Mammaglobin and Lipophilin B Expression in Breast Tumors and their Lack of Effect on Breast Cancer Cell Proliferation

Abstract

Background: Mammaglobin (SCGB2A2) and lipophilin B (SCGB1D2) are members of the secretoglobin polypeptide family. Mammaglobin has been shown to be overexpressed in breast tumor tissue, indicating that mammaglobin might confer a growth advantage to mammaglobin-expressing tumor cells. Materials and Methods: The mammaglobin and lipophilin B mRNA expression levels were investigated in seven breast tumors and matched non-neoplastic tissues from the same patients using quantitative real-time RT-PCR. The effect of mammaglobin and lipophilin B expression on breast cancer cell proliferation rates was investigated by analyzing retrovirally transduced Hs578T cell clones. Cell proliferation rates were determined during the exponential growth phase by analyzing the change in lactate dehydrogenase activity over time. Results: All analyzed breast cancer tumors had lower expression levels of mammaglobin and lipophilin B than the respective mean level of the non-neoplastic breast tissues; no prominent overexpression was evident. There was high variability in the expression of mammaglobin and lipophilin B among the non-neoplastic samples, showing that caution should be taken when evaluating their over- and underexpression in tumors. The expression levels of mammaglobin and lipophilin B correlated with each other in the analyzed samples (p=0.001). Ectopic overexpression of mammaglobin and lipophilin B did not affect the cell proliferation rate of Hs578T breast carcinoma cells in vitro. Conclusion: Our findings suggest that the overexpression of mammaglobin observed in certain breast tumors is an epiphenomenon not causally involved in breast carcinogenesis.