Urokinase Induces Activation and Formation of Stat4 and Stat1-Stat2 Complexes in Human Vascular Smooth Muscle Cells

Abstract

Urokinase-type plasminogen activator (uPA) and its specific receptor (uPAR) act in concert to stimulate cytoplasmic signaling machinery and transcription factors responsible for cell migration and proliferation. Recently we demonstrated that uPA activates the Janus kinase/signal transducers and activators of transcription (Stat1) signaling in human vascular smooth muscle and endothelial cells. However, the important question whether other transcription factors of the Stat family, in addition to Stat1, are involved in the uPAR-related signaling has not been addressed. In this study, we demonstrate that Stat4 and Stat2, but not Stat3, Stat5, or Stat6, are rapidly activated in response to uPA. We demonstrate further that Stat4 and Stat2 rapidly and transiently translocate to the cell nucleus where they bind specifically to the regulatory DNA elements. Analysis of Stat complexes formed in response to uPA revealed a Stat2-Stat1 heterodimer, which lacks p48, a DNA-binding protein known to combine with Stat1-Stat2. This new uPA-induced Stat2-Stat1 heterodimer binds to GAS (the interferon-␥ activation site) distinct from the interferon-stimulated response element to which the p48 protein containing complexes generally bind. We conclude that uPA activates a specific and unusual subset of latent cytoplasmic transcription factors in human vascular smooth muscle cells that suggests a critical role of uPA in these cells.

Urokinase–urokinase receptor interaction mediates an inhibitory signal for HIV-1 replication

“…Furthermore, we did not observe activation of the IFN-related Janus kinase͞STAT (JAK͞STAT) pathway of signal transduction (36), as reported for smooth muscle cells treated with pro-uPA (37), that we have correlated to the anti-HIV effect of IFNs in U937 cells (ref. 38, and data not shown).…”

Recruitment of Stat4 to the Human Interferon-α/β Receptor Requires Activated Stat2

“…However, until recently, Stat2 was known to be activated only by the IFN-␣/␤ pathway, restricting a general test of this hypothesis. A recent report has shown that the urokinase receptor, expressed by human vascular smooth muscle cells, also activates Stat2, and that indeed Stat4 is also activated in response to urokinase signaling (36). This observation supports the idea that human Stat2 is involved in Stat4 recruitment and activation.…”

Urokinase/urokinase receptor and vitronectin/αvβ3 integrin induce chemotaxis and cytoskeleton reorganization through different signaling pathways

“…In addition to their direct involvement in the proteolytic (uPAR) and adhesive properties of cells, both pro-uPA (Gudewicz and Bilboa, 1987; Boyle et Fibbi et al, 1988;Del Rosso et al, 1992;Resnati et al, 1996;Gyetko et al, 1996;Degryse et al, 1999) and VN (Yebra et al, 1996;Kjùller et al, 1997;Stahl and Mueller, 1997;Carriero et al, 1999; directly stimulate cell migration. The interaction of uPAR with several integrins and the modulation of their function is an established fact; for example, the presence and the level of uPAR a ects the choice between adhesion on ®bronectin v. vitronectin, the internalization of ®brinogen or even the constitutive activation of MAP-K in certain cancer cells leading to cell proliferation Simon et al, 1996;Xue et al, 1997;Dumler et al, 1999;Aguirre Ghiso et al, 1999;Kusch et al, 2000). Direct interactions of uPAR with integrins has been shown by several techniques, including¯uorescence resonance energy transfer and co-immuno-precipitation (Bohuslav et al, 1995;Wei et al, 1996;Yebra et al, 1996;Xue et al, 1997;Carriero et al, 1999Simon et al, 2000.…”

“…Migration responses are generally observed at low (physiological) levels of uPAR expression, while proliferation responses may require higher levels as observed in cancer cells (Aguirre Ghiso et al, 1999;Ossowski and Aguirre Ghiso, 2000;Webb et al, 2000). Several signal transducing molecules have been identi®ed (Konakova et al, 1998;Webb et al, 2000;Degryse et al, 1999;Dumler et al, 1999).…”