title: Posttranscriptional regulation of the telomerase hTERT by gambogic acid in human gastric carcinoma 823 cells.
abstract: We previously reported that gambogic acid (GA), a natural product, was an effective telomerase inhibitor by repressing hTERT promoter. In this study, posttranscriptional regulation of the telomerase hTERT by GA was investigated in BGC-823 human gastric carcinoma cells. The telomerase activity was detected by PCR-TRAP assay. RT-PCR assay and Western blot were performed to examine the repression of telomerase hTERT and c-Myc after GA or c-Myc-specific siRNA treatment. The results indicated that GA repressed telomerase activity and hTERT transcriptional activity via down-regulation of c-Myc expression in BGC-823 human gastric carcinoma cells. We further observed that hTERT transcriptional activity was not completely blocked by c-Myc-specific siRNA, suggesting that additional factors are involved in the repression of telomerase activity. The results of Western blot and immunoprecipitation assay revealed that GA inhibits the phosphorylation of Akt. The further results also confirmed that celecoxib, an inhibitor of Akt phosphorylation, could significantly repressed telomerase activity alone and enhance the repression of telomerase activity combined with GA. These data suggested that GA inhibits the posttranslational modification of hTERT by inhibiting the phosphorylation of Akt. Collectively, we suggest that GA represses telomerase activity not only by repressing hTERT transcriptional activity via c-Myc but also by posttranslational modification of hTERT via Akt.
authors.affiliation: Jiangsu Key Laboratory of Carcinogenesis and Intervention, China Pharmaceutical University, Nanjing 210009, People's Republic of China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Zhao
authors.forename: Yong
authors.initials: Y
authors.lastname: Yang
authors.forename: Jun
authors.initials: J
authors.lastname: Yu
authors.forename: Qi-Dong
authors.initials: QD
authors.lastname: You
authors.forename: Shi
authors.initials: S
authors.lastname: Zeng
authors.forename: Hong-Yan
authors.initials: HY
authors.lastname: Gu
authors.forename: Na
authors.initials: N
authors.lastname: Lu
authors.forename: Qi
authors.initials: Q
authors.lastname: Qi
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Xiao-Tang
authors.initials: XT
authors.lastname: Wang
authors.forename: Qing-Long
authors.initials: QL
authors.lastname: Guo
mesh_terms: D000068579:Celecoxib; D045744:Cell Line, Tumor; D016259:Genes, myc / Q000187:drug effects; D006801:Humans; D051058:Oncogene Protein v-akt / Q000235:genetics; D011720:Pyrazoles / Q000494:pharmacology; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects*; D013274:Stomach Neoplasms / Q000235:genetics*; D013449:Sulfonamides / Q000494:pharmacology; D019098:Telomerase / Q000235:genetics*; D014162:Transfection; D044004:Xanthones / Q000494:pharmacology*
chemical_list: D011720:Pyrazoles; D013449:Sulfonamides; D044004:Xanthones; C052659:gambogic acid; D051058:Oncogene Protein v-akt; C509186:TERT protein, human; D019098:Telomerase; D000068579:Celecoxib