C-SRC PROTEIN EXPRESSION IS INCREASED IN HUMAN BREAST-CANCER - AN IMMUNOHISTOCHEMICAL AND BIOCHEMICAL-ANALYSIS

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 acti vity is accompanied by an increase in c-Src protein expression. In thi s study, c-Src activity and protein expression were determined in a se ries of human breast cancers and in normal breast tissue, using immune complex kinase assays and immunoblotting. As the heterogeneity of bre ast 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 increa sed 4- to 30-fold, compared with normal breast tissue. This enhanced a ctivity is accompanied by an increase in c-Src protein expression, as shown by both immunoblotting and immunohistochemistry. Immunohistochem istry 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-Sr c activity is increased in human breast cancer. In addition, this stud y provides strong immunohistochemical evidence that the c-Src protein is also overexpressed, enabling a distinction to be made between norma l and malignant cells.