ISOLATION AND CHARACTERIZATION OF FULL AND TRUNCATED FORMS OF HUMAN BREAST-CARCINOMA PROTEIN BA46 FROM HUMAN-MILK FAT GLOBULE MEMBRANES

We have isolated and characterized two proteins of 50 and 30 kDa from human milk fat globule membranes of healthy donors. N-terminal and int ernal sequencing revealed that the 50-kDa protein is the full-length h uman breast carcinoma protein BA46 that is highly expressed in human b reast tumors. The 30-kDa protein is a truncated form of protein BA46 w hich consists of the C-terminal factor V/VIII-like domain of BA46 and which appears to anchor BA46 to the milk fat globule membrane. Defecti ve release of the epidermal growth factor domain containing a surface RGD motif may be related to involvement of BA46 in breast cancer.