The Kinase Domain and Membrane Localization Determine Intracellular Interactions between Epidermal Growth Factor Receptors

Receptor tyrosine kinases play a central role in cellular growth, differentiation, and oncogenesis. All of these responses are triggered by growth factors interacting with the extracellular domain of transmembrane-spanning receptors, leading to dimerization and activation of an intrinsic tyrosine-specific kinase activity by an allosteric mechanism. Precise mechanisms of receptor dimerization remain poorly understood, and current models suggest that the ligand binding domain plays a major determining role. To examine the role of the intracellular domain in the association of juxtaposing receptor molecules, the full-length epidermal growth factor receptor was transiently co-expressed in human 293 fibroblasts with a truncated receptor that lacks the extracellular domain. After metabolic labeling with [35S]methionine, the association of these receptor constructs was monitored by co-immunoprecipitation with an extracellular domain-specific antibody. Specific interactions found between these receptors were independent of ligand binding or an intact ATP-binding site. Truncated receptors that had sequences necessary for membrane localization, and that were capable of interacting with full-length receptor tyrosine kinase, also displayed constitutive kinase activity as well as the capacity to transphosphorylate kinase-negative receptors. Receptor co-immunoprecipitation occurred between constructs that comprise the intracellular domains of the epidermal growth factor and beta-platelet-derived growth factor receptors, and HER-2. Subsequent deletion analysis has identified the major region of epidermal growth factor receptor intracellular interaction to be within the kinase domain.