Suppressor of Cytokine Signaling 3 Regulates Proliferation and Activation of T-helper Cells

Cheng-Rong Yu,Rashid M Mahdi,Samuel Ebong,Barbara P Vistica,Igal Gery,Charles E Egwuagu

doi:10.1074/jbc.m300489200

Cheng-Rong Yu, Rashid M Mahdi + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m300489200

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Abstract

Suppressors of cytokine signaling (SOCS) have been implicated in regulation of T-cell activation and cytokine-mediated differentiation of T-helper cells. In this study we have characterized the pattern of SOCS expression in naïve and activated primary T-helper cells, examined whether expression of SOCS genes is regulated by cytokine or T-cell receptor signaling, and analyzed the function of SOCS in differentiated T-cells. We show that SOCS1, SOCS2, SOCS3, CIS (cytokine-induced SH2 protein) genes are constitutively expressed in naïve T-helper cells, with SOCS3 being the most abundant. Antigen stimulation of naïve T-helper cells down-regulates SOCS3 expression and concomitantly up-regulates SOCS1, SOCS2, and CIS gene transcription, suggesting that SOCS genes are regulated differentially by T-cell activation. Down-regulation of SOCS3 expression is subsequently followed by gradual increase in SOCS3 level and corresponding decline in interleukin 2 (IL-2) secretion. In fact, SOCS3 mRNA levels are inversely correlated with the amount of IL-2 secretion and proliferative responses of differentiating T-helper cells, suggesting mutually antagonistic effects of SOCS3 and IL-2 and feedback regulation of T-cell activation by SOCS3. Furthermore, the degree of SOCS3 inhibition is antigen concentration-dependent and is mediated in part by growth factor independence-1, a T-cell transcription factor that regulates S-phase entry in T-cells. Forced overexpression of SOCS3 inhibits proliferation of T-helper cells, whereas depletion of endogenous SOCS3 by antisense SOCS3 cDNA enhances T-cell receptor- and cytokine-induced proliferation. Taken together, these results suggest a role for SOCS3 in maintaining T-helper cells in a quiescent state. Transient inhibition of SOCS3 by antigen stimulation may therefore be essential in allowing activation of resting T-cells.

Highlights

Suppressors of cytokine signaling (SOCS) are a newly described family of intracellular cytokineinducible negative feedback regulators that target cytokine receptors and cytoplasmic signaling adaptor molecules [6, 7]
SOCS Genes Are Regulated Differentially by T-helper Cell Activation—We examined effects of TCR signaling on regulation of SOCS gene expression in naıve and activated T-helper cells from hen egg lysozyme (HEL) TCR transgenic (3A9) mice
We show here by real-time quantitative 5Ј-nuclease fluorogenic RT-PCR analysis that SOCS1, SOCS2, SOCS3, and CIS mRNAs are constitutively expressed in naıve T-helper cells (Fig. 1A, see Day 0), with SOCS3 being the most abundant SOCS member detected (Fig. 1A)

Summary

The abbreviations used are

T-helper; Ag, antigen; HEL, hen egg lysozyme; SOCS, suppressor of cytokine signaling; CIS, cytokine-induced Src homology 2 protein; Gfi-1, growth factor independence-1; IFN␥, interferon ␥; IL, interleukin; APC, antigen presenting cell; Ab, antibody; RT, reverse transcriptase; TK, thymidine kinase; TCR, T-cell receptor. We sought to determine whether transcription of SOCS genes is regulated by TCR in primary responses of naıve T-helper cells. An early event in the activation of naıve T-helper cell is a transient down-regulation of SOCS3, and the degree of SOCS3 inhibition is inversely correlated with the levels of T-cell proliferation and IL-2 secretion. We further show that the transient down-regulation of SOCS3 may be mediated in part by increased expression of Gfi-1, a positive regulator of T-cell proliferation, and a suppressor of SOCS genes transcription [19, 20]. Overexpression of SOCS3 in Th2 cells inhibits T-cell proliferation whereas depletion of endogenous SOCS3 enhances proliferation These results suggest that SOCS3 may function in concert with other proteins to maintain quiescent state in lymphocytes, and transient inhibition of SOCS3 expression may be essential to allow resting T-cells to respond to growth signals and proliferate

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DISCUSSION