Molecular Cloning and Characterization of Endosialin, a C-type Lectin-like Cell Surface Receptor of Tumor Endothelium

Abstract

Endosialin, the antigen identified with monoclonal antibody FB5, is a highly restricted 165-kDa cell surface glycoprotein expressed by tumor blood vessel endothelium in a broad range of human cancers but not detected in blood vessels or other cell types in many normal tissues. Functional analysis of endosialin has been hampered by a lack of information about its molecular structure. In this study, we describe the purification and partial amino acid sequencing of endosialin, leading to the cloning of a full-length cDNA with an open reading frame of 2274 base pairs. The endosialin cDNA encodes a type I membrane protein of 757 amino acids with a predicted molecular mass of 80.9 kDa. The sequence matches with an expressed sequence tag of unknown function in public data bases, named TEM1, which was independently linked to tumor endothelium by serial analysis of gene expression profiling. Bioinformatic evaluation classifies endosialin as a C-type lectin-like protein, composed of a signal leader peptide, five globular extracellular domains (including a C-type lectin domain, one domain with similarity to the Sushi/ccp/scr pattern, and three EGF repeats), followed by a mucin-like region, a transmembrane segment, and a short cytoplasmic tail. Carbohydrate analysis shows that the endosialin core protein carries abundantly sialylated, O-linked oligosaccharides and is sensitive toO-sialoglycoprotein endopeptidase, placing it in the group of sialomucin-like molecules. The N-terminal 360 amino acids of endosialin show homology to thrombomodulin, a receptor involved in regulating blood coagulation, and to complement receptor C1qRp. This structural kinship may indicate a function for endosialin as a tumor endothelial receptor for as yet unknown ligands, a notion now amenable to molecular investigationAJ295846. Endosialin, the antigen identified with monoclonal antibody FB5, is a highly restricted 165-kDa cell surface glycoprotein expressed by tumor blood vessel endothelium in a broad range of human cancers but not detected in blood vessels or other cell types in many normal tissues. Functional analysis of endosialin has been hampered by a lack of information about its molecular structure. In this study, we describe the purification and partial amino acid sequencing of endosialin, leading to the cloning of a full-length cDNA with an open reading frame of 2274 base pairs. The endosialin cDNA encodes a type I membrane protein of 757 amino acids with a predicted molecular mass of 80.9 kDa. The sequence matches with an expressed sequence tag of unknown function in public data bases, named TEM1, which was independently linked to tumor endothelium by serial analysis of gene expression profiling. Bioinformatic evaluation classifies endosialin as a C-type lectin-like protein, composed of a signal leader peptide, five globular extracellular domains (including a C-type lectin domain, one domain with similarity to the Sushi/ccp/scr pattern, and three EGF repeats), followed by a mucin-like region, a transmembrane segment, and a short cytoplasmic tail. Carbohydrate analysis shows that the endosialin core protein carries abundantly sialylated, O-linked oligosaccharides and is sensitive toO-sialoglycoprotein endopeptidase, placing it in the group of sialomucin-like molecules. The N-terminal 360 amino acids of endosialin show homology to thrombomodulin, a receptor involved in regulating blood coagulation, and to complement receptor C1qRp. This structural kinship may indicate a function for endosialin as a tumor endothelial receptor for as yet unknown ligands, a notion now amenable to molecular investigationAJ295846. monoclonal antibody base pair(s) epidermal growth factor expressed sequence tag O-sialoglycoprotein endopeptidase polyacrylamide gel electrophoresis high performance liquid chromatography 4-morpholinepropanesulfonic acid rapid amplification of cDNA ends serial analysis of gene expression tumor endothelial marker 1 The endosialin antigen was identified in a survey of normal and neoplastic human tissues conducted at the Ludwig Institute for Cancer Research in pursuit of new targets for antibody-based cancer therapies (37Old L.J. Sci. Am. 1996; 275: 102-109Crossref Scopus (63) Google Scholar). The hallmark of monoclonal antibody (mAb)1 FB5, the probe used to discover endosialin (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), is its distinctive pattern of reactivity with human tissues. Thus, in a detailed study of biopsy and surgical specimens representing diverse cancer types, FB5 immunostaining was found primarily in tumor blood vessels and not in malignant tumor cells. Significantly, the antigen was not observed in all cancer samples examined, and even in cancers showing FB5-immunoreactive endothelial cells, the antigen was frequently detected with a heterogeneous pattern in the tumor vascular bed. Such a mixed pattern might be expected for a molecule involved in the reorganization of blood vessels in tissues such as cancers, in which areas of stable blood supply and histology are juxtaposed to regions of necrosis, hypoxia, excessive growth, tissue invasion, and remodeling. The normal tissues examined were unreactive with mAb FB5, including the blood vessel endothelium present in the respective organs.The expression of the FB5 antigen by cultured normal and tumor cells was also investigated (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), revealing that the standard test cells for normal endothelial differentiation markers, cultured human umbilical vein endothelial cells, and microvascular endothelial cells derived from bone marrow and dermis are antigen-negative. Human umbilical vein endothelial cell cultures stimulated with a range of mediators known to induce the expression of endothelial activation antigens (2Lasky L.A. Science. 1992; 258: 964-969Crossref PubMed Scopus (1148) Google Scholar, 3Carlos T.M. Harlan J.M. Blood. 1994; 84: 2068-2101Crossref PubMed Google Scholar) maintain their FB5-negative phenotype (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar). Among a host of cultured epithelial, neuroectodermal, mesenchymal, and hematopoietic cell types tested, most were FB5 antigen-negative. Notable exceptions are short term cultures of normal fibroblasts and neuroblastoma cell lines, which consistently express the antigen in tissue culture (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), allowing the chromosomal assignment of an FB5 coding gene to human chromosome 11q13-qter, based on the serologic analysis of mouse-human neuroblastoma cell hybrids. The reason why cultured fibroblasts and neuroblastomas are FB5 positive in vitro, yet the corresponding cells in uncultured tissue sections are FB5 negative, is not known. Presumably, some of these findings reflect cell type-restricted, adaptive changes of the cell surface phenotype triggered by tissue culture factors (38Rettig W.J. Old L.J. Annu. Rev. Immunol. 1989; 7: 481-511Crossref PubMed Scopus (41) Google Scholar); the mechanism underlying such induction and its relationship to FB5 antigen induction in tumor blood vessels are not known.Methods are not generally available to examine the biochemical nature of antigens with restricted expression in tumor endothelium, because of to three properties of these cells: (i) they constitute a very minor fraction in most tumor tissues; (ii) they are not readily purified in sufficient numbers for direct protein analysis; and (iii) no cell culture model of tumor endothelium exists that faithfully reproduces its distinctive in vivo phenotype. With no source for antigen characterization in tumor endothelium, the target molecule for mAb FB5 was studied in cultured neuroblastoma and sarcoma cells and fibroblast cultures. In these cell types, the antigen is a unique 165-kDa glycoprotein, comprised of a core protein that migrates as a 95-kDa species on SDS gels and carries the mAb FB5-defined epitope, and abundant, highly sialylated O-linked carbohydrate moieties. There has been no proof that the same protein carries the FB5 epitope in tumor endothelium, but in recognition of the characteristic biochemical properties and the tumor endothelial expression pattern the molecule was designated endosialin.In the absence of detailed information about the molecular of endosialin, no were available its function in the in as a of cancer and 1996; PubMed Scopus Google Scholar) and as a target for cancer therapies PubMed Scopus Google Scholar), this study to the endosialin gene and the and structural information to endosialin function in model and in human the gene coding for the human endosialin core protein based on of of endosialin cDNA cells to induction of cell surface reactivity with the mAb mAb FB5 the expected 165-kDa in the with a core protein as a 95-kDa species on SDS the endosialin gene to chromosome the assignment to based on serologic analysis of cell with mAb the amino acid sequence the for of present study is not the endosialin induction to vascular endothelial cells in human an of at gene expression in cancers with the serial analysis of gene expression has in tumor A. Science. PubMed Scopus Google Scholar) to survey about unique gene for expression in purified tumor endothelium endothelium of The study identified at in tumor endothelium, and the and most was for a as of unknown function in data and designated tumor endothelial marker 1 by A. Science. PubMed Scopus Google Scholar). show that is the endosialin their study, A. Science. PubMed Scopus Google Scholar) the data and by in that expression in vivo is for tumor endothelium, with no in the malignant cells of and other a range of normal and a of cultured tumor cell was not unique to tumor blood vessels because endothelial cells with and also gene expression by in the endosialin expression data with mAb FB5 (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar) and the expression data derived from and in A. Science. PubMed Scopus Google Scholar), a of endosialin induction in tumor endothelium Such a epitope and expression is for a molecule endosialin, which the group of There is for and other for which epitope expression and of been S. Immunol. PubMed Scopus Google Scholar, A. S. 1989; PubMed Scopus Google Scholar, U. Blood. PubMed Google Scholar, PubMed Scopus Google Scholar), including (i) on core that are by or (ii) on carbohydrate by or and (iii) on or of the same core In the of endosialin, the observed for the FB5 epitope and that mAb FB5 to an epitope on the 95-kDa core this to be for cell type because epitope and show cell type in the of tumor is the of and that may of tumor endothelial cells in a tumor with to their from blood vessels or new vessel and their function and of activation in to of and the of a or tumor mass areas of stable blood supply and tissue and juxtaposed or regions of hypoxia, necrosis, excessive tissue invasion, or cell in this of malignant tissue of tumor might be expected to a heterogeneous pattern of expression as a the in FB5 in tumor vessels (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), it may be that the on A. Science. PubMed Scopus Google Scholar) not this that endosialin is expressed in tumor endothelium and that of endothelial cells the endosialin protein or protein with the FB5 as is no such a it may be that in is the sensitive for endosialin and that FB5 immunostaining tumor endothelium with the of a tumor endothelial cell may be in the of the available on endosialin analysis shows that the N-terminal extracellular of endosialin is to of five domains with globular and in this homology to and the complement receptor with and amino acid sequence is a pattern of is highly the three and a of for on a C-type lectin domain, and a in the extracellular endosialin, is expressed on a of normal cell types and on normal vascular endothelium as a receptor for the and the PubMed Scopus Google Scholar). The on the EGF and of E.A. 7: PubMed Scopus Google 275: PubMed Scopus Google Scholar), which are not present in endosialin, it that the in this The complement receptor is also expressed on a of cell types endosialin, including and normal vascular The extracellular of is composed of a C-type lectin domain, a of five and a mucin-like The molecule the complement factor and protein PubMed Scopus Google Scholar). cells, of but the function of on normal endothelial cells is unknown J.M. PubMed Scopus Google about the extracellular domain on structural Thus, the high of and for O-linked carbohydrate with the sialomucin-like of endosialin U. Blood. PubMed Google Scholar, A. 275: PubMed Scopus Google Scholar). been in growth factors to the membrane and these factors to endothelial cell surface A. 275: PubMed Scopus Google Scholar, PubMed Scopus Google Scholar); endosialin may be a for such a function unique to tumor from biochemical that from the of mAb FB5 and endosialin protein, study of in endosialin gene expression and are now including in and which a of In are now to the endosialin in human and and to these amenable of endosialin may even new to cancer and The endosialin antigen was identified in a survey of normal and neoplastic human tissues conducted at the Ludwig Institute for Cancer Research in pursuit of new targets for antibody-based cancer therapies (37Old L.J. Sci. Am. 1996; 275: 102-109Crossref Scopus (63) Google Scholar). The hallmark of monoclonal antibody (mAb)1 FB5, the probe used to discover endosialin (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), is its distinctive pattern of reactivity with human tissues. Thus, in a detailed study of biopsy and surgical specimens representing diverse cancer types, FB5 immunostaining was found primarily in tumor blood vessels and not in malignant tumor cells. Significantly, the antigen was not observed in all cancer samples examined, and even in cancers showing FB5-immunoreactive endothelial cells, the antigen was frequently detected with a heterogeneous pattern in the tumor vascular bed. Such a mixed pattern might be expected for a molecule involved in the reorganization of blood vessels in tissues such as cancers, in which areas of stable blood supply and histology are juxtaposed to regions of necrosis, hypoxia, excessive growth, tissue invasion, and remodeling. The normal tissues examined were unreactive with mAb FB5, including the blood vessel endothelium present in the respective The expression of the FB5 antigen by cultured normal and tumor cells was also investigated (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), revealing that the standard test cells for normal endothelial differentiation markers, cultured human umbilical vein endothelial cells, and microvascular endothelial cells derived from bone marrow and dermis are antigen-negative. Human umbilical vein endothelial cell cultures stimulated with a range of mediators known to induce the expression of endothelial activation antigens (2Lasky L.A. Science. 1992; 258: 964-969Crossref PubMed Scopus (1148) Google Scholar, 3Carlos T.M. Harlan J.M. Blood. 1994; 84: 2068-2101Crossref PubMed Google Scholar) maintain their FB5-negative phenotype (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar). Among a host of cultured epithelial, neuroectodermal, mesenchymal, and hematopoietic cell types tested, most were FB5 antigen-negative. Notable exceptions are short term cultures of normal fibroblasts and neuroblastoma cell lines, which consistently express the antigen in tissue culture (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), allowing the chromosomal assignment of an FB5 coding gene to human chromosome 11q13-qter, based on the serologic analysis of mouse-human neuroblastoma cell hybrids. The reason why cultured fibroblasts and neuroblastomas are FB5 positive in vitro, yet the corresponding cells in uncultured tissue sections are FB5 negative, is not known. Presumably, some of these findings reflect cell type-restricted, adaptive changes of the cell surface phenotype triggered by tissue culture factors (38Rettig W.J. Old L.J. Annu. Rev. Immunol. 1989; 7: 481-511Crossref PubMed Scopus (41) Google Scholar); the mechanism underlying such induction and its relationship to FB5 antigen induction in tumor blood vessels are not known. are not generally available to examine the biochemical nature of antigens with restricted expression in tumor endothelium, because of to three properties of these cells: (i) they constitute a very minor fraction in most tumor tissues; (ii) they are not readily purified in sufficient numbers for direct protein analysis; and (iii) no cell culture model of tumor endothelium exists that faithfully reproduces its distinctive in vivo phenotype. With no source for antigen characterization in tumor endothelium, the target molecule for mAb FB5 was studied in cultured neuroblastoma and sarcoma cells and fibroblast cultures. In these cell types, the antigen is a unique 165-kDa glycoprotein, comprised of a core protein that migrates as a 95-kDa species on SDS gels and carries the mAb FB5-defined epitope, and abundant, highly sialylated O-linked carbohydrate moieties. There has been no proof that the same protein carries the FB5 epitope in tumor endothelium, but in recognition of the characteristic biochemical properties and the tumor endothelial expression pattern the molecule was designated In the absence of detailed information about the molecular of endosialin, no were available its function in the in as a of cancer and 1996; PubMed Scopus Google Scholar) and as a target for cancer therapies PubMed Scopus Google Scholar), this study to the endosialin gene and the and structural information to endosialin function in model and in human the gene coding for the human endosialin core protein based on of of endosialin cDNA cells to induction of cell surface reactivity with the mAb mAb FB5 the expected 165-kDa in the with a core protein as a 95-kDa species on SDS the endosialin gene to chromosome the assignment to based on serologic analysis of cell with mAb the amino acid sequence the for of present study is not the endosialin induction to vascular endothelial cells in human an of at gene expression in cancers with the serial analysis of gene expression has in tumor A. Science. PubMed Scopus Google Scholar) to survey about unique gene for expression in purified tumor endothelium endothelium of The study identified at in tumor endothelium, and the and most was for a as of unknown function in data and designated tumor endothelial marker 1 by A. Science. PubMed Scopus Google Scholar). show that is the endosialin their study, A. Science. PubMed Scopus Google Scholar) the data and by in that expression in vivo is for tumor endothelium, with no in the malignant cells of and other a range of normal and a of cultured tumor cell was not unique to tumor blood vessels because endothelial cells with and also gene expression by in the endosialin expression data with mAb FB5 (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar) and the expression data derived from and in A. Science. PubMed Scopus Google Scholar), a of endosialin induction in tumor endothelium Such a epitope and expression is for a molecule endosialin, which the group of There is for and other for which epitope expression and of been S. Immunol. PubMed Scopus Google Scholar, A. S. 1989; PubMed Scopus Google Scholar, U. Blood. PubMed Google Scholar, PubMed Scopus Google Scholar), including (i) on core that are by or (ii) on carbohydrate by or and (iii) on or of the same core In the of endosialin, the observed for the FB5 epitope and that mAb FB5 to an epitope on the 95-kDa core this to be for cell type because epitope and show cell type in the of tumor is the of and that may of tumor endothelial cells in a tumor with to their from blood vessels or new vessel and their function and of activation in to of and the of a or tumor mass areas of stable blood supply and tissue and juxtaposed or regions of hypoxia, necrosis, excessive tissue invasion, or cell in this of malignant tissue of tumor might be expected to a heterogeneous pattern of expression as a the in FB5 in tumor vessels (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), it may be that the on A. Science. PubMed Scopus Google Scholar) not this that endosialin is expressed in tumor endothelium and that of endothelial cells the endosialin protein or protein with the FB5 as is no such a it may be that in is the sensitive for endosialin and that FB5 immunostaining tumor endothelium with the of a tumor endothelial cell may be in the of the available on endosialin analysis shows that the N-terminal extracellular of endosialin is to of five domains with globular and in this homology to and the complement receptor with and amino acid sequence is a pattern of is highly the three and a of for on a C-type lectin domain, and a in the extracellular endosialin, is expressed on a of normal cell types and on normal vascular endothelium as a receptor for the and the PubMed Scopus Google Scholar). The on the EGF and of E.A. 7: PubMed Scopus Google 275: PubMed Scopus Google Scholar), which are not present in endosialin, it that the in this The complement receptor is also expressed on a of cell types endosialin, including and normal vascular The extracellular of is composed of a C-type lectin domain, a of five and a mucin-like The molecule the complement factor and protein PubMed Scopus Google Scholar). cells, of but the function of on normal endothelial cells is unknown J.M. PubMed Scopus Google about the extracellular domain on structural Thus, the high of and for O-linked carbohydrate with the sialomucin-like of endosialin U. Blood. PubMed Google Scholar, A. 275: PubMed Scopus Google Scholar). been in growth factors to the membrane and these factors to endothelial cell surface A. 275: PubMed Scopus Google Scholar, PubMed Scopus Google Scholar); endosialin may be a for such a function unique to tumor from biochemical that from the of mAb FB5 and endosialin protein, study of in endosialin gene expression and are now including in and which a of In are now to the endosialin in human and and to these amenable of endosialin may even new to cancer and the gene coding for the human endosialin core protein based on of of endosialin cDNA cells to induction of cell surface reactivity with the mAb mAb FB5 the expected 165-kDa in the with a core protein as a 95-kDa species on SDS the endosialin gene to chromosome the assignment to based on serologic analysis of cell with mAb the amino acid sequence the for of The present study is not the endosialin induction to vascular endothelial cells in human an of at gene expression in cancers with the serial analysis of gene expression has in tumor A. Science. PubMed Scopus Google Scholar) to survey about unique gene for expression in purified tumor endothelium endothelium of The study identified at in tumor endothelium, and the and most was for a as of unknown function in data and designated tumor endothelial marker 1 by A. Science. PubMed Scopus Google Scholar). show that is the endosialin In their study, A. Science. PubMed Scopus Google Scholar) the data and by in that expression in vivo is for tumor endothelium, with no in the malignant cells of and other a range of normal and a of cultured tumor cell was not unique to tumor blood vessels because endothelial cells with and also gene expression by in the endosialin expression data with mAb FB5 (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar) and the expression data derived from and in A. Science. PubMed Scopus Google Scholar), a of endosialin induction in tumor endothelium Such a epitope and expression is for a molecule endosialin, which the group of There is for and other for which epitope expression and of been S. Immunol. PubMed Scopus Google Scholar, A. S. 1989; PubMed Scopus Google Scholar, U. Blood. PubMed Google Scholar, PubMed Scopus Google Scholar), including (i) on core that are by or (ii) on carbohydrate by or and (iii) on or of the same core In the of endosialin, the observed for the FB5 epitope and that mAb FB5 to an epitope on the 95-kDa core this to be for cell type because epitope and show cell type in the of tumor is the of and that may of tumor endothelial cells in a tumor with to their from blood vessels or new vessel and their function and of activation in to of and the of a or tumor mass areas of stable blood supply and tissue and juxtaposed or regions of hypoxia, necrosis, excessive tissue invasion, or cell in this of malignant tissue of tumor might be expected to a heterogeneous pattern of expression as a the in FB5 in tumor vessels (1Rettig W.J. Garin-Chesa P. Healey J.H. Su S.L. Jaffe E.A. Old L.J. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 10832-10836Crossref PubMed Scopus (204) Google Scholar), it may be that the on A. Science. PubMed Scopus Google Scholar) not this that endosialin is expressed in tumor endothelium and that of endothelial cells the endosialin protein or protein with the FB5 as is no such a it may be that in is the sensitive for endosialin and that FB5 immunostaining tumor endothelium with the of a tumor endothelial cell may be in the of the available on endosialin analysis shows that the N-terminal extracellular of endosialin is to of five domains with globular and in this homology to and the complement receptor with and amino acid sequence is a pattern of is highly the three and a of for on a C-type lectin domain, and a in the extracellular endosialin, is expressed on a of normal cell types and on normal vascular endothelium as a receptor for the and the PubMed Scopus Google Scholar). The on the EGF and of E.A. 7: PubMed Scopus Google 275: PubMed Scopus Google Scholar), which are not present in endosialin, it that the in this The complement receptor is also expressed on a of cell types endosialin, including and normal vascular The extracellular of is composed of a C-type lectin domain, a of five and a mucin-like The molecule the complement factor and protein PubMed Scopus Google Scholar). cells, of but the function of on normal endothelial cells is unknown J.M. PubMed Scopus Google Scholar). about the extracellular domain on structural Thus, the high of and for O-linked carbohydrate with the sialomucin-like of endosialin U. Blood. PubMed Google Scholar, A. 275: PubMed Scopus Google Scholar). been in growth factors to the membrane and these factors to endothelial cell surface A. 275: PubMed Scopus Google Scholar, PubMed Scopus Google Scholar); endosialin may be a for such a function unique to tumor from biochemical that from the of mAb FB5 and endosialin protein, study of in endosialin gene expression and are now including in and which a of In are now to the endosialin in human and and to these amenable of endosialin may even new to cancer and The of and is cell purified mAb Old for and was in partial of the of the