Endothelin-1 induces tumor proteinase activation and invasiveness of ovarian carcinoma cells.

Endothelin-1 (ET-1) is present at high concentrations in ovarian cancer ascites and is overexpressed in primary and metastatic ovarian carcinoma. In these cells, ET-1 acts as an autocrine mitogenic and angiogenic factor selectively through the ET(A) receptor (ET(A)R). We investigated at mRNA and protein levels whether ET-1 could affect the expression and activation of metastasis-related proteinases and whether this process was associated with ovarian tumor cell invasion. ELISA, gelatin zymography, Western blot, and reverse transcription-PCR analyses demonstrated that in two ovarian carcinoma cell lines (HEY and OVCA 433), the expression of matrix metalloproteinase (MMP) -2, -9, -3, -7, and -13 was up-regulated and activated by ET-1. Moreover we observed that ET-1 was able to enhance the secretion and activation of membrane-type metalloproteinase-1, a critical mediator of invasiveness. The secretion of tissue inhibitor of metalloproteinase-1 and -2 was decreased by ET-1, which increased the net MMP/tissue inhibitor of metalloproteinase balance and the gelatinolytic capacity. In addition, ET-1 induced overexpression of urokinase-type plasminogen activator, its receptor, and plasminogen activator inhibitor type-1 and -2. Finally, we demonstrated that, in HEY and OVCA 433 cells, ET-1 dose-dependently increased migration and MMP-dependent invasion through Matrigel. BQ123, an antagonist of the ET(A)R, inhibited the ET-1-induced tumor protease activity and subsequent increase in cell migration and invasion. These findings demonstrate that ET-1 promotes ovarian carcinoma cell invasion, acting through the ET(A)R by up-regulating secretion and activation of multiple tumor proteinases. Therefore, ET-1 may represent a key component of more aggressive ligand-induced invasiveness of ovarian carcinoma.

Endothelin A receptor drives invadopodia function and cell motility through the ß-arrestin/PDZ-RhoGEF pathway in ovarian carcinoma.

The endothelin-1 (ET-1)/ET A receptor (ETAR) signalling pathway is a well-established driver of epithelial ovarian cancer (EOC) progression. One key process promoted by ET-1 is tumor cell invasion, which requires the scaffolding functions of ß-arrestin-1 (ß-arr1) downstream of the receptor; however, the potential role of ET-1 in inducing invadopodia, which are crucial for cellular invasion and tumor metastasis, is completely unknown. We describe here that ET-1/ETAR, through ß-arr1, activates RhoA and RhoC GTPase and downstream ROCK (Rho-associated coiled coil-forming kinase) kinase activity, promoting actin-based dynamic remodelling and enhanced cell invasion. This is accomplished by the direct interaction of ß-arr1 with PDZ-RhoGEF (postsynaptic density protein 95/disc-large/zonula occludens-RhoGEF). Interestingly, ETAR-mediated invasive properties are related to the regulation of invadopodia, as evaluated by colocalization of actin with cortactin, as well as with TKS5 and MT1-MMP (membrane type 1-matrix metalloproteinase) with areas of matrix degradation, and activation of cofilin pathway, which is crucial for regulating invadopodia activity. Depletion of PDZ-RhoGEF, or ß-arr1, or RhoC, as well as the treatment with the dual ET-1 receptor antagonist macitentan, significantly impairs invadopodia function, MMP activity and invasion, demonstrating that ß-arr1/PDZ-RhoGEF interaction mediates ETAR-driven ROCK-LIMK-cofilin pathway through the control of RhoC activity. In vivo, macitentan is able to inhibit metastatic dissemination and cofilin phosphorylation. Collectively, our data unveil a noncanonical activation of the RhoC/ROCK pathway through the ß-arr1/PDZ-RhoGEF complex as a regulator of ETAR-induced motility and metastasis, establishing ET-1 axis as a novel regulator of invadopodia protrusions through the RhoC/ROCK/LIMK/cofilin pathway during the initial steps of EOC invasion.

Selective 'in synthesis' labeling of peptides with biotin and rhodamine.

A new method is described for the selective 'in synthesis' labeling of peptides by rhodamine or biotin at a single, predetermined epsilon-amino group of a lysine residue. The alpha-amino group and other lysyl residues of the peptide remain unmodified. Peptides are assembled by the Fmoc approach, which requires mild operative conditions for the final deprotection and cleavage, and ensures little damage of the reporter group. The labeling technique involves the previous preparation of a suitable Lysine derivative, easily obtained from commercially-available protected amino acids. This new derivative, where the reporter group (biotin, or rhodamine) acts now as permanent protection of lysyl side chain functions, is then inserted into the synthesis program as a conventional protected amino acid, and linked to the preceding residue by aid of carbodiimide. A simpler, alternative method is also described for the selective 'in synthesis' labeling of peptides with N-terminal lysyl residues. Several applications of labeled peptides are reported.

Selective 'in synthesis' labelling of peptides by fluorochromes.

A new method is described for producing fluorescently-tagged peptides containing specific internal derivatives of lysyl residues. The technique employs the base-labile Boc-Lys(Fmoc)-COOH derivative with base-catalyzed removal of the Fmoc protecting group during peptide synthesis and subsequent fluorescent derivatization of the deprotected epsilon-amino group of lysine. By this technique, other lysine residues and the alpha-amino group of the fragment remain unmodified, which could have some value in studies where it might be required to tag a single individual lysine residue within the peptide, but not the amino terminus. In spite of the fact that poly-substituted peptides are badly soluble and might seldom find a practical application, this technique also allows the introduction of different fluorochromes at different lysyl residues within the peptide, thus obtaining double fluorescence. The method, fast and easy, requires a limited number of manual operations during the automatic synthesis of peptides. Although peptide synthesizers provided with an oscillating glass reactor are more suitable for the manual interventions described, this technique might be also adapted to the newer instruments utilizing continuous-flow columns.

Polystyrene beads coated with antibodies directed to HLA class I intracytoplasmic domain: the use in quantitative measurement of peptide-HLA class I binding by flow cytometry.

Protein-reactive, conformation-independent anti-peptide antibodies were raised in rabbits against a C-terminal sequence SDSAQGSDVSLA, common to most HLA-A and -B locus products. Antibodies were coupled to 4.5-microm polystyrene beads through the Fc portion by the use of protein A. The antibody-coupled beads showed a high capacity to bind HLA-A and -B proteins as well as their alpha chains by the intracytoplasmic domain, keeping the extracellular domains solvent exposed. The density of HLA class I proteins bound on the beads was approximately the same as that on cultured B cells. The antibody beads made it possible to quantitate peptide-HLA class I binding, i.e., in vitro HLA class I assembly by flow cytometry. The assembly rate determined by the provisionally called flow cytometric HLA class I assay was 15%-19% for the reassembly of dissociated HLA class I proteins with the released selfpeptides. With single synthetic peptides, the highest rate so far obtained was 6.5%. The assay specificity and reproducibility were satisfactory.

Flexibility of amino acid residues at position four of nonapeptides enhances their binding to human leucocyte antigen (HLA) molecules.

The binding affinity of synthetic nonapeptides to human leucocyte antigens (HLA) molecules of the A0201 allotype, the most common in Caucasian, is enhanced or reduced by suitable amino acid substitutions at position 4, as a result of increased or decreased chain flexibility. A higher flexibility of the bond at this position correlates with an easier accommodation of the fragment into the HLA groove, while rigidity of the peptide chain appears to interfere. These data are based on two lines of evidence: a) most natural high affinity ligands for HLA-A0201 possess, at position 4, flexible residues b) substitutions of such residues by rigid amino acids results in a decrease of binding affinity.

Definition of essential amino acid residues in the recognition of a peptide by a mouse monoclonal antibody.

A mouse monoclonal antibody reacting in ELISA with a synthetic peptide representing a linear amino acid stretch of the protein antigen was tested on all overlapping 5-mer to 9-mer fragments of the peptide, as prepared by multi-pin synthesis. Analysis of the binding data suggests that several residues in the peptide might be relatively unrelevant for recognition, while few others seem to play a critical role as key residues. On the basis of such observations, we attempted to reconstruct an alternative essential epitope by introducing multiple amino acid substitutions in the 9-mer peptide exhibiting the best binding activity, and then tested its ability to be recognized by the monoclonal antibody.

ß-arrestin-1 is a nuclear transcriptional regulator of endothelin-1-induced ß-catenin signaling.

Despite the fundamental pathophysiological importance of ß-catenin in tumor progression, the mechanism underlying its final transcriptional output has been partially elucidated. Here, we report that ß-arrestin-1 (ß-arr1) is an epigenetic regulator of endothelin (ET)-1-induced ß-catenin signaling in epithelial ovarian cancer (EOC). In response to ET A receptor (ETAR) activation by ET-1, ß-arr1 increases its nuclear translocation and direct binding to ß-catenin. This in turn enhanced ß-catenin nuclear accumulation and transcriptional activity, which was prevented by expressing a mutant ß-arr1 incapable of nuclear distribution. ß-arr1-ß-catenin interaction controls ß-catenin target gene expressions, such as ET-1, Axin 2, Matrix metalloproteinase 2, and Cyclin D1, by promoting histone deacetylase 1 (HDAC1) dissociation and the recruitment of p300 acetyltransferase on these promoter genes, resulting in enhanced H3 and H4 histone acetylation, and gene transcription, required for cell migration, invasion and epithelial-to-mesenchymal transition. These effects are abrogated by ß-arr1 silencing or by mutant ß-arr1, as well as by ß-catenin or p300 silencing, confirming that nuclear ß-arr1 forms a functional complex capable of regulating epigenetic changes in ß-catenin-driven invasive behavior. In a murine orthotopic model of metastatic human EOC, silencing of ß-arr1 or mutant ß-arr1 expression, as well as ETAR blockade, inhibits metastasis. In human EOC tissues, ß-arr1-ß-catenin nuclear complexes are selectively enriched at ß-catenin target gene promoters, correlating with tumor grade, confirming a direct in vivo ß-arr1-ß-catenin association at specific set of genes involved in EOC progression. Collectively, our study provides insights into how a ß-arr1-mediated epigenetic mechanism controls ß-catenin activity, unraveling new components required for its nuclear function in promoting metastasis.

Aims and limitations in the use of antipeptide antibodies in molecular biology.

Antibodies to peptides obtained by synthesis and, to a much lesser extent, prepared by enzymatic digestion of proteins, have been widely used in the last ten years in a variety of immunochemical and biological investigations. There are however several limitations in the correct utilization of such reagents. In fact, in spite of their 'predetermined specificity', antipeptide antibodies often fail to discriminate related molecules, and their reactivity with native proteins may be scarce or even absent, even if the peptide has been selected from surface regions of the protein. Our critical point of view, concerning two main aspects of antipeptide antibody features, i.e. specificity and reactivity, will be presented here, as confronted with information from the available literature. We have selected a restricted number of references among hundreds of publications dealing with antipeptide antibodies: for sure we neglected outstanding papers on the subject, and we apologize in advance.

MHC-peptide binding: dimers of cysteine-containing nonapeptides bind with high affinity to HLA-A2.1 class I molecules.

Small peptides, 8-10 amino acids long, derived from degradation of cytoplasmic proteins by a proteasome-proteinase complex, are usually presented and recognized by CD8+ cytolytic T lymphocytes (CTLs) associated with major histocompatibility complex (MHC) class I molecules. Recently synthetic peptides were used for the in vitro induction of tumor-specific CTLs, offering another strategy in the study of the immune-response repertoire and providing a new tool in cancer vaccination and immunotherapy. Peptides derived from otherwise normal proteins, overexpressed in many tumors as products of the protooncogene, may represent a target for an immune response. This is the case of HER-2/neu gene (also known as ErbB-2), encoding a cysteine-rich glycoprotein transmembrane receptor with tyrosine kinase activity (gp185neu). Recent data, demonstrating that HLA-A2.1-related peptides are able to stimulate in vitro CD8+ lymphocytes, Prompted us to study the binding to HLA-A2.1 molecules of several gp185 synthetic peptides containing a cystein residue and to define the relevance of this amino acid residue in the reduced or oxidated form of the sulfhydryl group. We found that monomers and their homodimers, linked by a disulfide bridge, bind to HLA-A2.1 molecules with overlapping affinity. These results suggest that additional amino acids of the nonapeptide do not prevent the binding and the HLA refolding through chemical or sterical interactions. This might be of particular relevance for the in vivo processing of cysteine-rich proteins. Because ErbB-2 molecules, as tumor-differentiation antigens in melanoma, are cysteine-rich molecules, it may be relevant to evaluate the possible role of the cystine residues interacting with the T-cell receptor. The recognition of these heterodimers by CD8+ lymphocytes will require functional in vivo studies.

Endothelin-1 induces an angiogenic phenotype in cultured endothelial cells and stimulates neovascularization in vivo.

The endothelial cell-derived endothelin-1 (ET-1) is a potent mitogen for endothelial cells, vascular smooth muscle cells, and tumor cells. In this study, we analyzed the role of ET-1 on human umbilical vein endothelial cell (HUVEC) phenotype related to different stages of angiogenesis. ET-1 promoted HUVEC proliferation, migration, and invasion in a dose-dependent manner. The ET(B) receptor (ET(B)R) antagonist, BQ 788, blocked the angiogenic effects induced by ET-1, whereas the ET(A)R antagonist was less effective. ET-1 stimulated matrix metalloproteinase-2 mRNA expression and metalloproteinase-2 production, as determined by reverse transcriptase-polymerase chain reaction and gelatin zymography. Furthermore ET-1 was able to enhance HUVEC differentiation into cord vascular-like structures on Matrigel. When tested in combination with vascular endothelial growth factor (VEGF), ET-1 enhanced VEGF-induced angiogenic-related effects on endothelial cells in vitro. Finally, using the Matrigel plug neovascularization assay in vivo, ET-1 in combination with VEGF stimulated an angiogenic response comparable to that elicited by basic fibroblast growth factor. These findings demonstrated that ET-1 induces angiogenic responses in cultured endothelial cells through ET(B)R and that stimulates neovascularization in vivo in concert with VEGF. ET-1 and its receptors acting as angiogenic regulators might represent new targets for anti-angiogenic therapy.

Endothelin receptor blockade inhibits proliferation of Kaposi's sarcoma cells.

Endothelin-1 (ET-1) has been shown to be mitogenic for endothelial and several tumor cells through an autocrine mechanism. In this study we evaluated whether the tumorigenic KS IMM cell line deriving from Kaposi's sarcoma (KS), a highly angiogenic tumor, is susceptible to ET-1 mitogenic activity. By reverse transcriptase-polymerase chain reaction, we detected ET-1 mRNA expression and both ET(A) receptor (ET(A)R) and ET(B)R mRNA transcripts in the KS IMM cells. High concentrations of ET-1 are released from the KS IMM cells and competition-binding studies demonstrated that these cells also express functional ET(A)R and ET(B)R with high affinity for ET-1 and ET-1/ET-3, respectively. Expression of ET-1 and cognate receptors could be detected by immunohistochemical method in vitro, in KS IMM xenograft, and in tissue sections of a human KS lesion. Furthermore ET-1 induces a marked and dose-dependent increase in [3H]thymidine incorporation comparable to that elicited by vascular endothelial growth factor. Addition of both selective ET(B)R antagonist (BQ 788) and ET(A)R antagonist (BQ 123), completely blocked ET-1-induced mitogenic response and reduced the basal growth rate of unstimulated cells, suggesting that both receptors mediated the proliferative signal. Such findings demonstrate that ET-1 participates on KS pathogenesis acting as an autocrine growth factor and that ET-1 receptor antagonists may thus be novel candidates for therapeutic intervention.

Role of endothelin-1 in neovascularization of ovarian carcinoma.

Endothelin-1 (ET-1) is overexpressed in ovarian carcinomas and acts, via ET(A) receptors (ET(A)R), as an autocrine growth factor. In this study we investigate the role of ET-1 in the neovascularization of ovarian carcinoma. Archival specimens of primary (n = 40) and metastatic (n = 8) ovarian tumors were examined by immunohistochemistry for angiogenic factor and receptor expression and for microvessel density using antibodies against CD31, ET-1, vascular endothelial growth factor (VEGF), and their receptors. ET-1 expression correlated with neovascularization and with VEGF expression. The localization of functional ET(A)R and ET(A)R mRNA expression, as detected by autoradiography and in situ hybridization, was evident in tumors and in intratumoral vessels, whereas ET(B)R were expressed mainly in endothelial cells. High levels of ET-1 were detected in the majority of ascitic fluids of patients with ovarian carcinoma and significantly correlated with VEGF ascitic concentration. Furthermore ET-1, through ET(A)R, stimulated VEGF production in an ovarian carcinoma cell line, OVCA 433, by an extent comparable to hypoxia. Finally, conditioned media from OVCA 433 as well as ascitic fluids caused an increase in endothelial cell migration and the ET-1 receptor blockade significantly inhibited this angiogenic response. These findings indicate that ET-1 could modulate tumor angiogenesis, acting directly and in part through VEGF.