title: Coupled down-regulation of mTOR and telomerase activity during fluorouracil-induced apoptosis of hepatocarcinoma cells.
abstract: BACKGROUND
  Hepatocellular carcinoma (HCC) is the most invasive and frequently diagnosed malignancy and the second leading cause of cancer death in many regions of Asia. The PI3K/Akt/mTOR signal pathway is involved in multiple cellular functions including proliferation, differentiation, tumorigenesis, and apoptosis. Up-regulation of telomerase activity is thought to be a critical step leading to cell transformation.
  
  
  METHODS
  This study investigated changes in mTOR pathway and telomerase activity in hepatocarcinoma cell line SMMC-7721 treated with chemotherapeutic agent 5-fluorouracil (5-Fu). We detected apoptosis of hepatocarcinoma cells by TUNEL assay. Telomerase activity, hTERT transcription level and p- p70 S6k was demonstrated by the telomeric repeat amplification protocol and silver staining assay, Dual-Luciferase Reporter Assay and Western blot analysis respectively.
  
  
  RESULTS
  Treating SMMC-7721 cells with 5-Fu leads to apoptosis of the cells, and reduction in telomerase activity, as well as a dramatic reduction in the activated form of p70 S6 kinase, a mTOR substrate. The 5-Fu treatment nearly abolishes transcription of hTERT (the major component of telomerase) mRNA. Treating SMMC-7721 cells with Rapamycin, a specific mTOR inhibitor, significantly reduce hTERT protein level but did not affect hTERT transcription. 5-Fu and rapamycin were synergistic in regards to down-regulation of telomerase activity in hepatocarcinoma cells.
  
  
  CONCLUSIONS
  These results suggest that chemotherapeutic agent 5-Fu may down-regulate telomerase activity at both transcriptional level and PI3K/Akt/mTOR pathway-dependent post-transcriptional level to facilitate hepatocellular carcinoma cell apoptosis.
authors.affiliation: Tumor Immunology and Gene Therapy Center, Eastern Hepatobiliary Hospital, Second Military Medical Universisty, 225 Changhai Road, Shanghai 200438, China. jesscica123@126.com
authors.forename: Xinxin
authors.initials: X
authors.lastname: Bu
authors.forename: Fengqi
authors.initials: F
authors.lastname: Jia
authors.forename: Weifeng
authors.initials: W
authors.lastname: Wang
authors.forename: Xianling
authors.initials: X
authors.lastname: Guo
authors.forename: Mengchao
authors.initials: M
authors.lastname: Wu
authors.forename: Lixin
authors.initials: L
authors.lastname: Wei
mesh_terms: D017209:Apoptosis; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005472:Fluorouracil / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020287:In Situ Nick-End Labeling; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology*; D011494:Protein Kinases / Q000096:biosynthesis*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D019098:Telomerase / Q000096:biosynthesis* / Q000502:physiology; D014158:Transcription, Genetic
chemical_list: D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D019098:Telomerase; D005472:Fluorouracil; D020123:Sirolimus