STAT1 and Suppressors of Cytokine Signaling (SOCS) Negatively Regulate STAT6 Signaling and Growth of Th2 Cells

Abstract

Abstract: : Purposes: Excessive production of CD4+Th1 cells causes autoimmune disease while too much Th2 promotes allergy. Understanding mechanisms that regulate Th1/Th2 balance and maintain immune homeostasis is critical in preventing T cell mediated diseases. In this study, we have investigated the role of JAK/STAT signaling pathways in regulating the growth, differentiation and effector functions of Th cells. Methods: Naive CD4+ Th lymphocytes were isolated from spleens/lymph nodes of WT, HEL TCR transgenic or STAT1KO mice. Cells were activated under Th1 or Th2 polarizing or neutral conditions and examined for STAT activation or SOCS–mediated negative regulation by Gel–shift, Northern, Western or real–time RT–PCR assay. Effect of SOCS on Th–cell growth was examined in a Th2 cell line (D10.G4.1) stably transfected with SOCS1 or anti–sense SOCS1 cDNA. Results: We show here that differentiation of naive to effector Th–cells is accompanied by activation of STAT1, STAT4 and STAT6 and these pathways are under negative regulation by SOCS1, SOCS proteins. Transcriptional activation of SOCS genes is compromised in STAT1KO naive cells, suggesting that STAT1 signals play major roles in negative regulatory pathways of Th cells. Surprisingly, IL–4 is found to be a potent inducer of STAT1 activation in Th2 but not Th1 cells. We further show that over–expression of SOCS1 in Th2 cells represses STAT6 activation and profoundly inhibits IL–4–induced proliferation, while depletion of SOCS1 by an anti–sense SOCS1 cDNA construct enhances cell proliferation and induces constitutive IL4–induced activation of STAT6 in Th2 cells. Conclusion:We show here for the first time that IL–4 selectively induces activation of STAT1 in Th2 but not Th1 cells and that STAT1 is a potent inducer of SOCS in differentiating Th–cells. These results are consistent with a model in which IL–4 has dual effects on differentiating T– cells: It simulates proliferation/differentiation through STAT6 and autoregulates its effects on Th2 growth & effector functions via STAT1–dependent up–regulation of SOCS proteins.

Keywords: immunomodulation/immunoregulation • autoimmune disease • gene/expression