Constitutive tyrosine and serine phosphorylation of STAT4 in T-cells transformed with HTLV-I.
STAT4 is a critical mediator of IL-12-stimulated gene regulation in T-helper type 1 (Th1) cell. IL-12 activates the Janus family tyrosine kinases JAK2 and Tyk2, which in turn phosphorylate STAT4 on tyrosine 693. The p38 mitogen-activated protein kinase (MAPK) signaling pathway is also activated in response to IL-12, followed by phosphorylation of STAT4 on serine 721, which is required for STAT4 full transcriptional activity. In the present study, we demonstrated constitutive activation of STAT4 in HTLV-I-transformed T-cell lines MT-2, MT-4 and HUT102 by immunoprecipitation, Western blotting and electrophoretic mobility shift assay (EMSA). In HTLV-I-transformed T-cell lines, STAT4 was constitutively phosphorylated not only on tyrosine 693 but also on serine 721, and formed a heterodimer with STAT3. Constitutive phosphorylation of its upstream activators, JAK2, Tyk2 and p38 MAPK was also observed in the cells. EMSA and transient transfection studies further showed that the high-affinity sis-inducible element (hSIE) preferentially binds the STAT3/STAT4 heterodimer and is constitutively transactivated in MT-2 cells in the absence of exogenous cytokine stimulation. When STAT4 expression vector was cotransfected along with STAT3 expression vector into MT-2 cells, STAT4 significantly synergized with STAT3 to transactivate hSIE, showing the functional importance of heterodimer formation between STAT4 and STAT3.
Higashi
Takehiro
T
The First Department of Internal Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Tsukada
Junichi
J
Yoshida
Yasuhiro
Y
Mizobe
Takamitsu
T
Mouri
Fumihiko
F
Minami
Yasuhiro
Y
Morimoto
Hiroaki
H
Tanaka
Yoshiya
Y
D015153:Blotting, Western; D002460:Cell Line; D002472:Cell Transformation, Viral; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation; D015368:Human T-lymphotropic virus 1; D006801:Humans; D047468:Immunoprecipitation; D007371:Interferon-gamma / Q000378:metabolism; D053614:Janus Kinase 2; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D050797:STAT4 Transcription Factor / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D013601:T-Lymphocytes / Q000201:enzymology / Q000378:metabolism*; D053634:TYK2 Kinase; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism*
D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D050796:STAT3 Transcription Factor; D050797:STAT4 Transcription Factor; C052912:liver plasma membrane protein p38; D014443:Tyrosine; D012694:Serine; D007371:Interferon-gamma; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D053634:TYK2 Kinase; C070139:TYK2 protein, human