DNA mismatch repair （MMR） processes the chemically induced mispairs following treatment with clinically important nucleoside analogs such as 6-thioguanine （6-TG） and 5-fluorouracil （5-FU）. MMR processing of thes...DNA mismatch repair （MMR） processes the chemically induced mispairs following treatment with clinically important nucleoside analogs such as 6-thioguanine （6-TG） and 5-fluorouracil （5-FU）. MMR processing of these drugs has been implicated in activation of a prolonged G2/M cell cycle arrest for repair and later induction of apoptosis and/or autophagy for irreparable DNA damage. In this study, we investigated the role of Bcl2 and adenovirus EIB Nineteen-kilodalton Interacting Protein （BNIP3） in the activation of autophagy, and the temporal relationship between a G2/M cell cycle arrest and the activation of BNIP3-mediated autophagy following MMR processing of 6-TG and 5-FU. We found that BNIP3 protein levels are upregulated in a MLHI （MMR＋）-dependent manner following 6-TG and 5-FU treatment. Subsequent small-interfering RNA （siRNA）-mediated BNIP3 knockdown abrogates 6-TG- induced autophagy. We also found that p53 knockdown or inhibition of mTOR activity by rapamycin cotreatment impairs 6-TG- and 5-FU-induced upregulation of BNIP3 protein levels and autophagy. Furthermore, suppression of Checkpoint kinase 1 （Chkl） expression with a subsequent reduction in 6-TG-induced G2/M cell cycle arrest by Chkl siRNA promotes the extent of 6-TG-induced autophagy. These findings suggest that BNIP3 mediates 6-TG- and 5-FU-induced autophagy in a p53- and mTOR-dependent manner. Additionally, the duration of Chkl-activated G2/ M cell cycle arrest determines the level of autophagy following MMR processing of these nucleoside analogs.展开更多
Objective To determine if DNA excision repair enzymes oxoguanine glycosylase 1 （OGG1） and xeroderma pigmentosum group F protein （XPF） are involved in the pathogenesis of Parkinson＇s disease （PD） in a cell model...Objective To determine if DNA excision repair enzymes oxoguanine glycosylase 1 （OGG1） and xeroderma pigmentosum group F protein （XPF） are involved in the pathogenesis of Parkinson＇s disease （PD） in a cell model. Methods PC12 cells were treated with 1-Methyl-4-phenylpyridine ion （MPP＋） for various periods of time to induce oxidative DNA damage. MTT assay was used to determine cell viability. Immunocytochemistry with antibody against 8-hydroxy-2＇- deoxyguanosine （8-oxodG） was used to evaluate oxidative DNA damage. Immunoblotting was used to detect the protein levels of OGG1 and XPF. Results MPP＋ treatment （1 mmol/L） for 18 h and 24 h reduced cell viability to 78.6% and 70.3% of the control, respectively, in a time-dependent way. MPP＋ increased the immunoreactivity of 8-oxodG in the cytoplasm at 3 h and in the nucleus at 24 h of treatment. With the treatment of MPP＋, the expression of OGG1 was significantly increased at 1 h, reaching a peak at 3 h, and then it was decreased at 24 h, as compared to that with vehicle treatment. The same effect was exerted on XPF level, except that the XPF level reached a peak at 18 h of MPP＋ treatment. Moreover, the maximally-increased protein level of OGG1 by MPP＋ was approximately 2-fold higher than that of XPF. Conclusion MPP＋ treatment could time- dependently induce increases in OGG1 and XPF expressions in PC12 cells. Also, this study indicates that the base and nucleotide excision repair pathways may be compensatorily activated in the early stage of pathogenesis in the cells after MPP＋ treatment.展开更多
文摘DNA mismatch repair （MMR） processes the chemically induced mispairs following treatment with clinically important nucleoside analogs such as 6-thioguanine （6-TG） and 5-fluorouracil （5-FU）. MMR processing of these drugs has been implicated in activation of a prolonged G2/M cell cycle arrest for repair and later induction of apoptosis and/or autophagy for irreparable DNA damage. In this study, we investigated the role of Bcl2 and adenovirus EIB Nineteen-kilodalton Interacting Protein （BNIP3） in the activation of autophagy, and the temporal relationship between a G2/M cell cycle arrest and the activation of BNIP3-mediated autophagy following MMR processing of 6-TG and 5-FU. We found that BNIP3 protein levels are upregulated in a MLHI （MMR＋）-dependent manner following 6-TG and 5-FU treatment. Subsequent small-interfering RNA （siRNA）-mediated BNIP3 knockdown abrogates 6-TG- induced autophagy. We also found that p53 knockdown or inhibition of mTOR activity by rapamycin cotreatment impairs 6-TG- and 5-FU-induced upregulation of BNIP3 protein levels and autophagy. Furthermore, suppression of Checkpoint kinase 1 （Chkl） expression with a subsequent reduction in 6-TG-induced G2/M cell cycle arrest by Chkl siRNA promotes the extent of 6-TG-induced autophagy. These findings suggest that BNIP3 mediates 6-TG- and 5-FU-induced autophagy in a p53- and mTOR-dependent manner. Additionally, the duration of Chkl-activated G2/ M cell cycle arrest determines the level of autophagy following MMR processing of these nucleoside analogs.
基金supported by the National Natural Science Foundation of China (No. 30770660,J0730860)
文摘Objective To determine if DNA excision repair enzymes oxoguanine glycosylase 1 （OGG1） and xeroderma pigmentosum group F protein （XPF） are involved in the pathogenesis of Parkinson＇s disease （PD） in a cell model. Methods PC12 cells were treated with 1-Methyl-4-phenylpyridine ion （MPP＋） for various periods of time to induce oxidative DNA damage. MTT assay was used to determine cell viability. Immunocytochemistry with antibody against 8-hydroxy-2＇- deoxyguanosine （8-oxodG） was used to evaluate oxidative DNA damage. Immunoblotting was used to detect the protein levels of OGG1 and XPF. Results MPP＋ treatment （1 mmol/L） for 18 h and 24 h reduced cell viability to 78.6% and 70.3% of the control, respectively, in a time-dependent way. MPP＋ increased the immunoreactivity of 8-oxodG in the cytoplasm at 3 h and in the nucleus at 24 h of treatment. With the treatment of MPP＋, the expression of OGG1 was significantly increased at 1 h, reaching a peak at 3 h, and then it was decreased at 24 h, as compared to that with vehicle treatment. The same effect was exerted on XPF level, except that the XPF level reached a peak at 18 h of MPP＋ treatment. Moreover, the maximally-increased protein level of OGG1 by MPP＋ was approximately 2-fold higher than that of XPF. Conclusion MPP＋ treatment could time- dependently induce increases in OGG1 and XPF expressions in PC12 cells. Also, this study indicates that the base and nucleotide excision repair pathways may be compensatorily activated in the early stage of pathogenesis in the cells after MPP＋ treatment.
