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

We explored the role of the NF-kappa B 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-kappa B alpha (inhibitor of kappa B alpha factor) mutant induced apoptosis, Using DNA arrays, we show that Bcl-x(L) features as a prominent anti-apoptotic member among a number of early CD28-inducible genes. A 1.2-kb segment of the proximal Bcl-x(L) promoter, linked to a luciferase reporter, responded to CD3/CD28 stimulation in Jurkat cells. Mutation of an NF-kappa B site around -840 decreased, while ectopic expression of I-kappa B kinase-beta (IKK beta) enhanced reporter gene activity. Na+-salicylate and cyclopentenone PGs, direct inhibitors of IKK beta, interfered in the activation of the Bcl-x(L) promoter and induced apoptosis in CD28-costimulated CD4(+) T cells. Moreover, salicylate blocked nuclear localization of NF-kappa B factors that bind to the NF-kappa B binding site in the Bcl-x(L) promoter, as well as the expression of Bcl-x(L) protein. HuT-78, a lymphoblastoid T cell line with constitutive NF-kappa B activity, contained elevated levels of Bcl-x(L) protein and, similar to proliferating CD4(+) T cells, was resistant to apoptotic stimuli such as anti-Fas and TNF-alpha, In contrast, the same stimuli readily induced apoptosis in a Jurkat T cell clone with no detectable Bcl-x(L) 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 IKK beta and expression of Bcl-x(L) promote the survival of primary human CD4+ T lymphocytes.