The murine receptor for urokinase-type plasminogen activator is primarily expressed in tissues actively undergoing remodeling

uPAR is a cellular receptor for urokinase plasminogen activator, an enzyme involved in extracellular matrix degradation during processes involving tis sue remodeling. We have expressed a recombinant soluble form of murine uPAR and raised rabbit polyclonal antibodies to study the expression of uPAR by immunohistochemistry. The immunohistochemical localization of uPAR was det ermined in normal mouse organs and in tumors formed by the highly metastati c Lewis lung carcinoma. uPAR immunoreactivity was found in the lungs, kidne ys, and spleen, and in endothelial cells in the uterus, urinary bladder, th ymus, heart, liver, and testis. No uPAR immunoreactivity was detected in mu scle. In general, strong uPAR immunoreactivity was observed in organs under going extensive tissue remodeling, as exemplified by trophoblast cells in p lacenta, and in migrating, but not resting, keratinocytes at the edge of in cisional wounds. Staining was not detected in any tissue sections derived f rom uPAR-deficient mice, thus confirming the specificity of the immunohisto chemical staining of uPAR in normal mouse tissues. In Lewis lung carcinoma, uPAR immunoreactivity was found in the tumor cells of the primary tumor an d in lung metastases.