Regulation of TGF-β Receptors.

In cells responding to extracellular polypeptide ligands, regulatory mechanisms at the level of cell surface receptors are increasingly seen to define the nature of the ligand-induced signaling responses. Processes that govern the levels of receptors at the plasma membrane, including posttranslational modifications, are crucial to ensure receptor function and specify the downstream signals. Indeed, extracellular posttranslational modifications of the receptors help define stability and ligand binding, while intracellular modifications mediate interactions with signaling mediators and accessory proteins that help define the nature of the signaling response. The use of various molecular biology and biochemistry techniques, based on chemical crosslinking, e.g., biotin or radioactive labeling, immunofluorescence to label membrane receptors and flow cytometry, allows for quantification of changes of cell surface receptor presentation. Here, we discuss recent progress in our understanding of the regulation of TGF-β receptors, i.e., the type I (TβRI) and type II (TβRII) TGF-β receptors, and describe basic methods to identify and quantify TGF-β cell surface receptors.