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Cleavage of uPAR; mechanism and prognostic<br />

significance<br />

Gunilla Høyer-Hansen, Charlotte Almasi, Helle Pappot, Keld Danø<br />

Finsen Laboratory, Strandboulevarden 49, DK-2100 Copenhagen Ø, Denmark<br />

Urokinase (uPA) cleaves its receptor, uPAR, thereby inactivating the binding potential<br />

of this molecule both with regards to uPA and vitronectin. The N-terminal domain<br />

I, uPAR(I) is liberated and the cleaved uPAR(II-III) stays on the cell surface. The<br />

cleavage takes place in the linker region between domains I and II after R 83 and<br />

R 89 . The cleavage is greatly accelerated on the cell surface compared to in solution<br />

and this acceleration is dependent on the uPA-uPAR binding. uPA cleaves glycolipid<br />

anchored uPAR (GPI-uPAR) but not soluble uPAR (suPAR), which lacks the glycolipid<br />

anchor. This is due to a difference in the conformation of the linker region between<br />

domains I and II and not because of a general difference in proteolytic susceptibility,<br />

since GPI-uPAR and suPAR are cleaved with equal efficiency by plasmin. The<br />

collective amounts of all uPAR forms measured by ELISA in tumour lysates or<br />

blood correlates to prognosis in several forms of cancer. However, the amounts of<br />

uPAR(II-III) and uPAR(I) may be directly related to the uPA activity and therefore<br />

be even stronger prognostic markers. Using combinations of monoclonal<br />

antibodies we have designed 3 time-resolved fluoroimmunoassays for the specific<br />

measurements of uPAR(I-III), uPAR(I-III) + uPAR(II-III), and uPAR(I). The amounts of<br />

uPAR(II-III) can be calculated. Applying these assays on tumour extracts from 63<br />

patients diagnosed with squamous cell lung carcinoma revealed a stronger prognostic<br />

impact of uPAR(I) compared to total uPAR as measured by ELISA.<br />

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