Urokinase-Receptor/Integrin Complexes Are Functionally Involved in Adhesion and Progression of Human Breast Cancer in Vivo

Abstract

Interactions between specific cell-surface molecules, which include the urokinase receptor (uPAR) and integrins, are crucial to processes of tumor invasion and metastasis. Here we demonstrate that uPAR and beta1-integrins may cluster at distinct sites at the cell surface of metastatic MDA-MB-231 breast cancer cells and form functional complexes. Attachment assays performed in the presence of a synthetic peptide (p25), which interferes with the formation of uPAR-integrin complexes, reveal that uPAR is able to regulate the adhesive function of integrins in breast cancer cells. On dissociation of the uPAR-integrin complexes by p25, tumor cell attachment to the extracellular matrix was either decreased (vitronectin) or increased (fibronectin). Moreover, the tumor cells display remarkable morphological changes when cultured on fibronectin in the continuous presence of p25, leading to increased cell spreading and attachment. In marked contrast to control conditions, increased cellular adhesion to fibronectin after p25 treatment was entirely beta1-integrin-mediated. The role of uPAR-integrin complexes in tumor progression was studied in an in vivo bone xenograft model. Stably transfected MDA-MB-231 cells that overexpress p25 showed a significant reduction in tumor progression in bone (P < or = 0.0001 versus mock-control). In line with these observations, continuous administration of p25 (25 microg/mouse/day, osmotic minipumps) for 28 days resulted in significantly reduced tumor progression of MDA-MB-231 cells in bone (P < or = 0.005) when compared to scrambled control peptide. In conclusion, our data demonstrate that uPAR can act as an adhesion receptor in breast cancer and is capable of regulating integrin function. Our findings strongly suggest that adhesive and proteolytic events are tightly associated in metastatic breast cancer cells and that functional integrin-uPAR complexes are involved in tumor progression in vivo.

Ascites induces modulation of α6β1 integrin and urokinase plasminogen activator receptor expression and associated functions in ovarian carcinoma

“…Previously, we have shown loss of uPA/ uPAR-mediated Erk activation with downregulation of uPAR expression in colon cancer cells (Ahmed et al, 2003a). uPA/uPAR interaction with b1 integrin has been shown to activate Erk pathway (Ahmed et al, 2003a) and disruption of this interaction can result in loss of adhesion and tumour progression in nude mice (van der Pluijm et al, 2001). The uPAR -integrin interaction is crucial as many integrin receptors activate intracellular signal pathways to fully activate cell survival and proliferation pathways (Miyamoto et al, 1996).…”

Deacetylated GM3 Promotes uPAR-Associated Membrane Molecular Complex to Activate p38 MAPK in Metastatic Melanoma

“…On the other hand, various subunits of integrin are abundantly expressed in melanomas and seem to play critical roles for melanoma metastasis. For instance, uPAR is known to associate with integrin b1 to promote tumor metastasis (16,31,33). In the current study, we have shown that d-GM3 promotes the association of uPAR and integrin a5b1, and the downstream activation of p38a is a key in melanoma invasion.…”

“…cDNA were prepared using High Capacity cDNA Reverse Transcription kit (Applied Biosystems) with 2 mg of total RNA according to the manufacturer's protocol. The expression of GM3S, caveolin-1, integrin a3, a5, and b1 in cells was examined by PCR using primers with 200 ng cDNA per reaction as described previously (27,32,33). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression was detected as an internal control (33).…”

“…The expression of GM3S, caveolin-1, integrin a3, a5, and b1 in cells was examined by PCR using primers with 200 ng cDNA per reaction as described previously (27,32,33). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression was detected as an internal control (33). PCR was carried out under the following conditions: 1 cycle at 42 C for 30 minutes; 1 cycle at 95 C for 5 minutes; 25 cycles at 95 C for 1 minute, and 72 C for 3 minutes; then 1 cycle at 72 C for 5 minutes (GeneAmp PCR system 2700; Applied Biosystems).…”

The Solution Structure of the N-terminal Domain of Human Vitronectin

“…There is a close interplay between uPAR, integrins, vitronectin, and PAI-1 in regulating cell invasiveness. Multiple lines of evidence exist for association of uPAR with integrins to coordinate the effects of the two classes of receptors in mediating signaling and promoting cellular rearrangement and/or migration (57)(58)(59)(60)(61)(62)(63)(64)(65). This new information defining the relative location of binding sites for PAI-1 and the two receptors within the SMB domain will be invaluable for considering mechanisms by which these receptors and the ECM communicate in a reciprocal manner, ultimately with the goal of developing new antitumor and anti-thrombotic agents.…”