世界生命科學前沿動態(tài)周報（八十）

（6.17-6.23/2012）
美寶國際集團:陶國新 

　　主要內(nèi)容：細胞周期同步停滯于G1期促進癌細胞對抗癌藥物的敏感性和細胞凋亡; 大腦的信息高速路; 發(fā)現(xiàn)Foxo3a助長癌癥改變目前的治療模式; 基質(zhì)剛性控制了內(nèi)皮分化和心臟前體的形態(tài)發(fā)生; 用于生物工程腎臟的“腳手架”; 增強Thbd-aPC通路的作用能夠緩解電離輻射損傷。

　　焦點動態(tài)：細胞周期同步停滯于G1期促進癌細胞對抗癌藥物的敏感性和細胞凋亡。

1. 細胞周期同步停滯于G1期促進癌細胞對抗癌藥物的敏感性和細胞凋亡

【動態(tài)】美國科學家最近發(fā)現(xiàn)了一種提高多發(fā)性骨髓瘤治療效率的策略. 通過兩種抗癌藥物精確掌握時機的順序使用, 分兩步使癌細胞先減弱抵抗力繼而被殺死.  首先是用試驗藥物PD0332991,繼而是已被批準用于骨髓瘤和淋巴瘤的藥物硼替佐米(bortezomib),一種蛋白酶抑制劑, 以低于正常的劑量，誘導從同步的細胞周期G1期剛剛釋放出來的癌細胞自殺。根本上講癌癥是一種細胞增殖失控的疾病，相對的，健康個體內(nèi)細胞分裂受細胞周期的調(diào)控，一系列有序的程序性基因表達產(chǎn)生的高度控制的蛋白網(wǎng)絡驅(qū)動細胞通過各個檢查站。 依賴細胞周期蛋白的激酶（CDKs）推動細胞經(jīng)歷其周期性的四個階段。其中CDK4和CDK6推動細胞通過G1期進入后面階段進行細胞分裂，而PD0332991是一個對CDK4和CDK6有高度選擇性的小分子，能夠可逆的抑制這兩個酶，連續(xù)使用PD0332991能夠?qū)⑺邪┘毎接贕1期，在G1期的長期停滯擾亂了癌細胞的基因表達，增大了其代謝負荷和復制DNA的能量需求，削弱并使癌細胞對傳統(tǒng)抗癌藥物更為敏感，大大增加了硼替佐米誘導的癌細胞自殺。進一步的研究發(fā)現(xiàn)在PD0332991造成的G1期停滯期間，骨髓瘤細胞失去了必須的存活因子IRF4蛋白，但出現(xiàn)了幾種促凋亡蛋白。

【點評】 這些發(fā)現(xiàn)首次表明癌細胞細胞周期調(diào)控關鍵的存活和凋亡基因，也代表了細胞周期的生物學基礎研究與直接醫(yī)學應用的無縫整合。該治療癌癥的策略能否治愈或大大改善多發(fā)性骨髓瘤還需等待人體臨床實驗的結(jié)果。

【參考論文】   
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.  大腦的信息高速路

【動態(tài)】荷蘭和美國科學家對人體大腦結(jié)構(gòu)神經(jīng)網(wǎng)絡連接的研究最近發(fā)現(xiàn)了一類特殊的大腦區(qū)域，它們高度互聯(lián)和處于中心地位，這些樞紐區(qū)域相互密切連接，在人腦中形成一個“富人俱樂部”，連接這些樞紐區(qū)域的那些通路形成了大腦通訊的一個中心的高花費（能量和空間上）高容量的主干網(wǎng)，占據(jù)了總體通訊花費的40%。而且，神經(jīng)節(jié)點之間69%的通訊最短通路要途經(jīng)“富人俱樂部”，大部分這類通訊途徑由井然有序的路段構(gòu)成，先進入再穿越，后離開“富人俱樂部”。這種有序的最短途通訊線路的普遍存在意味著中樞通訊利用不同腦區(qū)之間信息傳遞的動態(tài)線路安排，其中高度中心地位的“富人俱樂部”其重要作用。這些研究結(jié)果表明“富人俱樂部”的骨干網(wǎng)在大腦區(qū)域間信號交通上起重要作用，形成了中樞地位的高花費高容量的大腦通訊主干網(wǎng)，在幾十億腦細胞間提供了快速有效的通訊，吸納，轉(zhuǎn)換和傳遞信息。

【點評】 該研究對于大腦如何高效處理繁重的信息傳遞有了更深入的理解。

【參考論文】   
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. 發(fā)現(xiàn)Foxo3a助長癌癥改變目前的治療模式

【動態(tài)】最近美國科學家發(fā)現(xiàn)一種被廣泛認為可以對抗多種癌癥的分子Foxo3a 實際上幫助了致命的甲狀腺癌生長，而目前在人體試驗中的癌癥療法可能助長這一作用。他們在未分化的甲狀腺癌中叉頭轉(zhuǎn)錄因子Foxo3a不是原以為的腫瘤抑制因子，相反是致命的腫瘤促進因子。在試驗室此種腫瘤模型中將Foxo3a關閉，癌細胞生長緩慢，但放開Foxo3a后癌細胞生長就快的多了。以前的認識是：Foxo3a應對各種細胞包括癌細胞中產(chǎn)生的壓力，打開細胞核里的觸發(fā)細胞死亡的基因，而癌細胞通過Akt蛋白將Foxo3a從細胞核轉(zhuǎn)移到細胞質(zhì)中分解掉而關閉其功能。該研究利用Akt抑制劑將癌細胞的Foxo3a留在細胞核里,  本想它幫助殺死癌細胞，卻觀察到它加速了癌細胞的生長。這使得我們需要重新考慮Akt抑制劑在癌癥治療中的使用，因其機理之一是使Foxo3a在細胞核中保持活性。該研究還發(fā)現(xiàn)Foxo3a打開了細胞周期蛋白A1的基因表達，而細胞周期蛋白A1是促進癌細胞生長的。

【點評】 該研究發(fā)現(xiàn)了Foxo3a對癌細胞的正反雙重作用，可能改變目前癌癥治療的一些既有模式。

【參考論文】   
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.  基質(zhì)剛性控制了內(nèi)皮分化和心臟前體的形態(tài)發(fā)生

【動態(tài)】組織發(fā)育和再生牽涉到緊密協(xié)調(diào)和整合的多種過程：常駐干細胞和前體細胞的選擇性增殖，分化為目標體細胞，空間形態(tài)的組織。美國科學家對這一過程中機械環(huán)境的最新研究顯示源自本地心臟組織的多能細胞持續(xù)監(jiān)測細胞基質(zhì)的剛度并顯示當剛度非常接近心肌細胞時會增強增殖，內(nèi)皮分化和形態(tài)發(fā)生。這些過程的機械調(diào)控需要p190RhoGAP，一種針對RhoA的鳥苷三磷酸酶激活蛋白，通過依賴和不依賴RhoA的機制起作用。這一發(fā)現(xiàn)可能引出更好的治療心臟病的方法。心肌組織經(jīng)歷心臟病發(fā)作后一般會形成虛弱的疤痕，而最近有一些報道可用干細胞生產(chǎn)健康組織阻止疤痕的產(chǎn)生。

【點評】 p190RhoGAP的發(fā)現(xiàn)及其機械調(diào)控作用會有助于干細胞順利變成特定健康組織。該研究增強了我們對干細胞生物學的理解并提示了新方式來控制心肌干細胞在移植入心臟前后的行為。

【參考論文】   
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.  用于生物工程腎臟的“腳手架”

【動態(tài)】美國科學家在實驗室中制造替代腎臟的長期項目最近到達了一個早期里程碑，他們用豬的腎臟去除所有動物細胞，只留器官骨架，制造出了支持結(jié)構(gòu)“腳手架”，病人自己的細胞可以在上面生長形成的器官理論上不會被病人自身所排斥。再生醫(yī)學已經(jīng)成功地制造了生物工程皮膚，軟骨，膀胱，輸尿管，氣管和血管植入患者體內(nèi)。這些結(jié)構(gòu)在發(fā)育出自身的血管之前能夠臨近的血管組織獲取氧氣和養(yǎng)料。但是，再生醫(yī)學的“圣杯”是制造出更復雜的器官如腎，肝，心臟和胰腺。這些器官含有大量細胞必須有自己的氧氣供應才能存活，這種生物工程就需要有完整脈管系統(tǒng)的“腳手架”。

【點評】 這種異種腳手架并不能完全排除機體的排斥，而且生物工程制造器官也不是再生醫(yī)學的圣杯，真正的圣杯是無需任何移植的器官原位再生。

【參考論文】   
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.  增強Thbd-aPC通路的作用能夠緩解電離輻射損傷

【動態(tài)】美國和德國科學家最近發(fā)現(xiàn)增強老鼠體內(nèi)血液中的一種蛋白通路能夠保護老鼠免受輻射傷害。他們發(fā)現(xiàn)通過重組的血栓調(diào)節(jié)蛋白或激活的蛋白C增強Thbd-aPC 通路的作用，能夠緩解電離輻射引起的組織損傷和致命性。該研究揭示了前所未知的Thbd-aPC 通路在緩解輻射傷害方面的作用。通常該通路是預防血栓形成，幫助機體抵抗感染，而該研究發(fā)現(xiàn)這一通路幫助骨髓血細胞從輻射損傷中恢復，但其保護作用只在被照射的老鼠模型體內(nèi)發(fā)生，體外沒有作用，意味著它需要體內(nèi)其它細胞或物質(zhì)的幫助。

【點評】 該研究證實動物體內(nèi)有幫助抵抗電離輻射的機制，也有方法去增強這一機制。

【參考論文】   
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.