Kawagoe Jun, Ohmichi Masahide, Takahashi Toshifumi, Ohshima Chika, Mabuchi Seiji, Takahashi Kazuhiro, Igarashi Hideki, Mori-Abe Akiko, Saitoh Maki, Du Botao, Ohta Tsuyoshi, Kimura Akiko, Kyo Satoru, Inoue Masaki, Kurachi Hirohisa
Department of Obstetrics and Gynecology, Yamagata University, School of Medicine, Iidanishi, Yamagata, Japan.
J Biol Chem. 2003 Oct 31;278(44):43363-72. doi: 10.1074/jbc.M304363200. Epub 2003 Aug 13.
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.
雷洛昔芬在乳腺癌化学预防中的作用机制尚不清楚。由于端粒酶活性参与雌激素诱导的致癌作用，我们研究了雷洛昔芬对雌激素诱导的MCF-7人乳腺癌细胞系中端粒酶活性上调的影响。雷洛昔芬抑制了17β-雌二醇（E2）诱导的细胞生长和端粒酶活性。雷洛昔芬抑制了E2诱导的人端粒酶催化亚基（hTERT）的表达，使用含有hTERT启动子不同片段的荧光素酶报告质粒进行的瞬时表达分析表明，雌激素反应元件似乎部分负责雷洛昔芬的作用。E2诱导Akt磷酸化，用磷脂酰肌醇3激酶（PI3K）抑制剂LY294002预处理可减弱E2诱导的端粒酶活性和hTERT启动子活性的增加。雷洛昔芬抑制E2诱导的Akt磷酸化。此外，雷洛昔芬还通过PI3K/Akt/NFκB级联反应抑制E2诱导的hTERT表达。此外，雷洛昔芬还抑制E2诱导的hTERT磷酸化、NFκB与hTERT的结合以及hTERT的核内积累。这些结果表明，雷洛昔芬不仅通过雌激素反应元件依赖性机制和PI3K/Akt/NFκB级联反应对hTERT进行转录调控，还通过hTERT磷酸化和与NFκB结合的翻译后调控来抑制E2诱导的端粒酶活性上调。
