Glycosylation-induced conformational modification positively regulates receptor-receptor association - A study with an aberrant epidermal growth factor receptor (EGFRvIII/Delta EGFR) expressed in cancer cells

The epidermal growth factor receptor (EGFR) is a multisited and multifuncti onal transmembrane glycoprotein with intrinsic tyrosine kinase activity. Up on ligand binding, the monomeric receptor undergoes dimerization resulting in kinase activation. The consequences of kinase stimulation are the phosph orylation of its own tyrosine residues (autophosphorylation) followed by as sociation with and activation of signal transducers, Deregulation of signal ing resulting from aberrant expression of the EGFR has been implicated in a number of neoplasms including breast, brain, and skin tumors, A mutant epi dermal growth factor (EGF) receptor missing 267 amino acids from the exopla smic domain is common in human glioblastomas. The truncated receptor (EGFRv III/Delta EGFR) lacks EGF binding activity; however, the kinase is constitu tively active, and cells expressing the receptor are tumorigenic. Our studi es revealed that the high kinase activity of the Delta EGFR is due to self- dimerization, and contrary to earlier reports, the kinase activity per mole cule of the dimeric Delta EGFR is comparable to that of the EGF-stimulated wild-type receptor. Furthermore, the phosphorylation patterns of both recep tors are similar as determined by interaction with a conformation-specific antibody and by phosphopeptide analysis. This eliminates the possibility th at the defective down-regulation of the Delta EGFR is due to its altered ph osphorylation pattern as has been suggested previously. Interestingly, the receptor-receptor self-association is highly dependent on a conformation in duced by N-linked glycosylation, We have identified four potential sites th at might participate in self-dimerization; these sites are located in a dom ain that plays an important role in EGFR functioning.