1: J Biol Chem. 2000 Dec 15;275(50):39466-73. 

Urokinase stimulates human vascular smooth muscle cell migration via a
phosphatidylinositol 3-kinase-Tyk2 interaction.

Kusch A, Tkachuk S, Haller H, Dietz R, Gulba DC, Lipp M, Dumler I.

Charite-Franz Volhard Clinic and Max Delbruck Center for Molecular Medicine,
Humboldt University Berlin, Wiltbergstrasse 50, 13125 Berlin-Buch, Germany.

Janus kinases Jak1 and Tyk2 play an important role in urokinase-type plasminogen
activator (uPA)-dependent signaling. We have recently demonstrated that both
kinases are associated with the uPA receptor (uPAR) and mediate uPA-induced
activation of signal transducers and activators of transcription (Stat1, Stat2,
and Stat4) in human vascular smooth muscle cells (VSMC). Janus kinases are not
only required for Stat activation but may also interfere with other
intracellular signaling pathways. Here we report that in VSMC, Tyk2 interacts
with a downstream signaling cascade involving phosphatidylinositol 3-kinase
(PI3-K). We demonstrate that uPA induces PI3-K activation, which is abolished in
VSMC expressing the dominant negative form of Tyk2. The regulatory subunit p85
of PI3-K co-immunoprecipitates with Tyk2 but not with Jak1, Jak2, or Jak3, and
uPA stimulation increases the PI3-K activity in Tyk2 immunoprecipitates. Tyk2
directly binds to either of the two Src homology 2(SH2)p85 domains in a
uPA-dependent fashion. We provide evidence that the Tyk2-mediated PI3-K
activation in response to uPA is required for VSMC migration. Thus, two
unrelated structurally distinct specific inhibitors of PI3-K, wortmannin and
LY294002, prevent VSMC migration induced by uPA. No migratory effect of uPA was
observed in VSMC expressing the dominant negative form of Tyk2. Our results
underscore the versatile function of Tyk2 in uPA-related intracellular signaling
and indicate that PI3-K plays a selective role in the regulation of VSMC
migration.

PMID: 10995743 [PubMed - indexed for MEDLINE]


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2: J Biol Chem. 1999 Aug 20;274(34):24059-65. 

Urokinase induces activation and formation of Stat4 and Stat1-Stat2 complexes in
human vascular smooth muscle cells.

Dumler I, Kopmann A, Wagner K, Mayboroda OA, Jerke U, Dietz R, Haller H, Gulba
DC.

Franz Volhard Clinic and Max-Delbruck Center for Molecular Medicine, Virchow
Klinikum-Charite, Humboldt University of Berlin, D-13125 Berlin, Germany.
dumler@fvk-berlin.de

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-gamma 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.

PMID: 10446176 [PubMed - indexed for MEDLINE]


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