LOCALIZATION AND QUANTITATION OF EXPRESSION OF THE CELL MOTILITY-RELATED PROTEIN THYMOSIN BETA-15 IN HUMAN BREAST-TISSUE

Thymosin beta 15 is a newly discovered 5300-Da protein that binds acti n monomers and inhibits actin polymerization and might thus increase c ellular motility. Thymosin beta 15 is upregulated at both the mRNA and protein levels in prostate cell lines in a manner directly related to their capacity to metastasize. We hypothesize that because this prote in is upregulated in cells with a propensity to metastasize, it might be a useful prognostic marker in breast cancer. Because this is a newl y described protein, neither the subcellular localization of thymosin beta 15 or its expression in breast cancer has been examined. We descr ibe the use of an affinity-purified polyclonal antibody to show that w ithin breast epithelium, thymosin beta 15 is localized diffusely throu ghout the cytoplasm and that thymosin beta 15 is upregulated in malign ant (compared with benign) breast tissue. Zn contrast to the prostate model, thymosin beta 15 is upregulated in nonmetastatic breast cancer and even ductal carcinoma in situ (compared with benign breast tissue) , and, consequently, it might represent a potential early marker for b reast malignancy. Additional studies are needed to evaluate the precis e role and prognostic value of thymosin beta 15 in breast cancer.