Besides stimulating the mitogen-activated protein kinase, phospholipase Cγ, and phosphatidylinositol 3-kinase cascades, in certain tissues and cells such as the heart, partotid gland, and luteal cells, activation of the epidermal growth factor (EGF) receptor also stimulates second-messenger systems that involve the heterotrimeric G proteins. For instance, in the heart EGF increases contractility and heart rate by elevating cellular cyclic adenosine monophosphate (cAMP) levels. This is the result of EGF-elicited activation of adenylyl cyclase via the stimulatory guanosine 5′-triphosphate (GTP)-binding protein Gs . In this context, the single transmembrane EGF receptor acts like a heptahelical G protein-coupled receptor. Here we have described the methods used to study interactions between the EGF receptor and heterotrimeric G proteins. Moreover, we have also described how the stoichiometry of EGF receptor association with the α subunit of Gs can be monitored in vitro. Several other single transmembrane receptors and proteins can also activate heterotrimeric G proteins, and, therefore, the methodologies described in this chapter can be adapted to other systems.
