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Overexpression of EGFR and c-erbB2 frequently occurs in human breast cancers, correlating with poor prognosis. Here we show that overexpression of EGFR and c-erbB2 in cell lines increases cell migration, an important step in metastasis formation. The effect of EGFR on migration is dependent on the addition of EGF to the cells. In contrast, c-erbB2 seems to act independently of its ligand in these assays. Overexpression of this receptor is sufficient to induce cell migration. In addition, we investigated the involvement of a number of signal transduction pathways known to be activated by the EGFR. We found that inactivation of MAPKK results in a decreased migration, while inactivation of PI3K increases migration.

In 20-30 per cent of human breast cancers, the receptor tyrosine kinases epidermal growth factor receptor (EGFR) and c-erbB2 are overexpressed. This overexpression leads to increased mitogenic signalling and is correlated with poor prognosis. Overexpression of associated adaptor proteins, like Grb2, can also induce upregulation of signalling pathways. In this study, the expression of the Grb2 adaptor protein was determined in both normal human breast tissue and mammary cancers, using immunoblotting experiments and immunostaining on paraffin-embedded tissue sections. Both biochemical and immunohistochemical techniques revealed overexpression of Grb2 in all breast cancer specimens. In addition, although Grb2 protein is described as localized in the cytoplasm, it can also be detected in the nucleus, both in normal and in tumour breast tissue. In tumour breast tissue, 58 per cent of Grb2 protein is found in the nucleus, while 37 per cent is detected in the cytoplasm. In normal breast tissue, 22 per cent of Grb2 is found in the nucleus and 70 per cent in the cytoplasm. These findings indicate that in human breast cancer, Grb2 is overexpressed and appears to be predominantly localized in the nucleus.

In human breast cancer, c-Src activity is elevated compared to normal breast tissue. It is not yet known whether this increase in c-Src activity is accompanied by an increase in c-Src protein expression. In this study, c-Src activity and protein expression were determined in a series of human breast cancers and in normal breast tissue, using immune complex kinase assays and immunoblotting. As the heterogeneity of breast cancer is not taken into account in these biochemical experiments, immunohistochemistry was also used to distinguish between normal and malignant cells. In human breast cancers, the c-Src activity is increased 4- to 30-fold, compared with normal breast tissue. This enhanced activity is accompanied by an increase in c-Src protein expression, as shown by both immunoblotting and immunohistochemistry. Immunohistochemistry indicates that the majority of c-Src appears to be concentrated around the nucleus in malignant cells, whereas in normal cells, it is distributed more evenly in the cytoplasm. These data confirm that c-Src activity is increased in human breast cancer. In addition, this study provides strong immunohistochemical evidence that the c-Src protein is also overexpressed, enabling a distinction to be made between normal and malignant cells.