The 5'-flanking region (-3260 to -27, upstream of the translation initiation site) exhibited progesterone-induced promoter activation and basal promoter activity in the presence of PR. Using successive deletion analysis, we determined the six regulatory regions in the EP2 gene. Three regions were found to be involved in progesterone-induced promoter activation, whereas the other three regions were involved in basal promoter activity in the presence of PR. We identified a novel PR-binding sequence, 5'-G(G/A)CCGGA-3', in the two basal promoter regions and Sp1- and Sp3-binding in the other basal promoter region.

CONCLUSIONS

We identified a novel PR-binding sequence, which may be involved in the regulation of basal promoter activity in the EP2 gene.

Dual regulation of ets-activated gene expression by SP1

The human folate receptor (hFR) type gamma gene is driven by a TATA-less promoter that uses a canonical Sp1 element for basal transcription. Using nuclear extract from 293 (human embryonic) cells, we mapped a second (non-canonical) Sp1 element to which Sp1 bound with a comparable affinity and which overlaps a functional ets binding site (EBS). Mutagenesis experiments revealed that the binding of ets to the EBS activates the promoter synergistically with Sp1 bound at the downstream site; however, binding of Sp1 to the EBS does not contribute to promoter activity. A further increase in Sp1 by inducible expression in recombinant 293 cells resulted in a small but significant decrease in the hFR-gamma promoter activity, but the decrease was abolished when the EBS was deleted from the promoter. In 293 cells, which do not express hFR-gamma, the Sp1 level was relatively high whereas in the hFR-gamma-positive HL60 leukemia cells, the Sp1 level was low and the EBS predominantly bound an ets protein. To account for the above observations, we propose a model in which when the Sp1 level is low, ets out competes Sp1 for binding to the EBS and synergistically enhances the hFR-gamma promoter activity by interacting with Sp1 bound at the canonical site whereas at higher levels, Sp1 represses the promoter by competitively inhibiting the binding of ets. As a partial extension of this model to the regulation of other ets activated genes, we show that Sp1 can predictably bind to a variety of ets elements including those responsive to Ets1 and Spi.1/Pu.1. A dual concentration-dependent action of Sp1 as an activator or a repressor offers a potential mechanism contributing to tissue-specific regulation of ets-dependent genes by Sp1.

Cloning and analysis of the thrombopoietin-induced megakaryocyte-specific glycoprotein VI promoter and its regulation by GATA-1, Fli-1, and Sp1

The exposure of collagen fibers at sites of vascular injury results in the adherence of platelets and their subsequent activation. The platelet collagen receptor glycoprotein (GP)(1) VI plays a crucial role in platelet activation and thrombus formation and decreased levels or defective GPVI may lead to excessive bleeding. In addition, elevated levels of collagen receptors may predispose individuals to coronary heart disease or strokes. GPVI expression is restricted to platelets and their precursor cell, the megakaryocyte. In this study we investigate the regulation of GPVI expression and show that thrombopoietin induces its expression in the megakaryocytic cell line UT-7/TPO. A 5'-region flanking the transcription start point of the GPVI gene was cloned (-694 to +29) and we report that this putative GPVI promoter bestows megakaryocye-specific expression. Deletion analyses and site-directed mutagenesis identified Sp1(227), GATA(177), and Ets(48) sites as essential for GPVI expression. We show that transcription factors GATA-1, Fli-1, and Sp1 can bind to and activate this promoter. Finally, GPVI mRNA was detected only in megakaryocytic cell lines expressing both Fli-1 and GATA-1, and we show that overexpression of Fli-1 in a stable cell line (which expresses endogenous GATA-1 and Sp1) results in expression of the endogenous GPVI gene.

Identification of distal regulatory regions in the human alpha IIb gene locus necessary for consistent, high-level megakaryocyte expression

The alphaIIb/beta3-integrin receptor is present at high levels only in megakaryocytes and platelets. Its presence on platelets is critical for hemostasis. The tissue-specific nature of this receptor's expression is secondary to the restricted expression of alphaIIb, and studies of the alphaIIb proximal promoter have served as a model of a megakaryocyte-specific promoter. We have examined the alphaIIb gene locus for distal regulatory elements. Sequence comparison between the human (h) and murine (m) alphaIIb loci revealed high levels of conservation at intergenic regions both 5' and 3' to the alphaIIb gene. Additionally, deoxyribonuclease (DNase) I sensitivity mapping defined tissue-specific hypersensitive (HS) sites that coincide, in part, with these conserved regions. Transgenic mice containing various lengths of the h(alpha)IIb gene locus, which included or excluded the various conserved/HS regions, demonstrated that the proximal promoter was sufficient for tissue specificity, but that a region 2.5 to 7.1 kb upstream of the h(alpha)IIb gene was necessary for consistent expression. Another region 2.2 to 7.4 kb downstream of the gene enhanced expression 1000-fold and led to levels of h(alpha)IIb mRNA that were about 30% of the native m(alpha)IIb mRNA level. These constructs also resulted in detectable h(alpha)IIb/m(beta)3 on the platelet surface. This work not only confirms the importance of the proximal promoter of the alphaIIb gene for tissue specificity, but also characterizes the distal organization of the alphaIIb gene locus and provides an initial localization of 2 important regulatory regions needed for the expression of the alphaIIb gene at high levels during megakaryopoiesis.

Sp1 and Sp3 recruit histone deacetylase to repress transcription of human telomerase reverse transcriptase (hTERT) promoter in normal human somatic cells

Activation of telomerase is crucial for cells to gain immortality. In human cells, telomerase activity is tightly regulated by the expression of its catalytic subunit, human telomerase reverse transcriptase (hTERT). In most normal human somatic cells, hTERT is not expressed, and its suppression acts as an important gatekeeper against tumorigenesis. Here we describe the systematic analyses of hTERT promoter to understand the transcriptional repression mechanism of the hTERT gene in normal human somatic cells. Through the serial deletion analysis of hTERT promoter in normal human fibroblasts, we identified a critical repressive element on the hTERT promoter. The repressive element formed DNA-protein complexes with Sp1 and Sp3 in nuclear extracts. Using formaldehyde cross-linked chromatin immunoprecipitation analysis, we found that Sp1 and Sp3 were associated with the endogenously repressed hTERT promoter in human fibroblasts. Furthermore, Sp1 and Sp3 interacted with histone deacetylase (HDAC) in these cells. Overexpression of dominant-negative mutants of Sp1 and Sp3, which contained mainly the HDAC2-binding domain, relieved the HDAC-mediated repression of the hTERT promoter. Taken together, these results suggest that Sp1 and Sp3 associate with the hTERT promoter, recruiting HDAC for the localized deacetylation of nucleosomal histones and transcriptional silencing of the hTERT gene in normal human somatic cells.

The transcription factors Sp1 and Sp3 are required for human angiotensin II type 1 receptor gene expression in H295-R cells

The peptide hormone angiotensin II regulates a variety of physiological responses which are mediated by its interaction with high affinity G protein-coupled receptors localized on the surface of target cells. Our previous studies have demonstrated that a 145 bp sequence within the promoter region was required for basal level expression of the human angiotensin II type 1 receptor (hAT(1)R) gene. In the present study, deletional analysis of the hAT(1)R promoter localized the major regulatory sequence to two overlapping GC boxes harbored within the -105 to -85 bp region relative to the transcription start site in H295-R cells. Electrophoretic mobility shift assays (EMSAs) using a double-stranded (ds) oligonucleotide corresponding to this region and H295-R cell nuclear extract resulted in five specific DNA-protein complexes. EMSAs performed with competitive ds-oligonucleotides which harbored the consensus binding site for Sp1 prevented the formation of the DNA-protein complexes. Supershift EMSAs also demonstrated that Sp1 and Sp3 could bind to the GC boxes present within the -105 to -85 bp region of the hAT(1)R promoter. Transactivation experiments utilizing Drosophila SL2 cells, which lack endogenous Sp family transcription factors, demonstrated that Sp1 and Sp3 activated the hAT(1)R promoter and that maximal activation was only achieved when both GC boxes were present. Taken together, these findings suggest that Sp1 and Sp3 are necessary for the expression of the hAT(1)R gene in H295-R cells.

Characterization of the rat GRIK5 kainate receptor subunit gene promoter and its intragenic regions involved in neural cell specificity

The GRIK5 (glutamate receptor ionotropic kainate-5) gene encodes the kainate-preferring glutamate receptor subunit KA2. The GRIK5 promoter is TATA-less and GC-rich, with multiple consensus initiator sequences. Transgenic mouse lines carrying 4 kilobases of the GRIK5 5'-flanking sequence showed lacZ reporter expression predominantly in the nervous system. Reporter assays in central glial (CG-4) and non-neural cells indicated that a 1200-base pair (bp) 5'-flanking region could sustain neural cell-specific promoter activity. Transcriptional activity was associated with the formation of a transcription factor IID-containing complex on an initiator sequence located 1100 bp upstream of the first intron. In transfection studies, deletion of exonic sequences downstream of the promoter resulted in reporter gene activity that was no longer neural cell-specific. When placed downstream of the GRIK5 promoter, a 77-bp sequence from the deleted fragment completely silenced reporter expression in NIH3T3 fibroblasts while attenuating activity in CG-4 cells. Analysis of the 77-bp sequence revealed a functional SP1-binding site and a sequence resembling a neuron-restrictive silencer element. The latter sequence, however, did not display cell-specific binding of REST-like proteins. Our studies thus provide evidence for intragenic control of GRIK5 promoter activity and suggest that elements contributing to tissue-specific expression are contained within the first exon.

Sp1 acts as a repressor of the human adenine nucleotide translocase-2 (ANT2) promoter

The human adenine nucleotide translocator-2 promoter is activated by adjacent Sp1 activation elements centered at nucleotides -79 and -68 (Abox and Bbox, respectively), and is repressed by Sp1 bound to a GC element (Cbox) that lies adjacent to transcription start. Here, we address the mechanism of this unique Sp1-mediated repression using transfected Drosophila SL2 and mammalian cell lines. We show that repression is not due to steric interference with assembly of the transcription machinery, as Sp1 bound to the Cbox can, under certain conditions, activate the promoter. Furthermore, ectopic expression of Sp1 deletion mutants in SL2 cells demonstrates that both the Sp1-mediated repression and activation require the D transactivation domain of Sp1 bound to the Cbox. In addition, repression of ABbox-mediated activation is eliminated by separating the Abox and Bbox. Thus, for Cbox-bound Sp1 to repress, Sp1 must be precisely positioned at the region of the ABboxes. Together, these data suggest that the D transactivation domain mediates interactions by Sp1 complexes on separate GC elements that results in repression of the activating Sp1 species.

Human sex hormone-binding globulin promoter activity is influenced by a (TAAAA)n repeat element within an Alu sequence

Sex hormone-binding globulin (SHBG) is the major sex steroid-binding protein in human plasma and is produced by the liver. Plasma SHBG levels vary considerably between individuals and are influenced by hormonal, metabolic, and nutritional factors. We have now found that a (TAAAA)(n) pentanucleotide repeat, located within an alu sequence at the 5' boundary of the human SHBG promoter, influences its transcriptional activity in association with downstream elements, including an SP1-binding site. Furthermore, SHBG alleles within the general population contain at least 6-10 TAAAA repeats, and the transcriptional activity of a human SHBG promoter-luciferase reporter construct containing 6 TAAAA repeats was significantly lower than for similar reporter constructs containing 7-10 TAAAA repeats when tested in human HepG2 hepatoblastoma cells. This difference in transcriptional activity reflected the preferential binding of a 46-kDa liver-enriched nuclear factor to an oligonucleotide containing 6 rather than 7-10 TAAAA repeats. Thus, a (TAAAA)(n) element within the human SHBG promoter influences transcriptional activity in HepG2 cells and may contribute to differences in plasma SHBG levels between individuals.

Characterization of Inherited Differences in Transcription of the Human Integrin alpha 2 Gene

Inherited, single-base substitutions are found at only two positions, C(-)52T and C(-)92G, within the proximal 5'-regulatory region (within -1096 to +48) of the human integrin alpha(2) gene. We recently reported that the T(-)52 substitution results in decreased binding of transcription factor Sp1 to adjacent binding sites, decreased transcription of the alpha(2) gene, and reduced densities of platelet alpha(2)beta(1). In this study, we identify an additional Sp1-binding site at position -107 to -99 and show that the adjacent dimorphic sequence C(-)92G also influences the rate of gene transcription. In the erythroleukemia cell line Dami, transfected promoter-luciferase constructs bearing the G(-)92 sequence exhibit roughly a 3-fold decrease in activity relative to the C(-)92 constructs. In transfected CHRF-288-11 megakaryocytic cells, the corresponding activity decreases by 5-fold. DNase I footprinting of the promoter region with Dami nuclear extracts showed a protected segment at -107 to -99 that can be deprotected by coincubation with molar excess of a consensus Sp1 oligonucleotide. Gel mobility shift assays and supershift assays with specific antibodies indicate that Sp1 binds to this region of the alpha(2) gene promoter. Mutation of the Sp1 binding element within -107 to -99 in constructs containing either C(-)92 or G(-)92 abolishes basal promoter activity and eliminates the binding of Sp1. The G(-)92 sequence has a gene frequency of 0.15 in a typical Caucasian population, and the presence of this allele correlates with reduced densities of platelet alpha(2)beta(1). The combined substitution G(-)92/T(-)52 has an additive influence on gene transcription, resulting in an 8-fold decrease in transfected Dami cells or a 20-fold decrease in transfected CHRF-288-11 cells. In summary, the natural dimorphism C(-)92G within the proximal 5'-regulatory region of the human integrin alpha(2) gene contributes to the regulation of integrin alpha(2)beta(1) expression on megakaryocytes and blood platelets and must thereby modulate collagen-related platelet function in vivo.

Selection and identification of proteins bound to DNA triple-helical structures by combination of 2D-electrophoresis and MALDI-TOF mass spectrometry

Identification of proteins binding specifically to peculiar nucleic acid structures can lead to comprehension of their role in vivo and contribute to the discovery of structure-related gene regulation. This work was devoted to establishing a reliable procedure to select proteins on the basis of their interaction with a nucleic acid probe chosen to fold into a given structure. 2D-electrophoresis and mass spectrometry were combined for protein identification. We applied this procedure to select and identify triplex-binding activities in HeLa nuclear extracts. To achieve this, we used a panel of deoxyribonucleic probes adopting intramolecular triple-helices, varying in their primary sequence, structure or triple-helix motif. A limited number of spots was reproducibly revealed by South-western blotting. Spots of interest were localised among a complex population of (35)S-labelled proteins according to their (32)P-specific emission. Position of the same spots was extrapolated on a preparative gel coloured with Coomassie blue, allowing excision and purification of the corresponding proteins. The material was subjected to mass spectrometry upon trypsin digestion and MALDI-TOF peptide fingerprinting was used for research in databases: five of them were identified and found to belong to the hnRNP family (K, L, A2/B1, E1 and I). The identities of several of them were confirmed by comparing western and South-western blots on the same membrane using specific antibodies. The recognition specificity of most of these proteins is large, according to previous reports and our own experiments. It includes pyrimidine-rich DNA sequences in different contexts: single strand to a small extent, triplex and possibly other higher-order structures.

Negative regulatory role of Sp1 in metal responsive element-mediated transcriptional activation

Transcription of mammalian metallothionein (MT) genes is activated by heavy metals via multiple copies of a cis-acting DNA element, the metal-responsive element (MRE). Our previous studies have shown that certain MREs of the human MT-IIA gene (MREb, MREc, MREd, and MREf) are less active than the others (MREa, MREe, and MREg). Gel shift analysis of HeLa cell nuclear proteins revealed that whereas the active MREs strongly bind the transcription factor MTF-1 essential for metal regulation, the less active MREs bind another distinct protein, MREb-BF. This protein recognizes the GC-rich region of MREb rather than the MRE core required for MTF-1 binding. All the MREs recognized by MREb-BF contain the CGCCC and/or CACCC motif, suggesting that the MREb-BF.MRE complex contains Sp1 or related proteins. Supershift analysis using antibodies against Sp1 family proteins as well as gel shift analysis using the recombinant Sp1 demonstrated that Sp1 represents the majority of MREb-BF activity. An MREb mutant with reduced affinity to Sp1 mediated zinc-inducible transcription much more actively than the wild-type MREb. Furthermore, when placed in the native promoter, this mutant MREb raised the overall promoter activity. These results strongly suggest that Sp1 acts as a negative regulator of transcription mediated by specific MREs.

Sp1 and Sp3 function as key regulators of leukotriene C(4) synthase gene expression in the monocyte-like cell line, THP-1

The goal of this study was to examine the mechanisms of leukotriene C(4) (LTC(4)) synthase gene expression in mononuclear phagocytes. Transfection of the monocyte-like cell line THP-1 with LTC(4) synthase promoter-reporter constructs demonstrated that the first 1.3 kb of the promoter mediated a 21.1-fold increase in reporter activity. Deletion analysis revealed that the region between -92 and -23 bp, which contains a signal protein (Sp)1 consensus site at -42 to -37 bp, mediated an 11.5-fold increase in reporter activity. Using a probe from -56 to -17 bp, electrophoretic mobility shift assays (EMSAs) demonstrated that Sp1 and THP-1 and HeLa nuclear extracts bind to this region. Binding was eliminated by mutation of the Sp1 consensus site. Supershift EMSAs using anti-Sp1 and anti-Sp3 antibodies demonstrated that these Sp family members bind to the region. Transfection of the Sp-deficient Drosophila SL-2 cell line with a construct containing the -92 to -23 bp promoter region and Sp expression vectors revealed that Sp1 and Sp3 transactivate gene transcription. We conclude that the Sp1 site is a necessary element for LTC(4) synthase gene transcription. Sp1 and Sp3 function through this site to positively regulate transcription. Thus, we provide evidence that the LTC(4) synthase gene is transcriptionally regulated in mononuclear phagocytes.

Activation of the human aldehyde oxidase (hAOX1) promoter by tandem cooperative Sp1/Sp3 binding sites: identification of complex architecture in the hAOX upstream DNA that includes a proximal promoter, distal activation sites, and a silencer element

Aldehyde oxidase (AOX) is a member of the molybdenum iron-sulfur flavoproteins and is of interest for its role in clinical drug metabolism and as a source of reactive oxygen species (ROS) potentially involved in human pathology. The ROS derived from AOX contribute significantly to alcohol-induced hepatotoxicity. Therefore, expression of AOX could determine both the susceptibility of certain cells and tissues to clinically important pharmacologic agents and the levels of ROS produced under certain pathophysiological conditions. Although some pharmacologic agents regulate AOX enzyme activity, very little is known about the activation or regulation of the human AOX gene (hAOX). In the present study, we sought to identify features in the upstream DNA of hAOX that could confer regulation of the gene, to locate and characterize the basal promoter apparatus activating hAOX, and to identify transcription factors that could mediate activation or regulation. We transfected promoter fusion constructs into epithelial cells from the lung and the mammary gland that express AOX in cell culture. The hAOX gene was found to possess a structurally complex region in the upstream DNA that contained sequences for a proximal promoter, enhancer sites, and silencer elements. In addition, we identified an essential role for the transcription factors Sp1 and Sp3 in the proximal promoter. Unexpectedly, hAOX was activated in lung and mammary epithelial cells by indistinguishable mechanisms. These observations reveal a potentially complex mode of hAOX gene expression in epithelial cells that is dependent on Spl and Sp3 transcription factors.

New functional promoter polymorphism, CETP/-629, in cholesteryl ester transfer protein (CETP) gene related to CETP mass and high density lipoprotein cholesterol levels: role of Sp1/Sp3 in transcriptional regulation

A new polymorphism located at position -629 (CETP/-629A/C) in the promoter of the cholesteryl ester transfer protein (CETP) gene is described. The -629A allele was associated with lower CETP mass (P<0. 0001) and higher high density lipoprotein cholesterol (P<0.001) than the C allele in a sample of 536 control subjects from the ECTIM study. Transfection studies in HepG2 cells with a luciferase expression vector incorporating a 777-bp fragment of the CETP promoter and containing either A or C at position -629 showed significantly lower luciferase activity with the promoter fragment of the A allele (-25%, P<0.05). By gel-shift assay, DNA-protein interactions were evaluated in nuclear extracts of HepG2 cells with the use of 2 probes (A or C probe) composed of 20 bp of the promoter sequence surrounding the polymorphic site. Two specific complexes of distinct migration rate were identified with the A and the C probe. Competition with an excess of oligonucleotide containing the Sp1 consensus binding site showed that a protein(s) of the Sp transcription factor family was implicated in complex formation with the A probe but not with the C probe. Incubation with specific antibodies indicated that Sp1 and Sp3 bound specifically to the A probe. We introduced mutations in the -629-Sp1 binding site to test its functionality and to define the characteristics of transcription factor binding. We showed, by gel-shift assay, that no nuclear proteins bound to the mutated sequence. Transient transfection of HepG2 cells revealed that the expression of the mutated fragment was significantly increased compared with that of the A promoter fragment (25%, P<0.05). The mutated fragment displayed the same activity as that of the C promoter. These results indicate that Sp1 and/or Sp3 repress CETP promoter activity, whereas nuclear factors binding the C allele are without effect on promoter expression.

Characterization of hematopoietic lineage-specific gene expression by ES cell in vitro differentiation induction system

The continuous generation of mature blood cells from hematopoietic progenitor cells requires a highly complex series of molecular events. To examine lineage-specific gene expression during the differentiation process, we developed a novel method combiningLacZ reporter gene analysis with in vitro hematopoietic differentiation induction from mouse embryonic stem cells. For a model system using this method, we chose the erythroid and megakaryocytic differentiation pathways. Although erythroid and megakaryocytic cells possess distinct functional and morphologic features, these 2 lineages originate from bipotential erythro-megakaryocytic progenitors and share common lineage-restricted transcription factors. A portion of the 5′ flanking region of the human glycoprotein IIb (IIb) integrin gene extending from base −598 to base +33 was examined in detail. As reported previously, this region is sufficient for megakaryocyte-specific gene expression. However, previous reports that used human erythro-megakaryocytic cell lines suggested that one or more negative regulatory regions were necessary for megakaryocyte-specific gene expression. Our data clearly showed that an approximately 200-base enhancer region extending from −598 to −400 was sufficient for megakaryocyte-specific gene expression. This experimental system has advantages over those using erythro-megakaryocytic cell lines because it recapitulates normal hematopoietic cell development and differentiation. Furthermore, this system is more efficient than transgenic analysis and can easily examine gene expression with null mutations of specific genes.