A cleaved form of the receptor for urokinase‐type plasminogen activator in invasive transplanted human and murine tumors

Abstract

It was recently found that urokinase-type plasminogen activator (uPA) is involved in the cleavage of its receptor (uPAR) on cultured cells, thereby releasing one of the receptor's 3 domains (the ligand binding domain I) and leaving the 2 others [uPAR(2 + 3)] anchored to the cell surface. With monoclonal antibodies (MAbs) we have now identified human uPAR(2 + 3) in lysates of invasive human MDA-MB-231 mammary carcinomas xenografted into nude mice. The production of peptide antibodies recognizing different domains of murine uPAR made it possible to identify a similar cleaved form of uPAR, murine uPAR(2 + 3), in extracts of primary Lewis lung carcinomas. Cleavage of uPAR also occurs in cultured MDA-MB-231 cells and Lewis lung carcinoma cells. This cleavage is inhibited by anticatalytic antibodies to either human or murine uPA, respectively, indicating that it is catalyzed by either uPA or plasmin generated by uPA. The amount of uPAR(2 + 3) may therefore be directly related to the activity of the uPA system and it is possible that the level of uPAR(2 + 3) in cancer tissue may prove to be a stronger prognostic parameter than the levels of either full-length uPAR or UPA.

Gelatinase-mediated migration and invasion of cancer cells

“…This suggests that uPA and MMPs are activated prior to integrin activation and remain associated to the integrins. Furthermore, uPAR can be cleaved by uPA (Hoyer-Hansen et al, 1992) or MMPs in vitro (Andolfo et al, 2002;Koolwijk et al, 2001) and the cleaved uPAR form is also found in invasive tumor xenografts (Solberg et al, 1994). The cleavage occurs between domains 1 and 2 impairs uPA and integrin binding (Montuori et al, 2002) and exposes a chemotactic epitope (Fazioli et al, 1997) suggesting that this cleavage is one of the cell migration regulating events on the cell surface.…”

“…We found that a gelatinase-selective smallmolecule inhibitor and the CTT peptide inhibited the cellular cleavage of uPAR. Importantly, the cleaved form of uPAR is found in invasive transplanted tumors in mice (Solberg et al, 1994). Moreover, appearance of the fragmented uPAR is associated with the presence of tumor cells in acute myeloid leukemia (Mustjoki et al, 2000).…”

Soluble urokinase receptor released from human carcinoma cells: A plasma parameter for xenograft tumour studies

“…Cell lysates were made of cultured MDA-MB-231 BAG cells using a Triton X-114 containing buffer together with the protease inhibitors aprotinin, PMSF and EDTA, and then subjected to temperature-induced phase separation (Solberg et al, 1994). Western blotting of the total lysate, detergent phase and water phase of Triton X-114 extracts (without immunoabsorption) showed in all cases two bands corresponding to full-length uPAR and a form consisting of uPAR domains (2+3) (Figure 3), i.e.…”

Cell‐Surface Acceleration of Urokinase‐Catalyzed Receptor Cleavage

“…This finding has since been extended to include several cell lines of neoplastic origin, among these HT 1080 fibrosarcoma cells [14, 1.51, MDA-MB-231 breast cancer cells and murine Lewis lung carcinoma cells [16]. Also extracts of experimental tumors contain considerable amount of uPAR(2+3) [16].…”

“…By this cleavage domain 1 is liberated from the remaining membrane-bound part of the molecule, designated uPAR(2+3), which was first identified on the surface of U937 histiocytic lymphoma cells [13]. This finding has since been extended to include several cell lines of neoplastic origin, among these HT 1080 fibrosarcoma cells [14, 1.51, MDA-MB-231 breast cancer cells and murine Lewis lung carcinoma cells [16]. Also extracts of experimental tumors contain considerable amount of uPAR(2+3) [16].…”