Rapamycin inhibits hTERT telomerase mRNA expression, independent of cell cycle arrest.
OBJECTIVE
Rapamycin and its analogues have been shown to be promising as anti-neoplastic agents but have not been extensively studied in gynecologic malignancies. Our goal was to examine the ability of rapamycin to suppress growth and regulate telomerase activity in cervical and ovarian cancer cell lines.


METHODS
Cell proliferation was assessed after exposure to rapamycin. Cell cycle progression was determined by flow cytometry, and apoptosis was evaluated by DNA fragmentation. hTERT mRNA levels were quantified by real-time RT-PCR. Western blot analysis was performed to assess PTEN status, phosphorylated S6 and total S6 expression.


RESULTS
Rapamycin inhibited growth of all the cervical cancer cell lines and 3 of the 4 ovarian cancer cell lines in a dose-dependent manner with IC50 values <50 nM. Loss of PTEN protein expression was seen in only one of the cervical cancer cell lines. Rapamycin induced G1 arrest in those cell lines sensitive to its growth inhibitory effects. In all cell lines, rapamycin rapidly inhibited phosphorylation of S6 and resulted in decreased levels of total S6 protein. Treatment with rapamycin reduced hTERT mRNA expression in both rapamycin-sensitive and -resistant cell lines within 24 h. Thus, the effect of rapamycin on hTERT expression was not dependent on its ability to induce G1 cell cycle arrest.


CONCLUSIONS
Our data suggest that rapamycin may potentially exert its anti-tumor effects through two independent pathways by G1 cell cycle arrest as well as suppression of telomerase activity by inhibition of hTERT mRNA transcription.
Bae-Jump
Victoria L
VL
Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, CB# 7570, Chapel Hill, NC 27599, USA.
Zhou
Chunxiao
C
Gehrig
Paola A
PA
Whang
Young E
YE
Boggess
John F
JF
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000502:physiology; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D006801:Humans; D051058:Oncogene Protein v-akt / Q000096:biosynthesis; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D051059:PTEN Phosphohydrolase / Q000096:biosynthesis; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D019098:Telomerase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics
D000903:Antibiotics, Antineoplastic; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D011494:Protein Kinases; C546842:MTOR protein, human; D051058:Oncogene Protein v-akt; D058570:TOR Serine-Threonine Kinases; D019098:Telomerase; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D020123:Sirolimus