Synergistic interaction of the Neu proto-oncogene product and transforming growth factor α in the mammary epithelium of transgenic mice

Transgenic mice expressing either the neu proto-oncogene or transforming growth factor (TGF-α) in the mammary epithelium develop spontaneous focal mammary tumors that occur after a lung latency. Since the epidermal growth factor receptor (EGFR) and Neu are capable of forming heterodimers that are responsive to EGFR ligands such as TGF-α, we examined whether coexpression of TGF-α and Neu in mammary epithelium could cooperate to accelerate the onset of mammary tumors. To test this hypothesis, we interbred separate transgenic strains harboring either a mouse mammary tumor virus/TGF-α or a mouse mammary tumor virus/neu transgene to generate bitransgenic mice that coexpress TGF-α and neu in the mammary epithelium. Female mice coexpressing TGF-α and neu developed multifocal mammary tumors which arose after a significantly shorter latency period than either parental strain alone. The development of these mammary tumors was correlated with the tyrosine phosphorylation of Neu and the recruitment of c-Src to the Neu complex. Immunoprecipitation and immunoblot analyses with EGFR- and Neu-specific antisera, however, failed to detect physical complexes of these two receptors. Taken together, these observations suggest that Neu and TGF-α cooperate in mammary tumorigenesis through a mechanism involving Neu and EGFR transactivation.