Plasminogen activator inhibitor 1 functions as a urokinase response modifier at the level of cell signaling and thereby promotes MCF-7 cell growth.
Plasminogen activator inhibitor 1 (PAI-1) is a major inhibitor of urokinase-type plasminogen activator (uPA). In this study, we explored the role of PAI-1 in cell signaling. In MCF-7 cells, PAI-1 did not directly activate the mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase (ERK) 1 and ERK2, but instead altered the response to uPA so that ERK phosphorylation was sustained. This effect required the cooperative function of uPAR and the very low density lipoprotein receptor (VLDLr). When MCF-7 cells were treated with uPA-PAI-1 complex in the presence of the VLDLr antagonist, receptor-associated protein, or with uPA-PAI-1(R76E) complex, which binds to the VLDLr with greatly decreased affinity, transient ERK phosphorylation (<5 min) was observed, mimicking the uPA response. ERK phosphorylation was not induced by tissue-type plasminogen activator-PAI-1 complex or by uPA-PAI-1 complex in the presence of antibodies that block uPA binding to uPAR. uPA-PAI-1 complex induced tyrosine phosphorylation of focal adhesion kinase and Shc and sustained association of Sos with Shc, whereas uPA caused transient association of Sos with Shc. By sustaining ERK phosphorylation, PAI-1 converted uPA into an MCF-7 cell mitogen. This activity was blocked by receptor-associated protein and not observed with uPA-PAI-1(R76E) complex, demonstrating the importance of the VLDLr. uPA promoted the growth of other cells in which ERK phosphorylation was sustained, including beta3 integrin overexpressing MCF-7 cells and HT 1080 cells. The MEK inhibitor, PD098059, blocked the growth-promoting activity of uPA and uPA-PAI-1 complex in these cells. Our results demonstrate that PAI-1 may regulate uPA-initiated cell signaling by a mechanism that requires VLDLr recruitment. The kinetics of ERK phosphorylation in response to uPAR ligation determine the function of uPA and uPA-PAI-1 complex as growth promoters.
Webb
D J
DJ
Department of Pathology, and Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, Virginia 22908, USA.
Thomas
K S
KS
Gonias
S L
SL
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D001943:Breast Neoplasms / Q000378:metabolism*; D002455:Cell Division; D002465:Cell Movement; D004347:Drug Interactions; D005260:Female; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017395:Plasminogen Activator Inhibitor 1 / Q000494:pharmacology*; D011506:Proteins / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D011973:Receptors, LDL / Q000378:metabolism; D055293:Receptors, Urokinase Plasminogen Activator; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D020664:Son of Sevenless Proteins / Q000378:metabolism; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014407:Tumor Cells, Cultured; D014568:Urokinase-Type Plasminogen Activator / Q000494:pharmacology*
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; C524898:PLAUR protein, human; D017395:Plasminogen Activator Inhibitor 1; D011506:Proteins; D011956:Receptors, Cell Surface; D011973:Receptors, LDL; D055293:Receptors, Urokinase Plasminogen Activator; C528024:SHC1 protein, human; D055765:Shc Signaling Adaptor Proteins; D020664:Son of Sevenless Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; C036053:VLDL receptor; D020928:Mitogen-Activated Protein Kinases; D014568:Urokinase-Type Plasminogen Activator