Both u-Pa inhibition and vitronectin binding by plasminogen activator inhibitor 1 regulate HT1080 fibrosarcoma cell metastasis

Overexpression of plasminogen activator inhibitor I (PAI-I) reduces tumor cell migration in vitro and metastasis in mice in vivo by mechanisms involving either inhibition of urokinase plasminogen activator (u-PA) activity or competition for an integrin binding site on vitronectin. To analyze the effects of PAI-I on tumor cell migration in vitro and metastasis in vivo, recombinant adenoviral vectors expressing wildtype or mutant PAI-I proteins were constructed. The mutant PAW proteins were defective in either vitronectin binding (PAI-IVN-), plasminogen activator inhibition (PAI-IINH-) or both (PAI-I-VN-,I-INH-). In vitro, migration of HT 1080 human fibrosarcoma cells through a reconstituted extracellular matrix (ECM) was reduced 73% by overexpression of wild-type PAI-I and 65% by PAI-IVN- compared with control virus-infected cells. Migration of cells infected by virus expressing either PAI-I IINH- or PAI-I-VN-,I-INH- was unaffected, indicating a requirement for plasminogen activator inhibitory activity. In vivo, however, only overexpression of wild-type PAI-I reduced the burden of metastasis by 68% compared with the control group. This indicates that both u-PA inhibition and PAI-I ECM interactions contribute to the mechanism of PAI-I-mediated regulation of cell migration. (C) 2002 Wiley-Liss, Inc.