No abstract

We examined the mechanism by which estrogen regulates telomerase activity in Caov-3 human ovarian cancer cell lines, which express ER, to determine whether the regulation affects the expression and/or phosphorylation of the telomerase catalytic subunit (hTERT). 17b-Estradiol (E 2 ) induced telomerase activity and hTERT expression. Transient expression assays using luciferase reporter plasmids containing various fragments of hTERT promoter showed that the estrogen-responsive element appeared to be partially responsible for the E 2 -induced activation of the hTERT promoter. Either pretreatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, or transfection with a dominantnegative Akt attenuated the E 2 -induced activation of the hTERT promoter. In addition, estrogen induced the phosphorylation of IjB inhibitor protein via the Akt cascade, and cotransfection with a dominant-negative subunit of NFjB attenuated the response of the ERE-deleted hTERT promoter to E 2 . Moreover, E 2 induced the phosphorylation of hTERT, the association of 14-3-3 protein and NFjB with hTERT, and nuclear accumulation of hTERT in an Akt-dependent manner. These results indicate that E 2 induces telomerase activity not only by transcriptional regulation of hTERT via an ERE-dependent mechanism and a PI3K/Akt/NFjB cascade, but also by post-transcriptional regulation via Akt-dependent phosphorylation of hTERT. Thus, the phosphorylation of Akt is a key event in the induction of telomerase activity by E 2 in human ovarian cancer cells.

The Forkhead family transcription factor FKHRL1 is an inducer of apoptosis in its unphosphorylated form and was recently reported to be a substrate of Akt kinase. We studied the roles of FKHRL1 in both cisplatin-resistant Caov-3 (a papillary adenocarcinoma cell line) and cisplatin-sensitive A2780 human ovarian cancer cell lines. Treatment of Caov-3 cells but not A2780 cells with cisplatin transiently stimulated the phosphorylation of FKHRL1. Transfection experiments revealed that a kinase inactive-mutant of Akt or a triple mutant (TM) of FKHRL1, in which all three of the putative Akt phosphorylation sites were converted to alanine, was unable to phosphorylate the FKHRL1 protein in cells treated with cisplatin. Because the phosphorylated form of FKHRL1 is known to be localized in the cytoplasm, we examined whether cisplatin-induced phosphorylation of FKHRL1 might have an effect on the subcellular distribution of FKHRL1. Cisplatin induced the localization of FKHRL1 in the cytoplasm in Caov-3 cells but not in A2790 cells. Moreover, cisplatin induced the association of 14-3-3 protein with phosphorylated-FKHRL1 in Caov-3 cells but not in A2790 cells. Because the unphosphorylated form of FKHRL1 binds the Fas ligand promoter, thereby inducing apoptosis, we further examined the effect of the phosphorylation status of FKHRL1 on the activity of the Fas ligand promoter in the presence of cisplatin. Transfection with the kinase-inactive mutant of Akt or TM of FKHRL1 induced the activity of the Fas ligand promoter in Caov-3 cells. Moreover, exogenous expression of TM of FKHRL1 in Caov-3 cells decreased the cell viability after treatment with cisplatin. Our findings suggest that cisplatin causes the phosphorylation of FKHRL1 via a phosphatidylinositol 3-kinase/Akt cascade, and inhibition of this cascade sensitizes ovarian cancer cells to cisplatin.

During early pregnancy, cytotrophoblast cells differentiate into extravillous trophoblast (EVT) cells and invade the uterine spiral arteries. This physiological process is essential for the development of maternal-fetal circulation. Because EVT cells are exposed to a low-oxygen environment during this process, we investigated the role of hypoxia in the mechanism that regulates the invasive behavior of EVT cells. Real-time PCR and immunofluorescent analysis were performed to investigate how hypoxia influences the expression of E-cadherin in villous explants cultures and in trophoblast-derived BeWo cells. We determined that hypoxia induced E-cadherin down-regulation through Snail up-regulation in villous explant cultures. The influence of E-cadherin loss was examined by analyzing the expression of alpha(5)-integrin and phosphorylated focal adhesion kinase (FAK) by Western blot and evaluating trophoblast invasion using a matrigel invasion assay. E-cadherin loss induced the up-regulation of alpha(5)-integrin, which leads to the tyrosine phosphorylation of FAK, resulting in an increase in the invasive activity of EVT cells. An alpha(5)-integrin neutralizing antibody inhibited the invasion of EVT cells by attenuating FAK tyrosine phosphorylation. Immunohistochemical analysis using clinical placental bed biopsies revealed that alpha(5)-integrin was up-regulated and FAK tyrosine phosphorylated (Try(861)) as EVT cells invade the uterine myometrium, whereas E-cadherin expression was down-regulated. These results suggest that alpha(5)-integrin up-regulation induced by E-cadherin loss under hypoxia has a crucial role in regulating the migration of EVT cells. This finding should help us reach a better understanding of the pathogenesis of critical gestational diseases, such as preeclampsia.

The proliferation of vascular smooth muscle cells (VSMC) is a crucial pathophysiological process in the development of atherosclerosis. Although estrogen is known to inhibit the proliferation of VSMC, the mechanism responsible for this effect remains to be elucidated. In addition, the effect of raloxifene on VSMC remains unknown. We have shown here that 17 -estradiol (E 2 ) and raloxifene significantly inhibited the platelet-derived growth factor (PDGF)-stimulated proliferation of cultured human VSMC. Flow cytometry demonstrated that PDGFstimulated S-phase progression of the cell cycle in VSMC was also suppressed by E 2 or raloxifene. We found that PDGF-induced phosphorylation of retinoblastoma protein (pRb), whose hyperphosphorylation is a hallmark of the G1-S transition in the cell cycle, was significantly inhibited by E 2 and raloxifene. These effects were associated with a decrease in cyclin D1 expression, without a change in cyclin-dependent kinase 4 or cyclin-dependent kinase inhibitor, p27 kip1 expression. ICI 182,780 abolished the inhibitory effects of E 2 and raloxifene on PDGFinduced pRb phosphorylation. Next, we examined which estrogen receptor (ER) is necessary for these effects of E 2 and raloxifene. Since VSMC express both ER and ER , A10, a rat aortic smooth muscle cell line that expresses ER but not ER , was used. The dose-dependent stimulation of A10 cell proliferation by PDGF was not inhibited by E 2 or raloxifene in contrast to the results obtained in VSMC. Moreover, E 2 and raloxifene significantly inhibited the PDGF-induced cyclin D1 promoter activity in A10 cells transfected with cDNA for ER but not in the parental cells. These results suggested that E 2 and raloxifene exert an antiproliferative effect in VSMC treated with PDGF, at least in part through inhibition of pRb phosphorylation, and that the inhibitory effects of E 2 and raloxifene may be mainly mediated by ER .