Plg-R(KT) Expression in Human Breast Cancer Tissues

The plasminogen activation system regulates the activity of the serine protease, plasmin. The role of plasminogen receptors in cancer progression is being increasingly appreciated as key players in modulation of the tumor microenvironment. The interaction of plasminogen with cells to promote plasminogen activation requires the presence of proteins exposing C-terminal lysines on the cell surface. Plg-R(KT) is a structurally unique plasminogen receptor because it is an integral membrane protein that is synthesized with and binds plasminogen via a C-terminal lysine exposed on the cell surface. Here, we have investigated the expression of Plg-R(KT) in human breast tumors and human breast cancer cell lines. Breast cancer progression tissue microarrays were probed with anti-Plg-R(KT) mAB and we found that Plg-R(KT) is widely expressed in human breast tumors, that its expression is increased in tumors that have spread to draining lymph nodes and distant organs, and that Plg-R(KT) expression is most pronounced in hormone receptor (HR)-positive tumors. Plg-R(KT) was detected by Western blotting in human breast cancer cell lines. By flow cytometry, Plg-R(KT) cell surface expression was highest on the most aggressive tumor cell line. Future studies are warranted to address the functions of Plg-R(KT) in breast cancer.