Single-molecule imaging reveals transforming growth factor-[beta]-induced type II receptor dimerization

Transforming growth factor-[beta] (TGF-[beta]) elicits its signals through two transmembrane serine/threonine kinase receptors, type II (T[beta]RII) and type I receptors. It is generally believed that the initial receptor dimerization is an essential event for receptor activation. However, previous studies suggested that TGF-[beta] signals by binding to the preexisting T[beta]RII homodimer. Here, using single molecule microscopy to image green fluorescent protein (GFP)-labeled T[beta]RII on the living cell surface, we demonstrated that the receptor could exist as monomers at the low expression level in resting cells and dimerize upon TGF-[beta] stimulation. This work reveals a model in which the activation of serine-threonine kinase receptors is also accomplished via dimerization of monomers, suggesting that receptor dimerization is a general mechanism for ligand-induced receptor activation. serine/threonine kinase receptor | subunit stoichiometry