Mutational activation of ErbB family receptor tyrosine kinases: insights into mechanisms of signal transduction and tumorigenesis

Signaling by the Epidermal Growth Factor Receptor (EGFR) and related ErbB family receptor tyrosine kinases can be deregulated in human malignancies as the result of mutations in the genes that encode these receptors. The recent identification of EGFR mutations that correlate with sensitivity and resistance to EGFR tyrosine kinase inhibitors in lung and colon tumors has renewed interest in such activating mutations. Here we review current models for ligand stimulation of receptor dimerization and for activation of receptor signaling by receptor dimerization. In the context of these models, we discuss ErbB receptor mutations that affect ligand binding and those that cause constitutive receptor phosphorylation and signaling as a result of constitutive receptor dimerization. We discuss mutations in the cytoplasmic regions that affect enzymatic activity, substrate specificity and coupling to effectors and downstream signaling pathways. Finally, we discuss how emergent mechanisms of ErbB receptor mutational activation could impact the search for clinically relevant ErbB receptor mutations.