Tyrosine-phosphorylated Low Density Lipoprotein Receptor-related Protein 1 (LRP1) Associates with the Adaptor Protein SHC in SRC-transformed Cells

v-Src transforms fibroblasts in vitroand causes tumor formation in the animal by tyrosine phosphorylation of critical cellular substrates. Exactly how v-Src interacts with these substrates remains unknown. One of its substrates, the adaptor protein Shc, is thought to play a crucial role during cellular transformation by v-Src by linking v-Src to Ras. We used Shc proteins with mutations in either the phosphotyrosine binding (PTB) or Src homology 2 domain to determine that phosphorylation of Shc in v-Src-expressing cells depends on the presence of a functional PTB domain. We purified a 100-kDa Shc PTB-binding protein from Src-transformed cells that was identified as the β chain of the low density lipoprotein receptor-related protein LRP1. LRP1 acts as an import receptor for a variety of proteins and is involved in clearance of the β-amyloid precursor protein. This study shows that LRP1 is tyrosine-phosphorylated in v-Src-transformed cells and that tyrosine-phosphorylated LRP1 binds in vivo and in vitro to Shc. The association between Shc and LRP1 may provide a mechanism for recruitment of Shc to the plasma membrane where it is phosphorylated by v-Src. It is at the membrane that Shc is thought to be involved in Ras activation. These observations further suggest that LRP1 could function as a signaling receptor and may provide new avenues to investigate its possible role during embryonal development and the onset of Alzheimer's disease. v-Src transforms fibroblasts in vitroand causes tumor formation in the animal by tyrosine phosphorylation of critical cellular substrates. Exactly how v-Src interacts with these substrates remains unknown. One of its substrates, the adaptor protein Shc, is thought to play a crucial role during cellular transformation by v-Src by linking v-Src to Ras. We used Shc proteins with mutations in either the phosphotyrosine binding (PTB) or Src homology 2 domain to determine that phosphorylation of Shc in v-Src-expressing cells depends on the presence of a functional PTB domain. We purified a 100-kDa Shc PTB-binding protein from Src-transformed cells that was identified as the β chain of the low density lipoprotein receptor-related protein LRP1. LRP1 acts as an import receptor for a variety of proteins and is involved in clearance of the β-amyloid precursor protein. This study shows that LRP1 is tyrosine-phosphorylated in v-Src-transformed cells and that tyrosine-phosphorylated LRP1 binds in vivo and in vitro to Shc. The association between Shc and LRP1 may provide a mechanism for recruitment of Shc to the plasma membrane where it is phosphorylated by v-Src. It is at the membrane that Shc is thought to be involved in Ras activation. These observations further suggest that LRP1 could function as a signaling receptor and may provide new avenues to investigate its possible role during embryonal development and the onset of Alzheimer's disease. phosphotyrosine binding low density lipoprotein phosphate-buffered saline Src homology-2 Src homology 3 LDL receptor-related protein 1 hemagglutinin dithiothreitol polyacrylamide gel electrophoresis glutathione S-transferase very low density lipoprotein Protein tyrosine phosphorylation is one of several mechanisms that have evolved to mediate signal transduction (1Fantl W.J. Johnson D.E. Williams L.T. Annu. Rev. Biochem. 1993; 62: 453-481Crossref PubMed Scopus (932) Google Scholar, 2van der Geer P. Hunter T. Lindberg R.A. Annu. Rev. Cell Biol. 1994; 10: 251-337Crossref PubMed Scopus (1245) Google Scholar, 3Heldin C.H. Cancer Surv. 1996; 27: 7-24PubMed Google Scholar). Protein-tyrosine kinases regulate cell division and differentiation in response to extracellular factors. Expression of constitutively active versions of these kinases results in cellular transformation in vitroand tumor formation in vivo (4Kolibaba K.S. Druker B.J. Biochim. Biophys. Acta. 1997; 1333: F217-F248PubMed Google Scholar). Protein-tyrosine kinases come in two varieties, receptor protein-tyrosine kinases and cytoplasmic protein-tyrosine kinases. Receptor protein-tyrosine kinases contain an extracellular ligand binding domain, a single transmembrane domain, and a cytoplasmic kinase domain (5Hubbard S.R. Prog. Biophys. Mol. Biol. 1999; 71: 343-358Crossref PubMed Scopus (158) Google Scholar). Upon activation, receptors autophosphorylate on tyrosine residues thereby creating binding sites for phosphotyrosine binding (PTB)1 domain and Src homology 2 (SH2) domain containing signaling proteins. These proteins are activated directly or indirectly as a consequence of their interaction with the receptor (6Pawson T. Scott J.D. Science. 1997; 278: 2075-2080Crossref PubMed Scopus (1900) Google Scholar, 7Pawson T. Nature. 1995; 373: 573-580Crossref PubMed Scopus (2228) Google Scholar). In general, association with the receptor precedes tyrosine phosphorylation and activation of receptor substrates (1Fantl W.J. Johnson D.E. Williams L.T. Annu. Rev. Biochem. 1993; 62: 453-481Crossref PubMed Scopus (932) Google Scholar, 2van der Geer P. Hunter T. Lindberg R.A. Annu. Rev. Cell Biol. 1994; 10: 251-337Crossref PubMed Scopus (1245) Google Scholar, 3Heldin C.H. Cancer Surv. 1996; 27: 7-24PubMed Google Scholar). The extracellular ligand binding domain is missing from cytoplasmic protein-tyrosine kinases (8Neet K. Hunter T. Mol. Cell. Biol. 1995; 15: 4908-4920Crossref PubMed Scopus (70) Google Scholar). They are often found associated with receptors that lack kinase domains themselves and are thought to function as signal transducing subunits for these receptors (9Bubeck-Wardenburg J. Wong J. Futterer K. Pappu R. Fu C. Waksman G. Chan A.C. Prog. Biophys. Mol. Biol. 1999; 71: 373-392Crossref PubMed Scopus (4) Google Scholar). Curiously, most cytoplasmic protein-tyrosine kinases also lack the autophosphorylation sites that act as binding sites for their substrates (8Neet K. Hunter T. Mol. Cell. Biol. 1995; 15: 4908-4920Crossref PubMed Scopus (70) Google Scholar). In some cases these sites are located on the associated non-kinase receptors (9Bubeck-Wardenburg J. Wong J. Futterer K. Pappu R. Fu C. Waksman G. Chan A.C. Prog. Biophys. Mol. Biol. 1999; 71: 373-392Crossref PubMed Scopus (4) Google Scholar, 10Ihle J.N. Cell. 1996; 84: 331-334Abstract Full Text Full Text PDF PubMed Scopus (1265) Google Scholar). In general, it remains to be established how activated cytoplasmic protein-tyrosine kinases interact with their substrates. To address this issue, we have investigated tyrosine phosphorylation of Shc in v-Src-transformed cells. Shc is an adaptor protein that is involved in signal transduction by protein-tyrosine kinases (11Pelicci G. Lanfrancone L. Grignani F. McGlade J. Cavallo F. Forni G. Nicoletti I. Grignani F. Pawson T. Pelicci P.G. Cell. 1992; 70: 93-104Abstract Full Text PDF PubMed Scopus (1138) Google Scholar, 12Bonfini L. Migliaccio E. Pelicci G. Lanfrancone L. Pelicci P.G. Trends Biochem. Sci. 1996; 21: 257-261Abstract Full Text PDF PubMed Scopus (235) Google Scholar, 13McGlade J. Cheng A. Pelicci G. Pelicci P.G. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 8869-8873Crossref PubMed Scopus (238) Google Scholar). The shc gene encodes three proteins that all contain an amino-terminal PTB domain, a central region that contains several tyrosine phosphorylation sites, and a carboxyl-terminal SH2 domain (11Pelicci G. Lanfrancone L. Grignani F. McGlade J. Cavallo F. Forni G. Nicoletti I. Grignani F. Pawson T. Pelicci P.G. Cell. 1992; 70: 93-104Abstract Full Text PDF PubMed Scopus (1138) Google Scholar). PTB domains bind to tyrosine residues in the context of an NPXY motif (14Forman-Kay J.D. Pawson T. Curr. Opin. Struct. Biol. 1999; 9: 690-695Crossref PubMed Scopus (107) Google Scholar, 15Margolis B. Borg J.P. Straight S. Meyer D. Kidney Int. 1999; 56: 1230-1237Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar). The Shc PTB domain binds to phosphorylated NPXY motifs preceded by a leucine, isoleucine, or valine residue five residues upstream of the phosphorylated tyrosine (16van der Geer P. Wiley S. Gish G.D. Lai V.K. Stephens R. White M.F. Kaplan D. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 963-968Crossref PubMed Scopus (94) Google Scholar). The Shc SH2 domain binds to phosphorylated tyrosine residues in the context of acidic or non-polar residues carboxyl-terminal to the tyrosine (17Songyang Z. Shoelson S.E. McGlade J. Olivier P. Pawson T. Bustelo X.R. Barbacid M. Sabe H. Hanafusa H. Yi T. Ren R. Baltimore D. Ratnofsky S. Feldman R.A. Cantley L.C. Mol. Cell. Biol. 1994; 14: 2777-2785Crossref PubMed Scopus (833) Google Scholar). Tyrosine phosphorylation sites on Shc function as binding sites for other signaling proteins. It is well established that tyrosine-phosphorylated Shc binds to Grb2 (18Rozakis-Adcock M. McGlade J. Mbamalu G. Pelicci G. Daly R. Thomas S. Brugge J. Pelicci P.G. Schlessinger J. Pawson T. Nature. 1992; 360: 689-692Crossref PubMed Scopus (827) Google Scholar, 19van der Geer P. Wiley S. Gish G.D. Pawson T. Curr. Biol. 1996; 6: 1435-1444Abstract Full Text Full Text PDF PubMed Scopus (189) Google Scholar). It is through the interaction with the Grb2-Sos complex that Shc is thought to be involved in activation of Ras and the mitogen-activated protein kinase pathway (7Pawson T. Nature. 1995; 373: 573-580Crossref PubMed Scopus (2228) Google Scholar). Following activation of receptor protein-tyrosine kinases such as the epidermal growth factor receptor or the nerve growth factor receptor, Shc uses either its PTB or its SH2 domain to bind to specific tyrosine phosphorylation sites on the receptor. Binding to the receptor is a prerequisite for tyrosine phosphorylation of Shc, and it is tyrosine-phosphorylated Shc that recruits the Grb2-Sos complex to the receptor at the inner leaf of the plasma membrane, in close proximity to Ras. v-Src is an activated version of the cytoplasmic protein-tyrosine kinase c-Src. Expression of v-Src results in protein tyrosine phosphorylation and in oncogenic transformation (20Levinson A.D. Oppermann H. Levontow L. Varmus H.E. Bishop J.M. Cell. 1978; 15: Full Text PDF PubMed Scopus Google Scholar, Nature. PubMed Scopus Google Scholar). v-Src is to cellular through a that is to its D. L. J. B. S. PubMed Scopus Google Scholar). Following its Src contains an SH2 domain, a Src homology 3 domain, and a protein-tyrosine kinase domain. The well autophosphorylation in v-Src is its kinase domain and is to regulate kinase H. Bishop J.M. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, H. Cheng Cell. Full Text PDF PubMed Scopus Google Scholar). In the protein the SH2 and the domain are involved in of kinase F. I. J. Nature. 1997; PubMed Scopus Google Scholar, Nature. 1997; PubMed Scopus Google Scholar). are some that suggest that in the SH2 and domains may play a role in the other Src with SH2 and domains have their H. Varmus H.E. Mol. Cell. Biol. 10: PubMed Google Scholar). This that the SH2 domain the domain is for the of substrates that are critical for cellular of proteins are phosphorylated on tyrosine in v-Src-transformed cells. It remains how these proteins are as substrates and of these substrates mediate cellular Shc is phosphorylated in v-Src-transformed and it is thought that it is Shc that the Ras activation that of v-Src J. Cheng A. Pelicci G. Pelicci P.G. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 8869-8873Crossref PubMed Scopus (238) Google Scholar, M. McGlade J. Mbamalu G. Pelicci G. Daly R. Thomas S. Brugge J. Pelicci P.G. Schlessinger J. Pawson T. Nature. 1992; 360: 689-692Crossref PubMed Scopus (827) Google Scholar). with this it is found that in v-Src-transformed cells Shc is associated with and M. R. J. Pawson T. D. Nature. 1993; PubMed Scopus Google Scholar). v-Src bind to Shc, and it remains how v-Src Shc for tyrosine Shc Ras activation it to Grb2-Sos to the plasma membrane, and it remains how this is To address some of these we Shc on the presence of a functional PTB or SH2 domain for phosphorylation by v-Src. that Shc depends on a functional PTB domain for its phosphorylation in v-Src-expressing cells. The PTB domain binds to a 100-kDa protein that was purified and identified as the low density lipoprotein receptor-related protein LRP1. LRP1 is a that of a extracellular that is to a The contains an extracellular domain, a transmembrane domain, and a cytoplasmic domain. NPXY motifs are in the cytoplasmic domain of LRP1. LRP1 is thought to function as an import receptor for a variety of proteins and β-amyloid precursor protein A. Annu. Rev. 1999; PubMed Scopus Google Scholar). The NPXY motifs thought to mediate receptor Annu. Rev. Cell Biol. 1993; 9: PubMed Scopus Google Scholar). suggest that at one of the NPXY motifs in LRP1 is involved in a signaling that depends on protein phosphorylation and PTB domain containing signaling proteins. and cells in containing cells are fibroblasts established from a at of development der Geer P. M. T. Pawson T. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). cells vitro by with containing the and the der Geer P. M. T. Pawson T. Mol. Cell. Biol. 1997; PubMed Scopus Google Scholar). is a v-Src-transformed cell E. Pawson T. Mol. Cell. Biol. 9: PubMed Scopus Google Scholar). cells in containing and The from was in with and was a SH2 protein. and from and and Shc the for of protein and a the hemagglutinin with a in by a to the Shc at the residue of the a chain to and the cells at with of with or 1 of and to the The PTB protein contains residues and the SH2 domain contains residues a chain to and the Expression of proteins was by in the presence of for several at by in phosphate-buffered saline containing 1 1 and was to a of was by for at at and proteins purified by binding to by and with containing 1 1 proteins to at in containing 1 1 and Protein by and protein and in the gel as A. I. B. M. M. 1997; PubMed Scopus Google Scholar, A. M. M. 1996; PubMed Scopus Google Scholar). proteins by with and was with at and from the gel and and to was on a and to on with and in 1 of 1 1 and by at in a at with of or 1 of for 1 on and for 1 with of protein or for 1 at on an by and with 3 in and and by 2 1 and by with and for in a at at To cells from a and for 3 in of 1 and 1 the in of 2 by with and for in a at at in vitro binding cell for 1 at on a with of containing of protein. with and proteins by and by in 1 2 on and by for protein by for at at and by for at at by for at at to a at gel for at for 1 at in containing and with of in for 1 at for with and for with and for with or in and as proteins by with with containing by an with the in and as for other The Shc adaptor protein is a for tyrosine phosphorylation in v-Src-transformed cells J. Cheng A. Pelicci G. Pelicci P.G. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 8869-8873Crossref PubMed Scopus (238) Google Scholar). It how Shc and Src To address this we versions of the of Shc with mutations in either the PTB or the SH2 domain These domains have the to bind with to their binding version and a version with mutations in domains used as To Shc depends on either its PTB domain or its SH2 domain for phosphorylation by the with v-Src in cells. by and The that v-Src Shc or Shc that a functional SH2 domain 2 of the PTB domain Shc tyrosine phosphorylation in v-Src-transformed cells 2 and 3 or and in 2 of the SH2 domain results in a in tyrosine The Shc proteins at 2 We have that Shc bind directly to and P. der These observations suggest that Shc uses its PTB domain to bind to an protein it be phosphorylated by depends on a functional PTB domain for phosphorylation by the v-Src protein-tyrosine or Shc proteins with v-Src in cells. by and cells with v-Src and a v-Src and v-Src and v-Src and v-Src and To investigate further the role of the PTB domain during phosphorylation of Shc in v-Src-transformed we used proteins containing the PTB domain to for the presence of PTB domain binding proteins. Cell of Src-transformed fibroblasts with proteins that on and proteins by a of fibroblasts also with these proteins. Shc in This that Shc is tyrosine-phosphorylated in Src-transformed cells. Tyrosine phosphorylation of all three of Shc and be tyrosine-phosphorylated proteins are in Shc from Src-transformed cells Shc is tyrosine-phosphorylated or associated with tyrosine-phosphorylated proteins in cells tyrosine-phosphorylated proteins in of Src-transformed cells to bind to either the PTB or the SH2 domain of Shc of these proteins also to be in the Shc that proteins. Shc depends on its PTB domain for phosphorylation by we on a 100-kDa protein that was in Shc and that with a protein that to the PTB domain bind to the domain protein. To is a specific domain binding protein we the of an PTB domain protein to bind to In Shc from Src-transformed cells either in in or by in for the presence of is a that contains is a that contains and all proteins are by in a of and the is in that on the presence of functional interaction domains are The that of in the to results in a of binding most proteins that with Shc in or are of the These that binds to Shc in v-Src-transformed cells and that binding depends on the presence of a functional PTB domain. To where in the cell is v-Src-transformed cells by in and by and the was a and a by for 1 at in and for the presence of PTB-binding proteins by with the protein. was found to be in the This that is associated with cellular In we have Shc and found that of cellular Shc is in the in v-Src-transformed cells In to its was purified from of v-Src-transformed cells on its to bind to the PTB domain. To of cells with and cellular protein-tyrosine In a from 2 cells in of and with of protein on of The a and proteins with at and by was from the PTB a the was with the and the from the PTB and PTB by and and could be the PTB domain was used and with a of was in the from the PTB this was missing in the from the PTB To for of the was of was purified and with and by for and the used to the The for five the of the LDL receptor-related protein LRP1 To that is and proteins from and cells in with by and LRP1 from v-Src-transformed cells to be tyrosine-phosphorylated and LRP1 with tyrosine phosphorylation of LRP1 and and in a in during and could be by with the LRP1 was to the protein. To Shc binds to LRP1 in Shc and LRP1 in by and in Shc with tyrosine-phosphorylated LRP1 and be by with the LRP1 was in with a These that LRP1 tyrosine-phosphorylated in cells containing the activated v-Src protein-tyrosine kinase and that tyrosine-phosphorylated LRP1 with the adaptor protein Shc. This association is by the PTB domain of Shc. It well established that Shc proteins are tyrosine-phosphorylated in cells by the v-Src protein-tyrosine kinase J. Cheng A. Pelicci G. Pelicci P.G. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 8869-8873Crossref PubMed Scopus (238) Google Scholar). Tyrosine phosphorylation in v-Src-transformed fibroblasts results in association of Shc with Grb2 and (18Rozakis-Adcock M. McGlade J. Mbamalu G. Pelicci G. Daly R. Thomas S. Brugge J. Pelicci P.G. Schlessinger J. Pawson T. Nature. 1992; 360: 689-692Crossref PubMed Scopus (827) Google Scholar). This that Shc may function as a between Src and the protein kinase It remains how this is In to play a role in Ras activation Shc to to the to the membrane is during v-Src transformation remains are in the that or the PTB or the SH2 domain are involved in this it remains to be established how Src and Shc In an to address some of these we either the PTB or the SH2 domain of Shc is for phosphorylation to in v-Src-expressing cells. The PTB domain was found to be for phosphorylation of Shc by v-Src in cells. of the SH2 domain results in a in are with a in phosphorylation of Shc by v-Src depends on the association of Shc through its PTB domain with a tyrosine-phosphorylated membrane protein The SH2 domain some role during Shc phosphorylation to be The PTB domain was found to bind to a 100-kDa protein that was also in Shc This protein was purified from Src-transformed fibroblasts and identified by as the of LRP1. This LRP1 as a for the v-Src protein-tyrosine LRP1 tyrosine phosphorylation may be for signal transduction of v-Src. To LRP1 is the 100-kDa protein that with Shc, we to the 100-kDa tyrosine-phosphorylated protein by with an This that be a 100-kDa protein that with Shc in v-Src-transformed cells. this may that the for the used in these is LRP1 is LRP1 is a of a of proteins that are to the LDL receptor A. Annu. Rev. 1999; PubMed Scopus Google Scholar). of the LDL receptor are involved in the of and protein A. Annu. Rev. 1999; PubMed Scopus Google Scholar). To these receptors between the cell and cytoplasmic LRP1 is of a and a J. U. S. H. J. PubMed Scopus Google Scholar, J. J. 9: PubMed Scopus Google Scholar). The is extracellular and is to the The contains an extracellular domain, a single membrane domain, and a cytoplasmic domain of J. U. S. H. J. PubMed Scopus Google Scholar, J. J. 9: PubMed Scopus Google Scholar). The cytoplasmic domain contains two NPXY motifs and NPXY motifs are in all of the LDL receptor and identified as Annu. Rev. Cell Biol. 1993; 9: PubMed Scopus Google Scholar). NPXY motifs as binding sites for PTB domains (16van der Geer P. Wiley S. Gish G.D. Lai V.K. Stephens R. White M.F. Kaplan D. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 963-968Crossref PubMed Scopus (94) Google Scholar, der Geer P. Pawson T. Trends Biochem. Sci. 1995; Full Text PDF PubMed Scopus Google Scholar). of PTB domains have some of bind phosphorylated NPXY bind NPXY motifs B. Borg J.P. Straight S. Meyer D. Kidney Int. 1999; 56: 1230-1237Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar). Binding are further by residues upstream of the NPXY der Geer P. Wiley S. Pawson T. 1999; PubMed Scopus Google Scholar, R. Mol. Cell. Biol. 1999; PubMed Scopus Google Scholar, M. Borg J.P. B. J. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). The Shc PTB domain binds to the in is or (16van der Geer P. Wiley S. Gish G.D. Lai V.K. Stephens R. White M.F. Kaplan D. Pawson T. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 963-968Crossref PubMed Scopus (94) Google and is The NPXY motif in the cytoplasmic domain of LRP1 to this J. U. S. H. J. PubMed Scopus Google Scholar). The that the Shc PTB domain binds to phosphorylated NPXY motifs is in with that LRP1 is tyrosine-phosphorylated in v-Src-transformed cells. are with a in LRP1 phosphorylation an role during cellular transformation by v-Src LRP1 is at the membrane, in proximity to v-Src. Upon phosphorylation of Shc is to the membrane where it a for the v-Src protein-tyrosine by v-Src a binding for Grb2 and results in the recruitment of Grb2-Sos to the In this LRP1 acts as an for Shc and Grb2-Sos at the membrane of to the membrane is a prerequisite for Ras activation A. D. Schlessinger J. M. Cell. 1994; Full Text PDF PubMed Scopus Google Scholar, L. L. A. U. Science. 1995; PubMed Scopus Google Scholar). are in with a study that to an interaction between the Shc PTB domain and LRP1 M. Borg J.P. B. J. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). It is most that LRP1 was used in this results that association between LRP1 and Shc depends on LRP1 tyrosine phosphorylation and that the association is by the Shc PTB domain. We have to LRP1 tyrosine phosphorylation in cell activation of a variety of receptor protein-tyrosine and it that LRP1 is phosphorylated by cytoplasmic protein-tyrosine suggest that LRP1 phosphorylated on tyrosine residues and that tyrosine-phosphorylated LRP1 is involved in signal transduction with the of adaptor proteins. observations are with that that two other of the LDL receptor are also involved in signal transduction Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). of the for the receptor and the receptor 2 results in development of the and the in M. M. T. J. J. J. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The and the have a of that is in the most as a consequence of in cell M. M. T. J. J. J. Cell. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). This that the receptor and receptor 2 are for of by the of the the in that lack the for either or R. P. Nature. 1997; PubMed Scopus Google Scholar, G. T. Nature. 1995; PubMed Scopus Google Scholar). is a that is in of the and is thought to provide to G. T. PubMed Scopus Google Scholar). is a cytoplasmic protein that be phosphorylated by a variety of protein-tyrosine kinases. The is that the receptor and the receptor 2 act as signaling receptors that the presence of on the of the cell to on the of the cell G. T. PubMed Scopus Google Scholar). is that either the receptor or the receptor 2 themselves are phosphorylated on tyrosine The NPXY motif in LRP1 is in the context of a five residues upstream of the tyrosine J. U. S. H. J. PubMed Scopus Google Scholar). motif is in of the LDL receptor A. Annu. Rev. 1999; PubMed Scopus Google Scholar). is that this vitro and in vivo to the PTB domain R. Mol. Cell. Biol. 1999; PubMed Scopus Google Scholar, J.D. Curr. Biol. 10: Full Text Full Text PDF PubMed Scopus Google Scholar). The PTB domain, in to the Shc PTB domain, binds to NPXY motifs that contain an five residues upstream of the tyrosine R. Mol. Cell. Biol. 1999; PubMed Scopus Google Scholar). This that the NPXY motif in LRP1 could function as a binding for The that NPXY motifs in LRP1 are involved in with signaling is with the that these motifs are for LRP1 M. P. G. J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). We several of the LRP1 β chain that from other in during and β as the of the cells with and protein-tyrosine This that the phosphorylation and that are phosphorylation sites in LRP1. are in with the that LRP1 be in vivo with Cell Biol. Int. PubMed Scopus Google Scholar). tyrosine phosphorylation of LRP1 on NPXY activation of Src could the association with and the association with Shc. This in a in signaling to the in the association with adaptor from to Shc. Shc depends on its PTB domain for tyrosine phosphorylation in v-Src-expressing cells. We to a interaction between Src and this is with the of a PTB domain binding in The Shc PTB domain binds in in vitro to the LRP1 β This interaction is most by the NPXY motif in the cytoplasmic domain of LRP1 β This that LRP1 is an for tyrosine phosphorylation in v-Src-transformed cells. Following tyrosine phosphorylation LRP1 an for Shc at the plasma membrane, and this for Shc tyrosine recruitment of the Grb2-Sos and Ras activation. The further suggest that LRP1 may have a signaling function that cytoplasmic protein-tyrosine kinases and PTB adaptor proteins. These observations are to the function of its role during signaling by the v-Src and its role during

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