Jeong Mi An

Xanthorrhizol induces apoptosis through ROS-mediated MAPK activation in human oral squamous cell carcinoma cells and inhibits DMBA-induced oral carcinogenesis in hamsters

Xanthorrhizol, a natural sesquiterpenoid compound isolated from Curcuma xanthorrhiza Roxb, has been known to inhibit the growth of human colon, breast, liver and cervical cancer cells. In this study, xanthorrhizol decreased cell viability, induced apoptosis and decreased the level of full‐length PARP in SCC‐15 oral squamous cell carcinoma (OSCC) cells. A decrease in cell viability and PARP degradation was not prevented by treatment with the caspase inhibitor Z‐VAD‐fmk in xanthorrhizol‐treated cells. Xanthorrhizol treatment elevated intracellular Ca2+ and ROS levels in SCC‐15 cells. Treatment with a Ca2+ chelator, EGTA/AM, did not affect xanthorrhizol‐ induced cytotoxicity, but cell viability was partly recovered by treatment with endogenous antioxidant, GSH, or hydroxy radical trapper, MCI‐186. Furthermore, the viability of xanthorrhizol‐treated SCC‐15 cells was significantly restored by treatment with SB203580 and/or SP600125 but not significantly by PD98059 treatment. Xanthorrhizol‐induced activation of p38 MAPK and JNK was blocked by MCI‐186. Finally, xanthorrhizol suppressed the number of tumors in buccal pouches and increased the survival rate in hamsters treated with 7,12‐dimethylbenz[a]anthracene. In conclusion, xanthorrhizol may induce caspase‐independent apoptosis through ROS‐mediated p38 MAPK and JNK activation in SCC‐15 OSCC cells and prevent chemical‐induced oral carcinogenesis. Therefore, xanthorrhizol seems to be a promising chemopreventive agent. Copyright

Carmustine induces ERK- and JNK-dependent cell death of neuronally-differentiated PC12 cells via generation of reactive oxygen species

Accumulation of reactive oxygen species (ROS) caused by the inhibition of glutathione reductase (GR) has been proposed as one of the mechanisms responsible for carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU)-induced cytotoxicity. Since mitogen-activated protein kinases (MAPKs) are known to mediate ROS-dependent cell death in multiple cell types, we examined whether redox-sensitive MAPK activation mediated the carmustine-induced cell death of neuronally differentiated PC12 cells. Carmustine induced a concentration- and time-dependent cell death, which was associated with increased caspase-3 activation, a reduction in GR activity accompanied by a concomitant decrease in reduced glutathione levels, and accumulation of ROS. Carmustine-induced caspase-3 activation and cell death were prevented by pretreatment with anti-oxidants or a reducing agent, indicating that carmustine-induced caspase-3 activation and cell death occur via redox-dependent processes. Carmustine induced phosphorylation of the MAPKs, such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. The activation of these kinases was inhibited by pretreatment with N-acetyl-L-cysteine (NAC). Although all the MAPKs were activated by carmustine, only the inhibitors of JNK and ERK prevented carmustine-induced cell death and caspase-3 activation. Our data suggest that carmustine-induced neurotoxicity is, at least in part, due to the activation of ROS-dependent JNK and ERK signaling.

Activation of Rac1-dependent redox signaling is critically involved in staurosporine-induced neurite outgrowth in PC12 cells.

Abstract Staurosporine, a non-specific protein kinase inhibitor, has been shown to induce neurite outgrowth in PC12 cells, but the mechanism by which staurosporine induces neurite outgrowth is still obscure. In the present study, we investigated whether the activation of Rac1 was responsible for the neurite outgrowth triggered by staurosporine. Staurosporine caused rapid neurite outgrowth independent of the ERK signaling pathways. In contrast, neurite outgrowth in response to staurosporine was accompanied by activation of Rac1, and the Rac1 inhibitor NSC23766 attenuated the staurosporine-induced neurite outgrowth in a concentration-dependent manner. In addition, suppression of Rac1 activity by expression of the dominant negative mutant Rac1N17 also blocked the staurosporine-induced morphological differentiation of PC12 cells. Staurosporine caused an activation of NADPH oxidase and increased the production of reactive oxygen species (ROS), which was prevented by NSC23766 and diphenyleneiodonium (DPI), an NADPH oxidase inhibitor. Staurosporine-induced neurite outgrowth was attenuated by pretreatment with DPI and exogenous addition of sublethal concentration of H2O2 accelerated neurite outgrowth triggered by staurosporine. These results indicate that activation of Rac1, which leads to ROS generation, is required for neurite outgrowth induced by staurosporine in PC12 cells.

Staurosporine Mobilizes Ca2+ from Secretory Granules by Inhibiting Protein Kinase C in Rat Submandibular Acinar Cells

Staurosporine was previously shown to mobilize Ca(2+) from the thapsigargin-insensitive Ca(2+) store in rat submandibular acinar cells. However, the nature of the store is not yet known. Therefore, in the present study, the staurosporine-releasable intracellular Ca(2+) store was characterized. Staurosporine increased the cytosolic Ca(2+) concentration ([Ca(2+)](c)) after the inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) store was depleted. Ionomycin caused only small increases in [Ca(2+)](c) after the depletion of the IP(3)-sensitive Ca(2+) store, whereas ionomycin+monensin caused large increases. However, ionomycin+monensin did not increase [Ca(2+)](c) when added after [Ca(2+)](c) was increased by staurosporine, indicating that the acidic Ca(2+) store was the main source of Ca(2+). The acidic Ca(2+) store appeared to be associated with secretory granules, since ionomycin+monensin- and staurosporine-induced [Ca(2+)](c) increases were significantly reduced when the acinar cells were degranulated. The effect of staurosporine on [Ca(2+)](c) was mimicked by other protein kinase C inhibitors. Therefore, we conclude that staurosporine mobilizes Ca(2+) from secretory granules, probably through the inhibition of protein kinase C in rat submandibular acinar cells.

Neuroprotective effect of 3-morpholinosydnonimine against Zn2+-induced PC12 cell death

Excessive intracellular accumulation of zinc (Zn(2+)) is neurotoxic and contributes to a number of neuropathological conditions. Here, we investigated the protective effect of 3-morpholinosydnonimine (SIN-1) against Zn(2+)-induced neuronal cell death in differentiated PC12 cells. We found that Zn(2+)-induced PC12 cell death was reduced in a concentration-dependent manner by pretreatment with SIN-1. The intracellular accumulation of Zn(2+) was not affected by pretreatment with SIN-1, indicating that SIN-1-induced neuroprotection was not attributable to reduced influx of Zn(2+) into cells. SIN-1C, the stable decomposition product of SIN-1, failed to prevent Zn(2+)-induced cell death. Furthermore, the protective effect of SIN-1 against Zn(2+)-induced PC12 cell death was almost completely abolished by uric acid, a free radical scavenger, suggesting that reactive oxygen and nitrogen species generated by SIN-1 may contribute to the protective effect. SIN-1 prevented the inactivation of glutathione reductase (GR) and the increase in the ratio of oxidized glutathione/total glutathione (GSSG/total GSH) induced by Zn(2+). Addition of membrane permeable GSH ethyl ester (GSH-EE) to PC12 cells prior to Zn(2+) treatment significantly increased cell viability. We therefore conclude that SIN-1 may exert neuroprotective effect against Zn(2+)-induced cell death in differentiated PC12 cells by preventing inhibition of GR and increase in GSSG/total GSH ratio.