The mechanism of escape from hypoxia-induced apoptosis in squamous cell carcinoma cells.

转录因子缺氧诱导因子1(HIF-1)在实体瘤细胞的生长和存活中起重要作用。缺氧诱导因子-1α的过度表达在许多人类肿瘤中已被证实，并预示着对化疗和放射治疗的不良反应。我们检测了低氧诱导因子-1α诱导的口腔鳞状细胞癌细胞系的存活途径以及低氧诱导因子-1α对化疗药物和γ射线敏感性的影响。结果表明，强制表达缺氧诱导因子-1α可通过抑制线粒体细胞色素c的释放而抑制缺氧诱导的口腔鳞癌细胞凋亡。HIF-1α的过表达抑制了细胞内ROS的产生、细胞内钙离子浓度的升高、线粒体膜电位的降低和细胞色素c的积累，从而导致caspase-9和caspase-3的失活。此外，抗凋亡的Bcl2和BclX_L水平升高，促凋亡的BAX和BAK水平降低，…在高表达HIF-1α的口腔鳞癌细胞系中有更多的表达。缺氧诱导因子-1α的过表达也增加了Akt和细胞外信号调节蛋白的磷酸化水平。这些结果表明，HIF-1α通过抑制细胞色素c的释放和激活Akt和ERK两种机制来防止细胞死亡。化疗药物和γ射线处理后，口腔鳞癌细胞对HIF-1α的表达和核转位增加，细胞对化疗药物和γ射线的敏感性与HIF-1α蛋白表达水平呈负相关。HIF-1α的过表达诱导口腔鳞癌细胞对抗癌药物的耐药性增强，小干扰α下调HIF-1基因的表达增强了口腔鳞癌细胞对抗癌药物的敏感性。在HIF-1α基因敲除的口腔鳞癌细胞中，P-糖蛋白、血红素加氧酶-1、锰超氧化物歧化酶和铜蓝蛋白的表达下调，细胞内化疗药物和活性氧水平维持在较高水平。这些结果表明，下调HIF-1α的表达是治疗肿瘤的有效策略。较少

The transcription factor hypoxia-inducible factor 1(HIF-1) plays an important role in solid tumor cell growth and survival. Over-expression of HIF-1α has been demonstrated in many human tumors and predicts a poor response to chemoradiotherapy. We examined the HIF-1α-induced survival pathways and the influence of HIF-1α on the susceptibility to chemotherapeutic drugs and γ-rays in human oral squamous cell carcinoma cell (OSCC) lines. The results showed that forced expression of HIF-1α suppressed hypoxia-induced apoptosis of OSCC lines by inhibiting cytochrome c release from mitochondria. Over-expression of HIF-1α inhibited the generation of reactive oxygen species (ROS), elevation of intracellular Ca^<2+> concentration, reduction of mitochondrial membrane potential, and cytosolic accumulation of cytochrome c, which resulted in the inactivation of caspase-9 and caspase-3. In addition, anti-apoptotic Bcl-2 and Bcl-X_L levels were increased and pro-apoptotic Bax and Bak levels were decreas … More ed in the HIF-1α-overexpressing OSCC line. Over-expression of HIF-1α also increased the levels of phosphorylation of Akt and extracellular signal-regulated kinases (ERK). These findings indicate that HIF-1α prevents apoptotic cell death through two mechanisms including inhibition of cytochrome c release and activation of Akt and ERK. Treatment with chemotherapeutic drugs and γ-rays enhanced the expression and nuclear translocation of HIF-1α and the susceptibility of OSCC cells to the drugs and γ-rays was negatively correlated with the expression level of HIF-1α protein. The over-expression of HIF-1α induced OSCC cells more resistant to the anticancer agents and the down-regulation of HIF-1α expression by small interfering RNA enhanced the susceptibility of OSCC cells to them. In the HIF-1α-knockdown OSCC cells, the expression of P-glycoprotein, heme oxygenase-1, manganese-superoxide dismutase and ceruloplasmin were down-regulated and the intracellular levels of chemotherapeutic drugs and reactive oxygen species were sustained at higher levels after the treatment with the anticancer agents. These results suggest that down-regulation of HIF-1α expression is an effective strategy for cancer treatment. Less