Cytokine-induced cell death in immortalized Schwann cells: roles of nitric oxide and cyclic AMP

Tumor necrosis factor-alpha and interferon-gamma are pleiotropic cytokines that regulate Schwann cell responses during injury and inflammatory demyelination. We have previously shown that cyclic AMP (cAMP)-elevating agents decrease the demyelination and Wallerian degeneration in experimental allergic neuritis. In this study, we examined the role of cAMP in cytokine-mediated signaling in a spontaneously immortal Schwann cell clone (iSC). We found that tumor necrosis factor-alpha and interferon-gamma exert synergistic inhibitory action on Schwann cell viability via the production of nitric oxide (NO) and ceramide (cer). Furthermore, we found that: (i) NO synthase inhibitors attenuate the cytokine-induced cer accumulation and cell death indicating that NO acts upstream of cer; and (ii) cytokine-induced cell death is decreased in iSCs pretreated continuously for 48-72 h with forskolin, an activator of adenylate cyclase. Although forskolin modulates the phosphorylation of ERKs and Akt, it decreases the susceptibility of iSC to cytokines via a separate mechanism operating after NO induction and before cer accumulation. We propose that the protective effect of cAMP-elevating agents in experimental allergic neuritis may be mediated in part via modulation of Schwann cell responses to cytokines.     

High-Resolution Cryo-EM Structure of the Cardiac Actomyosin Complex

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Repair of 3-methyladenine and 7-methylguanine in nuclear DNA of Chlamydomonas: Requirement for protein synthesis

The removal of 3-methyladenine and 7-methylguanine from nuclear DNA was determined following exposure of Chlamydomonas reinhardi to methyl methanesulfonate (MMS). The amount of 3-methyladenine in DNA was determined using an extract from Micrococcus luteus that has a 3-methyladenine-DNA glycosylase. The amount of 7-methylguanine was estimated by heating the DNA for 30 min at 70° followed by alkaline hydrolysis of the resulting apurinic sites. The molecular weight of the DNA was determined using alkaline sucrose gradients. The 3-methyladenine is removed with a half-life of 2–3 h whereas the 7-methylaguanine is removed with a half-life of 10–12 h. The rate of removal of the 7-methylguanine is more than an order of magnitude faster than the estimated non-enzymatic hydrolysis rate indicating the probability of enzymatic repair. Addition of cycloheximide immediately after MMS treatment inhibits the removal of 3-methyladenine and 7-methylguanine from DNA. If cycloheximide is added 1.5 h after treatment with MMS, there is much less inhibition of the removal of 3-methyladenine. These results are interpreted to mean that MMS induces the synthesis of 1 or more proteins that are required for the repair of 3-methyladenine from Chlamydomonas DNA.