Local hypoxia that occurs during menstruation triggers angiogenesis that is crucial for cyclical remodeling of the endometrium during the menstrual cycle. Hypoxia is thought to be important for the expression of vascular endothelial growth factor (VEGF) via its transcriptional factor, hypoxia inducible factor (HIF)-1alpha, in the endometrium. The activation of the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway may modulate HIF-1alpha protein levels. Stathmin, a microtubule regulatory protein, was expressed in the stroma, glandular epithelium, and vascular endothelium in human endometrium. In this study, we examined a possible role of stathmin in hypoxia-induced HIF-1alpha and VEGF expression in primary isolated and immortalized human endometrial stromal cells, glandular epithelial cells, and human umbilical venous endothelial cells (HUVEC). Knocking down stathmin expression using small interfering RNA caused microtubule stabilization and inhibited hypoxia-induced VEGF mRNA expression via the reduction of HIF-1alpha protein levels in endometrial cells and HUVEC. Treatment of the cells with a PI3K inhibitor, wortmannin, inhibited the expression of VEGF mRNA and the accumulation of HIF-1alpha protein. Silencing of stathmin expression repressed the activation (phosphorylation) of Akt in endometrial cells and HUVEC. These results suggest that endometrial stathmin is linked to HIF-1alpha protein accumulation and VEGF expression through the PI3K/Akt signaling pathway and may be involved in regeneration of the endometrium during the menstrual cycle in human uterine cells.
Stathmin, a microtubule-destabilizing phosphoprotein, is highly expressed in ovarian cancer, but the pathophysiological significance of this protein in ovarian carcinoma cells remains poorly understood. This study reports the involvement of stathmin in the mTOR/HIF-1α/VEGF pathway in ovarian clear cell adenocarcinoma (CCA) during hypoxia. HIF-1α protein and VEGF mRNA levels were markedly elevated in RMG-1 cells, a CCA cell line, cultured under hypoxic conditions. Rapamycin, an inhibitor of mTOR complex 1, reduced the level of HIF-1α and blocked phosphorylation of ribosomal protein S6 kinase 1 (S6K), a transcriptional regulator of mTOR, demonstrating that hypoxia activates mTOR/S6K/HIF-1α signaling in CCA. Furthermore, stathmin knockdown inhibited hypoxia-induced HIF-1α and VEGF expression and S6K phosphorylation. The silencing of stathmin expression also reduced Akt phosphorylation, a critical event in the mTOR/HIF-1α/VEGF signaling pathway. By contrast, stathmin overexpression upregulated hypoxia-induced HIF-1α and VEGF expression in OVCAR-3 cells, another CCA cell line. In addition, suppression of Akt activation by wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor, decreased HIF-1α and VEGF expression. These results illustrate that regulation of HIF-1α through the PI3K/Akt/mTOR pathway is controlled by stathmin in CCA. Our findings point to a new mechanism of stathmin regulation during ovarian cancer.
BackgroundLeuprorelin acetate, a luteinizing hormone-releasing hormone agonist, is used worldwide in premenopausal women with hormone receptor-positive breast cancer. This study was conducted to assess the non-inferiority of the 6-month depot formulation, TAP-144-SR (6M) 22.5 mg to the 3-month depot formulation, TAP-144-SR (3M) 11.25 mg in postoperative, premenopausal patients with hormone receptor-positive breast cancer.MethodsThis was a 96-week phase III, randomized, open-label, parallel-group comparative study. All patients concomitantly received oral tamoxifen (20 mg daily). The primary endpoint was the suppression rate of serum estradiol (E2) to the menopausal level (≤30 pg/mL) from Week 4 through Week 48.ResultsIn total, 167 patients were randomized to receive TAP-144-SR (6M) (n = 83) or TAP-144-SR (3M) (n = 84) and the E2 suppression rate was 97.6 and 96.4 %, respectively. The estimated between-group difference was 1.2 % (95 % confidence interval −5.2 to 7.8). The non-inferiority of TAP-144-SR (6M) to TAP-144-SR (3M) for E2 suppression was confirmed. As for safety, common adverse events were hot flush and injection site reactions including induration, pain, and erythema in both treatment groups, which were of ≤Grade 2 in severity and not serious. No significant between-group differences in safety profiles and tolerability were observed.ConclusionsTAP-144-SR (6M) was not inferior to TAP-144-SR (3M) for its suppressive effect on serum E2. TAP-144-SR (6M) was also as well tolerated as TAP-144-SR (3M).
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