Significance of metallothionein expression in breast myoepithelial cells

Metallothioneins (MTs), a group of cysteine rich proteins with a small mole cular mass, are known to have metalloregulatory functions. MT gene expressi on has been demonstrated to be cell type-specific and differentially regula ted (possibly related to their germ layer origin and different functional s tates). In vitro studies suggest that MT-2A, MT-IE, and MT-1F isoforms may be related to breast cancer. In this study, data on MT-2A, MT-1E, MT-1F mRN A analysis via reverse transcription-polymerase chain reaction in invasive ductal breast cancer tissues and their adjacent benign breast tissues from 27 mastectomies are presented. Expression of mRNA in all the three MT isofo rms was detected in both cancerous and adjacent benign breast tissues (with MT-2A mRNA expression being the highest). MT-1F expression was significant ly higher in benign breast tissues compared with the breast cancers (P=0.01 7). In situ hybridization confirmed the expression of MT-2A mRNA in the myo epithelial cells of the breast tissues. Immunohistochemical localization of the MT protein revealed that myoepithelial cells consistently expressed th e MT protein, while the cancer cells expressed MT with great variation. Bas ed on our immunohistochemical and mRNA analysis, it is likely that the thre e MT isoforms are specifically expressed in myoepithelial cells of beni,on breast tissues and cancer cells of the invasive ductal breast cancer tissue s. As MT expression occurs in myoepithelial cells and ductal breast cancer cells, our finding supports the proposition that loss of myoepithelial cell s in invasive mammary cancers may be compensated in part by changes in the tumor cells, which may subsequently be the basis for studying the role of M T in breast physiology and carcinogenesis. Differential MT-1F expression in breast myoepithelial cells warrants further study.