Signaling via the T cell antigen receptor induces phosphorylation of Stat1 on serine 727
ABSTRACT The Stat1 transcription factor plays a pivotal role in both, the antiviral and antigrowth actions of interferons. Stat1 acquires the ability to bind DNA by becoming phosphorylated on Tyr(701). However, to effectively stimulate gene transcription, it must also be phosphorylated on Ser(727). We show that engagement of T cell antigen receptor (TCR)/CD3 complex in either Jurkat cells or peripheral blood lymphocytes stimulates phosphorylation of Ser(727) but not Tyr(701) of Stat1. This process does not require the expression of tyrosine kinases Lck and Zap-70. Interestingly, pretreatment of T cells with the Src kinase inhibitor PP1 completely abrogated CD3-mediated serine phosphorylation of Stat1, whereas inhibitors to MEK1 and phosphatidylinositol 3-kinase had no effect. Phosphorylation of Ser(727) of Stat1 in T cells is not restricted to TCR/CD3 but also results when cells are stimulated via the costimulatory molecule CD28. The combination of CD3 and CD28 did not augment phosphorylation of Stat1 Ser(727). Surprisingly, Stat1-mediated transcriptional activity in response to IFN-alpha was enhanced with CD3 stimulation, whereas CD3 alone had little effect. These findings suggest that Stat1 is a signaling molecule in TCR signaling and may play a role in T cell function.
- [Show abstract] [Hide abstract]
ABSTRACT: The ability of interferon (IFN)-alpha to induce autoimmunity and exacerbate Th1 diseases is well known. We have recently described enhanced expression of IFN-alpha in the mucosa of patients with celiac disease (CD), a gluten-sensitive Th1-mediated enteropathy, characterized by villous atrophy and crypt cell hyperplasia. Previous studies from this laboratory have shown that T cell activation in explant cultures of human fetal gut can also result in villous atrophy and crypt cell hyperplasia. We have, therefore, examined changes that take place in explant cultures of human fetal gut after activation of T cells with anti-CD3 and/or IFN-alpha. We show that activation of T cells with anti-CD3 alone elicits a small IFN-gamma and TNF-alpha response with no tissue injury. Similarly, no changes are seen in explants cultured with IFN-alpha alone. However, addition of IFN-alpha with anti-CD3 results in enhanced Th1 response and crypt cell hyperplasia. This is associated with enhanced phosphorylation of STAT1, STAT3, and Fyn, a Src homology tyrosine kinase, which interacts with both TCR and IFN-alpha signal components. Together these data indicate that IFN-alpha can facilitate activation of Th1-reactive cells in the gut and drive immunopathology.European Journal of Immunology 08/2001; 31(8):2247-55. DOI:10.1002/1521-4141(200108)31:8<2247::AID-IMMU2247>3.0.CO;2-4 · 4.52 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: STAT1 must be phosphorylated on serine 727 to be fully active in transcription. We show that phosphatidylinositol 3-kinase (PI3K) and its effector kinase Akt play an important role in the serine phosphorylation of STAT1 and in the activation of gene expression in response to interferon-gamma (IFN gamma). IFN gamma activates PI3K as well as Akt in a variety of cell lines. Specific inhibition of PI3K abrogates IFN gamma-induced, but not interleukin-1- or tumor necrosis factor-alpha-induced, phosphorylation of STAT1 on serine and reduces STAT1-dependent transcription and gene expression by approximately 7-fold. Constitutively active forms of PI3K or Akt activate and their dominant-negative derivatives inhibit STAT1-driven transactivation in response to IFN gamma. In addition to PI3K and Akt, JAK1, JAK2, and the tyrosine 440 STAT1 docking residue of IFNGR1 are required for STAT1 to be phosphorylated on serine. Taken together, these results suggest that the following events lead to the activation of STAT1 upon IFN gamma stimulation: 1) PI3K and Akt are activated by the occupied receptor and Tyr-440 is phosphorylated by the activated JAKs; 2) STAT1 docks to Tyr-440; and 3) Tyr-701 is phosphorylated by the JAKs and Ser-727 is phosphorylated by a kinase downstream of Akt.Journal of Biological Chemistry 10/2001; 276(36):33361-8. DOI:10.1074/jbc.M105070200 · 4.60 Impact Factor