Occurrence of thymosin β4 in human breast cancer cells and in other cell types of the tumor microenvironment

Previous studies have shown that the G-actin sequestering polypeptide thymosin beta 4 frequently is overexpressed in cancers and that such overexpression correlates to malignant progression. However, the localization of thymosin beta 4 in human cancers has not been determined. We now demonstrate that there is a considerable heterogeneity in the cellular distribution of thymosin beta 4 in breast cancer. In most tumors examined, cancer cells showed low or intermediate reactivity for thymosin beta 4, whereas leukocytes and macrophages showed intense reactivity. In addition, endothelial cells showed variable reactivity to thymosin beta 4, whereas myofibroblasts were negative. There was no correlation between the intensity of tumor cell staining and histological grade, whereas there was a tendency toward a correlation between endothelial cell staining and grade. These results demonstrate that multiple cell types within the tumor microenvironment produce thymosin beta 4 and that such expression varies from tumor to turner. Such heterogeneity of expression should be taken into account when the role of thymosin beta 4 in tumor biology is assessed. (c) 2007 Elsevier Inc. All rights reserved.