描述：
Stat (
S
ignal
t
ransducer and
a
ctivators of
t
ranscription) proteins are critical mediators of the biologic activity of cytokines, including
interleukins, interferons, erythropoietin, and growth factors. Ligand-receptor interaction leads to activation of constitutively associated JAK
family kinases and subsequent recruitment/activation of Stat proteins by tyrosine phosphorylation. Active Stat proteins then move to the
nucleus to promote transcription of cytokine-inducible genes. Seven Stat proteins have been cloned, each of which is differentially expressed
and/or activated in a cytokine-specific and cell type-specific manner. Stat1 and Stat2 are components of the ISGF3 (
I
nterferon-
S
timulated
G
ene
F
actor
3
) complex, which is the primary transcription activator induced by the binding of the interferon to a specific cell-surface
receptor. Stat1 has two alternatively spliced isoforms, 91-kDa Stat1α and 84 kDa Stat1β
;
Stat1α has 38 additional C-terminal amino acids. In
response to the binding of IFNα, IFNγ, EGF, PDGF, or CSF-1 to their respective receptors, the Stat1 subunits become
tyrosine-phosphorylated at Y701, and the complex is translocated to the nucleus. This results in the formation of an active complex that
includes the DNA-binding p48 subunit. This complex is responsible for modulating the transcription of the interferon-stimulated genes
(ISGs). Thus, phosphorylation of Y701 in Stat1 occurs in response to growth factors and cytokines, and is essential for normal transcriptional
activity of the ISGF3 complex.
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