Portal de Periódicos da CAPES

The C-type Lectin Receptor Endo180 Displays Internalization and Recycling Properties Distinct from Other Members of the Mannose Receptor Family

2002; Elsevier BV; Volume: 277; Issue: 35 Linguagem: Inglês

10.1074/jbc.m203631200

1083-351X

Matthew J. Howard, Clare M. Isacke,

Glycosylation and Glycoproteins Research

Endo180/urokinase plasminogen activator receptor-associated protein together with the mannose receptor, the phospholipase A2 receptor, and DEC-205/MR6-gp200 comprise the four members of the mannose receptor family. These receptors have a unique structural composition due to the presence of multiple C-type lectin-like domains within a single polypeptide backbone. In addition, they are all constitutively internalized from the plasma membrane via clathrin-mediated endocytosis and recycled back to the cell surface. Endo180 is a multifunctional receptor displaying Ca2+-dependent lectin activity, collagen binding, and association with the urokinase plasminogen activator receptor, and it has a proposed role in extracellular matrix degradation and remodeling. Within their short cytoplasmic domains, all four receptors contain both a conserved tyrosine-based and dihydrophobic-based putative endocytosis motif. Unexpectedly, Endo180 was found to be distinct within the family in that the tyrosine-based motif is not required for efficient delivery to and recycling from early endosomes. By contrast, receptor internalization is completely dependent on the dihydrophobic motif and modulated by a conserved upstream acidic residue. Furthermore, unlike the mannose receptor, Endo180 does not function as a phagocytic receptor in vitro. These findings demonstrate that despite an overall structural similarity, members of this receptor family employ distinct trafficking mechanisms that may reflect important differences in their physiological functions. Endo180/urokinase plasminogen activator receptor-associated protein together with the mannose receptor, the phospholipase A2 receptor, and DEC-205/MR6-gp200 comprise the four members of the mannose receptor family. These receptors have a unique structural composition due to the presence of multiple C-type lectin-like domains within a single polypeptide backbone. In addition, they are all constitutively internalized from the plasma membrane via clathrin-mediated endocytosis and recycled back to the cell surface. Endo180 is a multifunctional receptor displaying Ca2+-dependent lectin activity, collagen binding, and association with the urokinase plasminogen activator receptor, and it has a proposed role in extracellular matrix degradation and remodeling. Within their short cytoplasmic domains, all four receptors contain both a conserved tyrosine-based and dihydrophobic-based putative endocytosis motif. Unexpectedly, Endo180 was found to be distinct within the family in that the tyrosine-based motif is not required for efficient delivery to and recycling from early endosomes. By contrast, receptor internalization is completely dependent on the dihydrophobic motif and modulated by a conserved upstream acidic residue. Furthermore, unlike the mannose receptor, Endo180 does not function as a phagocytic receptor in vitro. These findings demonstrate that despite an overall structural similarity, members of this receptor family employ distinct trafficking mechanisms that may reflect important differences in their physiological functions. phospholipase A2 receptor C-type lectin-like domain monoclonal antibody fluorescein isothiocyanate bovine serum albumin fluorescence-activated cell sorting 4-morpholineethanesulfonic acid phosphate-buffered saline relative fluorescence intensity R-phycoerythrin Endo180 was first identified as a recycling endocytic receptor expressed in fibroblastic cells (1Isacke C.M. van der Geer P. Hunter T. Trowbridge I.S. Mol. Cell. Biol. 1990; 10: 2606-2618Crossref PubMed Scopus (56) Google Scholar). Based on peptide sequences obtained from purified protein, a full-length human cDNA clone was isolated, and Endo180 was demonstrated to be the fourth and last member of the mannose receptor family (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar, 3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar, 4East L. Isacke C.M. Biochim. Biophys. Acta. 2002; (in press)PubMed Google Scholar). In addition to Endo180, the mannose receptor family comprises the mannose receptor, the M-type phospholipase A2 receptor (PLA2R),1 and DEC-205/MR6-gp200. This family grouping is based on an overall structural conservation with the four receptors containing a large extracellular domain comprising an N-terminal signal sequence followed by a cysteine-rich domain, a fibronectin type II domain, and 8 or 10 C-type lectin-like domains (CTLDs). The single pass transmembrane domains are followed by a short cytoplasmic domain. As a family, these receptors have two striking features. First, although they belong to the large C-type lectin superfamily (information available on the World Wide Web at ctld.glycob.ox.ac.uk), they uniquely contain multiple CTLDs within a single polypeptide backbone (4East L. Isacke C.M. Biochim. Biophys. Acta. 2002; (in press)PubMed Google Scholar, 5Taylor M.E. Glycobiology. 1997; 7: v-viiiCrossref PubMed Google Scholar, 6Weis W.I. Taylor M.E. Drickamer K. Immunol. Rev. 1998; 163: 19-34Crossref PubMed Scopus (870) Google Scholar, 7Valentin E. Lambeau G. Biochim. Biophys. Acta. 2000; 1488: 59-70Crossref PubMed Scopus (313) Google Scholar, 8Jiang W. Swiggard W.J. Heufler C. Peng M. Mirza A. Steinman R.M. Nussenzweig M.C. Nature. 1995; 375: 151-155Crossref PubMed Scopus (797) Google Scholar, 9McKay P.F. Imami N. Johns M. Taylor-Fishwick D.A. Sedibane L.M. Totty N.F. Hsuan J.J. Palmer D.B. George A.J. Foxwell B.M. Ritter M.A. Eur. J. Immunol. 1998; 28: 4071-4083Crossref PubMed Scopus (34) Google Scholar). Second, they share the ability to be recycled between the plasma membrane and intracellular compartments of the cell (1Isacke C.M. van der Geer P. Hunter T. Trowbridge I.S. Mol. Cell. Biol. 1990; 10: 2606-2618Crossref PubMed Scopus (56) Google Scholar, 8Jiang W. Swiggard W.J. Heufler C. Peng M. Mirza A. Steinman R.M. Nussenzweig M.C. Nature. 1995; 375: 151-155Crossref PubMed Scopus (797) Google Scholar, 10Kruskal B.A. Sastry K. Warner A.B. Mathieu C.E. Ezekowitz R.A. J. Exp. Med. 1992; 176: 1673-1680Crossref PubMed Scopus (68) Google Scholar, 11Zvaritch E. Lambeau G. Lazdunski M. J. Biol. Chem. 1996; 271: 250-257Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar).As a consequence of their structural and recycling characteristics, it was initially assumed that these receptors would commonly function to internalize glycosylated ligands for intracellular delivery. However, further characterization has revealed the following. (a) Although the receptors contain multiple CTLDS, only CTLDs 4 and 5 of the mannose receptor and CTLDs 1 and 2 of Endo180 contain the conserved amino acids found in functional C-type lectins, and accordingly only these two receptors have been demonstrated to exhibit Ca2+-dependent sugar binding (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar, 12Taylor M.E. Bezouska K. Drickamer K. J. Biol. Chem. 1992; 267: 1719-1726Abstract Full Text PDF PubMed Google Scholar). (b) At least some of the CTLDs in this receptor family have evolved to mediate protein/protein interactions rather than protein/sugar interactions. This is exemplified in the PLA2R, which binds nonglycosylated secretory phospholipase A2 in a Ca2+-independent manner via CTLD5 (13Nicolas J.P. Lin Y. Lambeau G. Ghomashchi F. Lazdunski M. Gelb M.H. J. Biol. Chem. 1997; 272: 7173-7181Abstract Full Text Full Text PDF PubMed Scopus (80) Google Scholar). (c) Domains in addition to the CTLDs can mediate ligand interactions. The cysteine-rich domain of the mannose receptor has been demonstrated to bind sulfated sugars, and structural studies and sequence analysis have suggested that this feature is not shared with other family members (4East L. Isacke C.M. Biochim. Biophys. Acta. 2002; (in press)PubMed Google Scholar, 14Liu Y. Chirino A.J. Misulovin Z. Leteux C. Feizi T. Nussenzweig M.C. Bjorkman P.J. J. Exp. Med. 2000; 191: 1105-1116Crossref PubMed Scopus (111) Google Scholar). The fibronectin type II domain of the PLA2R has been demonstrated to bind collagen, and similarly structural and sequence analysis predicts that this feature will be shared with other family members with the possible exception of DEC-205. In the case of Endo180, collagen binding both in vitro and in vivo has been demonstrated (3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar). 2D. Wienke and C. M. Isacke, unpublished observations. 2D. Wienke and C. M. Isacke, unpublished observations. (d) In addition to binding soluble ligands, members of this receptor family can bind transmembrane ligands, and this can occur both incis and trans. For example, the mannose receptor on lymphatic endothelia interacts with leukocyte l-selectin (15Irjala H. Johansson E.L. Grenman R. Alanen K. Salmi M. Jalkanen S. J. Exp. Med. 2001; 194: 1033-1042Crossref PubMed Scopus (135) Google Scholar), whereas Endo180 was identified independently as part of a trimolecular complex with the urokinase plasminogen activator receptor and pro-urokinase plasminogen activator, hence its alternative name, urokinase plasminogen activator receptor-associated protein, or uPARAP (3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar). (e) In addition to variation in ligand binding properties, these four family members do not share a common intracellular destination. Recently, it has been demonstrated that whereas the mannose receptor is predominantly localized to early endosomes, DEC-205 is targeted to late endosome/lysosomal compartments (16Mahnke K. Guo M. Lee S. Sepulveda H. Swain S.L. Nussenzweig M. Steinman R.M. J. Cell Biol. 2000; 151: 673-684Crossref PubMed Scopus (444) Google Scholar). Moreover, the mannose receptor is unusual in that, in addition to its ability to be internalized via the clathrin-mediated endocytic pathways, it can also mediate phagocytosis of nonopsonized microorganisms or synthetic large particular ligands (17Ezekowitz R.A. Sastry K. Bailly P. Warner A. J. Exp. Med. 1990; 172: 1785-1794Crossref PubMed Scopus (413) Google Scholar, 18Fraser I.P. Koziel H. Ezekowitz R.A. Semin. Immunol. 1998; 10: 363-372Crossref PubMed Scopus (198) Google Scholar). Together, these data demonstrate that rather than representing a group of related lectin receptors, the mannose receptor family is a group of multidomain receptors with distinct ligand binding and trafficking properties.In situ hybridization analysis together with immunohistochemistry has revealed that most tissues have Endo180 expression but that this is generally restricted to stromal cells, macrophages, and a subset of endothelial cells (1Isacke C.M. van der Geer P. Hunter T. Trowbridge I.S. Mol. Cell. Biol. 1990; 10: 2606-2618Crossref PubMed Scopus (56) Google Scholar, 2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar, 19Nielsen B.S Rank F. Engelholm L.H. Holm A. Dano K. Behrendt N. Int. J. Cancer. 2002; 98: 656-664Crossref PubMed Scopus (55) Google Scholar, 20Engelholm L.H. Nielsen B.S. Netzel-Arnett S. Solberg H. Chen X.D. Lopez Garcia J.M. Lopez-Otin C. Young M.F. Birkedal-Hansen H. Dano K. Lund L.R. Behrendt N. Bugge T.H. Lab. Invest. 2001; 81: 1403-1414Crossref PubMed Scopus (61) Google Scholar, 21Wu K. Yuan J. Lasky L.A. J. Biol. Chem. 1996; 271: 21323-21330Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar). In addition, high levels of expression are found in the embryo and neonate in chondrocytes at areas of active cartilage deposition and in tissues undergoing primary ossification and on chondrocyte (data not shown) and osteoblast (22Bailey L. Wienke D. Howard M. Knauper V. Isacke C.M. Murphy G. Biochem. J. 2002; 363: 67-72Crossref PubMed Scopus (16) Google Scholar) cell lines. This distribution pattern together with its C-type lectin activity (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar), collagen binding ability, and interaction with urokinase plasminogen activator receptor (3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar) suggests a role for Endo180 in regulating extracellular matrix degradation and remodeling. In support of this hypothesis is the observed up-regulation of Endo180 on angiogenic endothelial cells (23St. Croix B. Rago C. Velculescu V. Traverso G. Romans K.E. Montgomery E. Lal A. Riggins G.J. Lengauer C. Vogelstein B. Kinzler K.W. Science. 2000; 289: 1197-1202Crossref PubMed Scopus (1631) Google Scholar) and on the stromal fibroblasts and myoepithelial cells in breast tumors (19Nielsen B.S Rank F. Engelholm L.H. Holm A. Dano K. Behrendt N. Int. J. Cancer. 2002; 98: 656-664Crossref PubMed Scopus (55) Google Scholar), where increased expression may be required for the dissolution of basement membranes lining the blood vessels or epithelial sheets and/or for degradation of extracellular matrix components associated with the tumor. Finally, the observed C-type lectin activity of Endo180 and the demonstration that it is expressed on macrophages (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar) raises the possibility that like the mannose receptor, Endo180 could function both as an endocytic receptor and as a phagocytic receptor. To understand the physiological role of Endo180, we have undertaken experiments to determine the mechanism by which Endo180 is internalized from the plasma membrane, the intracellular destination of this receptor, and the potential that Endo180 can mediate phagocytosis in addition to endocytosis. Endo180 was first identified as a recycling endocytic receptor expressed in fibroblastic cells (1Isacke C.M. van der Geer P. Hunter T. Trowbridge I.S. Mol. Cell. Biol. 1990; 10: 2606-2618Crossref PubMed Scopus (56) Google Scholar). Based on peptide sequences obtained from purified protein, a full-length human cDNA clone was isolated, and Endo180 was demonstrated to be the fourth and last member of the mannose receptor family (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar, 3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar, 4East L. Isacke C.M. Biochim. Biophys. Acta. 2002; (in press)PubMed Google Scholar). In addition to Endo180, the mannose receptor family comprises the mannose receptor, the M-type phospholipase A2 receptor (PLA2R),1 and DEC-205/MR6-gp200. This family grouping is based on an overall structural conservation with the four receptors containing a large extracellular domain comprising an N-terminal signal sequence followed by a cysteine-rich domain, a fibronectin type II domain, and 8 or 10 C-type lectin-like domains (CTLDs). The single pass transmembrane domains are followed by a short cytoplasmic domain. As a family, these receptors have two striking features. First, although they belong to the large C-type lectin superfamily (information available on the World Wide Web at ctld.glycob.ox.ac.uk), they uniquely contain multiple CTLDs within a single polypeptide backbone (4East L. Isacke C.M. Biochim. Biophys. Acta. 2002; (in press)PubMed Google Scholar, 5Taylor M.E. Glycobiology. 1997; 7: v-viiiCrossref PubMed Google Scholar, 6Weis W.I. Taylor M.E. Drickamer K. Immunol. Rev. 1998; 163: 19-34Crossref PubMed Scopus (870) Google Scholar, 7Valentin E. Lambeau G. Biochim. Biophys. Acta. 2000; 1488: 59-70Crossref PubMed Scopus (313) Google Scholar, 8Jiang W. Swiggard W.J. Heufler C. Peng M. Mirza A. Steinman R.M. Nussenzweig M.C. Nature. 1995; 375: 151-155Crossref PubMed Scopus (797) Google Scholar, 9McKay P.F. Imami N. Johns M. Taylor-Fishwick D.A. Sedibane L.M. Totty N.F. Hsuan J.J. Palmer D.B. George A.J. Foxwell B.M. Ritter M.A. Eur. J. Immunol. 1998; 28: 4071-4083Crossref PubMed Scopus (34) Google Scholar). Second, they share the ability to be recycled between the plasma membrane and intracellular compartments of the cell (1Isacke C.M. van der Geer P. Hunter T. Trowbridge I.S. Mol. Cell. Biol. 1990; 10: 2606-2618Crossref PubMed Scopus (56) Google Scholar, 8Jiang W. Swiggard W.J. Heufler C. Peng M. Mirza A. Steinman R.M. Nussenzweig M.C. Nature. 1995; 375: 151-155Crossref PubMed Scopus (797) Google Scholar, 10Kruskal B.A. Sastry K. Warner A.B. Mathieu C.E. Ezekowitz R.A. J. Exp. Med. 1992; 176: 1673-1680Crossref PubMed Scopus (68) Google Scholar, 11Zvaritch E. Lambeau G. Lazdunski M. J. Biol. Chem. 1996; 271: 250-257Abstract Full Text Full Text PDF PubMed Scopus (110) Google Scholar). As a consequence of their structural and recycling characteristics, it was initially assumed that these receptors would commonly function to internalize glycosylated ligands for intracellular delivery. However, further characterization has revealed the following. (a) Although the receptors contain multiple CTLDS, only CTLDs 4 and 5 of the mannose receptor and CTLDs 1 and 2 of Endo180 contain the conserved amino acids found in functional C-type lectins, and accordingly only these two receptors have been demonstrated to exhibit Ca2+-dependent sugar binding (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar, 12Taylor M.E. Bezouska K. Drickamer K. J. Biol. Chem. 1992; 267: 1719-1726Abstract Full Text PDF PubMed Google Scholar). (b) At least some of the CTLDs in this receptor family have evolved to mediate protein/protein interactions rather than protein/sugar interactions. This is exemplified in the PLA2R, which binds nonglycosylated secretory phospholipase A2 in a Ca2+-independent manner via CTLD5 (13Nicolas J.P. Lin Y. Lambeau G. Ghomashchi F. Lazdunski M. Gelb M.H. J. Biol. Chem. 1997; 272: 7173-7181Abstract Full Text Full Text PDF PubMed Scopus (80) Google Scholar). (c) Domains in addition to the CTLDs can mediate ligand interactions. The cysteine-rich domain of the mannose receptor has been demonstrated to bind sulfated sugars, and structural studies and sequence analysis have suggested that this feature is not shared with other family members (4East L. Isacke C.M. Biochim. Biophys. Acta. 2002; (in press)PubMed Google Scholar, 14Liu Y. Chirino A.J. Misulovin Z. Leteux C. Feizi T. Nussenzweig M.C. Bjorkman P.J. J. Exp. Med. 2000; 191: 1105-1116Crossref PubMed Scopus (111) Google Scholar). The fibronectin type II domain of the PLA2R has been demonstrated to bind collagen, and similarly structural and sequence analysis predicts that this feature will be shared with other family members with the possible exception of DEC-205. In the case of Endo180, collagen binding both in vitro and in vivo has been demonstrated (3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar). 2D. Wienke and C. M. Isacke, unpublished observations. 2D. Wienke and C. M. Isacke, unpublished observations. (d) In addition to binding soluble ligands, members of this receptor family can bind transmembrane ligands, and this can occur both incis and trans. For example, the mannose receptor on lymphatic endothelia interacts with leukocyte l-selectin (15Irjala H. Johansson E.L. Grenman R. Alanen K. Salmi M. Jalkanen S. J. Exp. Med. 2001; 194: 1033-1042Crossref PubMed Scopus (135) Google Scholar), whereas Endo180 was identified independently as part of a trimolecular complex with the urokinase plasminogen activator receptor and pro-urokinase plasminogen activator, hence its alternative name, urokinase plasminogen activator receptor-associated protein, or uPARAP (3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar). (e) In addition to variation in ligand binding properties, these four family members do not share a common intracellular destination. Recently, it has been demonstrated that whereas the mannose receptor is predominantly localized to early endosomes, DEC-205 is targeted to late endosome/lysosomal compartments (16Mahnke K. Guo M. Lee S. Sepulveda H. Swain S.L. Nussenzweig M. Steinman R.M. J. Cell Biol. 2000; 151: 673-684Crossref PubMed Scopus (444) Google Scholar). Moreover, the mannose receptor is unusual in that, in addition to its ability to be internalized via the clathrin-mediated endocytic pathways, it can also mediate phagocytosis of nonopsonized microorganisms or synthetic large particular ligands (17Ezekowitz R.A. Sastry K. Bailly P. Warner A. J. Exp. Med. 1990; 172: 1785-1794Crossref PubMed Scopus (413) Google Scholar, 18Fraser I.P. Koziel H. Ezekowitz R.A. Semin. Immunol. 1998; 10: 363-372Crossref PubMed Scopus (198) Google Scholar). Together, these data demonstrate that rather than representing a group of related lectin receptors, the mannose receptor family is a group of multidomain receptors with distinct ligand binding and trafficking properties. In situ hybridization analysis together with immunohistochemistry has revealed that most tissues have Endo180 expression but that this is generally restricted to stromal cells, macrophages, and a subset of endothelial cells (1Isacke C.M. van der Geer P. Hunter T. Trowbridge I.S. Mol. Cell. Biol. 1990; 10: 2606-2618Crossref PubMed Scopus (56) Google Scholar, 2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar, 19Nielsen B.S Rank F. Engelholm L.H. Holm A. Dano K. Behrendt N. Int. J. Cancer. 2002; 98: 656-664Crossref PubMed Scopus (55) Google Scholar, 20Engelholm L.H. Nielsen B.S. Netzel-Arnett S. Solberg H. Chen X.D. Lopez Garcia J.M. Lopez-Otin C. Young M.F. Birkedal-Hansen H. Dano K. Lund L.R. Behrendt N. Bugge T.H. Lab. Invest. 2001; 81: 1403-1414Crossref PubMed Scopus (61) Google Scholar, 21Wu K. Yuan J. Lasky L.A. J. Biol. Chem. 1996; 271: 21323-21330Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar). In addition, high levels of expression are found in the embryo and neonate in chondrocytes at areas of active cartilage deposition and in tissues undergoing primary ossification and on chondrocyte (data not shown) and osteoblast (22Bailey L. Wienke D. Howard M. Knauper V. Isacke C.M. Murphy G. Biochem. J. 2002; 363: 67-72Crossref PubMed Scopus (16) Google Scholar) cell lines. This distribution pattern together with its C-type lectin activity (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar), collagen binding ability, and interaction with urokinase plasminogen activator receptor (3Behrendt N. Jensen O.N. Engelholm L.H. Mortz E. Mann M. Dano K. J. Biol. Chem. 2000; 275: 1993-2002Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar) suggests a role for Endo180 in regulating extracellular matrix degradation and remodeling. In support of this hypothesis is the observed up-regulation of Endo180 on angiogenic endothelial cells (23St. Croix B. Rago C. Velculescu V. Traverso G. Romans K.E. Montgomery E. Lal A. Riggins G.J. Lengauer C. Vogelstein B. Kinzler K.W. Science. 2000; 289: 1197-1202Crossref PubMed Scopus (1631) Google Scholar) and on the stromal fibroblasts and myoepithelial cells in breast tumors (19Nielsen B.S Rank F. Engelholm L.H. Holm A. Dano K. Behrendt N. Int. J. Cancer. 2002; 98: 656-664Crossref PubMed Scopus (55) Google Scholar), where increased expression may be required for the dissolution of basement membranes lining the blood vessels or epithelial sheets and/or for degradation of extracellular matrix components associated with the tumor. Finally, the observed C-type lectin activity of Endo180 and the demonstration that it is expressed on macrophages (2Sheikh H. Yarwood H. Ashworth A. Isacke C.M. J. Cell Sci. 2000; 113: 1021-1032Crossref PubMed Google Scholar) raises the possibility that like the mannose receptor, Endo180 could function both as an endocytic receptor and as a phagocytic receptor. To understand the physiological role of Endo180, we have undertaken experiments to determine the mechanism by which Endo180 is internalized from the plasma membrane, the intracellular destination of this receptor, and the potential that Endo180 can mediate phagocytosis in addition to endocytosis. We thank Annegret Pelchen-Matthews and Mark Marsh for advice with the endocytosis assays, Laura Machesky and Robin May for advice and reagents for the phagocytosis assays, Helen Yarwood for help with the FACS analysis, David Robertson for confocal microscopy expertise, and Dirk Wienke and Lucy East for comments on the manuscript.