| First Author | Aykul S | Year | 2017 |
| Journal | J Biol Chem | Volume | 292 |
| Issue | 10 | Pages | 4138-4151 |
| PubMed ID | 28126904 | Mgi Jnum | J:241347 |
| Mgi Id | MGI:5901942 | Doi | 10.1074/jbc.M116.747501 |
| Citation | Aykul S, et al. (2017) Biochemical and Cellular Analysis Reveals Ligand Binding Specificities, a Molecular Basis for Ligand Recognition, and Membrane Association-dependent Activities of Cripto-1 and Cryptic. J Biol Chem 292(10):4138-4151 |
| abstractText | Transforming growth factor beta (TGF-beta) pathways are key determinants of cell fate in animals. Their basic mechanism of action is simple. However, to produce cell-specific responses, TGF-beta pathways are heavily regulated by secondary factors, such as membrane-associated EGF-CFC family proteins. Cellular activities of EGF-CFC proteins have been described, but their molecular functions, including how the mammalian homologs Cripto-1 and Cryptic recognize and regulate TGF-beta family ligands, are less clear. Here we use purified human Cripto-1 and mouse Cryptic produced in mammalian cells to show that these two EGF-CFC homologs have distinct, highly specific ligand binding activities. Cripto-1 interacts with BMP-4 in addition to its known partner Nodal, whereas Cryptic interacts only with Activin B. These interactions depend on the integrity of the protein, as truncated or deglycosylated Cripto-1 lacked BMP-4 binding activity. Significantly, Cripto-1 and Cryptic blocked binding of their cognate ligands to type I and type II TGF-beta receptors, indicating that Cripto-1 and Cryptic contact ligands at their receptor interaction surfaces and, thus, that they could inhibit their ligands. Indeed, soluble Cripto-1 and Cryptic inhibited ligand signaling in various cell-based assays, including SMAD-mediated luciferase reporter gene expression, and differentiation of a multipotent stem cell line. But in agreement with previous work, the membrane bound form of Cripto-1 potentiated signaling, revealing a critical role of membrane association for its established cellular activity. Thus, our studies provide new insights into the mechanism of ligand recognition by this enigmatic family of membrane-anchored TGF-beta family signaling regulators and link membrane association with their signal potentiating activities. |
