IFN-gamma suppresses STAT6 phosphorylation by inhibiting its recruitment to the IL-4 receptor.
Polarized Th1 cells show a stable phenotype: they become insensitive to IL-4 stimulation and lose the potential to produce IL-4. Previously, we reported that IFN-gamma played a critical role in stabilizing Th1 phenotype. However, the mechanism by which IFN-gamma stabilizes Th1 phenotype is not clear. In this study, we compared STAT6 phosphorylation in wild-type (WT) and IFN-gamma receptor knockout (IFNGR(-/-)) Th1 cells. We found a striking diminution of STAT6 phosphorylation in differentiated WT Th1 cells, but not in differentiated IFNGR(-/-) Th1 cells. The impairment of STAT6 phosphorylation in differentiated WT Th1 cells was not due to a lack of IL-4R expression or phosphorylation. Jak1 and Jak3 expression and phosphorylation were comparable in both cell types. No differential expression of suppressor of cytokine signaling 1 (SOCS1), SOCS3, or SOCS5 was observed in the two cell types. In addition, Src homology 2-containing phosphatase mutation did not affect IL-4-induced STAT6 phosphorylation in differentiated Th1 cells derived from viable motheaten (me(v)/me(v)) mice. These results led us to focus on a novel mechanism. By using a pulldown assay, we observed that STAT6 in WT Th1 cells bound less effectively to the phosphorylated IL-4R/GST fusion protein than that in IFNGR(-/-) Th1 cells. Our results suggest that IFN-gamma may suppress phosphorylation of STAT6 by inhibiting its recruitment to the IL-4R.
Huang
Zan
Z
Graduate Program in Molecular Biology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
Xin
Junping
J
Coleman
John
J
Huang
Hua
H
D000818:Animals; D002352:Carrier Proteins / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology*; D015847:Interleukin-4 / Q000096:biosynthesis; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D008822:Mice, Transgenic; D010766:Phosphorylation; D021381:Protein Transport / Q000276:immunology; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D011506:Proteins / Q000502:physiology; D017471:Receptors, Interferon / Q000172:deficiency / Q000235:genetics; D019948:Receptors, Interleukin-4 / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000502:physiology; D050800:STAT6 Transcription Factor; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D018417:Th1 Cells / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000378:metabolism* / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology; D000096743:Interferon gamma Receptor
D002352:Carrier Proteins; D007371:Interferon-gamma; D015847:Interleukin-4; D047908:Intracellular Signaling Peptides and Proteins; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; D011506:Proteins; D017471:Receptors, Interferon; D019948:Receptors, Interleukin-4; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D050800:STAT6 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D000096743:Interferon gamma Receptor; C491590:Socs1 protein, mouse; C491411:Socs3 protein, mouse; C485811:Socs5 protein, mouse; C494100:Stat6 protein, mouse; C509248:Ptpn6 protein, mouse