TISSUE-SPECIFIC TRANSFORMATION BY ONCOGENIC MUTANTS OF EPIDERMAL GROWTH-FACTOR RECEPTOR

Mutations in the receptor for the epidermal growth factor provide valuable insight into mechanisms of growth control. Oncogenic mutants of this receptor tyrosine kinase cause erythroid leukemia, fibrosarcoma, angiosarcoma, glioblastoma, and melanoma. Mutations in the avian protooncogene occur by retroviral mechanisms. Deletion of the ligand-binding domain results in erythroblastosis, while additional mutations in cytoplasmic structures broaden the disease potential to other cell types. A carboxyl-terminal structure of erbB oncogenes modulates growth responses in a complex, cell-specific manner; this tissue-specificity region appears to promote growth in erythroblasts and to produce trans-dominant inhibition in fibroblasts. Human glioblastoma multiforme frequently contains receptor mutations that are reminiscent of avian oncogenes. In hereditary melanoma of Xiphophorus, aberrant regulation of transcription by a recombinant promoter determines tissue-specific tumorigenesis. The diversity of oncogenic mutations raises important questions concerning the roles of several receptor structures. The extracellular domain inhibits the receptor when unoccupied by ligand, for example, through a mechanism that is unknown. The auto-phosphorylation sites are dispensable for transformation, so their function in neoplastic growth is unclear. The carboxyl-terminal region promotes or blocks transformation in different tissues, suggesting complex regulation by unknown cellular factors. These issues are critical to understanding of the mechanisms of receptor activation and tissue tropism for this family of oncogenes.