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

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, downregulation 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 125 I-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.The human CR-1 gene encodes for an EGF 1 -related peptide that was isolated and sequenced from a human NTERA2/D1 embryonal carcinoma cDNA expression library (1). A homologous gene has also been identified in the mouse from an F-9 mouse embryonal carcinoma cDNA expression library (2). More recently, additional Cripto-related genes have been identified in Xenopus laevis (FRL1), in mouse embryonic stem cell-derived mesoderm cells (Cryptic), and in Zebrafish (One-eyed pinhead) (3-5). Based on the strong sequence similarities, CR-1, FRL1, Cryptic, and One-eyed pinhead represent a new family of growth factor-like molecules named CFC (CR-1, FRL1, and Cryptic) family. These genes share a potential Nterminal leader sequence, a modified EGF-like domain, a second cysteine-rich region, and a C-terminal hydrophobic domain (5, 6). The modified EGF-like domain found in the CFC family is highly conserved. All EGF-like motifs contain six cysteines, which form three disulfide bonds in the case of EGF and the other related peptides in this family. In CR-1, FRL1, Cryptic, and One-eyed pinhead, the EGF-like domain is quite unusual. In fact, the first two cysteines are adjacent, thereby eliminating the A loop that is normally found between these residues. In addition, 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. In fact, we have previously shown th...

Emerging Roles of Nodal and Cripto-1: From Embryogenesis to Breast Cancer Progression

“…In addition, Cripto-1 is frequently coexpressed with other EGF-related peptides, such as TGFα, amphiregulin (AR), and heregulin in human primary breast carcinomas suggesting that Cripto-1 might cooperate with these different growth factors in supporting the autonomous proliferation of breast cancer cells. A positive correlation between nuclear HER-4 expression and Cripto-1 expression in primary human breast carcinomas has also been described [96] further supporting the finding that Cripto-1 can indirectly enhance the tyrosine phosphorylation of HER-4 [97].…”

An Acute Effect of Neuregulin 1β to Suppress α7-Containing Nicotinic Acetylcholine Receptors in Hippocampal Interneurons

“…Non-NRG ligands must also be considered. ErbB4 in tumor cells or heterologous system can be activated by other members of the EGF family (Beerli and Hynes, 1996;Bianco et al, 1999).…”

Molecular Analysis of the Cripto Growth Factor Receptor

“…Experiments using the refolded CRIPTO peptide have shown that CRIPTO can induce tyrosine phosphrylation of the SH2 adapter protein She in HC-11 cells, resulting in increased association of She with Grb2 and elevated MAPK kinase activity [2,9]. More recently it has been shown that recombinant CRIPTO can transactivate erbB-A receptor, but not EGF receptor, erbB-2 and erbB-3 [10]. These results suggest that Cripto may be involved in a Ras signaling pathway.…”