The ErbB-2/HER2 oncoprotein of human carcinomas may function solely as a shared coreceptor for multiple stroma-derived growth factors

The erbB-2/HER2 oncogene is overexpressed in a significant fraction of huma n carcinomas of the breast, ovary, and lung in a manner that correlates wit h poor prognosis. Although the encoded protein resembles several receptors for growth factors, no high affinity ligand of ErbB-2 has so far been fully characterized. However, several lines of evidence have raised the possibil ity that ErbB-2 can augment signal transduction initiated by binding of cer tain growth factors to their direct receptors. Here, we contrasted these tw o models of ErbB-2 function: First, examination of a large series of epider mal growth factor (EGF)-like ligands and neuregulins, including virus-encod ed ligands as well as related motifs derived from the precursor of EGF, fai led to detect interactions with ErbB-2 when this protein,vas singly express ed. Second, by using antibodies that block inter-ErbB interactions and cell s devoid of surface ErbB-2, we learned that signaling by all ligands examin ed, except those derived from the precursor of EGF, was enhanced by the onc oprotein. These results imply that ErbB-2 evolved as a shared receptor subu nit of all ErbB-specific growth factors. Thus, oncogenicity of ErbB-2 in hu man epithelia may not rely on the existence of a specific ligand but rather on its ability to act as a coreceptor for multiple stroma-derived growth f actors.