Functional characterization of mouse syndecan-1 promoter

Syndecan-1 (CD138), Carcinomas and EMT

Cell surface proteoglycans are known to be important regulators of many aspects of cell behavior. The principal family of transmembrane proteoglycans is the syndecans, of which there are four in mammals. Syndecan-1 is mostly restricted to epithelia, and bears heparan sulfate chains that are capable of interacting with a large array of polypeptides, including extracellular matrix components and potent mediators of proliferation, adhesion and migration. For this reason, it has been studied extensively with respect to carcinomas and tumor progression. Frequently, but not always, syndecan-1 levels decrease as tumor grade, stage and invasiveness and dedifferentiation increase. This parallels experiments that show depletion of syndecan-1 can be accompanied by loss of cadherin-mediated adhesion. However, in some tumors, levels of syndecan-1 increase, but the characterization of its distribution is relevant. There can be loss of membrane staining, but acquisition of cytoplasmic and/or nuclear staining that is abnormal. Moreover, the appearance of syndecan-1 in the tumor stroma, either associated with its cellular component or the collagenous matrix, is nearly always a sign of poor prognosis. Given its relevance to myeloma progression, syndecan-1-directed antibody—toxin conjugates are being tested in clinical and preclinical trials, and may have future relevance to some carcinomas.

A stem cell reporter based platform to identify and target drug resistant stem cells in myeloid leukemia

Intratumoral heterogeneity is a common feature of many myeloid leukemias and a significant reason for treatment failure and relapse. Thus, identifying the cells responsible for residual disease and leukemia re-growth is critical to better understanding how they are regulated. Here, we show that a knock-in reporter mouse for the stem cell gene Musashi 2 (Msi2) allows identification of leukemia stem cells in aggressive myeloid malignancies, and provides a strategy for defining their core dependencies. Specifically, we carry out a high throughput screen using Msi2-reporter blast crisis chronic myeloid leukemia (bcCML) and identify several adhesion molecules that are preferentially expressed in therapy resistant bcCML cells and play a key role in bcCML. In particular, we focus on syndecan-1, whose deletion triggers defects in bcCML growth and propagation and markedly improves survival of transplanted mice. Further, live imaging reveals that the spatiotemporal dynamics of leukemia cells are critically dependent on syndecan signaling, as loss of this signal impairs their localization, migration and dissemination to distant sites. Finally, at a molecular level, syndecan loss directly impairs integrin β7 function, suggesting that syndecan exerts its influence, at least in part, by coordinating integrin activity in bcCML. These data present a platform for delineating the biological underpinnings of leukemia stem cell function, and highlight the Sdc1-Itgβ7 signaling axis as a key regulatory control point for bcCML growth and dissemination.

Estrogen receptor α regulates the expression of syndecan-1 in human breast carcinoma cells

Breast cancer (BC) is the primary cause of cancer-related mortality among women. Patients who express the estrogen receptor (ER), which mediates the tumorigenic effects of estrogens, respond to antihormonal therapy. Loss of ER expression or acquired resistance to E2 is associated with aggressive malignant phenotypes, which lead to relapse. These BC subtypes overexpress syndecan-1 (SDC1), a transmembrane heparan sulfate proteoglycan that mediates angiogenesis as well as the proliferation and invasiveness of cancer cells. We showed here that the activation of ER-alpha (ERα) by estrogens induces downregulation of SDC1 expression in ER(+) MCF7 cells but not in T47D cells. Loss of ERα expression, induced by RNA interference or a selective ER downregulator, led to subsequent SDC1 overexpression. E2-dependent downregulation of SDC1 expression required de novo protein synthesis and was antagonized by treatment with BAY 11-7085, an irreversible inhibitor of IκBα phosphorylation, which inhibits the activation of NFκB. Downregulation of SDC1 expression required ERα and activation of IKK, but was independent to downstream transcriptional regulators of NFκB. BAY 11-7085 prevented E2-mediated phosphorylation of ERα on Ser118, increasing its proteasomal degradation, suggesting that IKK stabilized E2-activated ERα, leading to subsequent downregulation of SDC1 expression. Our results showed that sustained ER signaling inhibits SDC1 expression. Such antagonism elucidates the inverse correlation between SDC1 and ER expression in ER(+) BC as well as the overexpression of SDC1 in hormone receptor-negative BC subtypes with the most aggressive phenotypes. These results identify SDC1 as an attractive therapeutic target for BC as well as for other endocrine-associated cancers.

Molecular targets and signaling pathways regulated by nuclear translocation of syndecan-1

Background

The cell-surface heparan sulfate proteoglycan syndecan-1 is important for tumor cell proliferation, migration, and cell cycle regulation in a broad spectrum of malignancies. Syndecan-1, however, also translocates to the cell nucleus, where it might regulate various molecular functions.

Results

We used a fibrosarcoma model to dissect the functions of syndecan-1 related to the nucleus and separate them from functions related to the cell-surface. Nuclear translocation of syndecan-1 hampered the proliferation of fibrosarcoma cells compared to the mutant lacking nuclear localization signal. The growth inhibitory effect of nuclear syndecan-1 was accompanied by significant accumulation of cells in the G0/G1 phase, which indicated a possible G1/S phase arrest.

We implemented multiple, unsupervised global transcriptome and proteome profiling approaches and combined them with functional assays to disclose the molecular mechanisms that governed nuclear translocation and its related functions. We identified genes and pathways related to the nuclear compartment with network enrichment analysis of the transcriptome and proteome. The TGF-β pathway was activated by nuclear syndecan-1, and three genes were significantly altered with the deletion of nuclear localization signal: EGR-1 (early growth response 1), NEK11 (never-in-mitosis gene a-related kinase 11), and DOCK8 (dedicator of cytokinesis 8). These candidate genes were coupled to growth and cell-cycle regulation. Nuclear translocation of syndecan-1 influenced the activity of several other transcription factors, including E2F, NFκβ, and OCT-1. The transcripts and proteins affected by syndecan-1 showed a striking overlap in their corresponding biological processes. These processes were dominated by protein phosphorylation and post-translation modifications, indicative of alterations in intracellular signaling. In addition, we identified molecules involved in the known functions of syndecan-1, including extracellular matrix organization and transmembrane transport.

Conclusion

Collectively, abrogation of nuclear translocation of syndecan-1 resulted in a set of changes clustering in distinct patterns, which highlighted the functional importance of nuclear syndecan-1 in hampering cell proliferation and the cell cycle. This study emphasizes the importance of the localization of syndecan-1 when considering its effects on tumor cell fate.

Electronic supplementary material

The online version of this article (10.1186/s12860-017-0150-z) contains supplementary material, which is available to authorized users.

Insights into the key roles of proteoglycans in breast cancer biology and translational medicine

Proteoglycans control numerous normal and pathological processes, among which are morphogenesis, tissue repair, inflammation, vascularization and cancer metastasis. During tumor development and growth, proteoglycan expression is markedly modified in the tumor microenvironment. Altered expression of proteoglycans on tumor and stromal cell membranes affects cancer cell signaling, growth and survival, cell adhesion, migration and angiogenesis. Despite the high complexity and heterogeneity of breast cancer, the rapid evolution in our knowledge that proteoglycans are among the key players in the breast tumor microenvironment suggests their potential as pharmacological targets in this type of cancer. It has been recently suggested that pharmacological treatment may target proteoglycan metabolism, their utilization as targets for immunotherapy or their direct use as therapeutic agents. The diversity inherent in the proteoglycans that will be presented herein provides the potential for multiple layers of regulation of breast tumor behavior. This review summarizes recent developments concerning the biology of selected proteoglycans in breast cancer, and presents potential targeted therapeutic approaches based on their novel key roles in breast cancer.

Increased SNAIL expression and low syndecan levels are associated with high Gleason grade in prostate cancer

Prostate cancer (PC) is a leading male oncologic malignancy wideworld. During malignant transformation, normal epithelial cells undergo genetic and morphological changes known as epithelial-mesenchymal transition (EMT). Several regulatory genes and specific marker proteins are involved in PC EMT. Recently, syndecans have been associated with malignancy grade and Gleason score in PC. Considering that SNAIL is mainly a gene repressor increased in PC and that syndecan promoters have putative binding sites for this repressor, we propose that SNAIL might regulate syndecan expression during PC EMT. The aim of this study was to analyze immunochemically the expression of SNAIL, syndecans 1 and 2 and other EMT markers in a tissue microarray (TMA) of PC samples and PC cell lines. The TMAs included PC samples of different Gleason grade and benign prostatic hyperplasia (BPH) samples, as non-malignant controls. PC3 and LNCaP cell lines were used as models of PC representing different tumorigenic capacities. Semi-quantitative immunohistochemistry was performed on TMAs and fluorescence immunocytochemistry and western blot analysis were conducted on cell cultures. Results show that SNAIL exhibits increased expression in high Gleason specimens compared to low histological grade and BPH samples. Accordingly, PC3 cells show higher SNAIL expression levels compared to LNCaP cells. Conversely, syndecan 1, similarly to E-cadherin (a known marker of EMT), shows a decreased expression in high Gleason grades samples and PC3 cells. Interestingly, syndecan 2 shows no changes associated to histological grade. It is concluded that increased SNAIL levels in advanced PC are associated with low expression of syndecan 1. The mechanism by which SNAIL regulates the expression of syndecan 1 remains to be investigated.

Alteration of endothelial proteoglycan and heparanase gene expression by high glucose, insulin and heparin

Heparan sulfate proteoglycans (HSPGs) contain a core protein with glycosaminoglycans attached. Reduced glycosaminoglycan, in endothelial HSPGs syndecan and perlecan, is associated with diabetic cardiovascular complications but changes in core protein remain controversial. Since heparanase degrades heparan sulfate, we wished to determine if changes in endothelial heparanase mRNA, by high glucose (HG), correlate with changes in syndecan and perlecan core proteins, and to observe effects of heparin or insulin. RNA was isolated from cultured human aortic endothelial cells treated with HG (30mM), insulin (0.01 units/mL), heparin (0.5μg/mL), HG plus heparin and/or insulin for 24h. Real time PCR revealed that HG alone significantly increased heparanase, decreased syndecan with no effect on perlecan mRNA. Heparin or insulin significantly prevented the increase in heparanase but decreased perlecan mRNA while heparin, but not insulin, prevented the decrease in syndecan mRNA in HG treated cells. HG plus heparin and insulin increased heparanase and syndecan mRNA compared to all other treatments and decreased perlecan mRNA compared to control and HG alone. Heparin may protect endothelium from HG injury by reducing heparanase and increasing syndecan while insulin inhibits heparanase expression. Effects with insulin plus heparin suggest interference in transcriptional regulation of heparanase and syndecan genes.

Syndecan-1 - A new piece in B-cell puzzle

Syndecans are transmembrane proteoglycans, with core proteins mainly decorated with heparan sulfate chains. Syndecan-1 is expressed in a tissue-, cell-and differentiation-specific manner. Its extra-cellular domain can bind via HS chains to matrix elements, to growth factors (especially "heparin-binding" proteins) and to certain biological agents. The ectodomain released by proteolysis can also be functionally active. The cytoplasmic domain can take part in signaling processes as well as in modifying cell shape. In hematopoietic cells syndecan-1 is expressed in normal pre-B-cells and plasma cells, as well as in plasmocytoid and lymphoplasmocytoid malignancies. According to our study syndecan-1 is expressed in B-CLL cells both in tissue environment and in circulation.

Analysis of syndecan-1 gene promoter during mouse tooth development

OBJECTIVE

Syndecan-1 plays an important role in cell proliferation in dental papilla during tooth development. This study aimed to clarify the transcription mechanisms that regulate syndecan-1 gene expression in dental papilla.

DESIGN

We analysed genomic conservation and putative transcriptional factor binding sites of syndecan-1 gene loci using the bioinformatics tool VISTA. To identify the region responsible for syndecan-1 gene expression in mouse dental papilla cells (MDPCs) in vitro, the 1.5-kb upstream region of the mouse syndecan-1 coding region was inserted upstream of the enhanced green fluorescent protein (EGFP) or luciferase gene, and promoter activity was examined by transient reporter gene expression assay in cultured MDPCs. To examine the binding of the upstream binding factor, we performed chromatin immunoprecipitation (ChIP) assay.

RESULTS

VISTA analysis showed that the 1.5-kb upstream region was highly conserved amongst species, and three GC-rich motifs, as well as a TATA-box-like motif, were identified in this region. Reporter gene assay showed that the 1.5-kb upstream region of mouse syndecan-1 induced reporter gene expression in MDPCs. Deletion of the promoter from the 5'-end to 339 bp upstream reduced luciferase activity by nearly half vs. the 1.5-kb sequence. Further deletion up to 68 bp resulted in further loss of luciferase activity. On ChIP assay, we found direct recruitment of Sp3 transcription factor to the GC-rich motif region.

CONCLUSION

The 1.5-kb upstream region of the syndecan-1 gene was sufficient to induce its expression in dental papilla, and binding of Sp3 transcription factor may play a pivotal role in this syndecan-1 induction.

In vitro and ex vivo green fluorescent protein expression in alveolar mammary epithelial cells and mammary glands driven by the distal 5'-regulative sequence and intron 1 of the goat beta-casein gene

The 5'-regulative sequence and intron 1 of the goat beta-casein gene from -4044 to +2123 bp was cloned and fused with the reporter gene of green fluorescent protein (GFP) to create a plasmid termed pGB562/GFP. To detect GFP expression, pGB562/GFP was transfected in vitro via liposomes into the mammary epithelial cell line NMuMG. Cells could not express GFP unless the transfected NMuMG cells lined up to create functional alveoli. These functional cells were cultured with lactogenic hormones, including insulin, dexamethasone and prolactin, and were grown on a layer of the extracellular matrix Matrigel. Green fluorescent protein expression levels in NMuMG cells were 25-, 55- and 42-fold those in the control group at 24, 48, and 72 h after pGB562/GFP transfection respectively. In addition, pGB562/GFP was transfected ex vivo by electroporation into mammary gland fragments and cells were then cultured in vitro with a supplement of lactogenic hormones. Strong GFP expression localized in fragments of the mammary gland was observed 24 h after gene transfer. The novel strategy of ex vivo gene transfer into mammary tissue using GFP as a reporter gene to detect the function of a tissue-specific promoter is efficient and convenient. The data obtained herein reveal that the 5'-regulative sequence and intron 1 of the 6.2 kb goat beta-casein gene can enhance the efficiency of transgene expression. Thus, the GB562 sequence may act as a good promoter and effectively elevate the production of exogenous protein in mammary glands.

Genomic Loci Modulating the Retinal Transcriptome in Wound Healing

Purpose

The present study predicts and tests genetic networks that modulate gene expression during the retinal wound-healing response.

Methods

Upstream modulators and target genes were defined using meta-analysis and bioinformatic approaches. Quantitative trait loci (QTLs) for retinal acute phase genes (Vazquez-Chona et al. 2005) were defined using QTL analysis of CNS gene expression (Chesler et al. 2005). Candidate modulators were defined using computational analysis of gene and motif sequences. The effect of candidate genes on wound healing was tested using animal models of gene expression.

Results

A network of early wound-healing genes is modulated by a locus on chromosome 12. The genetic background of the locus altered the wound-healing response of the retina. The C57BL/6 allele conferred enhanced expression of neuronal marker Thy1 and heat-shock-like crystallins, whereas the DBA/2J allele correlated with greater levels of the classic marker of retinal stress, glial fibrillary acidic protein (GFAP). Id2 and Lpin1 are candidate upstream modulators as they strongly correlated with the segregation of DBA/2J and C57BL/6 alleles, and their dosage levels correlated with the enhanced expression of survival genes ( Thy1 and crystallin genes).

Conclusion

We defined a genetic network associated with the retinal acute injury response. Using genetic linkage analysis of natural transcript variation, we identified regulatory loci and candidate modulators that control transcript levels of acute phase genes. Our results support the convergence of gene expression profiling, QTL analysis, and bioinformatics as a rational approach to discover molecular pathways controlling retinal wound healing.

Reduced expression of syndecan-1 correlates with histologic dedifferentiation, lymph node metastasis, and poor prognosis in intrahepatic cholangiocarcinoma

Syndecan-1, a cell-surface transmembrane heparan sulfate proteoglycan, has been reported to correlate with the biologic behavior of malignant tumors in various organs. We examined the correlation between the expression of syndecan-1 at the protein and mRNA levels and clinicopathologic features of 37 intrahepatic cholangiocarcinomas (ICCs). Noncancerous bile duct epithelial cells showed basolateral membranous expression of syndecan-1, whereas ICC cells showed membranous and also diffuse cytoplasmic expression. In situ hybridization demonstrated a distribution of syndecan-1 mRNA similar to that of the protein in carcinoma tissue, suggesting that syndecan-1 expression in ICC is regulated at the transcriptional level. Reduction of syndecan-1 expression in carcinoma was associated with poor histological differentiation (P <0.01): syndecan-1 expression was intense and extensive in well-differentiated (10 cases) and largely negative or weakly positive in poorly differentiated (13 cases) adenocarcinoma, and its expression in moderately differentiated tumors (14 cases) was intermediate. Patients with ICCs demonstrating negative or weak expression of syndecan-1 frequently had lymph node metastases and had a rather poor prognosis after surgical resection compared with those whose tumors demonstrated moderate or strong expression (P <0.05). However, syndecan-1 expression was not correlated with tumor size, stromal desmoplasia, gross classification, vascular invasion, or perineural invasion. We conclude that expression of syndecan-1 could correlate with some aspects of the biologic behaviors of ICCs and may be a useful prognostic marker.

Proximal promoter of the murine syndecan-1 gene is not sufficient for the developmental pattern of syndecan expression in B lineage cells

Syndecan-1 (CD138) is a cell membrane proteoglycan that binds extracellular matrix components and various growth factors. The role of syndecan-1 in the control of cell growth and morphology has been illustrated by its altered expression in hematological malignancies such as multiple myeloma as well as some solid tumors. It has been reported that the expression of syndecan-1 in cells of the B lineage is developmentally regulated such that pre-B cells and plasma cells express syndecan-1 while mature B cells do not. Thus, we investigated whether the proximal promoter region of the murine syndecan-1 promoter was able to confer the observed on-off-on expression of syndecan-1 in cells of the B lineage as they develop from pre-B cells to plasma cells. Experiments carried out using deletion mutants of the proximal promoter cloned upstream of the CAT reporter gene transfected into murine cell lines, representing the above stages of B-cell development, such as BA/F3 (pro-B cell), 70Z/3 (pre-B cell), 2PK3 (late mature B cell), and MPC-11 (plasma cell), showed detectable levels of CAT expression. The WEHI-231 (mature B cell) cell lines did not show detectable levels of CAT reporter activity. The strong levels of expression were observed with a fragment of the proximal promoter spanning the region from -365 to -95 (from the translation start point). However, Northern analysis of RNA obtained from the five murine B-cell lines, representing various stages of B-cell development, showed that the 70Z/3, MPC-11 but not BA/F3, and 2PK3 cells expressed detectable levels of syndecan-1 mRNA. By FACS analysis, using a rat anti mouse syndecan-1 antibody, syndecan-1 expression on the cell surface was found to correlate with the observed mRNA expression patterns in these cell lines. Our results indicate that the proximal promoter of the murine syndecan-1 promoter is not sufficient for the observed developmental pattern of syndecan expression in B cells.

Proximal promoter-independent activation of the far-upstream FGF-inducible response element of syndecan-1 gene

Far upstream enhancers are predicted to act by looping and activating general transcription factors on core promoters and to require proximal promoter sequences for appropriate gene activation in time and space. We have previously described an FGF-inducible response element (FiRE) located far upstream on the syndecan-1 gene. The FiRE is activated specifically by members of the fibroblast growth factor (FGF) family in NIH3T3 cells. Here we describe the requirements of syndecan-1 proximal promoter for the activation of FiRE by FGF-2. Transient and stable transfections revealed that neither proximal promoter SP1 sites nor TATA-box are required for the FGF-2 induced activation of FiRE. Notably, the enhancer is activated in both orientations by FGF-2 even in the absence of proximal promoter. Importantly, removal of the promoter did not affect the growth factor specificity of FiRE. Proximal promoter independent activation of syndecan-1 gene by FGF-2 might be required during development when syndecan-1 proximal promoter needs to be largely attenuated but simultaneous transient and rapid FGF-2 induced transcription is required.

Syndecan-1 expression is up-regulated in pancreatic but not in other gastrointestinal cancers

Syndecan-1 belongs to the syndecan family of cell surface transmembrane heparan-sulfate proteoglycans, which participate in cell proliferation, cell migration and cell-matrix interactions. Decreased expression of syndecan-1 has been observed in some gastrointestinal malignancies, and it is thought that high levels of syndecan-1 correlate with the maintenance of epithelial morphology and inhibition of invasiveness. In our study, we characterized the expression of syndecan-1 in normal, chronic pancreatitis and primary and metastatic human pancreatic cancer tissues, in cultured pancreatic cancer cell lines and in esophageal, gastric, colon, and liver cancers. Pancreatic cancer cell lines expressed syndecan-1 mRNA and protein at variable levels. In addition, these cells also released syndecan-1 into the culture medium. Pancreatic cancer tissues markedly over-expressed syndecan-1 mRNA in comparison with both chronic pancreatitis (2.4-fold increase, p < 0.01) and normal pancreatic samples (10.6-fold increase, p < 0.01). There was no difference in syndecan-1 mRNA expression between early and advanced tumors. By in situ hybridization and immunohistochemistry, syndecan-1 expression was evident at relatively low levels in the ductal cells and less frequently in acinar cells of the normal pancreas. In chronic pancreatitis, syndecan-1 was present at low to moderate levels in areas with atrophic acinar cells and ductular complexes. In contrast, in pancreatic cancer tissues, syndecan-1 was present at moderate to high levels in the majority of the cancer cells within the tumor mass and also in metastatic lesions of pancreatic tumors. Syndecan-1 mRNA levels in other gastrointestinal malignancies (esophageal, gastric, colon and liver cancers) were not significantly different from the levels observed in the corresponding normal samples. Together, our findings suggest that syndecan-1 expression by pancreatic cancer cells may be of importance in the pathobiology of this disorder and that its role in pancreatic cancer seems to be different from that in other gastrointestinal malignancies.

Transcriptional targeting of adenoviral gene delivery into migrating wound keratinocytes using FiRE, a growth factor-inducible regulatory element

Impaired cutaneous wound healing is a common complication in diabetes, ischemia and venous insufficiency of lower extremities, and in long-term treatment with corticosteroids or other immunosuppressive agents. In development of gene therapy for wound repair, expression of therapeutic transgenes should be precisely targeted and controlled. Here, we describe a recombinant adenovirus RAdFiRE-EGFP, in which a growth factor inducible element (FiRE) of the murine syndecan-1 gene controls the expression of enhanced green fluorescent protein (EGFP) reporter gene. Treatment of RAdFiRE-EGFP-transduced murine epidermal keratinocytes in culture with FiRE-activating growth factor markedly enhanced the expression of EGFP. In ex vivo organ culture of wounded murine skin transduced with RAdFiRE-EGFP, the EGFP expression was specifically detected in wound margin keratinocytes, but not in intact skin. Activity of EGFP was first detected 2 days after a single application of RAdFiRE-EGFP and persisted up to 10 days. Similarly, FiRE-driven EGFP expression was detected specifically in epidermal keratinocytes in the edge of incisional wounds in murine skin transduced with RAdFiRE-EGFP. In contrast, adenovirus-mediated lacZ expression driven by CMV promoter was detected scattered in epidermal, dermal and subcutaneous layers in ex vivo and in vivo wounds, as well as in intact skin. These data demonstrate the feasibility of FiRE as a tool for transcriptional targeting of adenovirus-mediated transgene expression to cutaneous wound edge keratinocytes.

Functions of cell surface heparan sulfate proteoglycans

The heparan sulfate on the surface of all adherent cells modulates the actions of a large number of extracellular ligands. Members of both cell surface heparan sulfate proteoglycan families, the transmembrane syndecans and the glycosylphosphoinositide-linked glypicans, bind these ligands and enhance formation of their receptor-signaling complexes. These heparan sulfate proteoglycans also immobilize and regulate the turnover of ligands that act at the cell surface. The extracellular domains of these proteoglycans can be shed from the cell surface, generating soluble heparan sulfate proteoglycans that can inhibit interactions at the cell surface. Recent analyses of genetic defects in Drosophila melanogaster, mice, and humans confirm most of these activities in vivo and identify additional processes that involve cell surface heparan sulfate proteoglycans. This chapter focuses on the mechanisms underlying these activities and on the cellular functions that they regulate.

Syndecans and the lymphoid system

Syndecans, transmembrane proteoglycans, play an important role in cell-matrix and cell-cell interactions, as well as modulators in receptor activation. These functions are partly non-specific and related to the heparan sulfate chains attached to the ectodomain, and partly specific due to the transmembrane and cytoplasmic domains of the core protein. In hemopoietic cells syndecan-1 is expressed only in B cells at certain differentiation stages (pre-B and plasma cells). In lymphoproliferative conditions this selective expression is retained in myelomas/plasmacytomas and other lymphoplasmacytic NHL subtypes, and primary effusional lymphomas. It is probably gained in B-CLL, and lost in other NHLs of pre- or post-follicular origin. It is concluded from these empiric results that the expression of syndecan is essential for some NHLs, probably ensuring the required connections to the microenvironment. From a diagnostic point of view, syndecan-1 is a very useful phenotypic marker to indentify cells with plasmacytic differentiation. The importance of syndecan expression in CLL and Hodgkin's lymphoma still requires further studies.

Transcriptional regulation of Syndecan-1 expression by growth factors

Syndecan-1 is a prototype member of a family of transmembrane heparan sulfate proteoglycans. Syndecan-1 binds extracellular matrix components and fibroblast growth factors (FGFs) and modifies the function of FGFs. Syndecan-1 is constitutively expressed by several epithelial cells, but expression is also induced during many biological phenomena, such as tissue regeneration and the epithelial-mesenchymal interactions during organ development. Growth factors have been the prime candidates to induce syndecan-1 expression in these situations. In fibroblasts syndecan-1 is induced by FGF-2 and in keratinocytes by epidermal growth factor (EGF) and keratinocyte growth factor (KGF). The search for cis-acting elements regulating the growth factor-induced syndecan-1 expression has led to identification of a novel FGF-inducible response element (FiRE). FiRE is activated in fibroblasts and keratinocytes by the same growth factors that induce syndecan-1 expression in these cells. In adult tissues the activation of FiRE is restricted to migrating keratinocytes of healing wounds. The composition of the transcription factor binding to FiRE differs depending on the cell type and the activating growth factor. The FiRE provides a powerful tool for studies on growth factor specificity and regeneration of tissues. Moreover, it implies a novel transcriptional link that creates an FGF action-controlling autoregulatory loop between the heparan sulfate proteoglycans and the heparin-binding FGFs.

Extracellular matrix-dependent activation of syndecan-1 expression in keratinocyte growth factor-treated keratinocytes

Syndecan-1 is a major heparan sulfate proteoglycan of the epidermis. Its expression is strongly induced in migrating and proliferating keratinocytes during wound healing and, on the other hand, diminished or lost in invasive squamous cell carcinoma. We have recently found in the syndecan-1 gene an enhancer (fibroblast growth factor-inducible response element (FiRE)) that activates gene expression in wound edge keratinocytes (Jaakkola, P., Kontusaari, S., Kauppi, T., Määttä, A., and Jalkanen, M. (1998) FASEB J. 12, 959-969). Now, we demonstrate that the activation of this enhancer by keratinocyte growth factor (KGF) is modulated by the components of the extracellular matrix (ECM). MCA-3D mouse immortal keratinocytes growing on fibrillar collagen failed to activate FiRE and subsequently to induce syndecan-1 in response to KGF. The same cells growing on fibronectin or laminin, however, increased FiRE-dependent reporter gene expression upon KGF treatment. The inhibition of the KGF induction by collagen appears to be specific for signaling to FiRE, as the increase in cell proliferation by KGF was not affected. The effect was selective to KGF, as EGF-induction was independent on ECM composition. Changes in the transcription factor binding were not involved in the differential activation of FiRE, as the levels and composition of the AP-1 complexes were unchanged. However, application of anisomycin, an activator of Jun amino-terminal kinase, resulted in a lower response in cells growing on collagen compared with fibronectin. These results indicate that the composition of ECM and availability of growth factors can play a role in the epidermal regulation of syndecan-1 expression and that FiRE is a novel target for gene regulation by the extracellular matrix.

Transcriptional and posttranscriptional regulation of proteoglycan gene expression

Proteoglycans are among the most complex and sophisticated molecules of mammalian systems in terms of their protein and carbohydrate moieties. These macromolecules are in a continuous interplay with each other and the cell surface signal-transducing pathways, some of which are beginning to be elucidated. Because of their domain structure, catalytic potential, and diversity, these molecules appear to be designed for integrating numerous signaling events. For example, some proteoglycans interact with hyaluronan and lectins, thereby linking cell surfaces and distant matrix molecules. Some interact with collagen during the complex process of fibrillogenesis and regulate this biological process fundamental to animal life. Others interact with growth factors and serve as depot available during growth or tissue remodeling. In this review, we center on the most recent developments of proteoglycan biology, focusing primarily on genomic organization and transcriptional and posttranscriptional control. We discuss only those proteoglycans whose gene and promoter elements have been characterized and proved to be functional. When possible, we correlate the effects of growth factors and cytokines on proteoglycan gene expression with the topology of cis-acting elements in their genomic control regions. The analysis leads to a comprehensive critical appraisal of the principles that underlie the regulation of proteoglycan gene expression and to the delineation of common regulatory mechanisms.

Biglycan gene expression in the human leiomyosarcoma cell line SK-UT-1. Basal and protein kinase A-induced transcription involves binding of Sp1-like/Sp3 proteins in the proximal promoter region

In this study we demonstrate that the gene encoding the small leucine-rich proteoglycan biglycan is expressed in human myometrial tissue and in the human leiomyosarcoma cell line SK-UT-1. Treatment of SK-UT-1 cells with forskolin or 8-bromo-cAMP strongly increased biglycan mRNA and this effect was transcriptional as shown by transient transfection experiments with biglycan promoter-luciferase reporter fusion genes. The cAMP-mediated induction of the transfected biglycan promoter in SK-UT-1 cells was abolished by coexpression of a specific protein kinase A inhibitor, and was mimicked by overexpression of the catalytic subunit (Cbeta) of protein kinase A. By 5' deletion analysis, part of the cAMP response was localized to the segment from residues -78 to -46 of the biglycan promoter. This region conferred strong cAMP responsiveness to a heterologous promoter. Electrophoretic mobility shift and antibody supershift assays identified two specific complexes that contained nuclear proteins antigenically related to the ubiquitous transcription factors Sp1 and Sp3, respectively. The binding site of these proteins was mapped to a CT-rich sequence extending from -59 to -49 in the biglycan promoter. Mutating this sequence eliminated complex formation and markedly reduced basal and cAMP-dependent promoter activity of transfected reporter genes. In vitro binding studies using recombinant Sp1 revealed that the nuclear factor binding to the CT element was not Sp1 but a Sp1-like protein(s). Western blot analysis of SK-UT-1 nuclear proteins confirmed expression of Sp3, Sp1 and nuclear proteins that crossreacted with Sp1 antibody but according to their molecular weight were not Sp1. These results indicate that all cAMP-dependent as well as some basal biglycan transcription in SK-UT-1 cells is mediated through activated protein kinase A and that both functions are conferred at the promoter level through the interaction of Sp1-like/Sp3 factors with the CT element at -59 in the biglycan promoter.

Wound reepithelialization activates a growth factor-responsive enhancer in migrating keratinocytes

Wound reepithelialization and keratinocyte migration require strictly ordered gene expression, which is assumed to be initiated by locally released mitogens and exposure of the cells to different matrix components. The mechanisms triggering gene expression specifically during reepithelialization are poorly understood. The far upstream AP-1-driven, FGF-inducible response element (FiRE) of the syndecan-1 gene was activated during cutaneous wound healing in transgenic mice. FiRE was induced selectively in migrating but not in proliferating keratinocytes at the wound edge. The activation was initiated at the start of the cell migration, was persistent throughout the merging and stratification phases, and was terminated after completion of reepithelialization. Although FiRE has been found within the gene of syndecan-1, the proximal promoter of syndecan-1 was not required for activation of FiRE in the migrating keratinocytes. The wounding induced activation was inhibited by blocking cell surface growth factor receptors with suramin. However, the activation of FiRE in resting skin required simultaneous growth factor- and stress-induced signals, but could also be elicited by the phosphatase inhibitor, okadaic acid. The activation by both wounding and chemical stimuli was blocked by inhibiting extracellular regulated kinase and p38 MAP kinases, suggesting the involvement of at least two parallel signal transduction pathways in wounding induced gene activation. As FiRE shows specificity for migrating keratinocytes only, it can be a useful tool for future wound healing studies and for targeting genes to injured tissues.

Organization, 5'-flanking sequence and promoter activity of the rat GPC1 gene

Glypicans are a member of a family of glycosylphosphatidylinositol anchored heparan sulfate proteoglycans that are expressed in cell and development specific patterns. Rat GPC1 cDNA probes were used to screen rat genomic libraries. Three overlapping genomic clones that contained the entire rat GPC1 gene were isolated. The rat GPC1 gene is approximately 15kb in length and consists of eight exons interrupted by introns of varying lengths. Two of the introns are quite short, with lengths of 41 and 43 base pairs. Each exon-intron splice junction exhibited the consensus splice site sequence. Exon 1 encodes the putative signal peptide and the serine residue of the first putative heparan sulfate attachment site. The last exon encodes the cluster of three potential COOH-terminal heparan sulfate attachment sites, the putative GPI anchor and polypeptide cleavage site, and the 3'-untranslated region including the polyadenylation signal. One of the genomic clones extended approximately 2.8 kb 5' of the exon 1 coding sequence, and is thus likely to contain sequences that regulate GPC1 gene expression. Sequence analysis of the 5'-flanking sequence revealed a lack of consensus TATA and CAAT boxes. A search for potential transcription factor binding sites revealed a number of such motifs, including Sp1 (GC box), NF-kappaB, and MyoD (E-box). This region of the rat GPC1 gene shows significant sequence homology to the 5'-flanking region of the human GPC3 gene. Functional promoter activity of the rat GPC1 sequence was demonstrated by its ability to drive the expression of a luciferase reporter gene in several cell types.

Expression of syndecan-1 in human B cell chronic lymphocytic leukaemia

Syndecan-1 is considered an important transmembrane proteoglycan in cell-microenvironment interactions, but its exact function in normal or in transformed B cells is still unknown. In this study, RNA was isolated from peripheral cells of chronic lymphocytic leukaemia (B-CLL) and 'normal', non-leukaemic patients, as controls. Reverse PCR showed no or very low syndecan-1 mRNA expression in controls, while in 11/13 B-CLL the circulating leukaemic cells expressed syndecan-1. Similar results were obtained for interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6). Furthermore, syndecan-1 protein was detected in the majority of circulating B-CLL cells by flow cytometry and immunocytochemistry using anti-syndecan-1 MAb. Control cells were practically negative. Further study is required to understand the biological significance of syndecan-1 on B-CLL cells.

Syndecans: multifunctional cell-surface co-receptors

This review will summarize our current state of knowledge of the structure, biochemical properties and functions of syndecans, a family of transmembrane heparan sulphate proteoglycans. Syndecans bind a variety of extracellular ligands via their covalently attached heparan sulphate chains. Syndecans have been proposed to play a role in a variety of cellular functions, including cell proliferation and cell-matrix and cell-cell adhesion. Syndecan expression is highly regulated and is cell-type- and developmental-stage-specific. The main function of syndecans appears to be to modulate the ligand-dependent activation of primary signalling receptors at the cell surface. Principal functions of the syndecan core proteins are to target the heparan sulphate chains to the appropriate plasma-membrane compartment and to interact with components of the actin-based cytoskeleton. Several functions of the syndecans, including syndecan oligomerization and actin cytoskeleton association, have been localized to specific structural domains of syndecan core proteins.

CpG islands from the alpha-globin gene cluster increase gene expression in an integration-dependent manner

In contrast to other globin genes, the human and rabbit alpha-globin genes are expressed in transfected erythroid and nonerythroid cells in the absence of an enhancer. This enhancer-independent expression of the alpha-globin gene requires extensive sequences not only from the 5' flanking sequence but also from the intragenic region. However, the features of these internal sequences that are responsible for their positive effect are unclear. We tested several possible determinants of this activity. One possibility is that a previously identified array of discrete binding sites for known and potential regulatory proteins within the alpha-globin gene comprise an intragenic enhancer specific for the alpha-globin promoter, but directed rearrangements of the sequences show that this is not the case. Alternatively, the promoter may extend into the gene, with the function of the discrete binding sites being dependent on maintenance of their proper positions and orientations relative to the 5' flanking sequence. However, the positive effects observed in gene fusions do not localize to a discrete region of the alpha-globin gene and the results of internal deletions and point mutations argue against a required role of the targeted discrete binding sites. A third possibility is that the CpG island, which includes both the 5' flanking and intragenic regions associated with the positive activity, may itself have a more general effect on expression in transfected cells. Indeed, we show that the size of the CpG island in constructs correlates with the level of gene expression. Furthermore, the alpha-globin promoter is more active in the context of a previously inactive CpG island than in an A+T-rich context, showing that the CpG island provides an environment more permissive for expression. These effects are seen only after integration, suggesting a possible mechanism at the level of chromatin structure.

Expression of perlecan, a proteoglycan that binds myogenic inhibitory basic fibroblast growth factor, is down regulated during skeletal muscle differentiation

Heparan sulfate proteoglycans (HSPG) have been shown to be involved in the activation of tyrosine kinase receptors by basic fibroblasts growth factor (bFGF), a strong inhibitor of skeletal muscle differentiation. Skeletal muscle fibers contact extracellular matrix (ECM) that surrounds individual fibers (endomysium) and bundles of several fibers (perimysium). Perlecan is a HSPG present in the majority of basement membranes. In this study we evaluated the expression and localization of perlecan during differentiation of C2C12 skeletal muscle cells. C2C12 myoblasts incubated with [35S]Na2SO4 synthesize a HSPG that can be specifically immunoprecipitated with antibodies against murine perlecan. The immunoprecipitated HSPG eluted from a Sepharose CL-4B with a Kav of 0.44. Analysis of the core protein of the HSPG immunoprecipitated from [35S]methionine-labeled C2C12 after treatment with heparitinase revealed two polypeptides of 170 and over 300 kDa. The amount of polypeptides immunoprecipitated decreased with muscle differentiation. Immunocytolocalization studies indicate that perlecan is localized on the myoblast surface and by immunogold staining we have demonstrated that it is associated with patches of incipient extracellular matrix. The expression of perlecan mRNA decreased substantially during skeletal muscle differentiation, in contrast to the increase in transcripts for specific skeletal muscle proteins such as myogenin and creatine kinase. By immunofluorescence microscopy almost no perlecan staining associated with the surface of myotubes was observed. All these results suggests that perlecan, a HSPG that binds myogenic inhibitory bFGF, normally associated with basement membranes in adult tissues is present on the surface of myoblasts and its expression is down regulated during skeletal muscle differentiation.

Syndecan-1 expression is down-regulated during myoblast terminal differentiation. Modulation by growth factors and retinoic acid

Syndecan-1 is an integral membrane proteoglycan involved in the interaction of cells with extracellular matrix proteins and growth factors. It is transiently expressed in several condensing mesenchymal tissues after epithelial induction. In this study we evaluated the expression of syndecan-1 during skeletal muscle differentiation. The expression of syndecan-1 as determined by Northern blot analyses and immunofluorescence microscopy is down-regulated during differentiation. The transcriptional activity of a syndecan-1 promoter construct is also down-regulated in differentiating muscle cells. The decrease in syndecan-1 gene expression is not dependent on the presence of E-boxes, binding sites for the MyoD family of transcription factors in the promoter region, or myogenin expression. Deletion of the region containing the E-boxes or treatment of differentiating cells with sodium butyrate, an inhibitor of myogenin expression, had no effect on syndecan-1 expression. Basic fibroblast growth factor and transforming growth factor type beta, which are inhibitors of myogenesis, had little effect on syndecan-1 expression. When added together, however, they induced syndecan-1 expression. Retinoic acid, an inducer of myogenesis, inhibited syndecan-1 expression and abolished the effect of the growth factors. These results indicate that syndecan-1 expression is down-regulated during myogenesis and that growth factors and retinoic acid modulate syndecan-1 expression by a mechanism that is independent of myogenin.

Activation of an enhancer on the syndecan-1 gene is restricted to fibroblast growth factor family members in mesenchymal cells

Fibroblast growth factors (FGFs) induce a variety of biological effects on different cell types. They activate a number of genes, including immediate-early genes, such as the transcription factors Fos and Jun, which are also common targets for other tyrosine kinase receptor-activating growth factors. Here we describe a secondary far-upstream enhancer on the syndecan-1 gene that is activated only by members of the FGF family in NIH 3T3 cells, not by other receptor tyrosine kinase-activating growth factors (e.g., epidermal growth factor, platelet-derived growth factor, insulin-like growth factor, or serum). This FGF-inducible response element (FiRE) consists of a 170-bp array of five DNA motifs which bind two FGF-inducible Fos-Jun heterodimers, one inducible AP-2-related protein, a constitutively expressed upstream stimulatory factor, and one constitutive 46-kDa transcription factor. Mutational analysis showed that both AP-1 binding motifs are required, but not sufficient, for FiRE activation. Moreover, agents such as 12-O-tetradecanoylphorbol-13-acetate, okadaic acid, or forskolin, which are known to activate AP-1 complexes and AP-1-driven promoters, fail to activate FiRE. However, FiRE can be activated by the tyrosine kinase phosphatase inhibitor orthovanadate. Taken together, this data implies a differential activation of growth factor-initiated signaling on AP-1-driven regulatory elements.

A GT-rich sequence binding the transcription factor Sp1 is crucial for high expression of the human type VII collagen gene (COL7A1) in fibroblasts and keratinocytes

Type VII collagen is the major component of anchoring fibrils, structural elements that stabilize the attachment of the basement membrane to the underlying dermis. In this study, we have dissected the human type VII collagen gene (COL7A1) promoter to characterize the cis-elements responsible for the expression of the gene in cultured fibroblasts and keratinocytes. Using transient cell transfections with various 5' end deletion COL7A1 promoter/chloramphenicol acetyltransferase reporter gene plasmid constructs, we determined that the region between nucleotides -524 and -456, relative to the transcription start site, is critical for high promoter activity in both cell types studied. Gel mobility shift assays using several DNA fragments spanning this region identified a GT-rich sequence between residues -512 and -505, necessary for the binding of nuclear proteins to this region of the promoter. Point mutations abolished the binding of nuclear proteins in gel shift assays and drastically diminished the activity of the promoter in transient cell transfections. Supershift assays with antibodies against various transcription factors including Sp1, Sp3, c-Jun/AP-1, and AP-2, and competition experiments with oligonucleotides containing consensus sequences for Sp1 and AP-1 binding identified Sp1 as the transcription factor binding to this region of the COL7A1 promoter. Indeed, recombinant human Sp1 was shown to bind the COL7A1 promoter GT-rich element but not its mutated form in gel mobility shift assays. In addition, co-transfection of pPacSp1, an expression vector for Sp1, together with the COL7A1 promoter/chloramphenicol acetyltransferase construct into Sp1-deficient Drosophila Schneider SL2 cells unequivocally demonstrated that Sp1 is essential for high expression of the COL7A1 gene. These data represent the first in-depth analysis of the human COL7A1 promoter transcriptional control.

Structural and functional characterization of the human perlecan gene promoter. Transcriptional activation by transforming growth factor-beta via a nuclear factor 1-binding element

Perlecan, a modular heparan sulfate proteoglycan of basement membranes and cell surfaces, plays a crucial role in regulating the assembly of extracellular matrices and the binding of nutrients and growth factors to target cells. To achieve a molecular understanding of perlecan gene regulation, we isolated the 5'-flanking region and investigated its functional promoter activity and its response to cytokines. Transient cell transfection assays, using plasmid constructs harboring the perlecan promoter linked to the chloramphenicol acetyltransferase reporter gene, demonstrated that the largest approximately 2.5-kilobase construct contained maximal promoter activity. This promoter region was functionally active in a variety of cells of diverse histogenetic origin, thus corroborating the widespread expression of this gene product. Stepwise 5' deletion analyses demonstrated that the -461-base pair (bp) proximal promoter retained approximately 90% of the total activity, and internal deletions confirmed that the most proximal sequence was essential for proper promoter activity. Nanomolar amounts of transforming growth factor-beta induced 2-3-fold perlecan mRNA and protein core levels in normal human skin fibroblasts, and this induction was transcriptionally regulated; in contrast, tumor necrosis factor-alpha had no effect and was incapable of counteracting the effects of TGF-beta. Using additional 5' deletions and DNase footprinting analyses, we mapped the TGF-beta responsive region to a sequence of 177 bp contained between -461 and -285. This region harbored a 14-bp element similar to a TGF-beta-responsive element present in the promoters of collagen alpha1(I), alpha2(I), elastin, and growth hormone. Electrophoretic mobility shift assays and mutational analyses demonstrated that the perlecan TGF-beta-responsive element bound specifically to TGF-beta-inducible nuclear proteins with high affinity for NF-1 member(s) of transcription factors.