Ligand-induced polyubiquitination of receptor tyrosine kinases

The platelet-derived growth factor beta-receptor undergoes polyubiquitination as a consequence of ligand binding. In the present study, we have examined the ligand-induced receptor ubiquitination also in the other receptor tyrosine kinase (structurally different) subfamilies by immunoblotting with anti-ubiquitin antiserum. In addition to the platelet-derived growth factor alpha- and beta-receptors, all the monomeric receptor tyrosine kinases examined, such as the receptors for epidermal growth factor (subfamily I), colony stimulating factor-1 (subfamily III), and fibroblast growth factor (subfamily IV), were found to be ubiquitinated after ligand stimulation. However, the insulin receptor (subfamily II), which is a tetrameric molecule, was not. These data suggest that the ligand-induced polyubiquitination of the receptor is a general phenomenon observed in most of the monomeric receptor tyrosine kinases.