The Human Splice Variant D16HER2 Induces Rapid Tumor Onset in a Reporter Transgenic Mouse

Several transgenic mice models solidly support the hypothesis that HER2 (ERBB2) overexpression or mutation promotes tumorigenesis. Recently, a HER2 splice variant lacking exon-16 (D16HER2) has been detected in human breast carcinomas. This alternative protein, a normal byproduct of HER2, has an increased transforming potency compared to wild-type (wt) HER2 receptors. To examine the ability of D16HER2 to transform mammary epithelium in vivo and to monitor D16HER2-driven tumorigenesis in live mice, we generated and characterized a mouse line that transgenically expresses both human D16HER2 and firefly luciferase under the transcriptional control of the MMTV promoter. All the transgenic females developed multifocal mammary tumors with a rapid onset and an average latency of 15.11 weeks. Immunohistochemical analysis revealed the concurrent expression of luciferase and the human D16HER2 oncogene only in the mammary gland and in strict correlation with tumor development. Transgenic D16HER2 expressed on the tumor cell plasma membrane from spontaneous mammary adenocarcinomas formed constitutively active homodimers able to activate the oncogenic signal transduction pathway mediated through Src kinase. These new transgenic animals demonstrate the ability of the human D16HER2 isoform to transform ‘‘per se’ ’ mammary epithelium in vivo. The high tumor incidence as well as the short latenc