Apoptosis induced by low-dose paclitaxel is associated with p53 upregulation in nasopharyngeal carcinoma cells.
Paclitaxel exerts its cytotoxic effect by kinetic suppression of microtubules that block cells in the G2/M phase of the cell cycle and trigger apoptosis. To investigate apoptosis induced by paclitaxel in nasopharyngeal carcinoma (NPC), and its possible molecular mechanism of action, the human NPC cell lines HNE-1 (bearing wild-type p53) and CNE-2 (bearing mutant p53) were treated with different concentrations of paclitaxel. Apoptosis was determined by staining with propidium iodide and also by DNA fragmentation. Protein expression levels of p53, bcl-2 and bcl-xl were examined by Western blotting. Activation of caspase-3 and cleavage of poly(ADP-ribose) polymerase (PARP) were also studied in paclitaxel-induced apoptosis. We showed that paclitaxel inhibited growth and induced apoptosis in both cell lines but that the p53 mutant line (CNE-2) was less sensitive to treatment with low-dose paclitaxel. Caspase-3 activity and cleavage of death substrate PARP were significantly increased in a dose-dependent manner, both in parallel with the induction of apoptosis and growth inhibition of NPC cells. We observed a striking increase of p53 protein levels in NPC cells exposed to 1 and 10 nM paclitaxel but a marked inhibition at 100 nM paclitaxel treatment. An inhibitor of caspase, zVAD.fmk, blocked the apoptotic morphologic changes and DNA fragmentation but did not change the rate of cell death or the protein levels of p53, bcl-2 and bcl-xl. In summary, low-dose paclitaxel inhibited cell growth in NPC cells and induced apoptosis possibly by upregulation of p53. In contrast, cell growth and apoptosis induced by a high dose of the drug occurred in a p53-independent manner, which may directly initiate downstream events of apoptosis.
Tan
Guolin
G
Department of Otolaryngology, Third Affiliated Hospital, Central-South University, Changsha, Hunan, People's Republic of China. gltan@ucdavis.edu
Heqing
Li
L
Jiangbo
Chen
C
Ming
Jiang
J
Yanhong
Ma
M
Xianghe
Liu
L
Hong
Sun
S
Li
Guiyuan
G
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019254:Genes, bcl-2; D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000378:metabolism* / Q000473:pathology; D017239:Paclitaxel / Q000008:administration & dosage / Q000494:pharmacology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D015854:Up-Regulation; D051020:bcl-X Protein
D000590:Amino Acid Chloromethyl Ketones; D000972:Antineoplastic Agents, Phytogenic; C494811:BCL2L1 protein, human; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051020:bcl-X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D017239:Paclitaxel