BNIP3基因促细胞凋亡研究新进展

分子靶向治疗将成为未来肿瘤治疗的主导方向.BNIP3作为一种促凋亡基因,其在恶性肿瘤中发挥出的积极促凋亡作用早已引起国内外肿瘤研究学者的广泛关注,尤其是在BNIP3的分子结构、作用机制(尤其是促细胞凋亡的最新进展)、临床实践和应用前景方面.BNIP3基因在缺氧条件下可诱导细胞发生程序性死亡,即细胞凋亡.BNIP3促细胞凋亡线粒体途径根据有否caspase的参与而具有不同的作用机制.此外,BNIP3还可诱导细胞自噬.BNIP3基因甲基化后表达沉默可导致肿瘤细胞耐受缺氧,对放疗和化疗产生抵抗.BNIP3核内转移可使细胞逃避凋亡.BNIP3促细胞凋亡介导的肿瘤治疗研究已获得了成效.BNIP3有望成为一种新型的靶向治疗基因,在未来的肿瘤综合治疗中发挥积极的作用.     

Bnip3基因的表达调控及其与肿瘤的关系

Bnip3基因属于Bcl-2基因家族BH3-only亚家族,是一种线粒体促凋亡基因,是缺氧诱导因子（HIF）的下游应答基因之一。在缺氧条件下,Bnip3可诱导细胞发生凋亡或自噬,目前研究发现Bnip3与多种肿瘤发生发展及治疗密切相关,针对Bnip3基因的分子靶向治疗与放化疗联合,在肿瘤治疗上有较好的应用前景。     

Bcl-2家族在肿瘤进展和治疗中的意义

Bcl-2家族对于线粒体途径细胞凋亡具有双重调控作用,其促凋亡蛋白与抑凋亡蛋白的比例与肿瘤形成、肿瘤耐药性的产生及预后密切相关.因此,Bcl-2家族成为肿瘤生物治疗中的重要靶点,针对Bcl-2家族的某些生物治疗手段和短肽、有机小分子等新药被开发应用于Bcl-2高表达肿瘤的治疗.     

BH3结构域拟似物BH3I-2''''诱导人白血病细胞凋亡机理的探讨

目的:探讨BH3结构域拟似物BH3I-2'诱导白血病细胞发生凋亡的潜在机制,为其临床应用提供理论依据。方法:应用流式细胞仪、ELISA分析、WesternBlotting印渍技术检测BH3I-2'作用后白血病细胞K562、CEM的凋亡情况、线粒体△Ψm、ROS变化、NF-κB活性及凋亡相关蛋白表达。结果:BH3I-2'能显著诱导白血病细胞凋亡,引起细胞线粒体跨膜电位△Ψm下降、ROS生成并同时激活核转录因子NF-κB及抗凋亡蛋白的上调。结论:BH3结构域拟似物BH3I-2'通过消耗线粒体跨膜电位,诱导细胞氧自由基ROS生成,进而造成线粒体内膜损伤,触发线粒体通路引起细胞凋亡;并且也同时诱导了NF-κB、抗凋亡蛋白激活表达,提示药物诱导肿瘤细胞凋亡的同时也启动了细胞自身的保护机制。     

BH3结构域拟似物BH3I-2′诱导人白血病细胞凋亡机理的探讨

目的:探讨BH3结构域拟似物BH3I-2′诱导白血病细胞发生凋亡的潜在机制,为其临床应用提供理论依据.方法:应用流式细胞仪、ELISA分析、Western Blotting印渍技术检测BH3I-2′作用后白血病细胞K562、CEM的凋亡情况、线粒体△ψm、ROS变化、NF-κB活性及凋亡相关蛋白表达.结果:BH3I-2′能显著诱导白血病细胞凋亡,引起细胞线粒体跨膜电位△ψm下降、ROS生成并同时激活核转录因子NF-κB及抗凋亡蛋白的上调.结论:BH3结构域拟似物BH3I-2′通过消耗线粒体跨膜电位,诱导细胞氧自由基ROS生成,进而造成线粒体内膜损伤,触发线粒体通路引起细胞凋亡;并且也同时诱导了NF-κB、抗凋亡蛋白激活表达,提示药物诱导肿瘤细胞凋亡的同时也启动了细胞自身的保护机制.     

bcl-2家族BH3-only蛋白在依托泊苷诱导胃腺癌细胞凋亡中的作用

目的研究bcl-2家族BH3-only蛋白Noxa、Bim和PUMA在依托泊苷诱导胃腺癌细胞凋亡中的作用。方法Annexin V-FITC染色,流式细胞仪(FCM)检测细胞凋亡率,半定量RT-PCR检测细胞中BH3-only蛋白的mRNA表达量。结果依托泊苷诱导胃腺癌细胞凋亡具有剂量、时间依赖性,SGC-7901细胞系比BGC-823更加敏感,100μM的依托泊苷作用48小时后SGC-7901的凋亡率达到50%,而BGC-823的凋亡率只有20%。BH3-only蛋白Noxa的mRNA表达明显上调,Bim少量上调与依托泊苷诱导的细胞凋亡有关系;相反,PUMA的mRNA表达量在依托泊苷治疗前后没有变化。结论依托泊苷诱导的胃腺癌细胞凋亡与BH3-only蛋白Noxa和Bim表达上调有关联。     

BH3-only蛋白在非小细胞肺癌靶向治疗中的作用及意义

肺癌死亡率居全球恶性肿瘤死亡之首,非小细胞肺癌是肺癌中最常见的类型。在传统的抗肺癌治疗中,促进细胞凋亡是非小细胞肺癌治疗的一个重要组成部分,但抗肿瘤药物存在毒副作用大和耐药性等问题。因此,寻找新的抗肿瘤药物作用靶点成为非小细胞肺癌治疗的重点之一。BH3-only蛋白在凋亡的启动及凋亡通路的沟通中发挥极其重要的作用。BIM是BH3-only蛋白家族中的核心成员。以BIM为靶点的治疗在非小细胞肺癌的治疗中具有不可取代的作用。本文简单介绍了BCL-2家族和其中的BH3-only促凋亡蛋白,并且阐述了BIM、BH3-only蛋白在非小细胞肺癌靶向治疗中的重要作用。     

促凋亡蛋白Bim在肿瘤治疗中的研究进展

摘 要：Bim(Bcl-2 interacting mediator of cell death)是Bcl-2家族中BH3-only亚家族的成员,是一种重要的凋亡调节蛋白,在维持内环境稳定中有着重要的作用。Bim蛋白低表达与人类多种肿瘤的发生、发展和预后相关,为基因治疗提供新靶点。另外,Bim在肿瘤的化疗及靶向治疗中也起到十分重要的作用。     

溶酶体在细胞死亡中的介导作用

溶酶体作为细胞内消化器官,参与细胞自溶、防御等生物过程。近年来研究发现,溶酶体在死亡信号作用下释放以组织蛋白酶为主的多种水解酶,参与包括自噬及凋亡在内的细胞死亡,这一过程称为溶酶体途径的凋亡。溶酶体膜通透性增加程度是决定细胞死亡类型的重要因素。释放的组织蛋白酶可通过剪切Bc l-2家族蛋白,引起一系列的促凋亡反应,如线粒体膜通透性改变、激活caspase等;还可以反作用于溶酶体促进其通透性改变。肿瘤的侵袭转移伴随着溶酶体功能改变及组织蛋白酶表达增加,溶酶体的这些改变能使肿瘤细胞对死亡途径的敏感性增加。研究肿瘤相关的溶酶体成分及功能改变,可以为肿瘤治疗提供新的思路。     

Bcl-2 family member Mcl-1 expression is reduced under hypoxia by the E3 ligase FBW7 contributing to BNIP3 induced cell death in glioma cells

Mcl-1 is an anti-apoptotic Bcl-2 family member that is often over-expressed in the malignant brain tumor glioblastoma (GBM). It has been previously shown that epidermal growth factor receptors up-regulate Mcl-1 contributing to a cell survival response. Hypoxia is a poor prognostic marker in glioblastoma despite the fact that hypoxic regions have areas of necrosis. Hypoxic regions of GBM also highly express the pro-cell death Bcl-2 family member BNIP3, yet when BNIP3 is overexpressed in glioma cells, it induces cell death. The reasons for this discrepancy are unclear. Herein we have found that Mcl-1 expression is reduced under hypoxia due to degradation by the E3 ligase FBW7 leading to increased hypoxia induced cell death. This cell death is reduced by EGFR activation leading to increased Mcl-1 expression under hypoxia. Conversely, BNIP3 is over-expressed in hypoxia at times when Mcl-1 expression is decreased. Knocking down BNIP3 expression reduces hypoxia cell death and Mcl-1 expression effectively blocks BNIP3 induced cell death. Of significance, BNIP3 and Mcl-1 are co-localized under hypoxia in glioma cells. These results suggest that Mcl-1 can block the ability of BNIP3 to induce cell death under hypoxia in GBM tumors.     

HIF-1-dependent regulation of hypoxic induction of the cell death factors BNIP3 and NIX in human tumors

Solid tumors contain regions of hypoxia, a physiological stress that can activate cell death pathways and, thus, result in the selection of cells resistant to death signals and anticancer therapy. Bcl2/adenovirus EIB 19kD-interacting protein 3 (BNIP3) is a cell death factor that is a member of the Bcl-2 proapoptotic family recently shown to induce necrosis rather than apoptosis. Using cDNA arrays and serial analysis of gene expression, we found that hypoxia induces up-regulation of BNIP3 and its homologue, Nip3-like protein X. Analysis of human carcinoma cell lines showed that they are hypoxically regulated in many tumor types, as well as in endothelial cells and macrophages. Regulation was hypoxia inducible factor-1-dependent, and hypoxia inducible factor-1 expression was suppressed by von Hippel-Lindau protein in normoxic cells. Northern blotting and in situ hybridization analysis has revealed that these factors are highly expressed in human tumors compared with normal tissue and that BNIP3 is up-regulated in perinecrotic regions of the tumor. This study shows that genes regulating cell death can be hypoxically induced and are overexpressed in clinical tumors.     

The pro-cell death Bcl-2 family member, BNIP3, is localized to the nucleus of human glial cells: Implications for glioblastoma multiforme tumor cell survival under hypoxia

The Bcl-2 nineteen kilodalton interacting protein 3 (BNIP3) is a hypoxia-inducible proapoptotic member of the Bcl-2 family that induces cell death by associating with the mitochondria. Under normal conditions, BNIP3 is expressed in skeletal muscle and in the brain at low levels. In many human solid tumors, BNIP3 is upregulated in hypoxic regions but paradoxically, this BNIP3 expression fails to induce cell death. Herein, we have determined that BNIP3 is primarily localized to the nucleus of glial cells of the normal human brain, as well as in the malignant glioma cell line U251. Upon exposure of U251 cells to hypoxia, BNIP3 expression in the cytoplasm increases and localizes with the mitochondria, contributing to induction of cell death. In contrast, when BNIP3 is forcibly over expressed in the nucleus, it fails to induce cell death. Expression of N-terminal BNIP3 (lacking the transmembrane and conserved domains) in U251 cells blocks hypoxia-induced cell death acting as a dominant negative protein by binding to wild-type BNIP3 and blocking its association with the mitochondria. In glioblastoma multiforme (GBM) tumors, BNIP3 expression is increased in hypoxic regions of the tumor and is primarily localized to the nucleus in approximately 80% of tumors. Hence, BNIP3 is sequestered in the nucleus within the brain but under hypoxic conditions, BNIP3 becomes primarily cytoplasmic, promoting cell death. In GBMs, BNIP3 expression is increased but it remains sequestered in the nucleus in hypoxic regions, thereby blocking BNIP3's ability to associate with the mitochondria, providing tumor cells with a possible survival advantage.     

The C. elegans orthologue ceBNIP3 interacts with CED-9 and CED-3 but kills through a BH3- and caspase-independent mechanism

We have studied ceBNIP3, the orthologue of BNIP3 in C. elegans. Sequence analysis reveals that the different domains of BNIP3 have been conserved throughout evolution. ceBNIP3 contains a C-terminal transmembrane (TM) domain, a conserved domain (CD) of 19 amino acids, a BCL-2 homology-3 (BH3)-like domain and a PEST sequence. ceBNIP3 is expressed primarily as a 25 kDa monomer and a 50 kDa homodimer. After transfection, ceBNIP3 protein is rapidly degraded through a ubiquitin-dependent pathway by the proteasome. Like BNIP3, the TM domain of ceBNIP3 mediates the localization of the protein to mitochondria and is also necessary for homodimerization and cell death in mammalian cells. Neither the putative BH3 domain nor conserved domain is necessary for killing. ceBNIP3 protein interacts with CED-9 and BCL-XL, but unlike other pro-apoptotic BCL-2 family members, the BH3-like domain does not participate in dimerization. The ceBNIP3 TM domain mediates interaction with both CED-9 and BCL-XL. ceBNIP3 interacts with CED-3 but co-expression of CED-3 and ceBNIP3 does not significantly enhance induction of cell death in the presence or absence of CED-4. ceBNIP3 kills mammalian cells by a caspase-independent mechanism. In conclusion, we find that although ceBNIP3 interacts with CED-9 and CED-3 it kills by a BH3- and caspase-independent mechanism.     

Functional identification of the apoptosis effector BH3 domain in cellular protein BNIP1

BCL-2 family proteins play a central role in apoptosis regulation in mammals and in C. elegans. Mammalian cellular and viral anti-apoptosis proteins such as BCL-2 and E1B-19K interact with several cellular proteins. Some of these interacting proteins promote apoptosis and belong to the BCL-2 family. Certain BCL-2 family proapoptotic proteins such as BAX and BAK share extensive sequence homology with BCL-2. In contrast, certain pro-apoptotic proteins such as BIK and BID share a single death effector domain, BH3, with other BCL-2 family proteins. By mutational analysis, we show that one of the cellular proteins, BNIP1 (previously Nip-1), that interacts with BCL-2 family anti-apoptosis proteins is a 'BH3 alone' pro-apoptotic protein. Transient transfection of BNIP1 induces a moderate level of apoptosis. Deletions of the N-terminal 32 amino acid region and the C-terminal trans-membrane domain did not significantly affect pro-apoptotic activity. In contrast, deletions encompassing a region containing a motif similar to the BH3-domain abrogated the apoptotic activity. Substitution of BNIP1 BH3 domain for the corresponding sequence in BAX efficiently restored the apoptotic activity of BAX, establishing the functional identity of the BH3 domain of BNIP1. The N-terminal deletions of BNIP1 (that retain the BH3 domain) enhanced the level of interaction with BCL-XL. Mutants containing the BH3 deletions were still able to heterodimerize with BCL-XL while mutants lacking both the N-terminal region and the BH3 domain were unable to heterodimerize, suggesting that BNIP1 may bind to BCL-XL via two different binding motifs.     

The ERBB4/HER4 intracellular domain 4ICD is a BH3-only protein promoting apoptosis of breast cancer cells

ERBB4/HER4 (referred to here as ERBB4) is a unique member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases. In contrast to the other three members of the EGFR family (i.e., EGFR, ERBB2/HER2/NEU, and ERBB3), which are associated with aggressive forms of human cancers, ERBB4 expression seems to be selectively lost in tumors with aggressive phenotypes. Consistent with this observation, we show that ERBB4 induces apoptosis when reintroduced into breast cancer cell lines or when endogenous ERBB4 is activated by a ligand. We further show that ligand activation and subsequent proteolytic processing of endogenous ERBB4 results in mitochondrial accumulation of the ERBB4 intracellular domain (4ICD) and cytochrome c efflux, the essential and committed step of mitochondrial regulated apoptosis. Our results indicate that 4ICD is functionally similar to BH3-only proteins, proapoptotic members of the BCL-2 family required for initiation of mitochondrial dysfunction through activation of the proapoptotic multi-BH domain proteins BAX/BAK. Similar to other BH3-only proteins, 4ICD cell-killing activity requires an intact BH3 domain and 4ICD interaction with the antiapoptotic protein BCL-2, suppressed 4ICD-induced apoptosis. Unique among BH3-only proteins, however, is the essential requirement of BAK but not BAX to transmit the 4ICD apoptotic signal. Clinically, cytosolic but not membrane ERBB4/4ICD expression in primary human breast tumors was associated with tumor apoptosis, providing a mechanistic explanation for the loss of ERBB4 expression during tumor progression. Thus, we propose that ligand-induced mitochondrial accumulation of 4ICD represents a unique mechanism of action for transmembrane receptors, directly coupling a cell surface signal to the tumor cell mitochondrial apoptotic pathway.     

Silencing of the hypoxia-inducible cell death protein BNIP3 in pancreatic cancer

Hypoxic conditions exist within pancreatic adenocarcinoma, yet pancreatic cancer cells survive and replicate within this environment. To understand the mechanisms involved in pancreatic cancer adaptation to hypoxia, we analyzed expression of a regulator of hypoxia-induced cell death, Bcl-2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3). We found that BNIP3 was down-regulated in nine of nine pancreatic adenocarcinomas compared with normal pancreas despite the up-regulation of other hypoxia-inducible genes, including glucose transporter-1 and insulin-like growth factor-binding protein 3. Also, BNIP3 expression was undetectable even after hypoxia treatment in six of seven pancreatic cancer cell lines. The BNIP3 promoter, which was remarkably activated by hypoxia, is located within a CpG island. The methylation status of CpG dinucleotides within the BNIP3 promoter was analyzed after bisulfite treatment by sequencing and methylation-specific PCR. Hypermethylation of the BNIP3 promoter was observed in all BNIP3-negative pancreatic cancer cell lines and eight of 10 pancreatic adenocarcinoma samples. Treatment of BNIP3-negative pancreatic cancer cell lines with a DNA methylation inhibitor, 5-aza-2' deoxycytidine, restored hypoxia-induced BNIP3 expression. BNIP3 expression was also restored by introduction of a construct consisting of a full-length BNIP3 cDNA regulated by a cloned BNIP3 promoter. Restoration of BNIP3 expression rendered the pancreatic cancer cells notably more sensitive to hypoxia-induced cell death. In conclusion, down-regulation of BNIP3 by CpG methylation likely contributes to resistance to hypoxia-induced cell death in pancreatic cancer.