世界生命科学前沿动态周报（八十）

（6.17-6.23/2012）
美宝国际集团:陶国新 

　　主要内容：细胞周期同步停滞于G1期促进癌细胞对抗癌药物的敏感性和细胞凋亡; 大脑的信息高速路; 发现Foxo3a助长癌症改变目前的治疗模式; 基质刚性控制了内皮分化和心脏前体的形态发生; 用于生物工程肾脏的“脚手架”; 增强Thbd-aPC通路的作用能够缓解电离辐射损伤。

　　焦点动态：细胞周期同步停滞于G1期促进癌细胞对抗癌药物的敏感性和细胞凋亡。

1. 细胞周期同步停滞于G1期促进癌细胞对抗癌药物的敏感性和细胞凋亡

【动态】美国科学家最近发现了一种提高多发性骨髓瘤治疗效率的策略. 通过两种抗癌药物精确掌握时机的顺序使用, 分两步使癌细胞先减弱抵抗力继而被杀死.  首先是用试验药物PD0332991,继而是已被批准用于骨髓瘤和淋巴瘤的药物硼替佐米(bortezomib),一种蛋白酶抑制剂, 以低于正常的剂量，诱导从同步的细胞周期G1期刚刚释放出来的癌细胞自杀。根本上讲癌症是一种细胞增殖失控的疾病，相对的，健康个体内细胞分裂受细胞周期的调控，一系列有序的程序性基因表达产生的高度控制的蛋白网络驱动细胞通过各个检查站。 依赖细胞周期蛋白的激酶（CDKs）推动细胞经历其周期性的四个阶段。其中CDK4和CDK6推动细胞通过G1期进入后面阶段进行细胞分裂，而PD0332991是一个对CDK4和CDK6有高度选择性的小分子，能够可逆的抑制这两个酶，连续使用PD0332991能够将所有癌细胞同步于G1期，在G1期的长期停滞扰乱了癌细胞的基因表达，增大了其代谢负荷和复制DNA的能量需求，削弱并使癌细胞对传统抗癌药物更为敏感，大大增加了硼替佐米诱导的癌细胞自杀。进一步的研究发现在PD0332991造成的G1期停滞期间，骨髓瘤细胞失去了必须的存活因子IRF4蛋白，但出现了几种促凋亡蛋白。

【点评】 这些发现首次表明癌细胞细胞周期调控关键的存活和凋亡基因，也代表了细胞周期的生物学基础研究与直接医学应用的无缝整合。该治疗癌症的策略能否治愈或大大改善多发性骨髓瘤还需等待人体临床实验的结果。

【参考论文】   
Blood, 2012; DOI: 10.1182/blood-2012-03-415984
Prolonged early G1 arrest by selective CDK4/CDK6 inhibition sensitizes myeloma cells to cytotoxic killing through cell cycle-coupled loss of IRF4
X. Huang, M. Di Liberto, D. Jayabalan, et al.   
Dysregulation of cyclin-dependent kinase (CDK)4 and CDK6 by gain of function or loss of inhibition is common in human cancer including multiple myeloma, but success in targeting CDK with broad-spectrum inhibitors has been modest. By selective and reversible inhibition of CDK4/CDK6, we have developed a strategy to both inhibit proliferation and enhance cytotoxic killing of cancer cells. We show that induction of prolonged early-G1 arrest (pG1) by CDK4/CDK6 inhibition halts gene expression in early-G1 and prevents expression of genes programmed for other cell cycle phases. Removal of the early-G1 block leads to S-phase synchronization (pG1-S) but fails to completely restore scheduled gene expression. Consequently, the IRF4 protein required to protect myeloma cells from apoptosis is markedly reduced in pG1 and further in pG1-S in response to cytotoxic agents such as the proteasome inhibitor bortezomib. The coordinated loss of IRF-4 and gain of Bim sensitize myeloma tumor cells to bortezomib-induced apoptosis in pG1 in the absence of Noxa and more profoundly in pG1-S in cooperation with Noxa in vitro. Induction of pG1 and pG1-S by reversible CDK4/CDK6 inhibition further augments tumor-specific bortezomib killing in myeloma xenografts. Reversible inhibition of CDK4/CDK6 in sequential combination therapy thus represents a novel mechanism-based cancer therapy.

 2.  大脑的信息高速路

【动态】荷兰和美国科学家对人体大脑结构神经网络连接的研究最近发现了一类特殊的大脑区域，它们高度互联和处于中心地位，这些枢纽区域相互密切连接，在人脑中形成一个“富人俱乐部”，连接这些枢纽区域的那些通路形成了大脑通讯的一个中心的高花费（能量和空间上）高容量的主干网，占据了总体通讯花费的40%。而且，神经节点之间69%的通讯最短通路要途经“富人俱乐部”，大部分这类通讯途径由井然有序的路段构成，先进入再穿越，后离开“富人俱乐部”。这种有序的最短途通讯线路的普遍存在意味着中枢通讯利用不同脑区之间信息传递的动态线路安排，其中高度中心地位的“富人俱乐部”其重要作用。这些研究结果表明“富人俱乐部”的骨干网在大脑区域间信号交通上起重要作用，形成了中枢地位的高花费高容量的大脑通讯主干网，在几十亿脑细胞间提供了快速有效的通讯，吸纳，转换和传递信息。

【点评】 该研究对于大脑如何高效处理繁重的信息传递有了更深入的理解。

【参考论文】   
Proceedings of the National Academy of Sciences, 2012 DOI:10.1073/pnas.1203593109
High-cost, high-capacity backbone for global brain communication
Martijn P. van den Heuvel, René S. Kahn, Joaquín Goñi and Olaf Sporns. 
Network studies of human brain structural connectivity have identified a specific set of brain regions that are both highly connected and highly central. Recent analyses have shown that these putative hub regions are mutually and densely interconnected, forming a “rich club” within the human brain. Here we show that the set of pathways linking rich club regions forms a central high-cost, high-capacity backbone for global brain communication. Diffusion tensor imaging (DTI) data of two sets of 40 healthy subjects were used to map structural brain networks. The contributions to network cost and communication capacity of global cortico-cortical connections were assessed through measures of their topology and spatial embedding. Rich club connections were found to be more costly than predicted by their density alone and accounted for 40% of the total communication cost. Furthermore, 69% of all minimally short paths between node pairs were found to travel through the rich club and a large proportion of these communication paths consisted of ordered sequences of edges (“path motifs”) that first fed into, then traversed, and finally exited the rich club, while passing through nodes of increasing and then decreasing degree. The prevalence of short paths that follow such ordered degree sequences suggests that neural communication might take advantage of strategies for dynamic routing of information between brain regions, with an important role for a highly central rich club. Taken together, our results show that rich club connections make an important contribution to interregional signal traffic, forming a central high-cost, high-capacity backbone for global brain communication.

 3. 发现Foxo3a助长癌症改变目前的治疗模式

【动态】最近美国科学家发现一种被广泛认为可以对抗多种癌症的分子Foxo3a 实际上帮助了致命的甲状腺癌生长，而目前在人体试验中的癌症疗法可能助长这一作用。他们在未分化的甲状腺癌中叉头转录因子Foxo3a不是原以为的肿瘤抑制因子，相反是致命的肿瘤促进因子。在试验室此种肿瘤模型中将Foxo3a关闭，癌细胞生长缓慢，但放开Foxo3a后癌细胞生长就快的多了。以前的认识是：Foxo3a应对各种细胞包括癌细胞中产生的压力，打开细胞核里的触发细胞死亡的基因，而癌细胞通过Akt蛋白将Foxo3a从细胞核转移到细胞质中分解掉而关闭其功能。该研究利用Akt抑制剂将癌细胞的Foxo3a留在细胞核里,  本想它帮助杀死癌细胞，却观察到它加速了癌细胞的生长。这使得我们需要重新考虑Akt抑制剂在癌症治疗中的使用，因其机理之一是使Foxo3a在细胞核中保持活性。该研究还发现Foxo3a打开了细胞周期蛋白A1的基因表达，而细胞周期蛋白A1是促进癌细胞生长的。

【点评】 该研究发现了Foxo3a对癌细胞的正反双重作用，可能改变目前癌症治疗的一些既有模式。

【参考论文】   
Journal of Cell Science, June 20, 2012 DOI: 10.1242/jcs.097428
Foxo3a drives proliferation in anaplastic thyroid carcinoma via transcriptional regulation of cyclin A1: A paradigm shift that impacts current therapeutic strategies
Laura A. Marlow, Christina A. von Roemeling, Simon J. Cooper, et al.
The Forkhead transcription factor, FoxO3a, is a known suppressor of primary tumor growth via transcriptional regulation of key genes regulating cell cycle arrest and apoptosis. In many types of cancer, in response to growth factor signaling, FoxO3a is phosphorylated by Akt, resulting in its exclusion from the nucleus. Here we show that FoxO3a remains nuclear in anaplastic thyroid carcinoma (ATC). This correlates with lack of Akt phosphorylation at S473 in ATC cell lines and patient ATC tissues, providing a potential explanation for nuclear FoxO3a. Mechanistically, nuclear FoxO3a promotes cell cycle progression by transcriptional upregulation of cyclin A1, promoting proliferation of human ATC cells. Silencing FoxO3a with a reverse genetics approach leads to down-regulation of CCNA1 mRNA and protein. This combined data implicates an entirely novel function for FoxO3a in ATC promotion by enhancing cell cycle progression and tumor growth via transcriptional upregulation of cyclin A1. This is clinically relevant since we detected highly elevated CCNA1 mRNA and protein levels in ATC patient tumor tissues. Our data indicate therapeutic inactivation of FoxO3a may lead to attenuation of tumor expansion in ATC. This new paradigm also suggests caution related to current dogma focused upon reactivation of FoxO3a as a therapeutic strategy against cancers harboring active PI3-K and Akt signaling pathways.

 4.  基质刚性控制了内皮分化和心脏前体的形态发生

【动态】组织发育和再生牵涉到紧密协调和整合的多种过程：常驻干细胞和前体细胞的选择性增殖，分化为目标体细胞，空间形态的组织。美国科学家对这一过程中机械环境的最新研究显示源自本地心脏组织的多能细胞持续监测细胞基质的刚度并显示当刚度非常接近心肌细胞时会增强增殖，内皮分化和形态发生。这些过程的机械调控需要p190RhoGAP，一种针对RhoA的鸟苷三磷酸酶激活蛋白，通过依赖和不依赖RhoA的机制起作用。这一发现可能引出更好的治疗心脏病的方法。心肌组织经历心脏病发作后一般会形成虚弱的疤痕，而最近有一些报道可用干细胞生产健康组织阻止疤痕的产生。

【点评】 p190RhoGAP的发现及其机械调控作用会有助于干细胞顺利变成特定健康组织。该研究增强了我们对干细胞生物学的理解并提示了新方式来控制心肌干细胞在移植入心脏前后的行为。

【参考论文】   
Science Signaling, 2012; 5 (227): ra41 DOI: 10.1126/scisignal.2003002
Matrix Rigidity Controls Endothelial Differentiation and Morphogenesis of Cardiac Precursors
Kshitiz, M. E. Hubbi, E. H. Ahn, et al.  
Tissue development and regeneration involve tightly coordinated and integrated processes: selective proliferation of resident stem and precursor cells, differentiation into target somatic cell type, and spatial morphological organization. The role of the mechanical environment in the coordination of these processes is poorly understood. We show that multipotent cells derived from native cardiac tissue continually monitored cell substratum rigidity and showed enhanced proliferation, endothelial differentiation, and morphogenesis when the cell substratum rigidity closely matched that of myocardium. Mechanoregulation of these diverse processes required p190RhoGAP, a guanosine triphosphatase–activating protein for RhoA, acting through RhoA-dependent and -independent mechanisms. Natural or induced decreases in the abundance of p190RhoGAP triggered a series of developmental events by coupling cell-cell and cell-substratum interactions to genetic circuits controlling differentiation.

 5.  用于生物工程肾脏的“脚手架”

【动态】美国科学家在实验室中制造替代肾脏的长期项目最近到达了一个早期里程碑，他们用猪的肾脏去除所有动物细胞，只留器官骨架，制造出了支持结构“脚手架”，病人自己的细胞可以在上面生长形成的器官理论上不会被病人自身所排斥。再生医学已经成功地制造了生物工程皮肤，软骨，膀胱，输尿管，气管和血管植入患者体内。这些结构在发育出自身的血管之前能够临近的血管组织获取氧气和养料。但是，再生医学的“圣杯”是制造出更复杂的器官如肾，肝，心脏和胰腺。这些器官含有大量细胞必须有自己的氧气供应才能存活，这种生物工程就需要有完整脉管系统的“脚手架”。

【点评】 这种异种脚手架并不能完全排除机体的排斥，而且生物工程制造器官也不是再生医学的圣杯，真正的圣杯是无需任何移植的器官原位再生。

【参考论文】   
Annals of Surgery, 2012; : 1 DOI:10.1097/SLA.0b013e31825a02ab
Production and Implantation of Renal Extracellular Matrix Scaffolds From Porcine Kidneys as a Platform for Renal Bioengineering Investigations
Giuseppe Orlando, Alan C. Farney, Samy S. Iskandar, et al.
BACKGROUND:
It is important to identify new sources of transplantable organs because of the critical shortage of donor organs. Tissue engineering holds the potential to address this issue through the implementation of decellularization-recellularization technology.
OBJECTIVE:
To produce and examine acellular renal extracellular matrix (ECM) scaffolds as a platform for kidney bioengineering.
METHODS:
Porcine kidneys were decellularized with distilled water and sodium dodecyl sulfate-based solution. After rinsing with buffer solution to remove the sodium dodecyl sulfate, the so-obtained renal ECM scaffolds were processed for vascular imaging, histology, and cell seeding to investigate the vascular patency, degree of decellularization, and scaffold biocompatibility in vitro. Four whole renal scaffolds were implanted in pigs to assess whether these constructs would sustain normal blood pressure and to determine their biocompatibility in vivo. Pigs were sacrificed after 2 weeks and the explanted scaffolds were processed for histology.
RESULTS:
Renal ECM scaffolds were successfully produced from porcine kidneys. Scaffolds retained their essential ECM architecture and an intact vascular tree and allowed cell growth. On implantation, unseeded scaffolds were easily reperfused, sustained blood pressure, and were tolerated throughout the study period. No blood extravasation occurred. Pathology of explantedscaffolds showed maintenance of renal ultrastructure. Presence of inflammatory cells in the pericapsular region and complete thrombosis of the vascular tree were evident.
CONCLUSIONS:
Our investigations show that pig kidneys can be successfully decellularized to produce renal ECM scaffolds. These scaffolds maintain their basic components, are biocompatible, and show intact, though thrombosed, vasculature.

 6.  增强Thbd-aPC通路的作用能够缓解电离辐射损伤

【动态】美国和德国科学家最近发现增强老鼠体内血液中的一种蛋白通路能够保护老鼠免受辐射伤害。他们发现通过重组的血栓调节蛋白或激活的蛋白C增强Thbd-aPC 通路的作用，能够缓解电离辐射引起的组织损伤和致命性。该研究揭示了前所未知的Thbd-aPC 通路在缓解辐射伤害方面的作用。通常该通路是预防血栓形成，帮助机体抵抗感染，而该研究发现这一通路帮助骨髓血细胞从辐射损伤中恢复，但其保护作用只在被照射的老鼠模型体内发生，体外没有作用，意味着它需要体内其它细胞或物质的帮助。

【点评】 该研究证实动物体内有帮助抵抗电离辐射的机制，也有方法去增强这一机制。

【参考论文】   
Nature Medicine, 24 June 2012 DOI:10.1038/nm.2813
Pharmacological targeting of the thrombomodulin–activated protein C pathway mitigates radiation toxicity
Hartmut Geiger, Snehalata A Pawar, Edward J Kerschen, et al.
Tissue damage induced by ionizing radiation in the hematopoietic and gastrointestinal systems is the major cause of lethality in radiological emergency scenarios and underlies some deleterious side effects in patients undergoing radiation therapy. The identification of target-specific interventions that confer radiomitigating activity is an unmet challenge. Here we identify the thrombomodulin (Thbd)-activated protein C (aPC) pathway as a new mechanism for the mitigation of total body irradiation (TBI)-induced mortality. Although the effects of the endogenous Thbd-aPC pathway were largely confined to the local microenvironment of Thbd-expressing cells, systemic administration of soluble Thbd or aPC could reproduce and augment the radioprotective effect of the endogenous Thbd-aPC pathway. Therapeutic administration of recombinant, soluble Thbd or aPC to lethally irradiated wild-type mice resulted in an accelerated recovery of hematopoietic progenitor activity in bone marrow and a mitigation of lethal TBI. Starting infusion of aPC as late as 24 h after exposure to radiation was sufficient to mitigate radiation-induced mortality in these mice. These findings suggest that pharmacologic augmentation of the activity of the Thbd-aPC pathway by recombinant Thbd or aPC might offer a rational approach to the mitigation of tissue injury and lethality caused by ionizing radiation.