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Interleukin (IL)-6 has been shown to protect neuronal cells from cell death induced by various stimulants. Although neuronal cells including PC12 cells were shown to produce IL-6, little is known about the effects of dopaminergic neurotoxins, 1,2,3,4-tetrahydroisoquinoline (TIQ) and 1-methyl-4-phenylpyridinium ion (MPP(+)), on IL-6 expression in PC12 cells. In the present study, we investigated the role of IL-6 in the TIQ- and MPP(+)-induced cell death in PC12 cells. Treatment with 3.2 mM TIQ for 24 h caused a delayed cell death (lactate dehydrogenase (LDH) leakage and nuclear DNA fragmentation) markedly 72 h after the addition. Addition of 0.4 mM MPP(+) caused LDH leakage and nuclear DNA fragmentation 24 h after the addition. The cell death induced by MPP(+) was inhibited by an inhibitor of caspases, z-Val-Ala-Asp(OMe)-fluoromethylketone. The cell death induced by TIQ or MPP(+) was inhibited by nerve growth factor and 10% serum and significantly enhanced by the treatment with anti-IL-6 antibody. Both neurotoxins decreased the IL-6 mRNA level in PC12 cells without changing the other tested mRNA levels (IL-1 alpha, beta-actin, etc.). These findings suggest that dopaminergic neurotoxins cause cell death in PC12 cells at least partially by changing IL-6 expression.

Arachidonic acid and nitric oxide (NO) act as retrograde and intercellular messengers in the nervous system. Regulation of cyclooxygenase is well established, but regulation of phospholipase A 2 , the enzyme responsible for the liberation of arachidonic acid, by NO has not been thoroughly investigated. Using the PC12 cell line as a neuronal model, we studied the effects of exogenous NO compounds on arachidonic acid release. Incubation with Ca 2+ ionophores or mastoparan (wasp venom peptide) stimulated [ 3 H]arachidonic acid release from prelabeled PC12 cells. [ 3 H]Arachidonic acid release was inhibited by cytosolic phospholipase A 2 inhibitors, but not by dithiothreitol. A cytosolic phospholipase A 2 protein band with a molecular mass of ∼100 kDa was detected by immunoblotting. S -Nitroso-cysteine inhibited basal and stimulated [ 3 H]arachidonic acid release in concentration-dependent manners. Other NO compounds such as sodium nitroprusside and S -nitroso- N -acetylpenicillamine did not affect [ 3 H]arachidonic acid release. N -Ethylmaleimide also inhibited [ 3 H]arachidonic acid release. The inhibitory effects of S -nitroso-cysteine and N -ethylmaleimide were irreversible, because [ 3 H]arachidonic acid release from PC12 cells preincubated with S -nitroso-cysteine or N -ethylmaleimide was much lower than that from nontreated cells. These findings suggest (a) cytosolic phospholipase A 2 is activated by Ca 2+ or mastoparan, and inhibited by S -nitroso-cysteine in a cyclic GMP-independent manner, (b) N -ethylmaleimide also inhibits cytosolic phospholipase A 2 and arachidonic acid release in PC12 cells. S -Nitroso-cysteine can regulate the production of other retrograde messenger arachidonic acid.