Cell-based Assay for Recruitment of DDR1 to Collagen-coated Beads.

The discoidin domain receptors, DDR1 and DDR2, are key signaling receptors for the extracellular matrix protein collagen. The interactions of cells with collagen are difficult to study because of the difficulty to obtain native collagen fibers for studies. Thus, studies often use acid-soluble collagens in the form of single triple helices, which are not representative of the densely packed insoluble collagen fibers found in tissues. In this protocol, we describe a method that allows stimulating DDR1 locally with collagen-coated beads. Latex beads are first coated with acid-soluble collagen, then added to cells expressing DDR1. Recruitment of DDR1 to the beads and collagen-induced DDR1 phosphorylation is visualized by immunofluorescence microscopy on a widefield microscope. In this method, densely packed collagen is presented to cells in an insoluble form. Bead coating is easy to perform, and this method thus presents a straightforward protocol with which to study local recruitment of collagen receptors to insoluble collagen.