The NF-κB Cascade Is Important in Bcl-xL Expression and for the Anti-Apoptotic Effects of the CD28 Receptor in Primary Human CD4+ Lymphocytes

Abstract

We explored the role of the NF-κB pathway in the survival of primary human CD4+ T lymphocytes during CD28 costimulation. Transduction of proliferating CD4+ T cells with a tetracycline-regulated retrovirus encoding for a dominant-interfering, degradation-resistant I-κBα (inhibitor of κBα factor) mutant induced apoptosis. Using DNA arrays, we show that Bcl-xL features as a prominent anti-apoptotic member among a number of early CD28-inducible genes. A 1.2-kb segment of the proximal Bcl-xL promoter, linked to a luciferase reporter, responded to CD3/CD28 stimulation in Jurkat cells. Mutation of an NF-κB site around −840 decreased, while ectopic expression of I-κB kinase-β (IKKβ) enhanced reporter gene activity. Na+-salicylate and cyclopentenone PGs, direct inhibitors of IKKβ, interfered in the activation of the Bcl-xL promoter and induced apoptosis in CD28-costimulated CD4+ T cells. Moreover, salicylate blocked nuclear localization of NF-κB factors that bind to the NF-κB binding site in the Bcl-xL promoter, as well as the expression of Bcl-xL protein. HuT-78, a lymphoblastoid T cell line with constitutive NF-κB activity, contained elevated levels of Bcl-xL protein and, similar to proliferating CD4+ T cells, was resistant to apoptotic stimuli such as anti-Fas and TNF-α. In contrast, the same stimuli readily induced apoptosis in a Jurkat T cell clone with no detectable Bcl-xL expression. Jurkat BMS2 cells also differed from HuT-78 in collapse of mitochondrial membrane potential and superoxide generation in the mitochondrium. Taken together, these data demonstrate that CD3/CD28-induced activation of IKKβ and expression of Bcl-xL promote the survival of primary human CD4+ T lymphocytes.

Nuclear Factor-κB Activation: A Question of Life or Death

“…The NF-κB cascade is important in the Bcl-xL expression and for the anti-apoptotic effects of the CD28 receptor in primary human CD4 + lymphocytes (Khoshnan et al, 2000). HuT-78, a lymphoblastoid T cell line with constitutive NF-κB activity, contains elevated levels of the Bcl-xL protein and, similar to the proliferating CD4 + T cells, is resistant to apoptotic stimuli such as anti-Fas and TNFα.…”

“…A large number of reports have demonstrated the anti-apoptotic effect of NF-κB in a wide variety of cell types. The protective role of NF-κB is shown in a large variety of cell types, including the human breast carcinoma (Liu et al, 1996) , T cells (Van Antwerp et al, 1996;Chu et al, 1997;Khoshnan et al, 2000), fibroblasts and macrophages (Beg and Baltimore, 1996), endothelial cells (Stehlik et al, 1998), EBV-infected lymphoblastoid cells (Asso-bonnet et al, 1998), non-small lung cancer cells , glomerular mesangial cells (Sugiyama et al, 1999), human ovarian cancer cells (Shao et al, 1997), human pancreatic cancer cell lines (Kajino et al, 2000), Ewing sarcoma cells (Javelaud and Besancon, 2001), cardiomyocytes (Bergmann et al, 2001), mouse embryos , and HT1080 fibrosarcoma . Treatment of RelA-deficient (the transcriptionally active subunit of NF-κB) mouse fibroblasts and macrophages with TNF significantly reduced cell viability, whereas RelA +/+ cells were unaffected.…”

PACS-2 mediates the ATM and NF-κB-dependent induction of anti-apoptotic Bcl-xL in response to DNA damage

“…11,12 Consistent with this model, pharmacologic inhibition of NF-κB signaling in primary thymocytes and cancer cell lines blocks Bcl-xL induction and increases cell death in response to treatment with apoptosis-inducing antibodies or exposure to DNA damage. 13,14 The canonical pathway of NF-κB activation starts with the binding of ligands, such as tumor necrosis factor-α (TNFα) or LPS, to their cognate cell surface receptors. This binding sets forth a series of intracellular signaling events leading to IκK complex activation and subsequent NF-κB activation.…”

RelA/NF-κB recruitment on the bax gene promoter antagonizes p73-dependent apoptosis in costimulated T cells

“…RelA/NF-kB acts as a key prosurvival factor by regulating the expression of antiapoptotic genes of the Bcl-2 family, in particular A1/Bfl-1 and bcl-xL. However, Bcl-xL upregulation promotes T-cell survival 28 but does not protect T cells from activation-induced cell death (AICD). 29,30 TCR-AICD has been recently described to depend on both E2F-1 and p73 14 and NF-kB may counteract TCR-driven apoptosis by inhibiting p73 expression.…”

“…20,21 CD28 is an important regulator of T-cell survival by inducing the expression of antiapoptotic proteins, in particular of Bcl-xL. 28 Data from Bcl-xL-deficient mice indicate that Bcl-xL is essential for the survival of double-positive thymocyte but not mature T lymphocytes. 32 We have recently demonstrated that CD28 stimulation, in the absence of TCR, protects primary T cells from IR-mediated apoptosis by inducing RelA-dependent transcription of bcl-xL.…”