Endogenous Membrane Receptor Labeling by Reactive Cytokines and Growth Factors to Chase Their Dynamics in Live Cells

Cytokine and growth factor receptors localized on cell membranes play key roles in many biological events. Because the dynamic behaviors of receptors are deeply involved in cytokine- and growth-factor-dependent signaling pathways, reliable techniques for real-time imaging of receptors in live cells are strongly desired. Here, we describe a method of covalently labeling and imaging membrane receptors in live cells by using chemically reactive cytokines and growth factors coupled with 4-dimethylaminopyridine (DMAP), an organocatalyst that facilitates acyl transfer. Construction of the DMAP cytokines and growth factors relies on non-covalent coordination chemistry between an oligo-histidine tag and dimeric Ni(II)-nitrilotriacetate in an in situ manner. This supramolecular approach is relatively simple and flexible and can be applied to labeling not only transiently but also endogenously expressed receptors. Moreover, given the benefit of this traceless labeling of the receptors, our technique allows real-time imaging of the ligand-induced dynamics of endogenously expressed receptors in live cells. Cytokine and growth factor receptors play crucial roles in signaling cascades that modulate cell survival, adhesion, proliferation, and migration. Because the dynamic behaviors of these receptors are highly related to their functions and to changes in ligand-dependent signals, reliable techniques for visualization of these receptors are strongly desired. Here, we have developed a method of covalently and tracelessly labeling membrane receptors in live cells by using chemically reactive cytokines and growth factors coupled with an organocatalyst that facilitates a selective acyl transfer reaction on the target receptors. Construction of the reactive cytokines and growth factors relies on non-covalent coordination chemistry in an in situ manner, and this supramolecular approach is relatively simple and flexible. It can be applied to not only the labeling of various receptors but also real-time imaging of ligand-induced dynamics of endogenously expressed receptors in live cells. With the use of supramolecule-based chemically reactive cytokines and growth factors, membrane receptor proteins can be covalently labeled with fluorescent small molecules. This supramolecular approach is quite simple and flexible, and various endogenous receptors can be visualized specifically; real-time imaging of the ligand-induced dynamics of the receptors is achieved in living mammalian cells.