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Mol. Cell. Biol., Apr 1996, 1595-1603, Vol 16, No. 4
X Cao, A Tay, GR Guy and YH Tan
STAT proteins are a group of latent cytoplasmic transcription factors which
function as signal transducers and activators of transcription. Stat1 and
-2 were originally identified to function in interferon signaling, and
Stat1 was also found to be activated by epidermal growth factor (EGF) and
other cytokines. New members of the STAT gene family are identified. Among
them, Stat3 has 52.5% amino acid sequence homology with Stat1 and is
activated by platelet-derived growth factor (PDGF), colony-stimulating
factor 1 (CSF-1), EGF, interleukin-6, and other cytokines. Treatment of
cells with EGF activates Stat1 and Stat3, which become phosphorylated on
tyrosine residues to form homo - or heterodimers and translocate into the
nucleus, binding to the sis- inducible element (SIE) in the c-fos promoter.
Somatic cell genetic analyses demonstrated that Jaks, a family of
nontransmembrane protein tyrosine kinases, are required for the activation
of Stat1 and Stat2 in interferon-treated cells. However, little is known
about the activation of Stat3 by growth factors. Here we report that in all
v-Src- transformed cell lines examined, Stat3 is constitutively activated
to bind to DNA and the phosphorylation of tyrosine on Stat3 is enhanced by
the induction of v-Src expression. We also report that Src is shown to be
associated with Stat3 in vivo, as well as in vitro, and phosphorylates
Stat3 in vitro. Stat3 is also activated by CSF-1, possibly through CSF-1
receptor-c Src association in NIH 3T3 cells overexpressing CSF-1 receptors.
Together, the data suggest that Src is involved in activation of Stat3 in
growth factor signal transduction.
Copyright © 1996, American Society for Microbiology
Activation and association of Stat3 with Src in v-Src-transformed cell lines
Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore.
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