Bmi1 regulates memory CD4 T cell survival via repression of the Noxa gene

The maintenance of memory T cells is central to the establishment of immunological memory, although molecular details of the process are poorly understood. In the absence of the polycomb group (PcG) gene Bmi1, the number of memory CD4+ T helper (Th)1/Th2 cells was reduced significantly. Enhanced cell death of Bmi1−/− memory Th2 cells was observed both in vivo and in vitro. Among various proapoptotic genes that are regulated by Bmi1, the expression of proapoptotic BH3-only protein Noxa was increased in Bmi1−/− effector Th1/Th2 cells. The generation of memory Th2 cells was restored by the deletion of Noxa, but not by Ink4a and Arf. Direct binding of Bmi1 to the Noxa gene locus was accompanied by histone H3-K27 methylation. The recruitment of other PcG gene products and Dnmt1 to the Noxa gene was highly dependent on the expression of Bmi1. In addition, Bmi1 was required for DNA CpG methylation of the Noxa gene. Moreover, memory Th2-dependent airway inflammation was attenuated substantially in the absence of Bmi1. Thus, Bmi1 controls memory CD4+ Th1/Th2 cell survival and function through the direct repression of the Noxa gene

(A) Enforced expression of Noxa-induced cell death in effector Th2 cells after cytokine depletion

Effector Th2 cells infected with a –containing retrovirus were cultured in vitro for 24 h without cytokines. hNGFR profiles (left) and annexin V staining profiles of the electronically gated hNGFR (gate #2) and hNGFR (gate #1) populations are shown. Three independent experiments were performed with similar results. (B) KJ1 effector Th2 cells infected with –containing retrovirus were transferred into BALB/c mice. 5 wk later, memory Th2 cell generation was determined by KJ1/EGFP expression. Expression of EGFP in pretransferred effector Th2 cells (top left) and a typical KJ1/GFP profile of freshly prepared memory Th2 cells (top right) are shown. In the bottom panels, the percentages of KJ1 cells and GFP Noxa-overexpressing cells and the mean fluorescence intensity of the GFP cells are shown with standard deviations ( = 4). The experiments were performed twice with similar results. (C) The effector Th2 cells from /, /, and / mice (Ly5.2) were transferred into Ly5.1 host mice, and the number of Ly5.2 memory Th2 cells was determined. A typical staining pattern of CD4/Ly5.2 (top) and the percentages of Ly5.2 cells among CD4 T cells are shown with standard deviations ( = 5; bottom). Three independent experiments were performed with similar results. (D) Deletion of the gene enhanced the generation of memory Th2 cells. In vitro–generated effector Th2 cells (Ly5.2) were transferred into Ly5.1 host mice. 5 wk after cell transfer, the number of Ly5.2 memory Th2 cells was determined. A representative CD4/Ly5.2 profile (left) and the mean values with standard deviations ( = 5; right) are shown. The experiments were performed twice with similar results.<p><b>Copyright information:</b></p><p>Taken from "Bmi1 regulates memory CD4 T cell survival via repression of the gene"</p><p></p><p>The Journal of Experimental Medicine 2008;205(5):1109-1120.</p><p>Published online 12 May 2008</p><p>PMCID:PMC2373843.</p><p></p

(A) mRNA expression of and p53-related proapoptotic genes in effector Th2 cells was determined by quantitative RT-PCR

The relative intensity (/HPRT; mean of three samples) is shown with standard deviations. Three independent experiments were performed with similar results. (B) mRNA expression of , p53-related proapoptotic genes, and antiapoptotic genes in memory Th2 cells was analyzed. The relative intensity (/HPRT; mean of three samples) is shown with standard deviations. Two independent experiments were performed with similar results. (C) Effects on p16 and p19 deficiency on the memory Th2 cell generation. The effector Th2 cells from the indicated mice (Ly5.2 background) were transferred into Ly5.1 host mice. 5 wk after cell transfer, the number of Ly5.2 memory Th2 cells was determined. The mean values are shown with standard deviations ( = 5; right). The experiments were performed twice with similar results. (D) mRNA levels of proapoptotic genes in // effector Th2 cells were determined by quantitative RT-PCR. The relative intensity (/HPRT; mean of three samples) is shown with standard deviations. The experiments were performed twice with similar results.<p><b>Copyright information:</b></p><p>Taken from "Bmi1 regulates memory CD4 T cell survival via repression of the gene"</p><p></p><p>The Journal of Experimental Medicine 2008;205(5):1109-1120.</p><p>Published online 12 May 2008</p><p>PMCID:PMC2373843.</p><p></p