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

Helen Barnes,Brett Larsen,Mike Tyers,Peter Van Der Geer

doi:10.1074/jbc.m011437200

Abstract

v-Src transforms fibroblasts in vitro and 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 beta 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 beta-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.

Highlights

Protein tyrosine phosphorylation is one of several mechanisms that have evolved to mediate signal transduction [1,2,3]
Following activation of receptor protein-tyrosine kinases such as the epidermal growth factor receptor or the nerve growth factor receptor, Shc uses either its phosphotyrosine binding (PTB) or its Src homology 2 (SH2) domain to bind to specific tyrosine phosphorylation sites on the receptor
Our data suggest that at least one of the NPXY motifs present in LRP1 is involved in a signaling process that depends on protein phosphorylation and PTB domain containing signaling proteins

Summary

Introduction

Protein tyrosine phosphorylation is one of several mechanisms that have evolved to mediate signal transduction [1,2,3]. LRP1 and Shc Association in Src-transformed Cells plex 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 proteintyrosine kinase c-Src. Expression of v-Src results in protein tyrosine phosphorylation and in oncogenic transformation [20, 21].

Results

Conclusion