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. 2009 Jan 16;206(1):51-9.
doi: 10.1084/jem.20081242. Epub 2009 Jan 12.

Runx3 and T-box proteins cooperate to establish the transcriptional program of effector CTLs

Fernando Cruz-Guilloty  1 , Matthew E Pipkin, Ivana M Djuretic, Ditsa Levanon, Joseph Lotem, Mathias G Lichtenheld, Yoram Groner, Anjana Rao
Affiliations

Runx3 and T-box proteins cooperate to establish the transcriptional program of effector CTLs

Fernando Cruz-Guilloty et al. J Exp Med. .

Abstract

Activation of naive CD8(+) T cells with antigen induces their differentiation into effector cytolytic T lymphocytes (CTLs). CTLs lyse infected or aberrant target cells by exocytosis of lytic granules containing the pore-forming protein perforin and a family of proteases termed granzymes. We show that effector CTL differentiation occurs in two sequential phases in vitro, characterized by early induction of T-bet and late induction of Eomesodermin (Eomes), T-box transcription factors that regulate the early and late phases of interferon (IFN) gamma expression, respectively. In addition, we demonstrate a critical role for the transcription factor Runx3 in CTL differentiation. Runx3 regulates Eomes expression as well as expression of three cardinal markers of the effector CTL program: IFN-gamma, perforin, and granzyme B. Our data point to the existence of an elaborate transcriptional network in which Runx3 initially induces and then cooperates with T-box transcription factors to regulate gene transcription in differentiating CTLs.

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Figures

Figure 1.
Figure 1.
Kinetics of gene expression during CD8+ T cell differentiation. (A) Kinetics of Prf1, Gzmb, Tbx21 (T-bet), and Eomes mRNA expression in differentiating P14 CD8+ T cells analyzed by Northern blotting. RNA from day 7 Th1 cells was used as a control. Sizes of mRNA transcripts are indicated. (B) Quantification of relative mRNA amounts by phosphorimager analysis. (C) Kinetics of protein expression in differentiating P14 CD8+ T cells analyzed by immunoblotting. Sizes of protein bands are indicated. (D) Relative protein amounts quantified from the Western blots. (E) Intracellular staining for granzyme B, IFN-γ, and TNF. Granzyme B staining was specific relative to an isotype control (not depicted). Cells were restimulated with PMA and ionomycin for 4 h. (F) FACS-based assay to measure cytolytic activity of P14 CD8+ T cells against EL4 targets loaded with 0 (−) or 1 (+) μM Gp33 peptide (effector-to-target ratio = 5:1). Percentage of Annexin V+ (apoptotic) target cells in the CD8-negative EL4 target population (dot plots) was determined (histograms). Cytolytic activity was blocked by incubation with 2 mM EGTA (not depicted), confirming involvement of the granule exocytosis (perforin–granzyme B) pathway. Data are representative of at least five (A–E) or three (F) independent experiments.
Figure 2.
Figure 2.
Regulation of perforin, granzyme B, and IFN-γ expression by T-bet and Eomes in differentiating CTLs. (A) IFN-γ expression by WT (Tbx21+/+) and T-bet–deficient (Tbx21−/−) T cells. Naive CD8+ T cells, or cells activated and cultured for 4 or 6 d, were restimulated with PMA and ionomycin for 6 h, and IFN-γ expression was assessed by intracellular staining. Numbers show the percentage of IFN-γ+ cells. (B) Northern blot analysis of Prf1 and GzmB mRNA expression in WT or T-bet–deficient CD8+ T cells activated and either left uninfected (uninf) or transduced with retroviruses expressing Eomes-VP16 (Eo-VP16) or an empty IRES-GFP cassette (GFP). Total cellular RNA was analyzed on day 6 of culture. The frequency of transduced cells in the cultures was equivalent for both constructs (∼65–70% GFP+ cells; not depicted). (C) Granzyme B and IFN-γ expression by Tbx21+/+ and Tbx21−/− T cells analyzed in restimulated cells that had been cultured for 5 d. (D) IFN-γ production by cells transduced with Eo-VP16 or control (GFP) retroviruses (RV) measured on day 4 after 6 h of restimulation with PMA and ionomycin. Numbers show the percentage of GFP+ IFN-γ+ cells. Results are representative of three (A and C) or two (B and D) independent experiments.
Figure 3.
Figure 3.
Key role for Runx3 in effector CTL differentiation. (A) Western analysis of Runx3, Eomes, T-bet, and perforin expression in Runx3+/+ versus Runx3−/− CD8+ SP T cells differentiated for 6 d. β-Actin was used as a loading control. (B) Northern blot analysis of Prf1 mRNA expression in Runx3+/+ versus Runx3−/− CD8+ T cells differentiated for 6 d. β–Actin was used as a loading control. (C) Expression of granzyme B, IFN-γ, TNF, and IL-2 by resting or restimulated (6 h) Runx3+/+ versus Runx3−/− CD8+ SP T cells differentiated for 6 d. The vertical gray line indicates the granzyme B MFI for WT GFP+ cells. Results in A–C are representative of two independent experiments. (D) ChIP analysis of binding of endogenous Runx3 and Eomes to the Prf1 locus. Enrichment of the indicated genomic regions was evaluated by real-time PCR of DNA from immunoprecipitated and input chromatin. The data are the means of duplicate measurements from two chromatin preparations from two independent CD8+ T cell differentiations. The efficiency of recovery of input for the −1-kb region of Prf1 was 0.97% for the Runx3 ChIP and 0.5% for the Eomes ChIP.
Figure 4.
Figure 4.
Runx3 controls Eomes, perforin, granzyme B, and IFN-γ expression in effector CTLs. Runx3+/+ or Runx3−/− CD8+ T cells were activated and transduced with retroviruses bearing an empty IRES-GFP cassette (GFP) or also encoding Eomes-VP16 (Eo-VP16) or Myc-Runx3 (Runx3). The frequency of transduced cells in the cultures was equivalent for all constructs (∼75–90% GFP+ cells; not depicted). (A) Protein expression in whole-cell extracts (day 6) was analyzed by immunoblotting. Overexpression of Eomes-VP16 cannot be detected with the Eomes antibody, as the C-terminal epitope is within the region that has been replaced with the VP16 transactivation domain. (B) Expression of granzyme B and IFN-γ after culture for 6 d and restimulation for 4 h with PMA and ionomycin was determined by intracellular staining. The percentage of positively stained cells is shown above the gate; the mean fluorescence intensity (MFI) of granzyme B staining for the total population is shown below the gate. The vertical gray lines indicate the MFI for WT GFP+ cells. Results are representative of at least two independent experiments. (C) Schematic diagram of the transcriptional network involving Runx3 and T-box factors. T-bet is induced by TCR signals and is essential for early IFN-γ expression. Runx3 is present in naive CD8+ T cells and represses Runx1 and induces Eomes, perforin, granzyme B, and IFN-γ expression. Eomes may participate in sustaining late IFN-γ expression, whereas Runx3 and Eomes (but not T-bet) may cooperate to activate perforin expression. The dotted line indicates the partial effect of T-bet deficiency on Gzmb mRNA but not granzyme B protein expression.
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