STAT4 serine phosphorylation is critical for IL-12-induced IFN-gamma production but not for cell proliferation.
T helper 1 (T(H)1) differentiation and IFN-gamma production are crucial in cell-mediated immune responses. IL-12 is an important regulator of this process and mediates its effects through signal transducer and activator of transcription 4 (STAT4). IFN-gamma production is also regulated by the p38 mitogen-activated kinase pathway, although the mechanisms are ill-defined. We show here that GADD45-beta and GADD45-gamma can induce STAT4 S721 phosphorylation via the MKK6/p38 pathway. Thus, STAT4 could be a target that accounts for the defects in cell-mediated immunity associated with perturbations in the p38 pathway. To investigate the biological significance of STAT4 S721 phosphorylation, we reconstituted primary spleen cells from STAT4-deficient mice with wild-type and mutated STAT4, by using a retroviral gene transduction. We demonstrated that expression of wild-type STAT4, but not the S721A mutant, restored normal T(H)1 differentiation and IFN-gamma synthesis. The inability of STAT4 S721 to restore IFN-gamma production was not caused by decreased IL-12R expression because the STAT4 S721 mutant also failed to restore IFN-gamma production in STAT4-deficient IL-12Rbeta2 transgenic cells. Importantly, STAT4 S721A-transduced cells showed normal proliferative response to IL-12, illustrating that serine phosphorylation is not required for IL-12-induced proliferation. Additionally, the results imply the existence of STAT4 serine phosphorylation-dependent and -independent target genes. We conclude that phosphorylation of STAT4 on both tyrosine and serine residues is important in promoting normal T(H)1 differentiation and IFN-gamma secretion.
Morinobu
Akio
A
Molecular Immunology and Inflammation Branch, National Institute of Arthritis, Musculoskeletal, and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA. morinoba@mail.nih.gov
Gadina
Massimo
M
Strober
Warren
W
Visconti
Roberta
R
Fornace
Albert
A
Montagna
Cristina
C
Feldman
Gerald M
GM
Nishikomori
Ryuta
R
O'Shea
John J
JJ
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D007371:Interferon-gamma / Q000096:biosynthesis*; D018664:Interleukin-12 / Q000378:metabolism / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D048669:MAP Kinase Kinase 6; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism; D018123:Receptors, Interleukin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D053707:Receptors, Interleukin-12; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050797:STAT4 Transcription Factor; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D018417:Th1 Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000737:chemistry; D048051:p38 Mitogen-Activated Protein Kinases; D000097642:GADD45 Proteins
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004268:DNA-Binding Proteins; D007371:Interferon-gamma; D018664:Interleukin-12; D047908:Intracellular Signaling Peptides and Proteins; D048669:MAP Kinase Kinase 6; D020928:Mitogen-Activated Protein Kinases; D011506:Proteins; D018123:Receptors, Interleukin; D053707:Receptors, Interleukin-12; D011994:Recombinant Proteins; D050797:STAT4 Transcription Factor; D012694:Serine; D015534:Trans-Activators; D014443:Tyrosine; D048051:p38 Mitogen-Activated Protein Kinases; D000097642:GADD45 Proteins; C494091:Stat4 protein, mouse; C482567:Map2k6 protein, mouse