Cripto-1 Indirectly Stimulates the Tyrosine Phosphorylation oferb B-4 through a Novel Receptor

Caterina Bianco,Subha Kannan,Marta De Santis,Masaharu Seno,Careen K Tang,Isabel Martinez-Lacaci,Nancy Kim,Brenda Wallace-Jones,Marc E Lippman,Andreas D Ebert,Christian Wechselberger,David S Salomon

doi:10.1074/jbc.274.13.8624

Abstract

Cripto-1 (CR-1) is a recently discovered protein of the epidermal growth factor family that fails to directly bind to any of the four known erb B type 1 receptor tyrosine kinases. The present study demonstrates that CR-1 indirectly induces tyrosine phosphorylation of erb B-4 but not of the epidermal growth factor-related receptors erb B-2 and erb B-3 in different mouse and human mammary epithelial cell lines. In addition, down-regulation of erb B-4 in NMuMG mouse mammary epithelial cells and in T47D human breast cancer cells, using an anti-erb B-4 blocking antibody or a hammerhead ribozyme vector targeted to erb B-4 mRNA, impairs the ability of CR-1 to fully activate mitogen-activated protein kinase. Finally, chemical cross-linking of 125I-CR-1 to mouse and human mammary epithelial cell membranes results in the labeling of two specific bands with a molecular weight of 130 and 60 kDa, suggesting that the CR-1 receptor represents a novel receptor structurally unrelated to any of the known type I receptor tyrosine kinases. In conclusion, these data demonstrate that CR-1, upon binding to an unknown receptor, can enhance the tyrosine kinase activity of erb B-4 and that a functional erb B-4 receptor is required for CR-1-induced MAPK activation.

Highlights

Cripto-1 (CR-1) is a recently discovered protein of the epidermal growth factor family that fails to directly bind to any of the four known erb B type 1 receptor tyrosine kinases
We have previously shown that CR-1 does not bind directly to the epidermal growth factor receptor (EGFR/erb B-1) or to erb B-2, erb B-3, or erb B-4 type 1 receptor tyrosine kinases that have been ectopically expressed in Ba/F3 mouse pro-B lymphocytes or in 32-D mouse myeloid cells either alone or in various pairwise combinations [7]
This receptor is specific for CR-1, because it does not bind other EGF-related peptides, such as EGF, heparin binding EGF-like growth factor, transforming growth factor ␣, amphiregulin, betacellulin, or heregulin ␤1 (HRG␤1) [7]

Summary

Introduction

Cripto-1 (CR-1) is a recently discovered protein of the epidermal growth factor family that fails to directly bind to any of the four known erb B type 1 receptor tyrosine kinases. The spacing between the third and fourth cysteines is reduced relative to other EGF-like repeats, resulting in a smaller B loop [6] Because these three disulfide-linked loops are important in the ability of these proteins to assume a specific secondary structure that is essential for binding to specific erb B type I receptor tyrosine kinases, it has been proposed that the presence of an unusual EGF-like domain in the CFC family may indicate that this subfamily of peptides binds to a unique receptor. A specific erb B-4-blocking antibody can interfere with the capacity of CR-1 to activate MAPK in mouse and human mammary epithelial cell lines These data suggest that erb B-4, not a direct receptor for this growth factor, is required for the activation of the signal transduction cascade by CR-1. The presence of two specific bands of 60 and 130 kDa suggests the possibility that this receptor has a multicomponent structure that renders the CR-1 receptor unique among the other erb B receptors

Methods

Results

Conclusion