Preassociation of STAT1 with STAT2 and STAT3 in separate signalling complexes prior to cytokine stimulation.
A variety of cytokines and growth factors act through an induction of gene expression mediated by a family of latent transcription factors called STAT (signal transducers and activators of transcription) proteins. Ligand-induced tyrosine phosphorylation of the STATs promotes their homodimer and heterodimer formation and subsequent nuclear translocation. We demonstrate here that STAT protein heterocomplexes exist prior to cytokine treatment. When unstimulated HeLa cells are ruptured in hypotonic buffer without salt or detergent, immunoadsorption of either STAT1 or STAT2 from the resulting cytosol yields coimmunoadsorption of the other STAT protein. Similarly, STAT1-STAT3 heterocomplexes are coimmunoadsorbed from hypotonic cytosol. STAT1 and STAT2 or STAT1 and STAT3 translated in reticulocyte lysate spontaneously form heterocomplexes when the translation lysates are mixed at 0 degrees C. Our data suggest that interferon-alpha /beta-induced tyrosine phosphorylation increases the stability of a preexisting, latent, STAT1-STAT2 signaling complex. Newly translated STAT1 binds in equilibrium fashion to STAT2 and STAT3, but we show that STAT2 and STAT3 exist in separate heterocomplexes with STAT1, consistent with a model in which STAT1 contains a common binding site for other STAT proteins.
Stancato
L F
LF
Department of Pharmacology, University of Michigan Medical School, Ann Arbor, 48109, USA.
David
M
M
Carter-Su
C
C
Larner
A C
AC
Pratt
W B
WB
D016475:3T3 Cells; D000209:Acute-Phase Proteins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D000077190:Interferon alpha-2; D016898:Interferon-alpha / Q000494:pharmacology*; D016899:Interferon-beta / Q000494:pharmacology*; D007371:Interferon-gamma / Q000494:pharmacology*; D051379:Mice; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000032:analysis; D014176:Protein Biosynthesis; D011817:Rabbits; D017471:Receptors, Interferon / Q000502:physiology; D011994:Recombinant Proteins / Q000494:pharmacology; D012156:Reticulocytes / Q000378:metabolism; D050794:STAT1 Transcription Factor; D050795:STAT2 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D014158:Transcription, Genetic
D000209:Acute-Phase Proteins; D004268:DNA-Binding Proteins; D000077190:Interferon alpha-2; D016898:Interferon-alpha; D017471:Receptors, Interferon; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050795:STAT2 Transcription Factor; C494084:STAT2 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494080:Stat1 protein, mouse; C494085:Stat2 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D019000:Phosphotyrosine; D016899:Interferon-beta; D007371:Interferon-gamma