Proteolysis of the urokinase-type plasminogen activator receptor by metalloproteinase-12: implication for angiogenesis in fibrin matrices.

Pericellular proteolysis plays an important role in cell migration and the formation of new capillary structures. The plasminogen activator/plasmin and matrix degrading metalloproteinase (MMP) cascades act together in the remodeling of matrix and cell-matrix contacts. Previously we have shown that the formation of capillary structures by human foreskin microvascular endothelial cells (hMVECs) in a 3-dimensional fibrin matrix requires a functional urokinase-type plasminogen activator receptor (u-PAR). Here we report on the unexpected finding that inhibition of hMVEC-derived MMP activity by BB94 (batimastat) increased the outgrowth of capillary structures in a fibrin matrix. BB94 prevented the release of the u-PA binding domain D1 of u-PAR and thereby increased the number of functional u-PARs on hMVECs without affecting the u-PAR messenger RNA levels. Comparison of various types of protease inhibitors pointed to the prime involvement of MMP activity. Using recombinant MMPs it was shown that MMP-12 activity was able to release the D1 domain of cellularly expressed u-PAR. In addition, the expression of MMP-12 in control and basic fibroblast growth factor/tumor necrosis factor-alpha-stimulated hMVECs was shown by reverse transcriptase-polymerase chain reaction, suggesting that endothelial cell-derived MMP-12 may be involved in angiogenesis-related u-PAR shedding. This new mechanism of u-PAR cleavage provides new insights into the mutual interactions between the MMP and u-PA/plasmin systems. Moreover, it may be helpful in the interpretation of recent data on the use of specific MMP inhibitors in the treatment of several types of cancer.