Tiwari Meenakshi, Kumar Ashok, Sinha Rohit Anthony, Shrivastava Ashutosh, Balapure Anil Kumar, Sharma Ramesh, Bajpai Virendra Kumar, Mitra Kalyan, Babu Satish, Godbole Madan Madhav
Department of Endocrinology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareli Road, Lucknow, 226 014, India.
Carcinogenesis. 2006 Oct;27(10):2047-58. doi: 10.1093/carcin/bgl051. Epub 2006 May 4.
N-(4-hydroxyphenyl)retinamide (4-HPR), a synthetic retinoid is under clinical evaluation as a therapeutic agent in a variety of cancers. Its mechanism(s) of action involves multiple overlapping pathways that still remain unclear. In glioma cells its mechanism of action is not well elucidated. Here, we show that 4-HPR and not all-trans retinoic acid and 9-cis retinoic acid effectively induce apoptosis in glioma cells. 4-HPR-induced apoptosis is associated with hydroperoxide production and loss of mitochondrial membrane potential (Delta Psi(m)). Ultrastructural changes further indicate 4-HPR-induced mitochondrial swelling, endoplasmic reticulum (ER) dilation as well as close proximity of mitochondria and ER. As suggested by dilated ER, 4-HPR treatment increased the free cytosolic Ca(2+) as well as mitochondrial Ca(2+). Chelation of extracellular Ca(2+) by EGTA did not prevent Ca(2+) elevation, thus suggesting involvement of intracellular calcium stores in the release. Buffering of intracellular calcium by BAPTA-AM did not prevent 4-HPR-induced apoptosis; however, blocking the release of Ca(2+) from ER by heparin inhibited apoptosis, indicating the role of depletion of Ca(2+) from ER stores in apoptosis. 4-HPR treatment also resulted in an increase in Bax levels along with its translocation to mitochondria that promote mitochondrial membrane permeabilization. 4-HPR-induced apoptosis was further associated with the release of cytochrome c and apoptosis-inducing factor (AIF) from mitochondria to cytosol and nucleus, respectively, along with caspase-3 and caspase-7 activation. However, AIF nuclear translocation, peripheral chromatin condensation and apoptosis were not completely prevented by general caspase inhibitors, thus suggesting involvement of a caspase-dependent and caspase-independent pathway in 4-HPR-induced apoptosis. Taken together, these results suggest the role of mitochondrial-mediated pathway and ER stress as a key event in 4-HPR-induced apoptosis in glioma cells.
N-(4-羟基苯基)视黄酸酰胺(4-HPR)，一种合成类视黄醇，正在作为多种癌症的治疗药物进行临床评估。其作用机制涉及多个重叠途径，目前仍不清楚。在胶质瘤细胞中，其作用机制尚未得到很好的阐明。在这里，我们表明4-HPR而非全反式视黄酸和9-顺式视黄酸能有效诱导胶质瘤细胞凋亡。4-HPR诱导的凋亡与过氧化氢的产生以及线粒体膜电位(ΔΨm)的丧失有关。超微结构变化进一步表明4-HPR诱导线粒体肿胀、内质网(ER)扩张以及线粒体与内质网紧密相邻。如内质网扩张所示，4-HPR处理增加了游离胞质Ca(2+)以及线粒体Ca(2+)。EGTA螯合细胞外Ca(2+)并不能阻止Ca(2+)升高，因此表明细胞内钙库参与了释放过程。BAPTA-AM缓冲细胞内钙并不能阻止4-HPR诱导的凋亡；然而，肝素阻断内质网Ca(2+)释放可抑制凋亡，表明内质网钙库中Ca(2+)耗竭在凋亡中的作用。4-HPR处理还导致Bax水平升高及其转位至线粒体，从而促进线粒体膜通透性增加。4-HPR诱导的凋亡还分别与细胞色素c和凋亡诱导因子(AIF)从线粒体释放到胞质溶胶和细胞核有关，同时伴有caspase-3和caspase-7激活。然而，一般的caspase抑制剂并不能完全阻止AIF核转位、外周染色质凝聚和凋亡，因此表明caspase依赖性和非依赖性途径参与了4-HPR诱导的凋亡。综上所述，这些结果表明线粒体介导的途径和内质网应激在4-HPR诱导的胶质瘤细胞凋亡中起关键作用。
