Dynamic modules and heterogeneity of function: a lesson from tyrosine kinase receptors in endothelial cells

An important unresolved issue related to tyrosine kinase receptor signaling pathways is the lack of specificity of the molecular effectors involved. T he specificity of the biological responses that are nevertheless elicited m ay be explained by differences in activation thresholds, as well as by temp oral (transient versus sustained) and topographical aspects of receptor act ivation. On the basis of recent lessons from endothelial cells, we argue th at an additional strategy can be adopted to generate specificity, i.e. tyro sine kinase receptors may form distinct signaling modules with other transm embrane proteins, such as adhesive receptors, to elicit different biologica l programs in stimulated cells.