Different mechanisms for suppression of apoptosis by cytokines and calcium mobilizing compounds

Overexpression of wild-type p53 in M1 myeloid leukemia cells induces apoptotic cell death that was suppressed by the calcium ionophore A23187 and the calcium ATPase inhibitor thapsigargin (TG). This suppression of apoptosis by A23187 or TG was associated with suppression of caspase activation but not with suppression of wild-type-p53-induced expression of WAF-1, mdm-2, or FAS. In contrast to suppression of apoptosis by the cytokines interleukin 6 (IL-6) and interferon γ, a protease inhibitor, or an antioxidant, suppression of apoptosis by A23187 or TG required extracellular Ca2+ and was specifically abolished by the calcineurin inhibitor cyclosporin A. IL-6 induced immediate early activation of junB and zif/268 (Egr-1) but A23187 and TG did not. A23187 and TG also suppressed induction of apoptosis by doxorubicin or vincristine in M1 cells that did not express p53 by a cyclosporin A-sensitive mechanism. Suppression of apoptosis by A23187 or TG was not associated with autocrine production of IL-6. Apoptosis induced in IL-6-primed M1 cells after IL-6 withdrawal was not suppressed by A23187 or TG but was suppressed by the cytokines IL-6, IL-3, or interferon γ. The results indicate that these Ca2+-mobilizing compounds can suppress some pathways of apoptosis suppressed by cytokines but do so by a different mechanism.

Stimulation of ionotropic glutamate receptors activates transcription factor NF-kappa B in primary neurons.

L-Glutamate is the most common excitatory neurotransmitter in the brain and plays a crucial role in neuronal plasticity as well as in neurotoxicity. While a large body of literature describes the induction of immediate-early genes, including c-fos, fosB, c-jun, junB, zif/268, and krox genes by glutamate and agonists in neurons, very little is known about preexisting transcription factors controlling the induction of such genes. This prompted us to investigate whether stimulation of glutamate receptors can activate NF-kappa B, which is present in neurons in either inducible or constitutive form. Here we report that brief treatments with kainate or high potassium strongly activated NF-kappa B in granule cells from rat cerebellum. This was detected at the single cell level by immunostaining with a monoclonal antibody that selectively reacts with the transcriptionally active, nuclear form of NF-kappa B p65. The activation of NF-kappa B could be blocked with the antioxidant pyrrolidine dithiocarbamate, suggesting the involvement of reactive oxygen intermediates. The data may explain the kainate-induced cell surface expression of major histocompatibility complex class I molecules, which are encoded by genes known to be controlled by NF-kappa B. Moreover, NF-kappa B activity was found to change dramatically in neurons during development of the cerebellum between days 5 and 7 after birth.