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

The intrinsic defects of T cells impact the efficacy of CAR-T therapy in patients with diffuse large B-cell lymphoma

CAR-T cell therapy did not achieve the desired efficacy in some patients with diffuse large B-cell lymphoma (DLBCL). We conducted single-cell RNA and TCR sequencing as well as methylation chip profiling of peripheral blood samples in DLBCL patients. Patients who achieved complete remission (CR) showed an upward trend in T-cell levels, especially CD8-effector T cells. The responders exhibited T-cell clone expansion, more active T-cell transformation, and frequent cell communication. Highly expressed genes in the CR group were enriched in functions like leukocyte-mediated cytotoxicity and activation of immune response, while the non-CR group was enriched in pathways related to DNA damage and P53-mediated intrinsic apoptotic. More differentially methylated probes (DMPs) were identified in the baseline of the non-CR group (779 vs 350). GSEA analysis revealed that the genes annotated by DMPs were associated with cellular immune functions in T cells, including the generation of chemokines, leukocyte-mediated cytotoxicity, and cell-killing functions. The genes with low expression in the non-CR group exhibited a high methylation status. There is heterogeneity in the cellular, molecular, and epigenetic characteristics of host T cells in patients with different clinical outcomes. Intrinsic defects in T cells are important factors leading to poor efficacy of CAR-T therapy.

Placental Galectins in Cancer: Why We Should Pay More Attention

The first studies suggesting that abnormal expression of galectins is associated with cancer were published more than 30 years ago. Today, the role of galectins in cancer is relatively well established. We know that galectins play an active role in many types of cancer by regulating cell growth, conferring cell death resistance, or inducing local and systemic immunosuppression, allowing tumor cells to escape the host immune response. However, most of these studies have focused on very few galectins, most notably galectin-1 and galectin-3, and more recently, galectin-7 and galectin-9. Whether other galectins play a role in cancer remains unclear. This is particularly true for placental galectins, a subgroup that includes galectin-13, -14, and -16. The role of these galectins in placental development has been well described, and excellent reviews on their role during pregnancy have been published. At first sight, it was considered unlikely that placental galectins were involved in cancer. Yet, placentation and cancer progression share several cellular and molecular features, including cell invasion, immune tolerance and vascular remodeling. The development of new research tools and the concomitant increase in database repositories for high throughput gene expression data of normal and cancer tissues provide a new opportunity to examine the potential involvement of placental galectins in cancer. In this review, we discuss the possible roles of placental galectins in cancer progression and why they should be considered in cancer studies. We also address challenges associated with developing novel research tools to investigate their protumorigenic functions and design highly specific therapeutic drugs.

Galectins: An Ancient Family of Carbohydrate Binding Proteins with Modern Functions

Galectins are a large family of carbohydrate binding proteins with members in nearly every lineage of multicellular life. Through tandem and en-mass genome duplications, over 15 known vertebrate galectins likely evolved from a single common ancestor extant in pre-chordate lineages. While galectins have divergently evolved numerous functions, some of which do not involve carbohydrate recognition, the vast majority of the galectins have retained the conserved ability to bind variably modified polylactosamine (polyLacNAc) residues on glycans that modify proteins and lipids on the surface of host cells and pathogens. In addition to their direct role in microbial killing, many proposed galectin functions in the immune system and cancer involve crosslinking glycosylated receptors and modifying signaling pathways or sensitivity to antigen from the outside in. However, a large body of work has uncovered intracellular galectin functions mediated by carbohydrate- and non-carbohydrate-dependent interactions. In the cytoplasm, galectins can tune intracellular kinase and G-protein-coupled signaling cascades important for nutrient sensing, cell cycle progression, and transformation. Particularly, but interconnected pathways, cytoplasmic galectins serve the innate immune system as sensors of endolysosomal damage, recruiting and assembling the components of autophagosomes during intracellular infection through carbohydrate-dependent and -independent activities. In the nucleus, galectins participate in pre-mRNA splicing perhaps through interactions with non-coding RNAs required for assembly of spliceosomes. Together, studies of galectin function paint a picture of a functionally dynamic protein family recruited during eons of evolution to regulate numerous essential cellular processes in the context of multicellular life.

The Emerging Role of Galectins and O-GlcNAc Homeostasis in Processes of Cellular Differentiation

Galectins are a family of soluble β-galactoside-binding proteins with diverse glycan-dependent and glycan-independent functions outside and inside the cell. Human cells express twelve out of sixteen recognized mammalian galectin genes and their expression profiles are very different between cell types and tissues. In this review, we summarize the current knowledge on the changes in the expression of individual galectins at mRNA and protein levels in different types of differentiating cells and the effects of recombinant galectins on cellular differentiation. A new model of galectin regulation is proposed considering the change in O-GlcNAc homeostasis between progenitor/stem cells and mature differentiated cells. The recognition of galectins as regulatory factors controlling cell differentiation and self-renewal is essential for developmental and cancer biology to develop innovative strategies for prevention and targeted treatment of proliferative diseases, tissue regeneration, and stem-cell therapy.

Proteomic Identification of the Galectin-1-Involved Molecular Pathways in Urinary Bladder Urothelial Carcinoma

Among various heterogeneous types of bladder tumors, urothelial carcinoma is the most prevalent lesion. Some of the urinary bladder urothelial carcinomas (UBUCs) develop local recurrence and may cause distal invasion. Galectin-1 de-regulation significantly affects cell transformation, cell proliferation, angiogenesis, and cell invasiveness. In continuation of our previous investigation on the role of galectin-1 in UBUC tumorigenesis, in this study, proteomics strategies were implemented in order to find more galectin-1-associated signaling pathways. The results of this study showed that galectin-1 knockdown could induce 15 down-regulated proteins and two up-regulated proteins in T24 cells. These de-regulated proteins might participate in lipid/amino acid/energy metabolism, cytoskeleton, cell proliferation, cell-cell interaction, cell apoptosis, metastasis, and protein degradation. The aforementioned dys-regulated proteins were confirmed by western immunoblotting. Proteomics results were further translated to prognostic markers by analyses of biopsy samples. Results of cohort studies demonstrated that over-expressions of glutamine synthetase, alcohol dehydrogenase (NADP⁺), fatty acid binding protein 4, and toll interacting protein in clinical specimens were all significantly associated with galectin-1 up-regulation. Univariate analyses showed that de-regulations of glutamine synthetase and fatty acid binding protein 4 in clinical samples were respectively linked to disease-specific survival and metastasis-free survival.

Towards molecular mechanisms regulating the expression of galectins in cancer cells under microenvironmental stress conditions

Galectins, a family of soluble β-galactoside-binding proteins, serve as mediators of fundamental biological processes, such as cell growth, differentiation, adhesion, migration, survival, and death. The purpose of this review is to summarize the current knowledge regarding the ways in which the expression of individual galectins differs in normal and transformed human cells exposed to various stimuli mimicking physiological and pathological microenvironmental stress conditions. A conceptual point is being made and grounded that the modulation of galectin expression profiles is a key aspect of cellular stress responses. Moreover, this modulation might be precisely regulated at transcriptional and post-transcriptional levels in the context of non-overlapping transcription factors and miRNAs specific to galectins.

Clinical significance of galectin-7 in vulvar squamous cell carcinoma

The present study reports the role of galectin-7 (Gal-7) expression in vulvar squamous cell carcinoma (VSCC) and its correlation with clinicopathological variables. Gal-7 expression was immunohistochemically detected in the paraffin-embedded sections of 20 normal vulvar biopsy samples and 50 VSCC specimens. Expression was also detected in 10 normal vulvar biopsy samples and 10 VSCC specimens by western blotting. In addition, the methylation status of the promoter of the Gal-7 gene was determined in 30 VSCC specimens and 20 samples of normal vulvar tissue by methylation-specific polymerase chain reaction. Gal-7 expression was found to be significantly downregulated in the VSCC tissues compared with the normal vulvar tissues (P<0.05). Downregulation of Gal-7 was correlated with advanced clinical stage, poor tumor differentiation and regional lymph node metastasis (P<0.05). Furthermore, methylation of the Gal-7 gene promoter was significantly reduced in the vulvar normal tissues compared with the VSCC tissues (P=0.023), while increased Gal-7 promoter methylation was correlated with advanced clinical stage, poor tumor differentiation and regional lymph node metastasis (P<0.05). There was no association between patient age and Gal-7 promoter methylation. Together, these results suggested that Gal-7 has a negative impact in patients with VSCC, with malignant potential correlating with Gal-7 promoter methylation.

Unraveling galectin-1 as a novel therapeutic target for cancer

Galectins belong to a family of carbohydrate-binding proteins with an affinity for β-galactosides. Galectin-1 is differentially expressed by various normal and pathologic tissues and displays a wide range of biological activities. In oncology, galectin-1 plays a pivotal role in tumor growth and in the multistep process of invasion, angiogenesis, and metastasis. Evidence indicates that galectin-1 exerts a variety of functions at different steps of tumor progression. Moreover, it has been demonstrated that galectin-1 cellular localization and galectin-1 binding partners depend on tumor localization and stage. Recently, galectin-1 overexpression has been extensively documented in several tumor types and/or in the stroma of cancer cells. Its expression is thought to reflect tumor aggressiveness in several tumor types. Galectin-1 has been identified as a promising drug target using synthetic and natural inhibitors. Preclinical data suggest that galectin-1 inhibition may lead to direct antiproliferative effects in cancer cells as well as antiangiogenic effects in tumors. We provide an up-to-date overview of available data on the role of galectin-1 in different molecular and biochemical pathways involved in human malignancies. One of the major challenges faced in targeting galectin-1 is the translation of current knowledge into the design and development of effective galectin-1 inhibitors in cancer therapy.

Nuclear reprogramming of sperm and somatic nuclei in eggs and oocytes

Eggs and oocytes have a prominent ability to reprogram sperm nuclei for ensuring embryonic development. The reprogramming activity that eggs/oocytes intrinsically have towards sperm is utilised to reprogram somatic nuclei injected into eggs/oocytes in nuclear transfer (NT) embryos. NT embryos of various species can give rise to cloned animals, demonstrating that eggs/oocytes can confer totipotency even to somatic nuclei. However, many studies indicate that reprogramming of somatic nuclei is not as efficient as that of sperm nuclei. In this review, we explain how and why sperm and somatic nuclei are differentially reprogrammed in eggs/oocytes. Recent studies have shown that sperm chromatin is epigenetically modified to be adequate for early embryonic development, while somatic nuclei do not have such modifications. Moreover, epigenetic memories encoded in sperm chromatin are transgenerationally inherited, implying unique roles of sperm. We also discuss whether somatic nuclei can be artificially modified to acquire sperm-like chromatin states in order to increase the efficiency of nuclear reprogramming.

Epigenetic regulation of galectin-3 expression by β1 integrins promotes cell adhesion and migration

Introduction of the integrin β1- but not the β3-subunit in GE11 cells induces an epithelial-to-mesenchymal-transition (EMT)-like phenomenon that is characterized by the loss of cell-cell contacts, cell scattering, increased cell migration and RhoA activity, and fibronectin fibrillogenesis. Because galactose-binding lectins (galectins) have been implicated in these phenomena, we investigated whether galectins are involved in the β1-induced phenotype. We examined 9 galectins and, intriguingly, found that the expression of galectin-3 (Gal-3) is specifically induced by β1 but not by β3. Using β1-β3 chimeric integrins, we show that the induction of Gal-3 expression requires the hypervariable region in the extracellular domain of β1, but not its cytoplasmic tail. Furthermore, Gal-3 expression does not depend on RhoA signaling, serum factors, or any of the major signal transduction pathways involving protein kinase C (PKC), p38 mitogen-activated protein kinase (p38MAPK), extracellular signal-regulated kinase-1/-2 (ERK-1/2), phosphatidylinositol-3-OH kinase (PI3-K), or Src kinases. Instead, Gal-3 expression is controlled in an epigenetic manner. Whereas DNA methylation of the Lgals3 promoter maintains Gal-3 silencing in GE11 cells, expression of β1 causes its demethylation, leading to transcriptional activation of the Lgals3 gene. In turn, Gal-3 expression enhances β1 integrin-mediated cell adhesion to fibronectin (FN) and laminin (LN), as well as cell migration. Gal-3 also promotes β1-mediated cell adhesion to LN and Collagen-1 (Col)-1 in cells that endogenously express Gal-3 and β1 integrins. In conclusion, we identify a functional feedback-loop between β1 integrins and Gal-3 that involves the epigenetic induction of Gal-3 expression during integrin-induced EMT and cell scattering.

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.

Epigenetic reprogramming: is deamination key to active DNA demethylation?

DNA demethylation processes are important for reproduction, being central in epigenetic reprogramming during embryonic and germ cell development. While the enzymes methylating DNA have been known for many years, identification of factors capable of mediating active DNA demethylation has been challenging. Recent findings suggest that cytidine deaminases may be key players in active DNA demethylation. One of the most investigated candidates is activation-induced cytidine deaminase (AID), best known for its role in generating secondary antibody diversity in B cells. We evaluate evidence for cytidine deaminases in DNA demethylation pathways in vertebrates and discuss possible models for their targeting and activity regulation. These findings are also considered along with alternative demethylation pathways involving hydroxymethylation.

Increased galectin-7 gene expression in lymphoma cells is under the control of DNA methylation

Recent studies have reported that elevated levels of galectin-7 in different types of cancer. The mechanisms underlying its abnormal regulation in cancer cells remain, however, unknown. Here, we have examined the relationship between galectin-7 and p53, a gene previously associated with upregulation of galectin-7. While RNA and protein analyses revealed a consistent and irreversible upregulation of galectin-7 throughout progression of lymphoma, no correlation with p53 was found. In fact, most of the lymphoma cell lines expressing high levels of galectin-7 did not express any detectable level of p53, although expressed p21(Waf1/Cip1) gene following doxorubicin treatment, indicating that p53 was functional in these cells. Methylation-specific polymerase chain reaction (MS-PCR) analyses rather suggested that galectin-7 expression was associated with changes in DNA methylation. This conclusion was supported by data using demethylating agent 5-aza-dC. Furthermore, disruption of the DNA methylases dnmt1 and dnmt3a induced galectin-7. Collectively, our data suggest that abnormal expression of galectin-7 in lymphoma cells is not dependent on p53, but is rather associated with DNA hypomethylation.

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.

Regulated expression of galectin-1 during T-cell activation involves Lck and Fyn kinases and signaling through MEK1/ERK, p38 MAP kinase and p70S6 kinase

Recent evidence has implicated galectins and their carbohydrate ligands as novel regulators of T-cell homeostasis. Galectin-1 (Gal-1), a member of this family, inhibits clonal expansion, induces apoptosis of antigen-primed T lymphocytes and suppresses the development of T-cell-mediated autoimmune diseases in vivo. Because the beta-galactoside-binding protein is expressed in activated but not resting T cells, it has been hypothesized that Gal-1-induced apoptosis may constitute an autocrine suicide mechanism to eliminate activated T cells contributing to the termination of an effector immune response. We undertook this study to investigate the signals and intracellular pathways leading to Gal-1 expression during T-cell activation. When T cells were stimulated either with anti-CD3 or anti-CD28 monoclonal antibody plus PMA in the presence of accessory cells, a sustained up-regulation of Gal-1 was observed, reaching a plateau between days 3 and 5 following CD3 engagement or costimulation through CD28. Investigation of the signal transduction events involved in this process revealed a role for Lck and Fyn kinases, since the Src kinase inhibitor PP1 inhibited the up-regulated expression of Gal-1 following T-cell activation. Downstream signaling routes involve mitogen-activated protein kinase (MAPK) kinase (MEK)1/extracellular signal-regulated kinase (ERK) and p38 MAPK, as Gal-1 expression was prevented by U0126 and SB202190. In addition, expression of Gal-1 involves interleukin (IL)-2-dependent signaling routes triggered by p70S6 kinase, as it could be inhibited by rapamycin. This is the first demonstration of the intracellular pathways that control activation-induced expression of Gal-1, which may reveal potential targets for immune intervention to modulate expression of this beta-galactoside-binding protein in pathological disorders.

Effects of DNA methylation on galectin-3 expression in pituitary tumors

Galectin-3 (Gal-3), a beta-galactoside-binding protein is expressed in a specific cell-type manner in pituitary tumors. Here we questioned the mechanism of Gal-3 expression in pituitary tumors, by using methylation-specific PCR and DNA sequence analyses to analyze the methylation status of the promoter region of the LGALS3 gene. DNA analysis of a human pituitary tumor, breast carcinoma cell lines, and thyroid carcinoma cell lines showed that in cells expressing Gal-3 protein, the LGALS3 gene was unmethylated, whereas in Gal-3 null cells, the promoter of the LGALS3 gene was methylated. Treatment of cells with 30 mumol/L 5-aza-2'-deoxycytidine induced Gal-3 mRNA and protein expression. Among pituitary tumors, 30% (7/23), mainly in follicle-stimulating hormone/luteinizing hormone-producing (38%) and null cell (57%) adenomas, the promoter of the LGALS3 was found to be methylated and silenced, although prolactin- and adrenocorticotropic hormone-producing tumors, which were unmethylated, expressed the Gal-3 protein. These results show for the first time that Gal-3 expression is regulated in part by promoter methylation in pituitary as well as in other tumors. Because it is functionally involved in cancer progression and metastasis, Gal-3 may serve as a possible therapeutic target in the treatment of pituitary tumors.

In vivo analysis of DNA methylation patterns recognized by specific proteins: coupling CHIP and bisulfite analysis

The three-way connection between DNA methylation, chromatin configuration, and transcriptional regulation is under increasing attention, but the fine rules governing the epigenetic control are still poorly understood. In several studies, the authors have concluded that the methylation status of CpG sites could be critical for the binding of factors to DNA and, consequently, for chromatin conformation. We tested the possibility that a novel technical approach combining chromatin immunoprecipitation and bisulfite genomic sequencing analysis (ChIP-BA) could provide useful information on the role of specific CpG methylation patterns in driving the association in vivo of proteins to given genomic regions. Our results show that ChIP-BA permits the establishment in vivo of the methylation patterns required for the binding of a methyl-CpG binding protein and, in addition, can potentially identify methylation patterns that do not allow a protein to bind specific genomic regions. Possible fields of application are discussed. We believe that wide use of ChIP-BA could make possible the exploration of a novel aspect of the intricate epigenetic web.

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.

The cell-specific expression of endothelial nitric-oxide synthase: a role for DNA methylation

The basis for the endothelial cell-restricted expression of endothelial nitric-oxide synthase (eNOS) is not known. While transgenic promoter/reporter mice demonstrated endothelium cell-specific eNOS expression, we found robust expression of episomal eNOS promoter/reporter constructs in cell types that do not express the native eNOS transcript. To explore the mechanism underlying this differential activity pattern of chromatin-versus episome-based eNOS promoters, we examined the methylation status of 5'-regulatory sequences of the human eNOS gene. DNA methylation differed dramatically between endothelial and nonendothelial cell types, including vascular smooth muscle cells. This same cell type-specific methylation pattern was observed in vivo in endothelial and vascular smooth muscle cells of the mouse aorta at the native murine eNOS promoter. We addressed the functional consequences of methylation on eNOS transcription using transient transfection of in vitro methylated promoter/reporter constructs and found that methylated constructs exhibited a marked decrease in the synergistic action of Sp1, Sp3, and Ets1 on eNOS promoter activity. The addition of methyl-CpG-binding protein 2 further reduced the transcriptional activity of methylated eNOS constructs. Importantly, chromatin immunoprecipitation demonstrated the presence of Sp1, Sp3, and Ets1 at the native eNOS promoter in endothelial cells but not in vascular smooth muscle cells. Finally, robust expression of eNOS mRNA was induced in nonendothelial cell types following inhibition of DNA methyltransferase activity with 5-azacytidine, demonstrating the importance of DNA methylation-mediated repression. This report is the first to show that promoter DNA methylation plays an important role in the cell-specific expression of a constitutively expressed gene in the vascular endothelium.

Molecular mechanisms regulating cell type specific expression of BMP/RA Inducible Neural-specific Protein-1 that suppresses cell cycle progression: roles of NRSF/REST and DNA methylation

We have recently identified a novel protein family, BMP/RA-Inducible Neural-specific Protein (BRINP) including BRINP1, 2, 3. Among BRINP family genes, BRINP1 is most highly and widely expressed in various regions of the mammalian nervous system, although its expression is also found in some non-neural tissues and cell types at low levels. We have previously suggested that BRINPs are involved in the suppression of cell-cycle progression in post-mitotic neuronal cells. In the present study, we investigated the transcriptional mechanisms regulating the cell type-specific expression of BRINP1. First, bisulfite analysis of the methylation status revealed hypermethylation of the CpG island surrounding BRINP1 exon 1 in a non-neural cell line, NIH 3T3, which expresses low but detectable levels of BRINP1, while methylation levels of the BRINP1 CpG island in either non-neural or neural tissues are very low. Treatment of NIH 3T3 cells with a demethylating agent, 5-azacytidine, upregulated the expression of BRINP1 remarkably. Then, we analyzed the promoter activity of 7 kb region surrounding BRINP1 exon 1 in neuronal and non-neuronal cells. Consequently, we found a basic promoter region and a non-neural-specific silencing region which contains neuron-restrictive silencing element/repressor element 1 (NRSE/RE-1) like element (BRINP1-NRSE). Mutation of BRINP1-NRSE recovered the BRINP1 promoter activity in non-neuronal cells. Furthermore, proteins in nuclear extract from non-neural cells bound to the BRINP1-NRSE. These results strongly suggest that BRINP1-NRSE determines neural-specific expression of BRINP1, while hypermethylation of the BRINP1-CpG island suppresses BRINP1 expression in NIH 3T3 cells.

Galectin 3 and its binding protein in rheumatoid arthritis

OBJECTIVE

To characterize the expression pattern and role of galectin 3 and galectin 3 binding protein (G3BP) in rheumatoid arthritis (RA), in comparison with galectin 1, and to explore whether soluble galectin 3 and G3BP, investigated in serum, synovial fluid, or cell culture supernatant, are associated with disease.

METHODS

Synovial tissues from patients with RA or osteoarthritis (OA), as well as from healthy controls, were analyzed for galectins 1 and 3 and G3BP by in situ hybridization and immunohistochemistry. Levels of galectin 3 and G3BP in serum and synovial fluid from patients with RA and OA and controls, as well as in cell culture supernatants, were determined by enzyme-linked immunosorbent assay (ELISA). In vitro, the intracellular expression of galectin 3 in RA and OA synovial fibroblasts after modulation with tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and anti-CD40 monoclonal antibodies was measured by flow cytometry.

RESULTS

In RA, galectin 3 messenger RNA and protein stained throughout the synovial membrane, whereas G3BP was particularly expressed at sites of bone destruction. In contrast, the expression of galectin 1 was not uniform in different RA specimens, and was never found at sites of invasion. In OA and normal synovial tissues, only a small number of cells were positive for galectins and/or G3BP. Galectin 3 was elevated in RA sera and synovial fluids, whereas G3BP was increased in RA synovial fluids only. In RA, serum galectin 3 correlated with C-reactive protein levels, whereas G3BP was associated with joint destruction and/or synovial cell activation as measured by the levels of cartilage oligomeric matrix protein. In vitro, RA synovial fibroblasts showed an increased release of galectin 3 into culture medium, as measured by ELISA, but decreased secretion of G3BP. In RA synovial fibroblasts with low basal expression of galectin 3, TNFalpha increased its intracellular level in a dose-dependent manner. In contrast, IL-1beta or anti-CD40 monoclonal antibodies showed no effect.

CONCLUSION

Our data indicate that galectin 3 and G3BP are not only involved in inflammation, but also contribute to the activation of synovial fibroblasts. The intracellular accumulation of galectin 3 can be enhanced by TNFalpha. Thus, galectin 3 and G3BP represent novel markers of disease activity in RA.

Hepatitis C virus core protein activates ERK and p38 MAPK in cooperation with ethanol in transgenic mice

In human chronic hepatitis C, alcohol intake is a synergistic factor for the acceleration of hepatocarcinogenesis. Recently, we showed a significant increase of reactive oxygen species (ROS) in hepatitis C virus (HCV) core-transgenic mice fed ethanol-containing diets. Because previous studies indicated that ROS is closely associated with mitogen-activated protein kinases (MAPK), we examined activities of c-Jun N-terminal kinase, p38 MAPK, and extracellular signal-regulated kinase (ERK) in the liver of core-transgenic and nontransgenic mice with short-term ethanol feeding. Activity of ERK and p38 MAPK was increased in core-transgenic mice compared with nontransgenic mice, whereas neither ERK nor p38 MAPK was activated in core-transgenic mice with normal diets. In addition, activity of cyclic-AMP and serum responsive element, downstream pathways of p38 MAPK and ERK, was also increased. Comparison of gene expression profiles by cDNA microarray and real-time PCR revealed that galectin-1, which is associated with cell transformation, was significantly increased in ethanol-fed core-transgenic mice. On the other hand, glutathione S-transferase (GST), which plays a key role in protecting cells from oxidative stress, was decreased. In conclusion, these results suggest that HCV core protein cooperates with ethanol for the activation of some MAPK pathways, and leads to the modulation of several genes, contributing to the pathogenesis of liver disease of HCV-infected patients with high ethanol consumption.

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.

Epigenetics wins over genetics: induction of differentiation in tumor cells

Malignant cells are genetically abnormal, but can the malignant phenotype revert to a non-malignant phenotype without correcting these genetic abnormalities? It has been found that this reversion can be achieved by reprogramming tumor cells by epigenetic changes induced by differentiation. The epigenetic suppression of malignancy by inducing differentiation bypasses the genetic abnormalities in tumor cells. Studies with myeloid leukemic cells have shown that some leukemic cells can be induced to differentiate by cytokines that control normal hematopoiesis, and that myeloid leukemic cells resistant to normal cytokines can be induced to differentiate by compounds that use alternative differentiation pathways. The epigenetic reprogramming of tumor cells by inducing differentiation has also been found with other types of tumors and can be used for tumor therapy. By this reversion of the malignant to non-malignant phenotype, epigenetics wins over genetics.

Effect of 5-azacytidine and galectin-1 on growth and differentiation of the human b lymphoma cell line bl36

BACKGROUND: 5-AzaCytidine (AzaC) is a DNA demethylating drugs that has been shown to inhibit cell growth and to induce apoptosis in certain cancer cells. Induced expression of the galectin1 (Gal1) protein, a galactoside-binding protein distributed widely in immune cells, has been described in cultured hepatoma-derived cells treated with AzaC and this event may have a role in the effect of the drug. According to this hypothesis, we investigated the effect of AzaC and Gal1 on human lymphoid B cells phenotype. METHODS: The effect of AzaC and Gal1 on cell growth and phenotype was determined on the Burkitt lymphoma cell line BL36. An immunocytochemical analysis for detection of Gal1 protein expression was performed in AzaC-treated cells. To investigate the direct effects of Gal1, recombinant Gal1 was added to cells. RESULTS: Treatment of lymphoid B cells with AzaC results in: i) a decrease in cell growth with an arrest of the cell cycle at G0/G1 phase, ii) phenotypic changes consistent with a differentiated phenotype, and iii) the expression of p16, a tumor-suppressor gene whose expression was dependent of its promoter demethylation, and of Gal1. A targeting of Gal 1 to the plasma membrane follows its cytosolic expression. To determine which of the effects of AzaC might be secondary to the induction of Gal1, recombinant Gal1 was added to BL36 cells. Treated cells displayed growth inhibition and phenotypic changes consistent with a commitment toward differentiation. CONCLUSIONS: Altered cell growth and expression of the cell surface plasma cell antigen, CD138 are detectable in BL36 cells treated by AzaC as well as by Gal1. It seems that AzaC-induced Gal1 expression and consequent binding of Gal1 on its cell membrane receptor may be, in part, involved in AzaC-induced plasmacytic differentiation.

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.

Sodium butyrate induces transcription from the G alpha(i2) gene promoter through multiple Sp1 sites in the promoter and by activating the MEK-ERK signal transduction pathway

Sodium butyrate, an erythroid differentiation inducer and a histone deacetylase inhibitor, increases G alpha(i2) levels in differentiating K562 cells. Here we show that sodium butyrate induces G alpha(i2) gene transcription via sequences at -50/-36 and -92/-85 in the G alpha(i2) gene promoter. Both sequences contain core sequence motif for Sp1 binding; electrophoretic mobility shift as well as supershift assays confirmed binding to Sp1. Transcription from the G alpha(i2) gene promoter was also activated by two other histone deacetylase inhibitors, trichostatin A and Helminthsporium carbonium toxin (HC toxin), which also induce erythroblastic differentiation in K562 cells. However, hydroxyurea, a potent erythroid differentiation inducer in these cells, did not activate transcription from this gene promoter, indicating that promoter activation is inducer-specific. Mutations within the Sp1 sites at -50/-36 and -92/-85 in the G alpha(i2) gene promoter substantially decreased transcriptional activation by sodium butyrate, trichostatin A, or HC toxin. Transfection with constitutively activated ERKs indicated that this promoter can be activated through the MEK-ERK signal transduction pathway. Inhibition of the MEK-ERK pathway with U0126 or reduction in the expression of endogenous ERK with an antisense oligonucleotide to ERK significantly inhibited sodium butyrate- and HC toxin-induced transcription but had no effect on trichostatin A-induced transcription. Inhibition of the JNK and p38 MAPKs, using selective inhibitors, had no effect on sodium butyrate-induced transcription. In cells in which sodium butyrate induction of promoter activation had been inhibited by various concentrations of U0126, constitutively activated ERK2 reversed this inhibition. These results show that the MEK-ERK signal transduction pathway is important in butyrate signaling, which eventually converges in the cell nucleus.

CpG methylation as a mechanism for the regulation of E2F activity

Regulation of gene expression in mammals through methylation of cytosine residues at CpG dinucleotides is involved in the development and progression of tumors. Because many genes that are involved in the control of cell proliferation are regulated by members of the E2F family of transcription factors and because some E2F DNA-binding sites are methylated in vivo, we have investigated whether CpG methylation can regulate E2F functions. We show here that methylation of E2F elements derived from the dihydrofolate reductase, E2F1, and cdc2 promoters prevents the binding of all E2F family members tested (E2F1 through E2F5). In contrast, methylation of the E2F elements derived from the c-myc and c-myb promoters minimally affects the binding of E2F2, E2F3, E2F4, and E2F5 but significantly inhibits the binding of E2F1. Consistent with these studies, E2F3, but not E2F1, activates transcription through methylated E2F sites derived from the c-myb and c-myc genes whereas both E2F1 and E2F3 fail to transactivate a reporter gene that is under the control of a methylated dihydrofolate reductase E2F site. Together, these data illustrate a means through which E2F activity can be controlled.

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.

Expression pattern of galectin-3 in neural tumor cell lines

Galectin-3 is a member of the galectin family of beta-galactoside-specific animal lectins. Here we show that galectin-3 is constitutively expressed in 15 out of 16 glioma cell lines tested, but not by normal or reactive astrocytes, oligodendrocytes, glial O-2A progenitor cells and the oligodendrocyte precursor cell line Oli-neu. Galectin-3 is also expressed by one oligodendroglioma cell line, but not by primitive neuroectodermal tumor and 4 neuroblastoma cell lines tested so far. In all galectin-3 expressing cell lines, the lectin is predominantly, if not exclusively, localized intracellularly and carries an active carbohydrate recognition domain (shown for C6 rat glioma cells). Moreover, in contrast to primary astrocytes, glioma cells do not or only weakly adhere to substratum-bound galectin-3, probably reflecting an unusual glycosylation pattern. Our findings indicate that the expression of galectin-3 selectively correlates with glial cell transformation in the central nervous system and could thus serve as a marker for glial tumor cell lines and glial tumors.

Methylation patterns of human parathyroid hormone (PTH)/PTH-related peptide receptor gene promoters are established several weeks prior to onset of their function

Expression of the human parathyroid hormone (PTH)/PTH-related peptide receptor (PTHR) gene is controlled by three promoters, P1-P3. P1 functions specifically in kidney, whereas P2 is ubiquitously active. P3 is also widely active, although more so in kidney than other tissues. However, only P2 functions at midgestation. We examined the role of methylation in controlling PTHR promoter activity. Function of all promoters was inhibited by CpG methylation in vitro. Significantly, P1 is selectively hypomethylated in adult kidney in vivo, strongly suggesting that demethylation is required for renal P1 function. Moreover, this pattern is established by 11. 75 weeks of fetal age, several weeks prior to the onset P1 activity. P3 is unmethylated at midgestation, although it is inactive at this stage of development, and thus exhibits characteristics of both tissue-specific and ubiquitously active promoters. These results show that adult methylation patterns of P1 and P3 are established several weeks prior to their induction, indicating that their function requires factors expressed late in development.

Expression of human histo-blood group ABO genes is dependent upon DNA methylation of the promoter region

We have investigated the regulatory role of DNA methylation in the expression of the human histo-blood group ABO genes. The ABO gene promoter region contains a CpG island whose methylation status correlates well with gene expression in the cell lines tested. The CpG island was found hypomethylated in some cell lines that expressed ABO genes, whereas the other cell lines that did not express ABO genes were hypermethylated. Whereas constitutive transcriptional activity of the ABO gene promoter was demonstrated in both expressor and nonexpressor cell lines by transient transfection of reporter constructs containing the ABO gene promoter sequence, HhaI methylase-catalyzed in vitro methylation of the promoter region prior to DNA transfection suppressed the promoter activity when introduced into the expressor gastric cancer cell line KATOIII cells. On the other hand, in the nonexpressor gastric cancer cell line MKN28 cells, treatment with DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine resulted in demethylation of the ABO gene promoter and appearance of A-transferase messages, as well as A-antigens synthesized by A-transferase. Taken together, these studies suggest that DNA methylation of the ABO gene promoter may play an important role in the regulation of ABO gene expression.

Demethylation and expression of methylated plasmid DNA stably transfected into HeLa cells

In vitro methylation at CG dinucleotides (CpGs) in a transfecting plasmid usually greatly inhibits gene expression in mammalian cells. However, we found that in vitro methylation of all CpGs in episomal or non-episomal plasmids containing the SV40 early promoter/enhancer (SV40 Pr/E) driving expression of an antibiotic-resistance gene decreased the formation of antibiotic-resistant colonies by only approximately 30-45% upon stable transfection of HeLa cells. In contrast, when expression of the antibiotic-resistance gene was driven by the Rous sarcoma virus long terminal repeat or the herpes simplex virus thymidine kinase promoter, this methylation decreased the yield of antibiotic-resistant HeLa transfectant colonies approximately 100-fold. The low sensitivity of the SV40 Pr/E to silencing by in vitro methylation was probably due to demethylation upon stable transfection. This demethylation may be targeted to the promoter and extend into the gene. By genomic sequencing, we showed that four out of six of the transfected SV40 Pr/E's adjacent Sp1 sites were hotspots for demethylation in the HeLa transfectants. High frequency demethylation at Sp1 sites was unexpected for a non-embryonal cell line and suggests that DNA demethylation targeted to certain aberrantly methylated regions may function as a repair system for epigenetic mistakes.

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.

galectin-1 and galectin-3 expression in human bladder transitional-cell carcinomas

Galectin-1 and galectin-3 are galactoside-binding proteins involved in different steps of tumor progression and potential targets for therapy. We have investigated the expression of these galectins in 38 human bladder transitional-cell carcinomas of different histological grade and clinical stage and in 5 normal urothelium samples. Galectin-1 mRNA levels were highly increased in most high-grade tumors compared with normal bladder or low-grade tumors. Western blot and immuno-histochemical analysis of normal and neoplastic tissues revealed a higher content of galectin-1 in tumors. Galectin-3 mRNA levels were also increased in most tumors compared with normal urothelium, but levels were comparable among tumors of different histological grade.

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.

DNA methylation contributes to expression of the human neurotensin/neuromedin N gene

The gut and liver share a common embryological origin. The gene encoding the gut hormone neurotensin/neuromedin N (NT/N) is expressed in the adult small bowel, and NT/N is transiently expressed in the fetal liver, suppressed in the adult liver, and reexpressed in certain liver cancers. In our present study, we found that the NT/N gene was expressed at high levels in the human hepatoma cell line Hep 3B but was not expressed in Hep G2 cells. To further determine the mechanisms regulating NT/N expression, we performed Southern blotting and gene cloning techniques. Neither alteration nor mutation of the NT/N gene was responsible for this differential NT/N expression pattern. Human NT/N promoter constructs were transfected into either Hep 3B or Hep G2. Both cell lines supported NT/N transcription, indicating that the absence of NT/N expression in Hep G2 cells was due to mechanisms other than the absence of positive transcription factors. The role of DNA methylation was next assessed. Methylation of NT/N promoter constructs in vitro resulted in a 67-fold reduction in promoter activity, whereas treatment with the demethylating agent 5-azacytidine induced NT/N expression in Hep G2 cells, thus suggesting that DNA methylation plays a role in the expression of the gut endocrine gene NT/N. Defining the mechanisms regulating NT/N expression in these hepatic-derived cell lines will provide not only a better understanding of cell-specific and developmental regulation of a gut endocrine gene but also possible insight into liver cell lineage patterns and the derivation of certain hepatocellular cancers.

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.

TGT3, thyroid transcription factor I, and Sp1 elements regulate transcriptional activity of the 1.3-kilobase pair promoter of T1alpha, a lung alveolar type I cell gene

Alveolar type I epithelial cells form the major surface for gas exchange in the lung. To explore how type I cells differ in gene expression from their progenitor alveolar type II cells, we analyzed transcriptional regulation of T1alpha, a gene expressed by adult type I but not type II cells. In vivo developmental patterns of T1alpha expression in lung and brain suggest active gene regulation. We cloned and sequenced 1.25 kilobase pairs of the T1alpha promoter that can drive reporter expression in lung epithelial cell lines. Deletion analyses identified regions important for lung cell expression. The base pair (bp) -100 to -170 fragment conferred differential regulation in lung epithelial cells compared with fibroblasts. Sequence alignment of this fragment with type II-specific surfactant protein B and C promoters shows similar consensus elements arranged in a different order. Gel retardation studies with alveolar epithelial cell line nuclear extracts, thyroid transcription factor I (TTF-1) homeodomain, hepatic nuclear factor (HNF)-3beta, or Sp1 proteins, and supershift assays were used to characterize TTF-1, HNF-3 (TGT3), and Sp1/Sp3 binding sites. The TGT3 site binds factors with binding properties similar to HNF-3/Fkh (hepatic nuclear factor-3/forkhead) proteins but different from HNF-3alpha or HNF-3beta. Co-transfection with a TTF-1 expression vector moderately transactivated the -170 bp-reporter construct. Mutational analysis of these three binding sites showed reduced transcriptional activity of the -170 bp promoter. Therefore, several regulatory sequences involved in type II cell gene regulation are also present in the T1alpha promoter, suggesting that genes of the peripheral lung epithelium may be regulated by similar factors.

Cloning and characterization of the 5'-flanking region of the mouse diastrophic dysplasia sulfate transporter gene

Dyastrophic dysplasia sulfate transporter (DTDST) plays an important role in proteoglycan synthesis in the extracellular matrix of bone and cartilage. Recently, we found that the mouse DTDST gene was induced in pluripotent C3H10T1/2 cells during differentiation by bone morphogenetic protein-2 (BMP-2). To clarify the transcriptional regulation of the DTDST gene, we have cloned the 5'-flanking region of the mouse DTDST gene by the PCR based gene walking method. Sequence analysis revealed the presence of the TATA box followed by GC rich sequences containing two Sp-1 binding sites and a CBFA1 binding site. Transient transfection assays demonstrated that the basal transcriptional activity in osteoblastic MC3T3-E1 cells was mainly present between -309 and -275 bp upstream of the transcription start site (Segment -309/-275) which contained the consensus sequence for the xenobiotic-responsible element (XRE). Nuclear proteins from MC3T3-E1 cells and C3H10T1/2 cells could bind to this short segment in vitro. BMP-2 increased the promoter activity as well as the nuclear protein binding to the sequence in C3H10T1/2 cells. The present data suggest that the DTDST gene expression in osteoblasts and differentiating precursor cells to osteoblast/chondrocyte lineage would be mainly regulated by undetermined XRE binding transcription factors.

Cis-elements required for the demethylation of the mouse M-lysozyme downstream enhancer

The mouse lysozyme downstream enhancer was previously colocalized with the DNase I-hypersensitive site in the chromatin of mature macrophages. This hypersensitive site was shown to be macrophage differentiation-dependent. Demethylation of CpG sequences within the enhancer is correlated with lysozyme expression in mature macrophages. Binding of the GABP heterotetrameric transcription factor to the enhancer core element (MLDE), only seen in vivo on the demethylated MLDE element in macrophages, is inhibited by DNA methylation. Here, we analyzed the DNA sequences required for demethylation. In electrophoretic mobility shift experiments we found that in addition to the complete methylated MLDE the hemimethylated form of the lower strand inhibits GABP binding as well. Therefore, GABP is unlikely to be the mediator of demethylation. In addition, we show by stable DNA transfections of methylated mouse lysozyme enhancer sequences that MLDE-flanking sequences are required for demethylation. We narrowed down these DNA elements to two short regions of 163 and 79 base pairs on either side of the MLDE, each of which is sufficient to mediate demethylation of the GABP site.