MASPIN, A SERPIN WITH TUMOR-SUPPRESSING ACTIVITY IN HUMAN MAMMARY EPITHELIAL-CELLS

A gene encoding a protein related to the serpin family of protease inh ibitors was identified as a candidate tumor suppressor gene that may p lay a role in human breast cancer. The gene product, called maspin, is expressed in normal mammary epithelial cells but not in most mammary carcinoma cell lines. Transfection of MDA-MB-435 mammary carcinoma cel ls with the maspin gene did not alter the cells' growth properties in vitro, but reduced the cells' ability to induce tumors and metastasize in nude mice and to invade through a basement membrane matrix in vitr o. Analysis of human breast cancer specimens revealed that loss of mas pin expression occurred most frequently in advanced cancers. These res ults support the hypothesis that maspin functions as a tumor suppresso r.