ABSTRACT
Cell growth and differentiation are controlled by a number of soluble factors acting either alone or synergistically. The biological effects of these factors are initiated by their binding to specific, high-affinity receptors. Biochemical and genetic evidence indicates that ligand binding to these receptors induces a conformational change which results in receptor oligomerization and transmembrane signal transduction. Genetic studies have shown that this activation process is instrumental in the pleiotropic cellular responses resulting from ligand binding to tyrosine kinase receptors. The role of receptor tyrosine kinase autophosphorylation has been studied extensively for Ins-R and epidermal growth factor-R. Evidence that abnormal expression of at least certain members of this class of receptor is involved in tumorigenesis comes from the identification of the mas proto-oncogene product as a functional receptor for a mitogenic angiotensin. The role of the mutations in the DNA-binding domain and alterations in the amino-terminal domain of v-erbA in its activity are yet unknown.
