Investigations of Functional and Structural Interactions Between c-src and HER2: Involvement in Human Breast Tumor Formation

Abstract

Abstract : Studies have shown that functional interaction between members of the human EGF receptor (HER) receptor tyrosine kinase family, and c-Src, a non-receptor tyrosine kinase, may be involved in breast tumor formation. We have demonstrated overexpression of HER1 and c-Src, in a murine fibroblast cell line, C3H10T1/2, results in an EGF-dependent synergistic increase in tumorigenicity, as compared to overexpression of either kinase alone. This increase in tumorigenicity correlates with formation of in vivo HER1/c-Src complexes, the appearance of two novel phosphorylation sites on HER1, and enhanced phosphorylation of receptor substrates. HER2 is overexpressed in 20-30% of human breast cancers, and is correlated with poor patient prognosis. Also, elevated levels and/or activity of c-Src have been demonstrated in human breast cancers. We propose HER1 and HER2 interact with c-Src through similar mechanisms to augment cellular growth and tumor progression. To examine potential interactions between HER2 and c-Src, we have studied human breast tumor tissue, and a panel of human breast carcinoma cell lines, for expression of HER family members and c-Src protein. Tumor samples and cell lines were also tested for HER2/c-Src heterocomplexes. In 3 of 13 tumor tissues, and in 3 of 9 human breast tumor cell lines, constitutive in vivo HER2/c-Src complexes were seen, suggesting structural and functional interactions between HER2 and c-Src. C3H10T1/2 fibroblast cell lines overexpressing HER2 and/or c-Src have been generated and will be tested for growth properties, heterocomplex formation and downstream signaling. Preliminary results indicate a HER2/c-Src complex in a cell line which overexpressed both kinases; no complex is seen in a cell line expressing c-Src alone.