uPAR, the three-domain membrane receptor of the serine protease urokinase-type plasminogen activator, plays an important role in tumor growth and metastasis. uPAR-del4/5 is a splice variant lacking domain DII and has been shown to be an independent prognostic marker for distant metastasis-free survival in node-negative breast cancer patients. Moreover, uPAR-del4/5 overexpression in breast cancer cells affects tumor biologically relevant processes such as proliferation, cellular adhesion to extracellular matrix proteins and the invasive capacity of the cells in vitro, as well as lung colonization in an experimental metastasis xenograft mouse mode. The aim of the present study was to investigate whether overexpression of uPAR-del4/5 in breast cancer cells modulates expression of other tumor-relevant proteins.
Gene expression of a series of tumor-associated proteases, inhibitors and extracellular matrix proteins was analyzed in stably transfected vector control versus uPAR-del4/5 overexpressing MDA-MB-231 breast cancer cells using a low density microarray. Several genes were identified to be up-regulated or repressed in uPAR-del4/5 overexpressing compared to vector control cells. One of these genes encodes the matrix metalloproteinase MMP-9 and was found to be more than 10-fold up-regulated in uPAR-del4/5 overexpressing cells. Zymograms as well as Western blot analysis confirmed enhanced secretion of MMP-9 into the supernatant of cultured breast cancer cells compared to vector control. uPAR-del4/5 may thus play an important role in the regulation of the extracellular proteolytic network of breast cancer cells and, by this, influence the metastatic potential of breast cancer cells.