Mammaglobin: a specific molecular target for immune based breast cancer therapy

B30 The mammaglobin (Mam) gene encodes a novel glycoprotein with largely unknown function even though expression of the Mam gene has been widely adapted as a marker for detection of micro-metastatic foci within pathologically negative lymph nodes and occult cancer cells in circulation. Mam also provides an attractive molecular target for immune-based breast cancer therapy. To determine if Mam stays associated with the membrane of the breast cancer cells after secretion, various cell lines were incubated with fluorescence (FITC) labeled anti-Mam antibody. Strong fluorescent signals were detected on the surface of the Mam expressing breast cancer cells. The cell viability assays were conducted after the antibody binding experiments. An increased number of dead cells were demonstrated. There was no obvious binding signal and cell death detected in the Mam negative cancer and normal cells. To further verify that the specific binding of anti-Mam induces apoptotic death of breast cancer cells, (1) the Mam expressing cancer cells were fixed and stained with HE (2) the anti-Mam treated breast cancer cells were harvested and the cellular protein lysates were used for Western blot assays. Obvious 89 kDa cleavage fragments of the PARP-1 protein (activation of pro-apoptototic processes) were demonstrated in the Mam expressing cancer cells. As parallel controls, we detected no increase either in the number of apoptotic cells or the cleavage fragment of PARP-1 in the antibody incubated T47D (Mam negative breast cancer cells), human dermal fibroblast (HDF) and human aortic epithelial cells (HAEC). Our findings indicate that Mam protein, at least some if not all, directly attaches to the membrane of breast cancer cells after secretion and the specific binding of anti-Mam induces apoptotic death of the cancer cells. The function of the membrane bound Mam protein may be related to the regulation of cell apoptosis. Mam emerges as a promise target for the development of antibody-based breast cancer therapy.