Smad3 Is Essential for TGF-β1 to Suppress IL-2 Production and TCR-Induced Proliferation, but Not IL-2-Induced Proliferation

Abstract

Transforming growth factor-β1 is essential to maintain T cell homeostasis, as illustrated by multiorgan inflammation in mice deficient in TGF-β1 signaling. Despite the physiological importance, the mechanisms that TGF-β1 uses to regulate T cell expansion remain poorly understood. TGF-β1 signals through transmembrane receptor serine/threonine kinases to activate multiple intracellular effector molecules, including the cytosolic signaling transducers of the Smad protein family. We used Smad3−/− mice to investigate a role for Smad3 in IL-2 production and proliferation in T cells. Targeted disruption of Smad3 abrogated TGF-β1-mediated inhibition of anti-CD3 plus anti-CD28-induced steady state IL-2 mRNA and IL-2 protein production. CFSE labeling demonstrated that TGF-β1 inhibited entry of wild-type anti-CD3 plus anti-CD28-stimulated cells into cycle cell, and this inhibition was greatly attenuated in Smad3−/− T cells. In contrast, disruption of Smad3 did not affect TGF-β1-mediated inhibition of IL-2-induced proliferation. These results demonstrate that TGF-β1 signals through Smad3-dependent and -independent pathways to inhibit T cell proliferation. The inability of TGF-β1 to inhibit TCR-induced proliferation of Smad3−/− T cells suggests that IL-2 is not the primary stimulus driving expansion of anti-CD3 plus anti-CD28-stimulated T cells. Thus, we establish that TGF-β1 signals through multiple pathways to suppress T cell proliferation.

TGF‐β1 production by CD4+CD25+ regulatory T cells is not essential for suppression of intestinal inflammation

“…We first confirmed that while Smad3 -/-CD4 + T cells are as susceptible to suppression by CD4 + CD25 + T cells as WT CD4 + T cells in vitro, they are resistant to the suppressive effects of TGF-b1, as they actively transcribe the IL-2 gene and proliferate following TCR stimulation in the presence of exogenous TGF-b1 (Fig. 4a) [27]. We next analyzed the role for Smad3 in our colitis model.…”

“…A second aspect of our studies was to determine the target cell for the immunosuppressive effects of TGF-b in our model of IBD. We first explored the possibility that TGF-b acts on the CD4 + CD25 + Treg cells themselves, as it has been shown that the production of this cytokine by islet cells during the priming phase of diabetes protects mice from disease and increases the number of intraislet CD4 + CD25 + T cells [27]. Furthermore, CD4 + CD25 + T cells from mice expressing a dominant negative form of TGF-bRII failed to expand in vivo and to suppress dextran sulfate sodium-induced colitis [31].…”

Protein Kinase Cε Regulates Proliferation and Cell Sensitivity to TGF-1β of CD4+ T Lymphocytes: Implications for Hashimoto Thyroiditis

“…Differently from PKCu, the overexpression of PKCε reduced Smad2, but not Smad3, phosphorylation. In line with previous data, demonstrating that both Smad2 and Smad3 contribute to TGF-1b-induced inhibition of IL-2-sustained T cell proliferation (43), it looks reasonable that pSmad2 is downstream PKCε signaling. However, because it is well-known that addition of IL-2 can override the growth arrest of T cells mediated by TGF-1b (10), we cannot exclude that the ability of PKCε to regulate IL-2R expression levels might also explain the increased TGF-1b sensitivity of siRNA PKCε -transfected cells.…”

“…Moreover, it is known that TGF inhibits IL-2 and anti-CD3/CD28-induced T cell proliferation in a Smad3-dependent manner. By contrast, Smad3 is not essential for TGF-1b-mediated inhibition of IL-2-induced T cell proliferation of lymphocytes activated by ConA (43). Looking for TGF-1b signaling intermediates potentially targeted by PKCε, we analyzed pSmad2 and pSmad3 levels in PKCε-overexpressing Jurkat cells and in primary activated CD4 cell cultures treated with TGF-1b for 2 h. Of note, PKCε overexpression significantly reduced TGF-1b-induced pSmad-2 levels in Jurkat cells (Fig.…”

Phosphoantigens Overcome Human TCRVγ9+ γδ Cell Immunosuppression by TGF-β: Relevance for Cancer Immunotherapy

“…We showed above that TGF-b also suppressed the proliferation of gd cells. We propose that TGF-b targets, on the one hand, the endogenous IL-2 production of TCRVg9 + T lymphocytes presumably through blockade of its gene promoter as in ab T lymphocytes (64,65) because exogenous IL-2 partially reversed this blockade. On the other hand, TGF-b inhibited the functions induced by TCR signaling, but this was reversed by increasing doses of PAg stimulus.…”