Das Arabinda, Banik Naren L, Ray Swapan K
Department of Neurosciences, Medical University of South Carolina, P.O. Box 250606, Charleston, SC 29425, USA.
Neurochem Res. 2007 Dec;32(12):2167-83. doi: 10.1007/s11064-007-9413-y. Epub 2007 Aug 13.
Glioblastoma is the deadliest and most prevalent brain tumor, which is not yet amenable to any treatments. Therefore, new and innovative therapeutic strategies need to be developed for treating this deadly disease. We found that all-trans retinoic acid (ATRA) or 13-cis retinoic acid (13-CRA) induced astrocytic differentiation with down regulation of telomerase activity in rat glioblastoma C6 cells and enhanced sensitivity of the cells to interferon-gamma (IFN-gamma) or taxol (TXL) for apoptosis. Sensitivity of differentiated cells to IFN-gamma or TXL was greatly increased for apoptosis with increases in calcineurin expression, Bax:Bcl-2 ratio, mitochondrial release of cytochrome c, and expression and activity of calpain and caspases. Treatment with IFN-gamma activated caspase-8 indicating induction of apoptosis via the receptor-mediated pathway. Notably, IFN-gamma activated the signal transducer and activator of transcription-1 (STAT-1) for signaling via binding to gamma activator sequence (GAS), whereas TXL activated Raf-1 kinase for inactivation of Bcl-2 by its phosphorylation. We confirmed involvement of different proteolytic mechanisms in cell death by pretreating the cells with caspase-8 inhibitor II, calpeptin (calpain inhibitor), and caspase-9 inhibitor I, and caspase-3 inhibitor IV. Results demonstrated that retinoids induced astrocytic differentiation with down regulation of telomerase activity and worked synergistically to enhance sensitivity of cells to the cytotoxic agent IFN-gamma and the cytostatic agent TXL for apoptosis. This combination therapy for differentiation and apoptosis could be highly effective for controlling the malignant growth of glioblastoma.
胶质母细胞瘤是最致命且最常见的脑肿瘤，目前尚无任何有效的治疗方法。因此，需要开发新的创新性治疗策略来治疗这种致命疾病。我们发现，全反式维甲酸（ATRA）或13-顺式维甲酸（13-CRA）可诱导大鼠胶质母细胞瘤C6细胞向星形细胞分化，同时下调端粒酶活性，并增强细胞对干扰素-γ（IFN-γ）或紫杉醇（TXL）诱导凋亡的敏感性。分化后的细胞对IFN-γ或TXL诱导凋亡的敏感性显著增加，同时钙调神经磷酸酶表达增加、Bax:Bcl-2比值升高、细胞色素c从线粒体释放以及钙蛋白酶和半胱天冬酶的表达及活性增强。IFN-γ处理可激活半胱天冬酶-8，表明通过受体介导的途径诱导凋亡。值得注意的是，IFN-γ通过与γ激活序列（GAS）结合激活信号转导子和转录激活子-1（STAT-1）进行信号传导，而TXL则激活Raf-1激酶，通过磷酸化使Bcl-2失活。我们通过用半胱天冬酶-8抑制剂II、钙肽素（钙蛋白酶抑制剂）、半胱天冬酶-9抑制剂I和半胱天冬酶-3抑制剂IV预处理细胞，证实了不同蛋白水解机制参与细胞死亡。结果表明，维甲酸可诱导星形细胞分化并下调端粒酶活性，并协同增强细胞对细胞毒性药物IFN-γ和细胞生长抑制剂TXL诱导凋亡的敏感性。这种分化和凋亡联合治疗可能对控制胶质母细胞瘤的恶性生长非常有效。
