Expression of transcription factor E2F1 and telomerase in glioblastomas: mechanistic linkage and prognostic significance.
BACKGROUND
Several tumor suppressor pathways have been identified as modulators of telomerase function. We examined the functional role of the retinoblastoma-E2F1 pathway in regulating telomerase activity in malignant gliomas.


METHODS
Adenovirus vectors were used to transfer cDNAs into human glioblastoma and sarcoma cells. Telomerase activity was assessed with a telomere repeat amplification protocol. Promoter activity in cancer cells was assessed with promoter-luciferase reporter constructs. Promoter binding was assessed with the chromatin immunoprecipitation (ChIP) assay. We isolated astrocytes from E2F1 transgenic mice and normal mice for in vivo studies. We evaluated the expression of E2F1 and hTERT (the catalytic subunit of human telomerase) mRNAs by reverse transcriptase-polymerase chain reaction and proteins in human glioblastoma samples by immunoblot analysis. Associations between survival among 61 glioblastoma multiforme patients and expression of E2F1 and hTERT mRNA and protein were examined with Kaplan-Meier analysis, the log-rank test, and Cox proportional hazards regression models. All statistical tests were two-sided.


RESULTS
Ectopic E2F1 expression increased hTERT promoter activity in cancer cells. We detected an interaction between E2F1 protein and the hTERT promoter. Transgenic E2F1 astrocytes contained functional telomerase protein. E2F1 mRNA expression and hTERT mRNA expression were statistically significantly correlated in human glioblastoma specimens (R = .8; P < .001). Longer median survival was statistically significantly associated with lower E2F1 mRNA expression in tumors (103.6 weeks) rather than with higher expression (46.1 weeks) (difference = 57.5 weeks; 95% confidence interval [CI] = 14.7 to 159.7; log-rank P = .002). E2F1 mRNA was the only factor that was statistically significantly associated with overall survival in a multivariable model (P = .04). Among 27 patients with glioblastoma multiforme samples, the expression of E2F1 protein was statistically significantly associated with survival (log-rank P < .001).


CONCLUSIONS
E2F1 may participate in telomerase activity regulation in malignant glioma cells. Its expression appears to be strongly associated with the survival of patients with malignant brain tumors.
Alonso
Marta M
MM
Department of Neuro-Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
Fueyo
Juan
J
Shay
Jerry W
JW
Aldape
Kenneth D
KD
Jiang
Hong
H
Lee
Ok-Hee
OH
Johnson
David G
DG
Xu
Jing
J
Kondo
Yasuko
Y
Kanzawa
Takao
T
Kyo
Satoru
S
Bekele
B Nebiyou
BN
Zhou
Xian
X
Nigro
Janice
J
McDonald
J Matthew
JM
Yung
W K Alfred
WK
Gomez-Manzano
Candelaria
C
D000818:Animals; D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism*; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D008040:Genetic Linkage; D005909:Glioblastoma / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008822:Mice, Transgenic; D011237:Predictive Value of Tests; D011379:Prognosis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012509:Sarcoma / Q000201:enzymology / Q000378:metabolism*; D019098:Telomerase / Q000378:metabolism*
D004268:DNA-Binding Proteins; D050687:E2F1 Transcription Factor; D012333:RNA, Messenger; D019098:Telomerase