A Constitutively Active Arylhydrocarbon Receptor Induces Growth Inhibition of Jurkat T Cells through Changes in the Expression of Genes Related to Apoptosis and Cell Cycle Arrest

Abstract

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to suppress T cell-dependent immune reactions through the activation of the arylhydrocarbon receptor (AhR).Our previous findings suggest that TCDD inhibits the activation and subsequent expansion of T cells following antigen stimulation in mice, leading to a decreased level of T cell-derived cytokines involved in antibody production. In the present study, we investigated the effects of activated AhR on T cells by transiently expressing a constitutively active AhR (CA-AhR) mutant in AhR-null Jurkat T cells. In agreement with our previous findings, CA-AhR markedly inhibited the growth of Jurkat T cells. The inhibited cell growth was found to be concomitant with both an increase in the annexin V-positive apoptotic cells and the accumulation of cells in the G 1 phase. The growth inhibition was also shown to be mediated by both xenobiotic response element (XRE)-dependent and -independent mechanisms, because an A78D mutant of the CA-AhR, which lacks the ability of XRE-dependent transcription, partially inhibited the growth of Jurkat T cells. Furthermore, we demonstrated that CA-AhR induces expression changes in genes related to apoptosis and cell cycle arrest. These expression changes were shown to be solely mediated in an XREdependent manner, because the A78D mutant of the CAAhR did not induce them. To summarize, these results suggest that AhR activation causes apoptosis and cell cycle arrest, especially through expression changes in genes related to apoptosis and cell cycle arrest by the XRE-dependent mechanism, leading to the inhibition of T cell growth.

Possible involvement of arylhydrocarbon receptor variants in TCDD-induced thymic atrophy and XRE-dependent transcriptional activity in Wistar Hannover GALAS rats

“…Second, being consistent with the effects of TCDD on T cells in the etiology of thymic atrophy shown in previous in vivo studies (Kamath et al, 1997;Laiosa et al, 2003), Jurkat T cells having constitutively active AhR showed cell cycle arrest and apoptosis (Ito et al, 2004). Third, the suppression of the growth of Jurkat T cells having constitutively active AhR has been shown to be caused by both XRE-dependent and XRE-independent mechanisms (Ito et al, 2004). In contrast to our expectation based on in vivo of Jurkat T cells to the AhR variants although the variants decreased the percentage of GFP-positive cells (Fig.6).…”

“…First, previous studies using knock-out, chimeric and transgenic mice showed that thymic T cells are the main target of TCDD to induce thymic atrophy (Laiosa et al, 2003;Nohara et al, 2005;Staples et al, 1998). Second, being consistent with the effects of TCDD on T cells in the etiology of thymic atrophy shown in previous in vivo studies (Kamath et al, 1997;Laiosa et al, 2003), Jurkat T cells having constitutively active AhR showed cell cycle arrest and apoptosis (Ito et al, 2004). Third, the suppression of the growth of Jurkat T cells having constitutively active AhR has been shown to be caused by both XRE-dependent and XRE-independent mechanisms (Ito et al, 2004).…”

“…11.3 ± 0. we used Jurkat T cells is that the exogenously introduced constitutively-active AhR suppresses the growth of the cells through apoptosis and cell cycle arrest (Ito et al, 2004), the observation of which is similar to the one in TCDD-exposed mice in vivo (Kamath et al, 1997;Laiosa et al, 2003).…”

“…To determine whether and how the AhR structure mediates TCDD actions on human T cell growth, Jurkat T cells (1 × 10 5 cells) were transiently cotransfected with 1.5 μg of pEB6-CAG-hrGFP and 3 μg of either of the four pEB6-CAG-AhR variants using the TransITJurkat Transfection Reagent (Mirus, Madison, WI, USA) according to manufacturer's instructions (Ito et al, 2004). They were cultured for 48 hr, followed by further maintenance in a medium containing 10 nM TCDD for 96 hr.…”

Aryl hydrocarbon receptor inhibition downregulates the TGF-β/Smad pathway in human glioblastoma cells

“…Stable AhR transfectants were obtained by transfection using pCA-Ahr/cytomegalovirus (CMV) 4 (McGuire et al, 2001). Expression of the CA-AhR construct was verified by PCR with specific primers (Ito et al, 2004).…”