PURIFICATION AND CHARACTERIZATION OF AN ALPHA-1-ANTICHYMOTRYPSIN-LIKE 66 KDA PROTEIN FROM THE HUMAN BREAST-CANCER CELL-LINE, MCF-7

The synthesis of a 66 kDa protein immunoreactive with antibodies to human alpha-1-antichymotrypsin (alpha-1-ACT) is induced by estradiol (E2) in the human breast cancer cell line MCF-7. We have purified this alpha-1-ACT-like 66 kDa protein from medium conditioned by MCF-7 cells, performed a comparative physico-chemical characterization with serum alpha-1-ACT, and analysed its presumed positive regulatory effect on growth of MCF-7 cells. The 66 kDa protein is a functional antiproteinase which is antigenically identical to serum alpha-1-ACT. The 66 kDa protein does however deviate from serum alpha-1-ACT with respect to mol. wt. and pattern of microheterogeneity, the molecular mechanism for this is probably an incomplete glycoprotein processing in the MCF-7 cells. The results of our growth experiments suggest that the 66 kDa protein is a minor positive growth regulatory factor, which may contribute to breast carcinoma cell proliferation in a cooperative manner.