Hee-Sun Chae

Mitogen‐activated protein kinase/extracellular signal‐regulated kinase attenuates 3‐hydroxykynurenine‐induced neuronal cell death

3‐Hydroxykynurenine (3‐HK), an endogenous tryptophan metabolite, is known to have toxic effects in brain. However, the molecular mechanism of the toxicity has not been well identified. In this study, we investigated the involvement of MAPK/extracellular signal‐regulated kinase (ERK) in the 3‐HK‐induced neuronal cell damage. Our results showed that 3‐HK induced apoptotic neuronal cell death and ERK phosphorylation occurred during cell death. Inhibition of ERK activation using PD98059 considerably increased cell death. Furthermore, cell death was preceded by mitochondrial malfunction including collapse of mitochondrial membrane potential (ΔΨm) and cytochrome c release from mitochondria to the cytosol. Interestingly, inhibition of ERK dramatically increased mitochondrial malfunction, and enhanced caspase activation, resulting in enhanced neuronal cell death. Thus, our results show that ERK plays a protective role by maintaining mitochondrial function and regulating caspase activity under conditions of cellular stress.

P53 mediates ceramide-induced apoptosis in SKN-SH cells

Ceramide induces apoptotic cell death in a dose- and time-dependent manner in neuroblastoma SKN-SH cells. Pretreatment with caspase inhibitors blocks cell death, suggesting that a set of caspase activities including caspase 1, as well as caspase 3, are involved in ceramide-induced apoptosis in SKN-SH cells. Treatment with a caspase inhibitor 3 h after ceramide addition did not inhibit cell death, although caspase activity was substantially reduced. Ceramide-induced apoptosis is accompanied by accumulation of p53 followed by an increase of Bax and decrease of Bcl-2 levels. Inhibition of p53 expression with p53 antisense oligonucleotides inhibits apoptosis and prevents the increase in Bax and decrease in Bcl-2. Furthermore, pretreatment with p53 antisense oligonucleotides markedly inhibits the induction of caspase activity. These results suggest that p53 regulates the ratio Bcl-2/Bax and the expression/activation of caspases during ceramide-induced apoptosis in SKN-SH cells. Caspase inhibition did not alter the expression of p53, Bcl-2 and Bax. Thus ceramide-induced reduction in the Bcl-2/Bax ratio, increase in caspase activity, and apoptosis is dependent upon increases in cellular p53 levels which play a critical role in the regulation of apoptotic cell death.

Estrogen attenuates cell death induced by carboxy-terminal fragment of amyloid precursor protein in PC12 through a receptor-dependent pathway.

In the present study, we investigated effects of estrogen on cell death induced by carboxy‐terminal fragment of amyloid precursor protein (CT), a candidate causative substance in the pathogenesis of Alzheimers disease. 17β‐Estradiol attenuated CT‐induced cell death in PC12 cells, whereas 17α‐estradiol, nonestrogenic stereoisomer, did not exert any significant protective effect on CT‐induced cell death. These results suggest that protective effects of estrogen may be mediated by estrogen receptor (ER) in PC12 cells. To confirm the results, we determined the effects of tamoxifen, an estrogen receptor antagonist. Tamoxifen blocked the protective effects of 17β‐estradiol, although it did not affect those of 17α‐estradiol. Overall, it might be thought that the protective effect of estradiol on CT‐induced cell death is achieved by hormonal properties mediated through the estrogen receptor rather than the structural properties as a reducing agent. J. Neurosci. Res. 65:403–407, 2001.