细胞自噬与肿瘤耐药

细胞自噬是一种细胞自我降解的过程,在适应代谢应激、保持基因组完整性及维持内环境稳定方面发挥重要作用. 在肿瘤治疗中,凋亡耐受是产生肿瘤耐药的重要机制. 细胞自噬可防止抗肿瘤药诱导的凋亡,促进肿瘤耐药. 然而,自噬性细胞死亡可能是凋亡耐受肿瘤细胞的一种死亡方式. 因此,细胞自噬对肿瘤细胞的耐药性有双重影响. 本文综述了细胞自噬的分子机制、细胞自噬与凋亡的关系、细胞自噬与肿瘤耐药以及治疗的主要研究进展.     

自噬抑制与肿瘤

自噬是一种在正常细胞和病理状态细胞中普遍存在的生理机制。自噬与肿瘤细胞的生存与凋亡关系密切,在很多肿瘤细胞中,其自噬活性均有改变。抑制肿瘤细胞中自噬活动可以促进肿瘤细胞的凋亡。在化疗诱导肿瘤细胞凋亡的同时,以自噬抑制剂抑制肿瘤细胞的自噬活动,可改善肿瘤的治疗效果。     

p53与细胞死亡

p53是一种重要的肿瘤抑制因子,是迄今发现与人类肿瘤相关性最高的分子之一。超过50%的人类肿瘤含有p53基因突变。因此,p53是肿瘤治疗中的重要分子靶点。p53依赖的细胞凋亡是其抑制肿瘤的重要机制之一。然而,最近研究发现,p53不仅参与细胞凋亡,还与程序性细胞坏死、细胞自噬以及铁诱导的细胞死亡等细胞死亡途径相关。促使肿瘤细胞死亡是肿瘤治疗的重要目标。因此,进一步了解p53与细胞死亡之间的关系,将有助于探索以p53为靶点的肿瘤治疗和p53相关肿瘤细胞耐药机制。     

自噬、自噬性细胞死亡与肿瘤的研究进展

自噬是绝大部分真核细胞中一种依赖于溶酶体的极度保守的生理过程,是细胞内物质再循环的有效机制。适度的自噬是细胞抵御不良环境的生存方式,但当发生过度的自噬时,将引起细胞的死亡,这种死亡方式称为自噬性细胞死亡。自噬性细胞死亡不同于凋亡,表现为细胞中出现大量包裹着细胞质和细胞器的自噬体。越来越多的研究提示,自噬与自噬性细胞死亡与某些恶性肿瘤的发生、发展关系密切。在各种不利环境下,自噬可作为一种应急机制维持肿瘤细胞的生存,而自噬性细胞死亡诱发后又可清除肿瘤细胞。现就自噬与肿瘤的研究进展作一综述。     

细胞自噬在肿瘤化疗耐药中的作用

肿瘤有多种机制产生化疗药物耐药性．自噬是一种在正常细胞和病理细胞中普遍存在的生理机制,调控自噬的分子和信号传导通路错综复杂．自噬与凋亡有着独特的交叉联系,使得自噬在肿瘤化疗耐药性中发挥着促进或抑制耐药的双重作用．自噬在肿瘤耐药中的这种截然相反的作用与化疗给药浓度、细胞类型、自噬强度等因素有关,但具体机制尚未完全明确．然而,将自噬途径作为治疗肿瘤、降低化疗药物耐药性的靶点有着广阔的应用前景．     

自噬的形态特征及分子调控

自噬过程是生物进化过程中保留下来的一种细胞蛋白和细胞器的循环利用机制,一般认为自噬过程对于细胞在恶劣环境下生存具有重要意义.而细胞的发育和凋亡与自噬有着密切的关系.本文通过自噬体的形成方式综述了三种自噬形式的形态特征以及自噬的分子调控对细胞的影响.     

自噬与DNA损伤修复及其对肿瘤的影响

DNA损伤与肿瘤的发生发展密切相关。当DNA损伤发生时,会触发一系列的损伤应答反应以帮助细胞生存,其中即包括对自噬的诱导。ATM、P53和PARP1等多种参与DNA损伤修复的效应因子通过影响AMPK、mTOR以及一些凋亡蛋白等启动自噬。而作为一种降解途径,自噬则可通过调节DNA修复相关蛋白的水平直接影响同源重组修复、非同源末端连接修复和核苷酸切除修复等促进DNA修复,以及通过维持细胞内稳态间接促进DNA修复,从而在正常细胞的恶性转化和肿瘤耐药等发生机制中扮演重要角色。此外,DNA修复失败时,自噬也可作为一种肿瘤细胞的程序性死亡方式。因此研究自噬通过调节DNA损伤修复而对肿瘤的影响对于理解肿瘤发生的机制和提供治疗思路都有重要意义。     

自噬与肿瘤耐受的关系

肿瘤是机体在各种致癌因素作用下,局部组织的某一个细胞在基因水平上失去对其生长的正常调控,导致其克隆性异常增生而形成的新生物。目前化疗和放疗是其治疗的重要手段,但一直以来,耐受性的产生成为肿瘤治疗的主要障碍。自噬是一种进化保守的溶酶体依赖的自身降解途径,越来越多的证据表明肿瘤的耐受性与自噬有关:放疗和化疗可以诱导保护性自噬的产生,帮助肿瘤细胞逃避凋亡途径。其机制可能与PI3KAkt-mTOR通路、Beclin 1、ATP、p53等有关,深入了解自噬与肿瘤耐受性之间的调控不仅为克服肿瘤细胞耐受性提供了靶点,也为自噬与凋亡关系的研究提供了线索。     

小檗碱对乳腺癌MDA-MB-231细胞增殖抑制作用及其分子机制研究

本研究的目的是为了探索小檗碱对乳腺癌MDA-MB-231细胞增殖的影响以及阐明小檗碱促乳腺癌细胞凋亡的分子机制。在实验过程中,我们通过MTT检测小檗碱对乳腺癌MDA-MB-231细胞增殖的抑制作用,采用Annexin-V/PI染色定量考察小檗碱对肿瘤细胞凋亡的影响,运用Western Blot实验检测肿瘤相关通路蛋白表达来进行研究。实验表明小檗碱对乳腺癌MDA-MB-231细胞增殖具有抑制作用,使细胞中自噬因子Beclin 1表达增加,诱导细胞自噬泡的形成,导致肿瘤细胞发生凋亡。综上说明小檗碱是通过抑制AKT-mTOR通路,诱导MDA-MB-231细胞的自噬以及凋亡,从而发挥抗肿瘤作用。     

雷公藤甲素诱导HeLa细胞p53依赖的自噬和凋亡

自噬与凋亡被认为是细胞程序性死亡的两种重要途径,二者的交互联系对阐明药物的抗肿瘤机理有重要价值.众多的研究表明,雷公藤甲素对多种肿瘤细胞都具有显著的抑制作用.细胞凋亡与自噬可被相同的因素所诱导,p53蛋白可以同时对二者起调控作用,在自噬与凋亡的交互作用(crosstalk)中扮演着重要角色.本文以He La细胞为模型,研究雷公藤甲素诱导He La细胞发生自噬和凋亡的机制,并通过抑制p53依赖的转录,研究雷公藤甲素诱导He La细胞p53依赖的自噬和凋亡交互联系.     

Exploiting death receptor signaling pathways for tumor therapy

Apoptosis or programmed cell death is a key regulator of physiological growth control and regulation of tissue homeostasis. Tipping the balance between cell death and proliferation in favor of cell survival may result in tumor formation. Moreover, current cancer therapies, e.g. chemotherapy, gamma-irradiation, immunotherapy or suicide gene therapy, primarily exert their antitumor effect by triggering an evolutionary conserved apoptosis program in cancer cells. For example, death receptor signaling has been implied to contribute to the efficacy of cancer therapy. Thus, failure to undergo apoptosis in response to anticancer therapy because of defects in death receptor pathways may result in resistance. Further insights into the mechanisms regulating apoptosis in response to anticancer therapy and how cancer cells evade cell death may provide novel opportunities for targeted therapeutics. Thus, agents designed to selectively activate death receptor pathways may enhance the efficacy of conventional therapies and may even overcome some forms of cancer resistance.     

Selective inactivation of a Fas-associated death domain protein (FADD)-dependent apoptosis and autophagy pathway in immortal epithelial cells

Although evasion of apoptosis is thought to be required for the development of cancer, it is unclear which cell death pathways are evaded. We previously identified a novel epithelial cell death pathway that works in normal cells but is inactivated in tumor cells, implying that it may be targeted during tumor development. The pathway can be activated by the Fas-associated death domain (FADD) of the adaptor protein but is distinct from the known mechanism of FADD-induced apoptosis through caspase-8. Here, we show that a physiological signal (tumor necrosis factor-related apoptosis-inducing ligand) can kill normal epithelial cells through the endogenous FADD protein by using the novel FADD death domain pathway, which activates both apoptosis and autophagy. We also show that selective resistance to this pathway occurs when primary epithelial cells are immortalized and that this occurs through a mechanism that is independent of known events (telomerase activity, and loss of function of p53, Rb, INK4a, and ARF) that are associated with immortalization. These data identify a novel cell death pathway that combines apoptosis and autophagy and that is selectively inactivated at the earliest stages of epithelial cancer development.     

Apoptosis resistance in tumor cells

Various antitumor agents induce apoptotic cell death in tumor cells. Since the apoptosis program in tumor cells plays a critical role in the chemotherapy-induced tumor cell killing, it is suggested that the defect in the signaling pathway of apoptosis could cause a new form of multidrug resistance in tumor cells. This article describes the recent findings concerning the mechanisms of chemotherapy-induced apoptosis and discusses the implication of apoptosis resistance in cancer chemotherapy. This revised version was published online in August 2006 with corrections to the Cover Date.     

细胞凋亡（Apoptosis）与癌基因

细胞凋亡是细胞衰老、死亡过程的主要形式.最近研究发现有多种癌基因与抑癌基因参与细胞凋亡过程.因此目前认为癌基因与抑癌基因不仅控制细胞增殖、分化,而且调节细胞凋亡.细胞凋亡受阻或缺陷可能是肿瘤发生的基础之一.     

Triazole analog 1-(1-benzyl-5-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)-2-(4-bromophenylamino)-1-(4-chlorophenyl)ethanol induces reactive oxygen species and autophagy-dependent apoptosis in both in vitro and in vivo breast cancer models

Autophagy is considered as an important cell death mechanism that closely interacts with other common cell death programs like apoptosis. Critical role of autophagy in cell death makes it a promising, yet challenging therapeutic target for cancer. We identified a series of 1,2,3-triazole analogs having significant breast cancer inhibition property. Therefore, we attempted to study whether autophagy and apoptosis were involved in the process of cancer cell inhibition. The lead molecule, 1-(1-benzyl-5-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)-2-(4-bromophenylamino)-1-(4-chlorophenyl)ethanol (T-12) induced significant cell cycle arrest, mitochondrial membrane depolarization, apoptosis and autophagy in MCF-7 and MDA-MB-231 cells. T-12 increased reactive oxygen species and its inhibition by N-acetyl-l-cysteine protected breast cancer cells from autophagy and apoptosis. Autophagy inhibitor, 3-methyladenine abolished T-12 induced apoptosis, mitochondrial membrane depolarization and reactive oxygen species generation. This suggested that T-12 induced autophagy facilitated cell death rather than cell survival. Pan-caspase inhibition did not abrogate T-12 induced autophagy, suggesting that autophagy precedes apoptosis. In addition, T-12 inhibited cell survival pathway signaling proteins, Akt, mTOR and Erk1/2. T-12 also induced significant regression of tumor with oral dose of as low as 10 mg/kg bodyweight in rat mammary tumor model without any apparent toxicity. In presence of reactive oxygen species inhibitor (N-acetyl-l-cysteine) and autophagy inhibitor (chloroquine), T-12 induced tumor regression was significantly decreased. In conclusion, T-12 is a potent inducer of autophagy-dependent apoptosis in breast cancer cells both in vitro and in vivo and can serve as an important lead in development of new anti-tumor therapy.     

Interplay between apoptosis and autophagy,a challenging puzzle: New perspectives on antitumor chemotherapies

Autophagy is a mechanism of protection against various forms of human diseases, such as cancer, in which autophagy seems to have an extremely complex role. In cancer, there is evidence that autophagy may be oncogenic in some contexts, whereas in others it clearly contributes to tumor suppression. In addition, studies have demonstrated the existence of a complex relationship between autophagy and cell death, determining whether a cell will live or die in response to anticancer therapies. Nevertheless, we still need to complete the autophagy–apoptosis puzzle in the tumor context to better address appropriate chemotherapy protocols with autophagy modulators. Generally, tumor cell resistance to anticancer induced-apoptosis can be overcome by autophagy inhibition. However, when an extensive autophagic stimulus is activated, autophagic cell death is observed. In this review, we discuss some details of autophagy and its relationship with tumor progression or suppression, as well as role of autophagy–apoptosis in cancer treatments.     

Inhibition of thromboxane synthase induces lung cancer cell death via increasing the nuclear p27

The role of thromboxane in lung carcinogenesis is not clearly known, though thromboxane B2 (TXB₂) level is increased and antagonists of thromboxane receptors or TXA2 can induce apoptosis of lung cancer cells. p27, an atypical tumor suppressor, is normally sequestered in the nucleus. The increased nuclear p27 may result in apoptosis of tumor cells. We hypothesize that the inhibition of thromboxane synthase (TXS) induces the death of lung cancer cells and that such inhibition is associated with the nuclear p27 level. Our experiment showed that the inhibition of TXS significantly induced the death or apoptosis in lung cancer cells. The activity of TXS was increased in lung cancer. The nuclear p27 was remarkably reduced in lung cancer tissues. The inhibition of TXS caused the cell death and apoptosis of lung cancer cells, likely via the elevation of the nuclear p27 since the TXS inhibition promoted the nuclear p27 level and the inhibition of p27 by its siRNA recovered the cell death induced by TXS inhibition. Collectively, lung cancer cells produce high levels of TXB₂ but their nuclear p27 is markedly reduced. The inhibition of TXS results in the p27-related induction of cell death in lung cancer cells.     

Caspase 3-mediated stimulation of tumor cell repopulation during cancer radiotherapy

In cancer treatment, apoptosis is a well-recognized cell death mechanism through which cytotoxic agents kill tumor cells. Here we report that dying tumor cells use the apoptotic process to generate potent growth-stimulating signals to stimulate the repopulation of tumors undergoing radiotherapy. Furthermore, activated caspase 3, a key executioner in apoptosis, is involved in the growth stimulation. One downstream effector that caspase 3 regulates is prostaglandin E(2) (PGE(2)), which can potently stimulate growth of surviving tumor cells. Deficiency of caspase 3 either in tumor cells or in tumor stroma caused substantial tumor sensitivity to radiotherapy in xenograft or mouse tumors. In human subjects with cancer, higher amounts of activated caspase 3 in tumor tissues are correlated with markedly increased rate of recurrence and death. We propose the existence of a cell death-induced tumor repopulation pathway in which caspase 3 has a major role.     

Autophagy-driven cell fate decision maker: Activated microglia induce specific death of glioma cells by a blockade of basal autophagic flux and secondary apoptosis/necrosis

Programmed cell death is classified into apoptosis and autophagic cell death. The extensive crosstalk that occurs between these two types of death often prevents a clear identification of the leading death mechanism in a given experimental system. An accurate assessment of the type of death at work is of crucial relevance for the design of efficient cancer therapies aiming at eliminating tumor cells. Indeed, accumulating evidence indicates that resistance of tumor cells to apoptosis can be overcome by induction of autophagy. The latter would thus seem to represent an ideal strategy for eliminating certain tumor cells, except for the fact that autophagy induction may also contribute to cell survival.

It therefore is of paramount importance to clarify the mechanistic links between autophagy and apoptosis as well as the nature of autophagy-dependent cell death. We recently reported that glioma cells resistant to death ligands were killed by the supernatant of activated microglia. What at first glance seemed to be apoptosis turned out to be autophagy-dependent cell death resulting from a blockade in the autophagic flux. This blockade most likely occurs at the level of lysosome recycling. We hypothesize that this autophagy-dependent process leads to either apoptosis or necrosis depending on the extent of lysosomal permeabilization and on the relative contribution of other cellular compartments. Autophagy therefore appears in our model as a cell-fate decision maker, not as a cell death execution pathway.