Raloxifene inhibits estrogen-induced up-regulation of telomerase activity in a human breast cancer cell line.
J Biol Chem
; 278(44): 43363-72, 2003 Oct 31.
Article
in En
| MEDLINE
| ID: mdl-12917431
ABSTRACT
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.
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Database:
MEDLINE
Main subject:
Breast Neoplasms
/
Up-Regulation
/
Telomerase
/
Raloxifene Hydrochloride
/
Estrogen Antagonists
/
Estrogens
Type of study:
Prognostic_studies
Limits:
Humans
Language:
En
Year:
2003
Type:
Article