Characterization and functional dissection of the galectin-1 gene promoter

Galectins in Early Pregnancy and Pregnancy-Associated Pathologies

Galectins are a family of conserved soluble proteins defined by an affinity for β-galactoside structures present on various glycoconjugates. Over the past few decades, galectins have been recognized as important factors for successful implantation and maintenance of pregnancy. An increasing number of studies have demonstrated their involvement in trophoblast cell function and placental development. In addition, several lines of evidence suggest their important roles in feto-maternal immune tolerance regulation and angiogenesis. Changed or dysregulated galectin expression is also described in pregnancy-related disorders. Although the data regarding galectins' clinical relevance are still at an early stage, evidence suggests that some galectin family members are promising candidates for better understanding pregnancy-related pathologies, as well as predicting biomarkers. In this review, we aim to summarize current knowledge of galectins in early pregnancy as well as in pregnancy-related pathologies.

Hypoxia Induces Galectin-1 Expression Via Autoinduction of Placental Growth Factor in Retinal Pigment Epithelium Cells

Purpose

Galectin-1/LGALS1, a β-galactoside-binding protein, contributes to angiogenesis and fibrosis in various ocular diseases. Hypoxia-dependent and -independent pathways upregulate galectin-1/LGALS1 expression in Müller glial cells. Here, we present novel findings on the galectin-1/LGALS1 regulatory system in human retinal pigment epithelium (RPE) cells, the major cellular participant in the pathogenesis of neovascular age-related macular degeneration (nAMD).

Methods

Human RPE cells were used to evaluate changes in gene and protein expression with real-time quantitative PCR and immunoblot analyses, respectively. The promoter and enhancer regions of LGALS1 were analyzed by reporter assay and chromatin immunoprecipitation. Immunofluorescence analysis of nAMD patient specimens was used to confirm the in vitro findings.

Results

Hypoxia induced galectin-1/LGALS1 expression via binding of hypoxia-inducible factor 1α (HIF-1α) to hypoxia-responsive elements in the LGALS1 promoter region. Blockade of vascular endothelial growth factor receptor 1 (VEGFR1) partially decreased hypoxia-induced galectin-1/LGALS1 expression. Among several VEGFR1 ligands induced by hypoxia, placental growth factor (PlGF)/PGF alone upregulated galectin-1/LGALS1 expression via phosphorylation of activator protein 1 (AP-1) subunits following AKT and p38 mitogen-activated protein kinase (MAPK) activation. An AP-1 site in the LGALS1 enhancer region was required for PlGF-induced galectin-1/LGALS1 expression in RPE cells. PlGF application upregulated PGF expression via extracellular signal-regulated kinase 1 and 2, AKT, and p38 MAPK pathways. nAMD patient specimens demonstrated co-localization of galectin-1 with HIF-1α, PlGF, and VEGFR1 in RPE cells.

Conclusions

Our present findings implicate the significance of hypoxia as a key inducer of galectin-1/LGALS1 in RPE cells and the autoinduction of hypoxia-induced PlGF as a vicious cycle amplifying the pathogenesis of nAMD.

Pressure regulated basis for gene transcription by delta-cell micro-compliance modeled in silico: Biphenyl, bisphenol and small molecule ligand models of cell contraction-expansion

Molecular diameter, lipophilicity and hydrophilicity exclusion affinity limits exist for small molecule carrier-mediated diffusion or transport through channel pores or interaction with the cell surface glycocalyx. The molecular structure lipophilicity limit for non-specific carrier-mediated transmembrane diffusion through polarity-selective transport channels of the cell membrane is L_{external structure} ∙ H_{polar group}^-1 of ≥ 1.07. The cell membrane channel pore size is > 0.752 and < 0.758 nm based on a 3-D ellipsoid model (biphenyl), and within the molecular diameter size range 0.744 and 0.762 nm based on a 2-D elliptical model (alkanol). The adjusted van der Waals diameter (vdWD, adj; nm) for the subset of halogenated vapors is predictive of the required MAC for anesthetic potency at an initial (-) Δ C_micro effect. The molecular structure L ∙ H_{polar group}^-1 for Neu5Ac is 0.080, and the L ∙ H_{polar group}^-1 interval range for the cell surface glycocalyx hydrophilicity barrier interaction is 0.101 (Saxitoxin, Stx; L_{internal structure} ∙ H_{polar group}^-1) - 0.092 (m-xylenediamine, L_{external structure} · H_{polar group}). Differential predictive effective pressure mapping of gene activation or repression reveals that p-dioxin exposure results in activation of AhR-Erβ (Arnt)/Nrf-2, Pparδ, Errγ (LxRα), Dio3 (Dio2) and Trα limbs, and due to high affinity Dio2 and Dio3 (OH-TriCDD, L_ext · H^-1: 1.91–4.31) exothermy-antagonism (Δ contraction) with high affinity T₄/rT₃-TRα-mediated agonism (Δ expansion). co-planar PCB metabolite exposure (L_ext · H^-1: 1.95–3.91) results in activation of AhR (Erα/β)/Nrf2, Rev-Erbβ, Errα, Dio3 (Dio2) and Trα limbs with a Δ C_micro contraction of 0.89 and Δ C_micro expansion of 1.05 as compared to p-dioxin. co-, ortho-planar PCB metabolite exposure results in activation of Car/PxR, Pparα (Srebf1,—Lxrβ), Arnt (AhR-Erβ), AR, Dio1 (Dio2) and Trβ limbs with a Δ C_micro contraction of 0.73 and Δ C_micro expansion of 1.18 (as compared to p-dioxin). Bisphenol A exposure (L_{ext struct} ∙ H^-1: 1.08–1.12, BPA–BPE, Errγ; BPAF, L_{ext struct} ∙ H^-1: 1.23, CM Erα, β) results in increased duration at P_eff for Timm8b (P_eff 0.247) transcription and in indirect activation of the AhR/Nrf-2 hybrid pathway with decreased duration at P_eff 0.200 (Nrf1) and increased duration at P_eff 0.257 (Dffa). The Bpa/Bpaf convergent pathway C_micro contraction-expansion response increase in the lower P_eff interval is 0.040; in comparison, small molecule hormone Δ C_micro contraction-expansion response increases in the lower P_eff intervals for gene expression ≤ 0.168 (Dex· GR) ≥ 0.156 (Dht · AR), with grade of duration at P_eff (min·count) of 1.33x10⁵ (Dex/Cort) and 1.8–2.53x10⁵ (Dht/R1881) as compared to the (-) coupled (+) Δ C_microP_eff to 0.136 (Wnt5a, Esr2) with applied DES (1.86x10⁶). The subtype of trans-differentiated cell as a result of an applied toxin or toxicant is predictable by delta-C_micro determined by P_eff mapping. Study findings offer additional perspective on the basis for pressure regulated gene transcription by alterations in cell micro-compliance (Δ contraction-expansion, C_micro), and are applicable for the further predictive modeling of gene to gene transcription interactions, and small molecule modulation of cell effective pressure (P_eff) and its potential.

Glucocorticoid-transactivated TSC22D3 attenuates hypoxia- and diabetes-induced Müller glial galectin-1 expression via HIF-1α destabilization

Galectin‐1/LGALS1, a newly recognized angiogenic factor, contributes to the pathogenesis of diabetic retinopathy (DR). Recently, we demonstrated that glucocorticoids suppressed an interleukin‐1β‐driven inflammatory pathway for galectin‐1 expression in vitro and in vivo. Here, we show glucocorticoid‐mediated inhibitory mechanism against hypoxia‐inducible factor (HIF)‐1α‐involved galectin‐1 expression in human Müller glial cells and the retina of diabetic mice. Hypoxia‐induced increases in galectin‐1/LGALS1 expression and promoter activity were attenuated by dexamethasone and triamcinolone acetonide in vitro. Glucocorticoid application to hypoxia‐stimulated cells decreased HIF‐1α protein, but not mRNA, together with its DNA‐binding activity, while transactivating TSC22 domain family member (TSC22D)3 mRNA and protein expression. Co‐immunoprecipitation revealed that glucocorticoid‐transactivated TSC22D3 interacted with HIF‐1α, leading to degradation of hypoxia‐stabilized HIF‐1α via the ubiquitin‐proteasome pathway. Silencing TSC22D3 reversed glucocorticoid‐mediated ubiquitination of HIF‐1α and subsequent down‐regulation of HIF‐1α and galectin‐1/LGALS1 levels. Glucocorticoid treatment to mice significantly alleviated diabetes‐induced retinal HIF‐1α and galectin‐1/Lgals1 levels, while increasing TSC22D3 expression. Fibrovascular tissues from patients with proliferative DR demonstrated co‐localization of galectin‐1 and HIF‐1α in glial cells partially positive for TSC22D3. These results indicate that glucocorticoid‐transactivated TSC22D3 attenuates hypoxia‐ and diabetes‐induced retinal glial galectin‐1/LGALS1 expression via HIF‐1α destabilization, highlighting therapeutic implications for DR in the era of anti‐vascular endothelial growth factor treatment.

Glucocorticoid receptor inhibits Müller glial galectin-1 expression via DUSP1-dependent and -independent deactivation of AP-1 signalling

Galectin‐1/LGALS1 is a hypoxia‐induced angiogenic factor associated with diabetic retinopathy (DR). Recently, we elucidated a hypoxia‐independent pathway to produce galectin‐1 in Müller glial cells stimulated by interleukin (IL)‐1β. Here we revealed glucocorticoid receptor (GR)‐mediated inhibitory mechanisms for Müller glial galectin‐1/LGALS1 expression. Activator protein (AP)‐1 site in the LGALS1 enhancer region, to which activating transcription factor2, c‐Fos and c‐Jun bind, was shown to be essential for IL‐1β‐induced galectin‐1/LGALS1 expression in Müller cells. Ligand (dexamethasone or triamcinolone acetonide)‐activated GR induced dual specificity phosphatase (DUSP)1 expression via the glucocorticoid response element and attenuated IL‐1β‐induced galectin‐1/LGALS1 expression by reducing phosphorylation of these AP‐1 subunits following AKT and extracellular signal‐regulated kinase (ERK)1/2 deactivation. Moreover, activated GR also caused DUSP1‐independent down‐regulation of IL‐1β‐induced LGALS1 expression via its binding to AP‐1. Administration of glucocorticoids to mice attenuated diabetes‐induced retinal galectin‐1/Lgals1 expression together with AKT/AP‐1 and ERK/AP‐1 pathways. Supporting these in vitro and in vivo findings, immunofluorescence analyses showed co‐localization of galectin‐1 with GR and phosphorylated AP‐1 in DUSP1‐positive glial cells in fibrovascular tissues from patients with DR. Our present data demonstrated the inhibitory effects of glucocorticoids on glial galectin‐1 expression via DUSP1‐dependent and ‐independent deactivation of AP‐1 signalling (transactivation and transrepression), highlighting therapeutic implications for DR.

Molecular characterization of the lgals1 gene in large scale loach Paramisgurnus dabryanus

Galectins constitute a group of lectins with binding specificity for β-galactoside sugars. Galectin-1 is a prototype galectin and the multifunctionality of mammalian galectin-1s is well-known, but only a few of fish galectin-1s have been identified. In this study, we obtained the full-length cDNA and genomic sequence of the galectin-1 gene (designated as Pdlgals1) from large scale loach (Paramisgurnus dabryanus), performed phylogenetic analysis, and characterized the expression pattern and the transcriptional activity of its 5' flanking region. The Pdlgals1 gene contains 4 exons that encode a peptide of 132 amino acids with all the galectin signature motifs. Phylogenetic analysis and sequence alignment indicated that Pdlgals1 is a homologue of human LGALS1. RT-PCR and whole-mount in situ hybridization revealed that Pdlgals1 is mainly expressed in the skin, muscle, intestine and cavum oropharyngeum. Transcriptional activity assays demonstrated that the basal promoter of Pdlgals1 is located in a region from -500bp to its transcriptional start site. Potential binding sites for transcription factors including C/EBP, AP-1, GATA, Oct-1, δEF1, NF-κB, c-Myb, SP-1, AP-2, AML-1α, and AP-4 were identified in the basal promoter, suggesting that these factors are associated with the regulation of Pdlgals1. These results provided clues for further investigation of galectin-1 functions in loaches.

Proteomic analysis of differentially expressed proteins in normal human thyroid cells transfected with PPFP

The fusion gene encoding the thyroid-specific transcription factor PAX8 and peroxisome proliferator-activated receptor γ (PPARγ (PPARG)) (designated as the PPFP gene) is oncogenic and implicated in the development of follicular thyroid carcinoma (FTC). The effects of PPFP transfection on the biological characteristics of Nthy-ori 3-1 cells were studied by MTT assay, colony formation, soft-agar colony formation, and scratch wound-healing assays as well as by flow cytometry. Furthermore, the differentially expressed proteins were analyzed on 2-DE maps and identified by MALDI-TOF-MS. Validation of five identified proteins (prohibitin, galectin-1, cytokeratin 8 (CK8), CK19, and HSP27) was determined by western blot analysis. PPFP not only significantly increased the viability, proliferation, and mobility of the Nthy-ori 3-1 cells but also markedly inhibited cellular apoptosis. Twenty-eight differentially expressed proteins were identified, among which 19 proteins were upregulated and nine proteins were downregulated in Nthy-ori 3-1(PPFP) (Nthy-ori 3-1 cells transfected with PPFP). The western blot results, which were consistent with the proteome analysis results, showed that prohibitin was downregulated, whereas galectin-1, CK8, CK19, and HSP27 were upregulated in Nthy-ori 3-1(PPFP). Our results suggest that PPFP plays an important role in malignant thyroid transformation. Proteomic analysis of the differentially expressed proteins in PPFP-transfected cells provides important information for further study of the carcinogenic mechanism of PPFP in FTCs.

Induction of galectin-1 expression by HTLV-I Tax and its impact on HTLV-I infectivity

Background

Cell-free Human T-cell Leukemia Virus type I (HTLV-I) virions are poorly infectious and cell-to-cell contact is often required to achieve infection. Other factors might thus importantly contribute in increasing infection by HTLV-I. Galectin-1 is a galactoside-binding lectin which is secreted by activated T lymphocytes. Several functions have been attributed to this protein including its capacity to increase cell-to-cell adhesion. Based on previous studies, we postulated that this protein could also accentuate HTLV-I infection.

Results

Herein, we demonstrate that galectin-1 expression and release are higher in HTLV-I-infected T cells in comparison to uninfected T cells. Furthermore, galectin-1 expression was activated in various cell lines expressing the wild type viral Tax protein while this induction was minimal upon expression of NF-κB activation-defective TaxM22. Cotransfection of these Tax expression vectors with galectin-1 promoter-driven luciferase constructs confirmed that Tax upregulated galectin-1 promoter activity. However, a NF-κB-independent mechanism was strongly favoured in this induction of galectin-1 expression as no activation of the promoter was apparent in Jurkat cells treated with known NF-κB activators. Using HTLV-I envelope pseudotyped HIV-1 virions, galectin-1 was shown to increase infectivity. In addition, a co-culture assay with HTLV-I-infected cells also indicated an increase in cell fusion upon addition of galectin-1. This effect was not mediated by factors present in the supernatant of the HTLV-I-infected cells.

Conclusion

These data suggest that HTLV-I Tax increases galectin-1 expression and that this modulation could play an important role in HTLV-I infection by stabilizing both cell-to-cell and virus-cell interactions.

Emergence of hormonal and redox regulation of galectin-1 in placental mammals: implication in maternal-fetal immune tolerance

Galectin-1 is an anti-inflammatory lectin with pleiotropic regulatory functions at the crossroads of innate and adaptive immunity. It is expressed in immune privileged sites and is implicated in establishing maternal-fetal immune tolerance, which is essential for successful pregnancy in eutherian mammals. Here, we show conserved placental localization of galectin-1 in primates and its predominant expression in maternal decidua. Phylogenetic footprinting and shadowing unveil conserved cis motifs, including an estrogen responsive element in the 5' promoter of LGALS1, that were gained during the emergence of placental mammals and could account for sex steroid regulation of LGALS1 expression, thus providing additional evidence for the role of galectin-1 in immune-endocrine cross-talk. Maximum parsimony and maximum likelihood analyses of 27 publicly available vertebrate and seven newly sequenced primate LGALS1 coding sequences reveal that intense purifying selection has been acting on residues in the carbohydrate recognition domain and dimerization interface that are involved in immune functions. Parsimony- and codon model-based phylogenetic analysis of coding sequences show that amino acid replacements occurred in early mammalian evolution on key residues, including gain of cysteines, which regulate immune functions by redox status-mediated conformational changes that disable sugar binding and dimerization, and that the acquired immunoregulatory functions of galectin-1 then became highly conserved in eutherian lineages, suggesting the emergence of hormonal and redox regulation of galectin-1 in placental mammals may be implicated in maternal-fetal immune tolerance.

TACC3 mediates the association of MBD2 with histone acetyltransferases and relieves transcriptional repression of methylated promoters

We have recently reported that a novel MBD2 interactor (MBDin) has the capacity to reactivate transcription from MBD2-repressed methylated promoters even in the absence of demethylation events. Here we show that another unrelated protein, TACC3, displays a similar activity on methylated genes. In addition the data reported here provide possible molecular mechanisms for the observed phenomenon. Immunoprecipitation experiments showed that MBD2/TACC3 form a complex in vivo with the histone acetyltransferase pCAF. MBD2 could also associate with HDAC2, a component of MeCP1 repression complex. However, we found that the complexes formed by MBD2 with TACC3/pCAF and with HDAC2 were mutually exclusive. Moreover, HAT enzymatic assays demonstrated that HAT activity associates with MBD2 in vivo and that such association significantly increased when TACC3 was over-expressed. Overall our findings suggest that TACC3 can be recruited by MBD2 on methylated promoters and is able to reactivate transcription possibly by favoring the formation of an HAT-containing MBD2 complex and, thus, switching the repression potential of MBD2 in activation even prior to eventual demethylation.

Galectin-1 is an inductor of pancreatic stellate cell activation

Pancreatic stellate cells (PSCs) play a key role in the development of pancreatic fibrosis, a pathological feature of chronic pancreatitis and pancreatic cancer. Here, we show that activation of rat PSCs in vitro is associated with increased expression of galectin-1 (gal-1) and that gal-1 modulates PSC function. Expression of the lectin was stimulated by fetal calf serum and platelet-derived growth factor. PSCs exposed to exogenous gal-1 proliferated at a higher rate and synthesised more collagen than controls. Gal-1-dependent collagen synthesis was blocked by lactose but not by cellobiose, suggesting that gal-1 acts on PSCs through targeting beta-galactoside-containing glycoconjugates. Analysis of gal-1 signalling in PSCs revealed an activation of the extracellular signal-regulated kinases 1 and 2 and enhanced DNA binding of AP-1 transcription factors. Together, our data implicate gal-1 in PSC activation and suggest further studies to analyse the role of endogenous lectins in the development of pancreatic fibrosis in vivo.

Galectin genes: regulation of expression

In this review we have summarized the more recent studies on the expression of mammalian galectins. One interesting observation that can be made is that in most of microarrays and/or differential display analysis performed in recent years one or more galectins have been picked up. From a critical evaluation of the pertinent studies the main conclusion that can be drawn is that, although it is not yet clear whether the 14 galectins identified so far have functions in common, a striking common feature of all galectins is the strong modulation of their expression during development, differentiation stages and under different physiological or pathological conditions. This suggests that the expression of different galectins is finely tuned and possibly coordinated. In spite of these observations it is rather unexpected that very few studies have been performed on the molecular mechanisms governing the activity of galectin genes.

MBDin, a novel MBD2-interacting protein, relieves MBD2 repression potential and reactivates transcription from methylated promoters

We have identified a human gene encoding a novel MBD2-interacting protein (MBDin) that contains an N-terminal GTP-binding site, a putative nuclear export signal (NES), and a C-terminal acidic region. MBDin cDNA was isolated through a two-hybrid interaction screening using the methyl-CpG-binding protein MBD2 as bait. The presence of the C-terminal 46-amino-acid region of MBD2 and both the presence of the acidic C-terminal 128-amino-acid region and the integrity of the GTP-binding site of MBDin were required for the interaction. Interaction between MBD2 and MBDin in mammalian cells was confirmed by immunoprecipitation experiments. Fluorescence imaging experiments demonstrated that MBDin mainly localizes in the cytoplasm but accumulates in the nucleus upon disruption of the NES or treatment with leptomycin B, an inhibitor of NES-mediated transport. We also found that MBDin partially colocalizes with MBD2 at foci of heavily methylated satellite DNA. An MBD2 deletion mutant lacking the C-terminal region maintained its subnuclear localization but failed to recruit MBDin at hypermethylated foci. Functional analyses demonstrated that MBDin relieves MBD2-mediated transcriptional repression both when Gal4 chimeric constructs and when in vitro-methylated promoter-reporter plasmids were used in transcriptional assays. Southern blotting and bisulfite analysis showed that transcriptional reactivation occurred without changes of the promoter methylation pattern. Our findings suggest the existence of factors that could be targeted on methylated DNA by methyl-CpG-binding proteins reactivating transcription even prior to demethylation.

The overlap of Inr and TATA elements sets the use of alternative transcriptional start sites in the mouse galectin-1 gene promoter

In the mouse gene encoding the protein galectin-1, transcription initiation at the +1 site is directed by a TATA box. Here we show that a consensus Inr element (TCCAGTT), which spans residues -34 to -28 and overlaps the TATA box, directs RNA initiation also from a previously uncharacterized site located at position -31. Upstream transcripts are polyadenylated and contribute to more than half of the galectin-1 mRNA population in all tissues analyzed. The promoter architecture is evolutionarily conserved to man, and galectin-1 mRNA size variants accumulate also in human HeLa cells. The 5' end terminus of the transcripts initiated at residue -31 is extremely GC-rich, and may fold into a relative stable hairpin which could influence translation and thus modulate the intracellular levels of galectin-1. The interval -63/+45 contains sufficient information to ensure RNA initiation from both -31 and +1 sites, and a Sp1 site spanning residues -57 to -48 is crucial for promoter functioning. The unusual overlap of core promoter elements suggests that RNA initiation from the -31 and the +1 sites may take place in a sequential manner.

Differential regulation of constitutive and retinoic acid-induced galectin-1 gene transcription in murine embryonal carcinoma and myoblastic cells

Galectin-1 (gal-1), a galactoside-binding lectin, is found in many vertebrate tissues and its expression is regulated during development. We had found that gal-1 expression is increased in F9 murine embryonal carcinoma cells concurrently with induction of differentiation by all-trans retinoic acid (RA). In contrast, gal-1 expression was constitutively high in murine myoblastic C2C12 cells. Therefore, we used these two cell types as models to begin to understand the mechanisms underlying constitutive and RA-induced gal-1 expression. We transfected transiently into F9 cells a series of reporter constructs containing different deletions of the 5' upstream region of the gal-1 gene promoter placed upstream of the chloramphenicol acetyltransferase reporter cDNA and evaluated the activation of transcription by RA treatment. The results indicate that the induction of gal-1 by RA is regulated at least partially at the level of transcription. A strong RA responsiveness region was found within the sequence from -1578 to -1448 upstream of the transcription start site (+1). In contrast, the high constitutive gal-1 expression in C2C12 cells appeared to be mediated by a sequence within the promoter region from -62 to +1, which contains an Sp1 consensus sequence. A gel electrophoretic mobility shift assay indicated that the transcription factor SP1 bound to the gal-1 Sp1 site and mutagenesis of this Sp1 site abolished both the binding of nuclear proteins to the mutated Sp1 site and the high constitutive expression of the gal-1 gene. The results demonstrate that gal-1 expression is cell type-specific and suggest that different factors regulate constitutive and RA-induced gal-1 expression.

A novel member of the BTB/POZ family, PATZ, associates with the RNF4 RING finger protein and acts as a transcriptional repressor

We have identified a novel human gene encoding a 59-kDa POZ-AT hook-zinc finger protein (PATZ) that interacts with RNF4, a mediator of androgen receptor activity, and acts as a transcriptional repressor. PATZ cDNA was isolated through a two-hybrid interaction screening using the RING finger protein RNF4 as a bait. In vitro and in vivo interaction between RNF4 and PATZ was demonstrated by protein-protein affinity chromatography and coimmunoprecipitation experiments. Such interaction occurred through a small region of PATZ containing an AT-hook DNA binding domain. Immunofluorescence staining and confocal microscopy showed that PATZ localizes in distinct punctate nuclear regions and colocalizes with RNF4. Functional analysis was performed by cotransfection assays: PATZ acted as a transcriptional repressor, whereas its partner RNF4 behaved as a transcriptional activator. When both proteins were overexpressed a strong repression of the basal transcription was observed, indicating that the association of PATZ with RNF4 switches activation to repression. In addition, RNF4 was also found to associate with HMGI(Y), a chromatin-modeling factor containing AT-hook domains.

Control of galectin gene expression

In this review we summarize the available information on the expression of mammalian galectins in normal and transformed cells. From all these studies it is apparent that each cell might express most of galectins; yet, during development or in various differentiation stages or under different physiological or pathological conditions, one or more galectins are preferentially expressed in each cell type. This implies a fine control of gene expression and suggests that such control should be coordinated. Nevertheless, to date very few studies have been performed on the mechanisms responsible for the regulation of galectin genes. We review the current knowledge on galectin promoter function. We believe that this area of galectin research will expand rapidly in the near future.

Transcriptional regulation by butyrate of mouse galectin-1 gene in embryonal carcinoma cells

Endogenous galactoside-binding lectins (galectins) have been implicated in cell adhesion, growth, differentiation, neoplastic transformation, and metastasis. Galectin-1 (gal-1), one member of this family, has been best characterized. We isolated a DNA clone containing the gal-1 gene from mouse genomic libraries, and the sequence of the 5' upstream region up to -2430 bp was determined. Our previous study showed that sodium butyrate (butyrate) induced expression of gal-1 at both mRNA and protein levels in the murine embryonal carcinoma (EC) cell line PCC4.aza1R and the induction of gal-1 by butyrate in PCC4.aza1R cells is at least partially regulated at transcriptional level. To locate the region which is responsible for the induction of gal-1 by butyrate, transient transfection of PCC4.aza1R cells with a series of gal-1 promoter/CAT chimeric gene, which have different deletions of the 5' region of the gal-1 promoter, showed that this 2430 bp sequence is a butyrate-inducible promoter, and butyrate-inducible ability remained when only a 62 bp sequence ahead of the transcription site (+1) existed. The sequence from -62 to -41 which contains an Sp1 site at -57 was important for the induction of gal-1 expression by butyrate. Gel shift assay indicated that transcription factor SP1 actually bound to that Sp1 site. The changes of two nucleotides within that Sp1 site, from GG to TT, abolished the nuclear proteins binding to that Sp1 site as well as the response to butyrate. These results suggest that the 5' proximal Sp1 site at -57 is crucial for the butyrate-induced expression of the gal-1, and the direct binding of SP1 to this Sp1 site may be involved in this induction.

High resolution methylation analysis of the galectin-1 gene promoter region in expressing and nonexpressing tissues

We conducted by bisulfite genomic sequencing a high resolution study of the methylation of the galectin-1 gene in expressing and nonexpressing tissues. We show that: (i) hypomethylation of galectin-1 promoter correlates with expression; (ii) differences in methylation occur in a small region, which include a CpG cluster; (iii) the density of methyl-CpGs rather than site-specific methylation distinguishes the nonexpressing from the expressing alleles; (iv) the modification profiles in nonexpressing tissues are highly heterogeneous; (v) a single CpG within 1300 bp is always methylated both in expressing and nonexpressing tissues; (vi) these features are conserved in rat and mouse.

Multiple downstream promoter modules regulate the transcription of the Drosophila melanogaster I, Doc and F elements

The basal promoters of three Drosophila long interspersed nuclear elements (LINEs), the I factor and the F and Doc elements, have the same architecture. In each, transcription is directed by an initiator which is faithfully and efficiently recognized only when flanked 3' by a DNA segment approximately 20 bp in length called the B region. The B regions of the three promoters are interchangeable and have a complex structure, comprising three functionally distinct elements: de1, de2 and de3. While de2 is relatively conserved, fitting the consensus RGACGTGY, de1 and de3 vary among the three promoters. At different levels, each downstream element is able to ensure accurate recognition of the initiator. The de2 domain stimulates transcription of the F, I and Doc promoters to the same extent. In contrast, the I de1 domain stimulates transcription much more efficiently than the corresponding domains of the F and Doc elements. The finding that de2 is selectively required in order to detect full activity of enhancer sequences found in the F element suggests that de1 and de2 interact with different proteins. The B regions can be replaced by and synergize with a TATA element, can functionally substitute for downstream promoter sequences in the Drosophila hsp70 gene, and significantly activate the mouse terminal deoxynucleotidyl transferase initiator. Our data suggest that the B regions stimulate transcription by providing sites of interaction for the TFIID complex. Sequences homologous to the del to de3 array are found downstream from the transcription start site(s) both in TATA-less and TATA-containing promoters.

Cell-specific transcriptional regulation and reactivation of galectin-1 gene expression are controlled by DNA methylation of the promoter region

The galectin-1 gene is developmentally regulated gene whose activity is strongly modulated during cell differentiation and transformation. We have previously shown that galectin-1 promoter constructs are highly active when transiently transfected in cells both expressing and not expressing the endogenous gene and that the basal activity is determined by a small region encompassing the transcription start site (from positions -50 to +50). We have now investigated the role of DNA methylation in galectin-1 gene expression. Southern blot analysis with HpaII and MspI endonucleases and sodium bisulfite analysis of genomic DNA from expressing and nonexpressing cell lines and cell hybrids showed a close correlation between gene activity and demethylation of the 5' region of the galectin-1 gene. We found that the galectin-1 promoter region is fully methylated, at every CpG site on both strands, in nonexpressing differentiated rat liver (FAO) and thyroid (PC C13) cells and unmethylated in the expressing undifferentiated liver (BRL3A) and thyroid transformed (PC myc/raf) cell lines. In addition, reactivation of the silent FAO alleles in FAO-human osteosarcoma (143tk-) hybrid cells is accompanied by a complete demethylation of the promoter region. Finally, when galectin-1 chloramphenicol acetyltransferase (CAT) promoter constructs were methylated in vitro by SssI methylase at every cytosine residue of the CpG doublets and transfected into mouse fibroblasts, the transcription of the CAT reporter gene was strongly inhibited.