Heat shock-induced apoptosis

描述（由申请人提供）：热疗或热休克疗法目前正用于II/III期临床试验，单独或与放疗或化疗联合治疗各种癌症。不幸的是，虽然强烈的热休克诱导细胞凋亡，其潜在的机制仍然存在争议和不清楚。我们最近表明，热休克不需要任何已知的引发剂半胱天冬酶或其激活复合物来诱导细胞凋亡。我们现在假设热休克诱导细胞死亡，部分是通过刺激快速内溶酶体膜透化（ELMP），这与胞质酸化和组织蛋白酶释放到细胞质中，这两者都参与加工的procaspase-3和促凋亡的BH 3-唯一的蛋白质投标。重要的是，热休克诱导的线粒体外膜透化（MOMP）对于细胞死亡是必不可少的，因为过表达Bcl-2或缺乏Bid或促凋亡Bcl-2家族成员Bax和Bak的细胞对细胞死亡具有抗性。MOMP对细胞死亡至关重要，很可能是因为它促进细胞凋亡抑制剂（IAP）拮抗剂的释放，这反过来又促进半胱天冬酶活性。值得注意的是，热休克还需要c-Jun N-末端激酶（JNKs）诱导MOMP，我们发现JNKs通过一个非常新颖的途径激活，涉及形成所谓的细胞质“应激颗粒”（SG）。我们推测，SG的形成是通过热诱导的RNA结合蛋白TIA-1的聚集而启动的，并且SG进而通过肿瘤坏死因子（TNF）受体相关因子2（TRAF 2）和TGF-2激活激酶1（TAK 1）依赖性途径激活JNK。我们进一步推测JNK通过激活额外的仅BH 3蛋白（如Bim）和/或通过抑制特异性抗凋亡Bcl-2家族成员（如Bcl-xL或Mcl-1）使细胞对热休克诱导的MOMP敏感。在以下三个具体目标中，我们提出（1）确定ELMP是否促进细胞溶质酸化并确定ELMP如何受热休克蛋白70（Hsp 70）调节，（2）确定组织蛋白酶在半胱氨酸蛋白酶原-3和Bid活化中的作用，以及（3）表征独特的SG-TRAF 2-TAK 1-MAPKK-JNK途径，其受Hsp 70调节，以及JNK在热休克后的下游靶点。总之，这项拨款提案将确定热休克诱导细胞凋亡的基本机制，这是高度相关的热疗作为一种临床上有用的治疗选择的新的兴趣。公共卫生相关性：该资助项目的重点是解开介导热休克诱导细胞死亡的细胞机制。热休克，或热疗，目前正在临床试验中使用，单独或作为辅助化疗或放疗治疗各种癌症。不幸的是，人们对热休克如何杀死细胞知之甚少。我们在这一领域的初步工作表明，热休克诱导细胞死亡的机制是非常不同的其他类型的刺激。因此，预计本文提出的工作将显着提高我们对热休克在临床中如何工作的理解，并可能揭示未来可用于治疗的新途径。

DESCRIPTION (provided by applicant): Hyperthermia or heat shock therapy is currently being utilized in phase II/III clinical trials, either alone or in combination with radiation or chemotherapy, for the treatment of various cancers. Unfortunately, though intense heat shock induces apoptosis, the underlying mechanisms remain controversial and unclear. We have recently shown that heat shock does not require any of the known initiator caspases or their activating complexes to induce apoptosis. We now hypothesize that heat shock induces cell death, in part by stimulating rapid endo-lysosomal membrane permeabilization (ELMP), which coincides with cytosolic acidification and release of cathepsins into the cytoplasm, both of which participate in the processing of procaspase-3 and the proapoptotic BH3-only protein Bid. Importantly, heat shock-induced mitochondrial outer membrane permeabilization (MOMP) is essential for cell death, as cells that overexpress Bcl-2-or are deficient in Bid or the proapoptotic Bcl-2 family members Bax and Bak-are resistant to cell death. MOMP is critical for cell death most likely because it facilitates the release of inhibitor of apoptosis (IAP) antagonists, which in turn promote caspase activity. Remarkably, heat shock also requires c-Jun N-terminal kinases (JNKs) to induce MOMP, and we find that JNKs are activated through a highly novel pathway involving the formation of so-called cytoplasmic "stress granules" (SGs). We hypothesize that formation of SGs is initiated through heat-induced aggregation of the RNA binding protein TIA-1, and that SGs in turn activate JNKs through a tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2) and TGF2- activating kinase 1 (TAK1)-dependent pathway. We further speculate that JNKs sensitize cells to heat shock-induced MOMP by activating additional BH3-only proteins, such as Bim, and/or by inhibiting specific antiapoptotic Bcl-2 family members, such as Bcl-xL or Mcl-1. In the following three specific aims, we propose (1) to determine if ELMP elicits cytosolic acidification and to determine how ELMP is regulated by heat shock protein 70 (Hsp70), (2) to establish the roles of cathepsins in the activation of procaspase-3 and Bid, and (3) to characterize the unique SG-TRAF2-TAK1-MAPKK-JNK pathway, its regulation by Hsp70, and the downstream targets of JNK following heat shock. In summary, this grant proposal would determine the basic mechanisms of heat shock-induced apoptosis, which are highly relevant given the renewed interest in hyperthermia as a clinically useful treatment option. PUBLIC HEALTH RELEVANCE: The focus of this grant project is to unravel the cellular mechanisms that mediate heat shock-induced cell death. Heat shock, or hyperthermia, is currently being used in clinical trials, either alone or as an adjunct to chemo- or radiotherapy for the treatment of various cancers. Unfortunately, very little is known about how heat shock kills cells. Our preliminary work in this area suggests that heat shock induces cell death through mechanisms that are very different from other types of stimuli. Thus, it is anticipated that the work proposed herein will significantly improve our understanding of how heat shock works in the clinic and may shed light on new pathways that can be exploited therapeutically in the future.