Selective Sp1 and Sp3 binding is crucial for activity of the integrin alphaV promoter in cultured endothelial cells

p53-dependent CD51 expression contributes to characteristics of cancer stem cells in prostate cancer

Castration-resistant prostate cancer (CRPC), which is considered to contain cancer stem cells (CSCs), leads to a high relapse rate in patients with prostate cancer (PCa). However, the markers of prostate CSCs are controversial. Here we demonstrate that CD51, in part, correlates with the poor prognosis of PCa patients. Further, we find that CD51 is a functional molecule that is able to promote the malignancy of PCa through enhancing tumor initiation, metastatic potential, and chemoresistance. Moreover, we find that elevated CD51 expression in PCa specimens correlates with p53 loss of function. Mechanistically, we demonstrate that p53 acts via Sp1/3 to repress CD51 transcription, and CD51 is required for PCa stemness and metastasis properties, and is downregulated by p53. Taken together, these results indicate that CD51 is a novel functional marker for PCa, which may provide a therapeutic target for the efficiently restricting PCa progression.

Role of the AP-1 transcription factor FOSL1 in endothelial cells adhesion and migration

Vasculogenesis and angiogenesis, the fundamental processes by which new blood vessels are formed, involve the proliferation, migration, and remodeling of endothelial cells. Dynamic adhesion of endothelial cells to extracellular matrix plays a fundamental role in all these events. Key regulators of endothelial cells adhesion and migration are the αvβ3 and uPA-uPAR complexes. The αvβ3 integrin heterodimer is the receptor for extracellular matrix components such as vitronectin and is overexpressed on the cell surface of angiogenic endothelial cells, but not quiescent cells lining normal vessels. The uPA-uPAR complex contributes to extracellular matrix remodeling by mediating proteolytic activity at the leading edge of migrating cells. We recently reported that the FOSL1 transcription factor of the AP-1 family plays a pivotal role in the regulation of the level of the αvβ3 and uPA-uPAR complexes on the surface of endothelial cells. In this commentary, we review the current knowledge of αv and β3 transcriptional regulation in endothelial cells and discuss the role of FOSL1 in angiogenesis.

Transcription of the transforming growth factor beta activating integrin beta8 subunit is regulated by SP3, AP-1, and the p38 pathway

Integrin alphavbeta8 is a critical regulator of transforming growth factor beta activation in vasculogenesis during development, immune regulation, and endothelial/epithelial-mesenchymal homeostasis. Recent studies have suggested roles for integrin beta8 in the pathogenesis of chronic obstructive pulmonary disease, brain arteriovenous malformations, and select cancers (Araya, J., Cambier, S., Markovics, J. A., Wolters, P., Jablons, D., Hill, A., Finkbeiner, W., Jones, K., Broaddus, V. C., Sheppard, D., Barzcak, A., Xiao, Y., Erle, D. J., and Nishimura, S. L. (2007) J. Clin. Invest. 117, 3551-3562; Su, H., Kim, H., Pawlikowska, L., Kitamura, H., Shen, F., Cambier, S., Markovics, J., Lawton, M. T., Sidney, S., Bollen, A. W., Kwok, P. Y., Reichardt, L., Young, W. L., Yang, G. Y., and Nishimura, S. L. (2010) Am. J. Pathol. 176, 1018-1027; Culhane, A. C., and Quackenbush, J. (2009) Cancer Res. 69, 7480-7485; Cambier, S., Mu, D. Z., O'Connell, D., Boylen, K., Travis, W., Liu, W. H., Broaddus, V. C., and Nishimura, S. L. (2000) Cancer Res. 60, 7084-7093). Here we report the first identification and characterization of the promoter for ITGB8. We show that a SP binding site and a cyclic AMP response element (CRE) in the ITGB8 core promoter are required for its expression and that Sp1, Sp3, and several AP-1 transcription factors form a complex that binds to these sites in a p38-dependent manner. Furthermore, we demonstrate the requirement for Sp3, ATF-2, and p38 for the transcription and protein expression of integrin beta8. Additionally, reduction of SP3 or inhibition of p38 blocks alphavbeta8-mediated transforming growth factor beta activation. These results place integrin beta8 expression and activity under the control of ubiquitous transcription factors in a stress-activated and pro-inflammatory pathway.

Sensing invasion: cell surface receptors driving spreading of glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant brain tumour in adults. One main source of its high malignancy is the invasion of isolated tumour cells into the surrounding parenchyma, which makes surgical resection an insufficient therapy in nearly all cases. The invasion is triggered by several cell surface receptors including receptor tyrosine kinases (RTKs), G protein-coupled receptors (GPCRs), TGF-beta receptor, integrins, immunoglobulins, tumour necrosis factor (TNF) family, cytokine receptors, and protein tyrosine phosphatase receptors. The cross-talk between cell-surface receptors and the redundancy of downstream effectors make analysis of invasive signals even more complex. Therapies involving inhibition of single receptors do not give promising outcomes and a thorough knowledge of invasive signals of common and exclusive signalling components is required for design of best combinatory treatment schemes to fight the disease.

Functional characterization of a -100_-102delAAG deletion-insertion polymorphism in the promoter region of the HTR3B gene

OBJECTIVE

The HTR3B gene encodes the B-subunit of the type 3 serotonin receptor (5-HT3). A -100_-102delAAG deletion in the promoter region has been associated with poor response to antiemetic medication and susceptibility to bipolar affective disorders. The molecular mechanisms underlying these associations, however, remained unclear.

METHODS

We performed electrophoretic mobility shift and luciferase reporter gene assays to elucidate the effect of this polymorphism on the HTR3B promoter activity in PC-12 and HEK293 cells. The reporter constructs carried a 2171 bp fragment of the native HTR3B promoter or 30 bp of the polymorphic locus in tandem triplication upstream of the thymidine kinase minimal promoter.

RESULTS

Deletion mapping indicated that the sequence around the -100_-102delAAG polymorphism had significant promoter activity. Electrophoretic mobility shift assays indicated differential binding of nuclear proteins to the polymorphic DNA region with stronger binding to the insertion than to the deletion allele. The activity of the native promoter carrying the deletion allele was 25% higher in PC-12 (P=0.016) and 40% higher in HEK cells (P=0.016) compared with the respective insertion construct. Constructs carrying the deletion allele in tandem triplicates showed 43% (PC-12 cells, P=0.002) and 28% (HEK293 cells, P=0.015) higher activity than those carrying the insertion allele. The polymorphism was not linked with known amino acid substitutions in HTR3A and HTR3B.

CONCLUSIONS

The -100_-102delAAG 3 bp deletion increases the HTR3B promoter activity in vitro. The consequences of this for the structure and the function of the resulting 5-HT3 receptors remain to be elucidated.

Expression of alpha V integrin is modulated by Epstein-Barr virus nuclear antigen 3C and the metastasis suppressor Nm23-H1 through interaction with the GATA-1 and Sp1 transcription factors

Epstein-Barr virus (EBV) is a lymphotrophic herpesvirus infecting most of the world's population. It is associated with a number of human lymphoid and epithelial tumors and lymphoproliferative diseases in immunocompromised patients. A subset of latent EBV antigens is required for immortalization of primary B-lymphocytes. The metastatic suppressor Nm23-H1 which is downregulated in human invasive breast carcinoma reduces the migration and metastatic activity of breast carcinoma cells when expressed from a heterologous promoter. Interestingly, the EBV nuclear antigen 3C (EBNA3C) reverses these activities of Nm23-H1. The alpha V integrins recognize a variety of ligands for signaling and are involved in cell migration and proliferation and also serve as major receptors for extracellular-matrix-mediated cell adhesion and migration. The goal of this study was to determine if Nm23-H1 and EBNA3C can modulate alpha V integrin expression and downstream activities. The results of our studies indicate that Nm23-H1 downregulates alpha V intregrin expression in a dose responsive manner. In contrast, EBNA3C can upregulate alpha V integrin expression. Furthermore, the study showed that the association of the Sp1 and GATA transcription factors with Nm23-H1 is required for modulation of the alpha V integrin activity. Thus, these results suggest a direct correlation between the alpha V integrin expression and the interaction of Nm23-H1 with EBNA3C.

A tumor vasculature targeted liposome delivery system for combretastatin A4: design, characterization, and in vitro evaluation

The objective of this study was to develop an efficient tumor vasculature targeted liposome delivery system for combretastatin A4, a novel antivascular agent. Liposomes composed of hydrogenated soybean phosphatidylcholine (HSPC), cholesterol, distearoyl phosphoethanolamine-polyethylene-glycol-2000 conjugate (DSPE-PEG), and DSPE-PEG-maleimide were prepared by the lipid film hydration and extrusion process. Cyclic RGD (Arg-Gly-Asp) peptides with affinity for alphavbeta3-integrins expressed on tumor vascular endothelial cells were coupled to the distal end of PEG on the liposomes sterically stabilized with PEG (long circulating liposomes, LCL). The liposome delivery system was characterized in terms of size, lamellarity, ligand density, drug loading, and leakage properties. Targeting nature of the delivery system was evaluated in vitro using cultured human umbilical vein endothelial cells (HUVEC). Electron microscopic observations of the formulations revealed presence of small unilamellar liposomes of approximately 120 nm in diameter. High performance liquid chromatography determination of ligand coupling to the liposome surface indicated that more than 99% of the RGD peptides were reacted with maleimide groups on the liposome surface. Up to 3 mg/mL of stable liposomal combretastatin A4 loading was achieved with approximately 80% of this being entrapped within the liposomes. In the in vitro cell culture studies, targeted liposomes showed significantly higher binding to their target cells than nontargeted liposomes, presumably through specific interaction of the RGD with its receptors on the cell surface. It was concluded that the targeting properties of the prepared delivery system would potentially improve the therapeutic benefits of combretastatin A4 compared with nontargeted liposomes or solution dosage forms.

Sequence specificity of formaldehyde-mediated covalent binding of anthracycline derivatives to DNA

Daunorubicin (DRB) and doxorubicin (DOX) in the presence of formaldehyde (CH2O) form covalent adducts with DNA. A G-specific adduct is formed by producing an aminal bridge between the C-3' of daunosamine and the C-2 of guanine. New derivatives of DRB, DOX and epidoxorubicin (EDOX) with an amidine group bonded to the C-3' of the daunosamine moiety, with either a morpholine or hexamethyleneimine ring attached to the amidine group, were studied in this paper. DNase I footprinting and analyses with restriction endonucleases were applied to compare the specificity of adduct formed by the amidine derivatives and their parent compounds. These approaches provide consistent results, proving that a GC pair is required for covalent binding of anthracycline derivatives to DNA and that different flanking sequences are able to modify the sequence preference of the drugs. The 5'-GC-3', 5'-CG-3' and 5'-TC-3' sequences were protected most efficiently by the parent compounds and their morpholine derivatives and some increased protection of 5'-TC-3' sequence was observed for morpholine analogues. Hexamethyleneimine derivatives bind to DNA with much lower efficiency. Finally, the sequence specificity of anthracycline derivatives was correlated with their ability to inhibit binding of transcription factors Sp1 and AP-1 to their DNA recognition sequences. The anthracycline derivatives were more potent in inhibiting Sp1 binding to its cognate GC box than in preventing AP-1 from binding to its mixed A.T and G.C site. Overall, the results indicate that the amidine derivatives of anthracyclines show similar, but not identical sequence specificity as parent compounds, though they exert their effect at a higher concentration.

Regulation of the human endothelial cell protein C receptor gene promoter by multiple Sp1 binding sites

The human endothelial cell protein C receptor (hEPCR) is normally expressed by the endothelium of large blood vessels, but the molecular basis for its in vivo specificity is uncertain. In this study, DNaseI hypersensitive site mapping demonstrated the presence of a hypersensitive site in the 5' flanking region of the hEPCR gene in endothelial cells and certain transformed cells (HeLa and U937) known to express hEPCR in vitro. Conversely, this site was only weakly hypersensitive in HepG2 cells, cells which do not express hEPCR mRNA. Functional analysis of this 5' flanking region by in vivo dimethylsulfate footprinting in cultured endothelial cells identified multiple regions, containing high and low homology consensus Sp1 binding sequences, that were protected from methylation in endothelial cells. These sequences were not protected in HepG2 cells. Reporter gene analysis of this region in endothelial cells demonstrated the presence of promoter activity conferred by the proximal 572 bp but failed to identify a functional TATA-box. This promoter was inactive in HepG2 cells. Electrophoresis mobility shift assays using endothelial cell nuclear extracts identified Sp1 family proteins binding to sites that were protected during footprinting. Sp1 sites were identified in regions at -368, -232, -226, -201, -146, and -102 bp relative to the translation start site. With the exception of the site at -102 bp, each identified Sp1 binding site made a positive contribution to reporter gene expression, although no individual site was critically important. We conclude that transcription factor binding to Sp1 binding sites in the 5' flanking region is critical for normal hEPCR gene expression in endothelial cells.

Glioma cell invasion: regulation of metalloproteinase activity by TGF-beta

Matrix metalloproteinases (MMPs) are a family of extracellular endopeptidases that selectively degrade components of the extracellular matrix. MMPs are implicated in tumor cell invasion because they mediate the breakdown of the basal membrane. In addition, they seem to be important for the creation and maintenance of a microenvironment that facilitates tumor cell survival. Among the essential characteristics of human malignant gliomas are infiltrative growth, angiogenesis and suppression of antitumor immune surveillance. Transforming growth factor-beta (TGF-beta) is intimately involved in the regulation of these processes. We have previously demonstrated that TGF-beta promotes the migration of LN- 18 and LN-229 glioma cells via a process that may involve the upregulation of alphaVbeta3 integrin expression. Furthermore, we have defined a novel pathway for hepatocyte growth factor (HGF)-induced glioma cell migration and invasion which requires the induction of TGF-beta2 expression. Here, we demonstrate that TGF-beta2 induces MMP-2 expression and suppresses tissue inhibitor of metalloproteinases (TIMP)-2 expression and that concentration-dependently promotes the invasion of U87MG and LN-229 glioma cells in a matrigel invasion assay. Similarly, ectopic expression of the anti-apoptotic BCL-x, protein leads to enhanced matrigel invasion by LN-18 and LN-229 glioma cells. We outline the possible interrelations of TGF-beta, proteins of the BCL-2 family, integrins and metalloprotease activity. By virtue of its promotion of glioma invasion and its growth regulatory and immunomodulatory properties. TGF-beta continues to be one of the most promising targets for the experimental therapy of human malignant glioma.

Glioma cell invasion: regulation of metalloproteinase activity by TGF-beta

Matrix metalloproteinases (MMPs) are a family of extracellular endopeptidases that selectively degrade components of the extracellular matrix. MMPs are implicated in tumor cell invasion because they mediate the breakdown of the basal membrane. In addition, they seem to be important for the creation and maintenance of a microenvironment that facilitates tumor cell survival. Among the essential characteristics of human malignant gliomas are infiltrative growth, angiogenesis and suppression of antitumor immune surveillance. Transforming growth factor-beta (TGF-beta) is intimately involved in the regulation of these processes. We have previously demonstrated that TGF-beta promotes the migration of LN- 18 and LN-229 glioma cells via a process that may involve the upregulation of alphaVbeta3 integrin expression. Furthermore, we have defined a novel pathway for hepatocyte growth factor (HGF)-induced glioma cell migration and invasion which requires the induction of TGF-beta2 expression. Here, we demonstrate that TGF-beta2 induces MMP-2 expression and suppresses tissue inhibitor of metalloproteinases (TIMP)-2 expression and that concentration-dependently promotes the invasion of U87MG and LN-229 glioma cells in a matrigel invasion assay. Similarly, ectopic expression of the anti-apoptotic BCL-x, protein leads to enhanced matrigel invasion by LN-18 and LN-229 glioma cells. We outline the possible interrelations of TGF-beta, proteins of the BCL-2 family, integrins and metalloprotease activity. By virtue of its promotion of glioma invasion and its growth regulatory and immunomodulatory properties. TGF-beta continues to be one of the most promising targets for the experimental therapy of human malignant glioma.

Malignant glioma biology: role for TGF-beta in growth, motility, angiogenesis, and immune escape

Characteristics of human malignant glioma are excessive proliferation, infiltrative growth, angiogenesis and suppression of anti-tumor immune surveillance. Transforming growth factor-beta (TGF-beta), a versatile cytokine, is intimately involved in the regulation of these processes. Here, we discuss the interactions of TGF-beta with growth factors, such as basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and platelet derived growth factor (PDGF), metalloproteinases (MMP-2, MMP-9) and their inhibitor, plasmin activator inhibitor-1 (PAI-1), and immune cells, like natural killer cells, T-cells and microglia. The differential effects of TGF-beta in glioma biology are outlined with emphasis on the induction of a survival advantage for glioma cells by enforced cell growth, migration, invasion, angiogenesis and immune paralysis. By virtue of its growth regulatory and immunomodulatory properties, TGF-beta promises to become a novel target for the experimental therapy of human malignant glioma.

Mouse integrin alphav promoter is regulated by transcriptional factors Ets and Sp1 in melanoma cells

A 17-bp region between the -31 and -15 bp region of the mouse integrin alphav gene is known to be one of the cis-acting elements for promoter activity. Experimental binding of nuclear proteins to the -31/-15 region reveals that the -27/-16 region mediates the binding. The -27/-16 region, GGCTCCTCCTCC, has a TCCTCC motif, one of the Sp1 binding motifs. An anti-Sp1 IgG and an Sp1-binding oligonucleotide interfered with the binding of nuclear proteins to the -27/-16 oligonucleotide, demonstrating that Sp1 binds to the -27/-16 region. In addition to the -27/-16 region, two other regions, -108/-89 and -64/-44, were found to bind to nuclear proteins within the -108/+1 alphav promoter region. An oligonucleotide containing the Ets-binding consensus sequence of CAGGAAGT interfered with their binding, indicating that both regions have a functional Ets-binding site; which is ACGGAAGT from -106 to -99 bp and ACTTCCTC from -61 to -54 bp, as deduced from the sequence. Mutations in or deletions from any one of three cis-acting elements, the two Ets-binding sites or one Sp1-binding site, remarkably decreased the promoter activity detected in the -108/+1 region. Cotransfection of both Sp1 and Ets-1 cDNAs with the -108/+1 region into B16F10 cells increased the promoter activity 2.9-fold. These results demonstrate that Sp1 and Ets cooperate to activate the -108/+1-alphav promoter region.

Transforming growth factors beta(1) (TGF-beta(1)) and TGF-beta(2) promote glioma cell migration via Up-regulation of alpha(V)beta(3) integrin expression

The migratory behaviour of malignant gliomas relies on the interaction of integrins with extracellular matrix (ECM) components. Transforming growth factor-beta(1) (TGF-beta(1)) potently stimulates glioma cell motility whereas TGF-beta(2) is known for its immunosuppressive properties. Here, we show that both TGF-beta(1) and TGF-beta(2) promote migration of glioma cells. In parallel, TGF-beta(1) and TGF-beta(2) induce alpha(V) and beta(3) intergrin mRNA expression and enhance cell surface expression of alpha(V)beta(3) integrin. TGF-beta-mediated promotion of migration is abrogated by echistatin, a Arg-Gly-Asp (RGD) peptide antagonist of alpha(V)beta(3) integrin, and by a neutralizing anti-alpha(V)beta(3) integrin antibody. Taken together, we report a novel mechanism by which TGF-beta modulates cell ECM interactions and promotes glioma cell motility.