Hypoxia-induced resistance to anticancer drugs is associated with decreased senescence and requires hypoxia-inducible factor-1 activity

Hypoxia in solid tumors is associated with the development of chemoresistance. Although many studies have focused on the effect of hypoxia on drug-induced apoptosis, the effect of nonapoptotic pathways on hypoxia-induced drug resistance has not been previously investigated. Here, we determined the effects of hypoxia on multiple forms of drug-induced death in human MDA-MB-231 breast carcinoma cells. Clonogenic assays showed that preexposure to hypoxia leads to resistance to various classes of chemotherapeutic agents, including anthracyclines (daunorubicin and doxorubicin), epipodophyllotoxins (etoposide), and anthracenediones (mitoxantrone). Results revealed a high degree of heterogeneity in nuclear and cytoplasmic alterations in response to acute drug exposure; however, the majority of exposed cells displayed morphologic and biochemical changes consistent with drug-induced senescence. Hypoxia decreased only the proportion of cells in the senescent population, whereas the small proportion of cells exhibiting features of apoptosis or mitotic catastrophe were unaffected. Similar results were obtained with human HCT116 colon carcinoma cells, indicating that the protective effect of hypoxia on drug-induced senescence is not unique to MDA-MB-231 cells. Treatment of MDA-MB-231 cells with small interfering RNA targeting the alpha-subunit of hypoxia-inducible factor-1 (HIF-1), a key regulator of cellular adaptations to hypoxia, prevented hypoxia-induced resistance. HIF-1alpha small interfering RNA also selectively abolished the hypoxia-induced changes in the senescent population, indicating that the increased survival was due to protection against drug-induced senescence. These results support a requirement for HIF-1 in the adaptations leading to drug resistance and reveal that decreased drug-induced senescence is also an important contributor to the development of hypoxia-induced resistance.     

缺氧诱导因子-1和肿瘤放射敏感性的研究进展

人体实体肿瘤中存在低氧微环境是放射治疗预后较差的一个重要原因,肿瘤细胞在低氧微环境中会产生一系列生理、生化改变,其中缺氧诱导因子-1(HIF-1)起重要作用。HIF-1在实体肿瘤中呈普遍高表达,其调控下游多个靶基因,而这些靶基因在肿瘤发展、侵袭和转移中发挥着重要作用,导致肿瘤放射治疗预后较差。因此,研究HIF-1与肿瘤放射敏感性的关系可以改善肿瘤的预后。本文就HIF-1生物学特性、HIF-1降低肿瘤放射敏感性的机制及HIF-1抑制剂能提高放射敏感性等方面进行综述,旨在探讨HIF-1与放射敏感性的关系,为以后进行更多前瞻性研究提供基础资料。     

Chrysin inhibits expression of hypoxia-inducible factor-1alpha through reducing hypoxia-inducible factor-1alpha stability and inhibiting its protein synthesis

Chrysin is a natural flavonoid and has been shown recently to have anticancer effects. However, the mechanisms that chrysin inhibits cancers are not well known. In this study, we investigated the effects of chrysin on expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor in human prostate cancer DU145 cells. Chrysin inhibited insulin-induced expression of HIF-1alpha by reducing its stability. Chrysin increases ubiquitination and degradation of HIF-1alpha by increasing its prolyl hydroxylation. In addition, chrysin interfered with interaction between HIF-1alpha and heat shock protein 90. Chrysin was also found to inhibit HIF-1alpha expression through AKT signaling. Inhibition of HIF-1alpha by chrysin resulted in abrogation of vascular endothelial growth factor expression. Finally, we showed that chrysin inhibited DU145 xenograft-induced angiogenesis in nude mice. Taken together, these results suggest that chrysin is a potent inhibitor of HIF-1alpha and provide a new sight into the mechanisms of chrysin against cancers.     

缺氧诱导因子1在糖尿病心肌病大鼠的表达

目的 研究缺氧诱导因子1(HIF-1)在糖尿病心肌病(DC)大鼠心肌的表达,并探讨氯沙坦钾干预对DC大鼠心肌HIF-1表达的影响.方法 单次腹腔注射链脲佐菌素(STZ)诱导糖尿病大鼠模型,将糖尿病鼠随机分为DC组(20只)和氯沙坦钾组(L组,20只),以正常大鼠(C组,20只)作对照.干预12周后,观察各组大鼠心率、血糖、脂代谢相关指标、心脏胶原含量变化;用实时荧光定量聚合酶链反应(PCR)分析心肌HIF-1.结果 ①DC组大鼠心肌HIF-1 mRNA水平较正常大鼠明显升高,0.78±0.33 vs0.33±0.18(P＜0.01);而L组大鼠上述指标明显下降,0.54±0.14vs0.33±0.18(P＜0.05).②DC组大鼠血糖、血脂均显著高于正常大鼠,干预后上述指标改善不明显.结论 氨沙坦钾可能通过下调DC大鼠心肌HIF-1表达,从而发挥其心肌保护作用.     

低氧诱导因子-1的生物学特性与胚胎发育

低氧诱导因子-1(hypoxia-induciblefactor-1,HIF-1)是由α,β两个亚单位形成的二聚体,其中的HIF-1α受低氧的调节,通过与靶基因特定序列DNA结合而调控制它们的转录,这些基因包括血管内皮生长因子,红细胞生成素和其他的一系列与机体氧代谢有关的基因。文章着重论述了HIF-1的生物学特性及其与胚胎发育的关系。     

Molecular mechanisms for the activity of PX-478, an antitumor inhibitor of the hypoxia-inducible factor-1alpha

We have reported previously that PX-478 (S-2-amino-3-[4'-N,N,-bis(chloroethyl)amino]phenyl propionic acid N-oxide dihydrochloride) has potent antitumor activity against a variety of human tumor xenografts associated with the levels of the hypoxia-inducible factor-1alpha (HIF-1alpha) within the tumor. We now report that PX-478 inhibits HIF-1alpha protein levels and transactivation in a variety of cancer cell lines. Hypoxia-induced vascular endothelial growth factor formation was inhibited by PX-478, whereas baseline levels of vascular endothelial growth factor in normoxia were unaffected. Studies of the mechanism of PX-478 action showed that HIF-1alpha inhibition occurs in both normoxia and hypoxia and does not require pVHL or p53. In addition, PX-478 decreases levels of HIF-1alpha mRNA and inhibits translation as determined by 35S labeling experiments and reporter assays using the 5' untranslated region of HIF-1alpha. Moreover, to a lesser extent, PX-478 also inhibits HIF-1alpha deubiquitination resulting in increased levels of polyubiquitinated HIF-1alpha. The inhibitory effect of PX-478 on HIF-1alpha levels is primarily due to its inhibition of translation because HIF-1alpha translation continues in hypoxia when translation of most proteins is decreased. We conclude that PX-478 inhibits HIF-1alpha at multiple levels that together or individually may contribute to its antitumor activity against HIF-1alpha-expressing tumors.     

缺氧诱导因子-1α在膀胱癌中的表达及意义

目的探讨缺氧诱导因子-1α（HIF-1α）在膀胱癌组织中的表达及其意义。方法采用免疫组织化学技术对30例新鲜的膀胱癌患者的肿瘤组织和15例正常膀胱组织检测HIF-1α的表达情况,比较两组之间的差异。结果 30例膀胱癌组织中23例（76.7%）呈阳性表达,而15例正常膀胱组织中仅1例阳性表达,差异有统计学意义（P〈0.05）。结论 HIF-1α蛋白的高表达可能与膀胱癌的发生、发展和复发有关。     

退变颈椎间盘组织中缺氧诱导因子1α的表达及意义木

目的:已有研究表明缺氧诱导因子1α参与血管生成与重塑、糖酵解、细胞的增殖与凋亡等,并发现其在人类腰椎间盘组织的表达,但尚未明确其在人类退行性变颈椎间盘的表达和生物学作用.实验拟进一步验证缺氧诱导因子1α在不同类型人颈椎间盘突出组织中的表达.方法:①对象:选取2005-12/2006-09中国医科大学盛京医院脊柱与关节外科因颈椎间盘突出症而行前路手术切除的椎间盘组织标本40例.男23例,女17例;年龄45-73岁:病程1个月～11年.其中纤维环破裂型20例,纤维环完整型20例.同时选择颈椎骨折行前路减压内固定术患者的颈椎间盘组织标本20例作为对照组,两组患者均知情同意.②实验过程及评估:采用苏木精伊红和链霉亲和素-过氧化物酶复合物免疫组织化学方法及显微图像分析技术,观察突出颈椎间盘组织学变化并测定颈椎间盘突出症患者椎间盘组织中缺氧诱导因子1α的表达情况.结果:①形态学变化:可见纤维环破裂型椎间盘退行性变严重程度高于纤维环完整型.②退行性变椎间盘组织中缺氧诱导因子1α表达:纤维环破裂组缺氧诱导因子1α在髓核和纤维环的表达高于纤维环完整组和对照组,差异有显著性(P<0.05),尤其在髓核细胞中表达更为显著:各组软骨终板中缺氧诱导因子1α呈低表达,差异无显著性(P>0.05).结论:退行性变颈椎间盘组织中缺氧诱导因子1α的表达与突出类型相关,推测缺氧诱导因子1α可能在抑制椎间盘的退行性变中发挥重要作用.     

构建双突变型低氧诱导因子1α腺病毒载体的实验

目的:前期实验已成功构建无突变及564位是单突变腺病毒载体。在此基础上构建人双突变型低氧诱导因子1α腺病毒表达载体,为进一步研究低氧诱导因子1α基因及其突变体的临床应用奠定基础。方法:实验于2005-12/2006-12在南方医院心内科重点实验室完成。①实验材料:限制性内切酶PacI(NEB),PI-SceI、I-CeuI(Clontech);IPTG、X-Gal(Takara),转染试剂Lipofectamine2000(Invitrogen),凝胶回收试剂盒(Omega);DMEM(Omega);小牛血清(PAA);北京天为时代公司病毒基因组提取试剂盒;HIF-1α单克隆抗体(Chemicon International公司);羊抗鼠辣根过氧化物酶标记二抗(北京鼎国生物公司)。质粒、菌珠、细胞系等:Adeno-XTM-Adenoviral Expression Systems(BD.CLONTECH):包括有pShuttle2、pShuttle2-lacZ、Adeno-XTMViralDNA等;重组穿梭质粒pShuttle2-HIF-1α-Ala564-Ala803及pShuttle2-lacZ(本室已构建成功);大肠杆菌DH5α(本室保存);HEK293A细胞(中科院上海细胞所)。②实验方法:采用分子克隆技术,以PI-SceI和I-CeuI双酶切重组穿梭质粒pShuttle2-HIF-1α-Ala564-Ala803,然后切下含有低氧诱导因子1αcDNA表达的盒片段,通过体外连接法与线性化的腺病毒骨架质粒Adeno-XViralDNA连接,重组成pAdeno-HIF-1α腺病毒质粒,经酶切及测序鉴定正确后,在HEK293A细胞中包装成为重组腺病毒Adeno-HIF-1α-Ala564-Ala803。③实验评估:进行PCR鉴定及滴度测定。用重组腺病毒转染293A,采用Westernblot鉴定低氧诱导因子1α蛋白表达。结果:提取重组腺病毒质粒pAdeno-HIF-1α-Ala564-Ala803以引物A、B和引物1、2、3、4进行PCR鉴定,分别扩增出287,460,214bp的3种引物片段,与预期一致,经酶切鉴定及基因测序证实重组腺病毒质粒构建成功。pAdeno-lacZ转染293A细胞后X-Gal原位染色,显示约有近20%左右细胞染成蓝色,病毒滴度为6.8×107pfu/mL。Adeno-HIF-1α-Ala564-Ala803转染293A后稳定表达低氧诱导因子1α蛋白。结论:成功构建了重组腺病毒突变型的Adeno-HIF-1α-Ala564-Ala803。     

Mitochondrial regulation by c-Myc and hypoxia-inducible factor-1 alpha controls sensitivity to econazole

Econazole is an azole antifungal with anticancer activity that blocks Ca(2+) influx and stimulates endoplasmic reticulum (ER) Ca(2+) release through the generation of mitochondrial reactive oxygen species (ROS), resulting in sustained depletion of ER Ca(2+) stores, protein synthesis inhibition, and cell death. c-Myc, a commonly activated oncogene, also promotes apoptosis in response to growth factor withdrawal and a variety of chemotherapeutic agents. We have investigated the role of c-myc in regulating sensitivity to econazole. Here, we show that c-myc-negative cells are profoundly resistant to econazole. c-Myc-negative rat fibroblasts failed to generate mitochondrial ROS in response to econazole and consequently failed to deplete the ER of Ca(2+). HL60 cells knocked down for c-myc expression also displayed decreased ROS generation and decreased econazole sensitivity. Addition of H(2)O(2) restored sensitivity to econazole in both c-myc-negative rat fibroblasts and c-myc knocked-down HL60 cells, supporting a role for ROS in cell death induction. c-Myc-negative cells and HL60 cells knocked down for c-myc have reduced mitochondrial content compared with c-myc-positive cells. The hypoxia sensor, hypoxia-inducible factor-1alpha (HIF-1alpha), interacts antagonistically with c-myc and also regulates mitochondrial biogenesis. Knockdown of HIF-1alpha in c-myc-negative cells increased mitochondrial content restored ROS generation in response to econazole and increased sensitivity to the drug. Taken together, these results show that c-myc and HIF-1alpha regulate sensitivity to econazole by modulating the ability of the drug to generate mitochondrial ROS.