Raloxifene inhibits estrogen-induced up-regulation of telomerase activity in a human breast cancer cell line.
The mechanism by which raloxifene acts in the chemoprevention of breast cancer remains unclear. Because telomerase activity is involved in estrogen-induced carcinogenesis, we examined the effect of raloxifene on estrogen-induced up-regulation of telomerase activity in MCF-7 human breast cancer cell line. Raloxifene inhibited the induction of cell growth and telomerase activity by 17beta-estradiol (E2). Raloxifene inhibited the E2-induced expression of the human telomerase catalytic subunit (hTERT), and transient expression assays using luciferase reporter plasmids containing various fragments of the hTERT promoter showed that the estrogen-responsive element appeared to be partially responsible for the action of raloxifene. E2 induced the phosphorylation of Akt, and pretreatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, attenuated the E2-induced increases of the telomerase activity and hTERT promoter activity. Raloxifene inhibited the E2-induced Akt phosphorylation. In addition, raloxifene also inhibited the E2-induced hTERT expression via the PI3K/Akt/NFkappaB cascade. Moreover, raloxifene also inhibited the E2-induced phosphorylation of hTERT, association of NFkappaB with hTERT, and nuclear accumulation of hTERT. These results show that raloxifene inhibited the E2-induced up-regulation of telomerase activity not only by transcriptional regulation of hTERT via an estrogen-responsive element-dependent mechanism and the PI3K/Akt/NFkappaB cascade but also by post-translational regulation via phosphorylation of hTERT and association with NFkappaB.
Kawagoe
Jun
J
Department of Obstetrics and Gynecology, Yamagata University, School of Medicine, Iidanishi, Yamagata, Japan.
Ohmichi
Masahide
M
Takahashi
Toshifumi
T
Ohshima
Chika
C
Mabuchi
Seiji
S
Takahashi
Kazuhiro
K
Igarashi
Hideki
H
Mori-Abe
Akiko
A
Saitoh
Maki
M
Du
Botao
B
Ohta
Tsuyoshi
T
Kimura
Akiko
A
Kyo
Satoru
S
Inoue
Masaki
M
Kurachi
Hirohisa
H
D001943:Breast Neoplasms / Q000378:metabolism*; D002455:Cell Division; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D004967:Estrogens / Q000378:metabolism*; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D020849:Raloxifene Hydrochloride / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019098:Telomerase / Q000378:metabolism*; D013997:Time Factors; D015854:Up-Regulation
D002867:Chromones; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D004967:Estrogens; D009025:Morpholines; D016328:NF-kappa B; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D020849:Raloxifene Hydrochloride; D008156:Luciferases; D019869:Phosphatidylinositol 3-Kinases; D019098:Telomerase