世界生命科学前沿动态周报（七十一）

（12.19-12.25/2011）
美宝国际集团:陶国新 

　　主要内容：产前喂食甘露糖避免新生老鼠的先天糖基化代谢疾病；失去Pten的基质纤维母细胞促进肿瘤发展；基于纳米线的单细胞内视镜；隐花色素辅受体介导节律性抑制糖皮质激素受体；HIF-1α缺失加速表皮老化影响再上皮化生；癌细胞能无限分裂的机理。

　　焦点动态：基于纳米线的单细胞内视镜。

1. 产前喂食甘露糖避免新生老鼠的先天糖基化代谢疾病
【动态】
　　糖基化Ia先天疾病是由编码磷酸甘露糖酶2（PMM2）的基因突变引起的糖代谢紊乱，造成多系统的疾病伴有严重的精神运动和智力障碍。德国科学家用一种次形态突变的老鼠模型，在交配前和怀孕期通过饮水饲喂母鼠甘露糖，其后代即使携带上述先天疾病的基因突变，也能正常发育，克服了该病对胚胎的伤害。该结果突显了胚胎发育中糖基化的必要作用，可能会引出治疗该种疾病的新方法。

【点评】
　　该研究有助于更好的理解这一代谢疾病的分子机理和胚胎发育的关键步骤，有可能第一次为该疾病找到治疗方法。

【参考论文】
Nature Medicine, 2011; DOI:10.1038/nm.2548
Successful prenatal mannose treatment for congenital disorder of glycosylation-Ia in mice
Anette Schneider, Christian Thiel, Jan Rindermann, et al.  
Congenital disorder of glycosylation-Ia (CDG-Ia, also known as PMM2-CDG) is caused by mutations in the gene that encodes phosphomannomutase 2 (PMM2, EC 5.4.2.8) leading to a multisystemic disease with severe psychomotor and mental retardation. In a hypomorphic Pmm2 mouse model, we were able to overcome embryonic lethality by feeding mannose to pregnant dams. The results underline the essential role of glycosylation in embryonic development and may open new treatment options for this disease.

2. 失去Pten的基质纤维母细胞促进肿瘤发展
【动态】
　　基质纤维母细胞的PTEN（磷酸酶）表达抑制了乳腺上皮癌的生长，但机理未明。利用蛋白质组学和表达图谱测定，美国科学家显示乳腺基质纤维母细胞缺失Pten基因会激活致癌的分泌蛋白组协调微环境中其他类型细胞的转录重编程。下调miR-320和上调其一个直接靶点ETS2是Pten缺失的基质纤维母细胞诱导致癌的分泌蛋白组的关键事件，致癌的分泌蛋白组转而促进肿瘤发生和肿瘤细胞侵袭。他们发现肿瘤微环境的纤维母细胞因缺失Pten而导致miR-320数量剧降，进而使ETS2蛋白数量大涨，最终大量的ETS2蛋白激活许多基因，使纤维母细胞分泌50多种因子刺激临近癌细胞的增殖和侵袭，也引起肿瘤中和整个乳腺里的其他纤维母细胞重编程。Pten–miR-320–Ets2调节的分泌蛋白组的表达区分开了人体正常的乳腺基质组织与肿瘤基质，并与乳腺癌的复发强烈相关。该研究表明miR-320是在基质纤维母细胞中重组肿瘤微环境并阻碍肿瘤发展的Pten肿瘤抑制轴的一个关键部分。

【点评】
　　该研究促进了对于肿瘤微环境在肿瘤发展中的作用的理解，并为防治癌症提供了新的研究途径。

【参考论文】
Nature Cell Biology, 2011; DOI: 10.1038/ncb2396
Reprogramming of the tumour microenvironment by stromal PTEN-regulated miR-320
Bronisz, J. Godlewski, J. A. Wallace, et al. 
PTEN (Phosphatase and tensin homolog deleted on chromosome 10) expression in stromal fibroblasts suppresses epithelial mammary tumours, but the underlying molecular mechanisms remain unknown. Using proteomic and expression profiling, we show that Pten loss from mammary stromal fibroblasts activates an oncogenic secretome that orchestrates the transcriptional reprogramming of other cell types in the microenvironment. Downregulation of miR-320 and upregulation of one of its direct targets, ETS2 (v-ets erythroblastosis virus E26 oncogene homolog 2) are critical events inPten-deleted stromal fibroblasts responsible for inducing this oncogenic secretome, which in turn promotes tumour angiogenesis and tumour-cell invasion. Expression of the Pten–miR-320–Ets2-regulated secretome distinguished human normal breast stroma from tumour stroma and robustly correlated with recurrence in breast cancer patients. This work reveals miR-320 as a critical component of the Pten tumour-suppressor axis that acts in stromal fibroblasts to reprogramme the tumour microenvironment and curtail tumour progression.

3. 基于纳米线的单细胞内视镜
【动态】
　　基于纳米线和纳米管的能够安全穿透细胞膜进入细胞的灵敏一维探针在高分辨率高通量的基因及药物递送，生物感测和单细胞电生理学中有潜在用途。但是，这些探针在次波长水平跨膜的光通讯中的使用还受到限制。美国科学家的最新研究显示在光纤锥形尖上贴附一个纳米线波导管能够将可见光引入活的哺乳动物细胞内的区域，也能够检测来自亚细胞区域的光信号并有高空间分辨率。而且，将内视镜插入细胞内及引导激光的光照没有在细胞内引起明显毒性。

【点评】
　　该技术的出现使得直接肉眼观察单个活细胞内亚细胞水平的结构和生命活动成为可能。

【参考论文】
Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.226
Nanowire-based single-cell endoscopy

Ruoxue Yan, Ji-Ho Park, Yeonho Choi, et al.
One-dimensional smart probes based on nanowires and nanotubes that can safely penetrate the plasma membrane and enter biological cells are potentially useful in high-resolution,  and high-throughput,  gene and drug delivery, biosensing, and single-cell electrophysiology. However, using such probes for optical communication across the cellular membrane at the subwavelength level remains limited. Here, we show that a nanowire waveguide attached to the tapered tip of an optical fibre can guide visible light into intracellular compartments of a living mammalian cell, and can also detect optical signals from subcellular regions with high spatial resolution. Furthermore, we show that through light-activated mechanisms the endoscope can deliver payloads into cells with spatial and temporal specificity. Moreover, insertion of the endoscope into cells and illumination of the guided laser did not induce any significant toxicity in the cells.
 
4. 隐花色素辅受体介导节律性抑制糖皮质激素受体
【动态】                      
　　哺乳动物的代谢有高度的节律性，涉及核激素受体的主要激素回路表现出互通的昼夜循环。然而，合乎逻辑的解释核激素受体与生物钟之协调的机理还不清楚。美国德国和荷兰的科学家的最新研究显示两个生理节奏的辅受体隐花色素1和2能够以配体依赖的方式与糖皮质激素受体相互作用，并在老鼠胚胎纤维母细胞中整体改变对糖皮质激素的转录反应：隐花色素缺失极大地减少了基因抑制，大约使地塞米松诱导的基因数量翻倍，提示隐花色素广泛的拮抗糖皮质激素受体激活并促进其抑制。在老鼠中，基因缺失隐花色素1和/或2会导致葡萄糖耐受和血循环中结构性的高水平的皮质酮，提示相耦联的肾上腺轴抑制的减少和糖皮质激素在肝脏中转活化的增加。从基因上说，隐花色素1和2 以激素依赖的方式与磷酸烯醇丙酮酸羧激酶1促进子中糖皮质激素反应成分相关联，并且地塞米松诱导的磷酸烯醇丙酮酸羧激酶1基因的转录在缺失隐花色素的肝脏中显著增加。这些结果表明存在一种特别机制，借此隐花色素将生物钟活动和受体靶基因与支撑正常代谢平衡的复杂基因回路相藕联。

【点评】
　　该研究发现了身体生物钟和糖代谢体系之间缺失的环节，可能有助于解释睡眠和营养代谢之间的关联。

【参考论文】
Nature. 2011, 480(7378):552-6. doi:10.1038/nature10700.
Cryptochromes mediate rhythmic repression of the glucocorticoid receptor
Katja A. Lamia, Stephanie J. Papp, Ruth T. Yu, et al. 
Mammalian metabolism is highly circadian and major hormonal circuits involving nuclear hormone receptors display interlinked diurnal cycling. However, mechanisms that logically explain the coordination of nuclear hormone receptors and the clock are poorly understood. Here we show that two circadian co-regulators, cryptochromes 1 and 2, interact with the glucocorticoid receptor in a ligand-dependent fashion and globally alter the transcriptional response to glucocorticoids in mouse embryonic fibroblasts: cryptochrome deficiency vastly decreases gene repression and approximately doubles the number of dexamethasone-induced genes, suggesting that cryptochromes broadly oppose glucocorticoid receptor activation and promote repression. In mice, genetic loss of cryptochrome 1 and/or 2 results in glucose intolerance and constitutively high levels of circulating corticosterone, suggesting reduced suppression of the hypothalamic-pituitary-adrenal axis coupled with increased glucocorticoid transactivation in the liver. Genomically, cryptochromes 1 and 2 associate with a glucocorticoid response element in the phosphoenolpyruvate carboxykinase 1 promoter in a hormone-dependent manner, and dexamethasone-induced transcription of the phosphoenolpyruvate carboxykinase 1 gene was strikingly increased in cryptochrome-deficient livers. These results reveal a specific mechanism through whichcryptochromes couple the activity of clock and receptor target genes to complex genomic circuits underpinning normal metabolic homeostasis.

5. HIF-1α缺失加速表皮老化影响再上皮化生
【动态】
　　在老鼠和人体的皮肤中，缺氧诱导因子HIF-1α是在表皮，主要是基底层中表达。HIF-1α已被证明有重要的系统性功能：在去除表皮中HIF-1α的老鼠中调节肾脏红细胞生成素的生产，以及表皮中HIF-1α高表达带来的血管型。但是，HIF-1α 在角化细胞生理中的局部作用还没有阐明。法国科学家用敲除靶向角化细胞的HIF-1α基因的老鼠模型来研究HIF-1α在表皮中的作用。这些老鼠皮肤延迟出现皮肤表型，并表现为皮肤萎缩和瘙痒发炎，部分原因是牵涉层粘连蛋白332（Ln-332）和整合素的基底膜失调。研究者门也用重建的表皮研究了老鼠实验结果与人体皮肤的相关性，结果显示在人体角化细胞中抑制HIF-1α基因妨碍了形成能存活的重建人体表皮。随着HIF-1α静默而降低的角化细胞生长潜力与Ln-322 、 α6 和β1整合素表达 的降低有关。总的说来，这些结果表明HIF-1α在皮肤稳态特别是表皮老化期间扮演一定的角色。

【点评】
　　该研究揭示了HIF-1α在表皮形成中的作用，有助于进一步了解皮肤的发育和生理。

【参考论文】
J Cell Sci, 2011, doi:10.1242/jcs.082370
Loss of epidermal hypoxia-inducible factor-1α accelerates epidermal aging and affects re-epithelialization in human and mouse
Hamid Reza Rezvani, Nsrein Ali, Martin Serrano-Sanchez, et al.
In mouse and human skin, HIF-1α is constitutively expressed in the epidermis, mainly in the basal layer. HIF-1α has been shown to have crucial systemic functions: regulation of kidney erythropoietin production in mice with constitutive HIF-1α epidermal deletion, and hypervascularity following epidermal HIF-1α overexpression. However, its local role in keratinocyte physiology has not been clearly defined. To address the function of HIF-1α in the epidermis, we used the mouse model of HIF-1α knockout targeted to keratinocytes (K14-Cre/Hif1aflox/flox). These mice had a delayed skin phenotype characterized by skin atrophy and pruritic inflammation, partly mediated by basement membrane disturbances involving laminin-332 (Ln-332) and integrins. We also investigated the relevance of results of studies in mice to human skin using reconstructed epidermis and showed that HIF-1α knockdown in human keratinocytes impairs the formation of a viable reconstructed epidermis. A diminution of keratinocyte growth potential, following HIF-1α silencing, was associated with a decreased expression of Ln-322 and α6 integrin and β1 integrin. Overall, these results indicate a role of HIF-1α in skin homeostasis especially during epidermal aging.

6. 癌细胞能无限分裂的机理
【动态】
　　德国、瑞典和瑞士的科学家最近发现了癌细胞能无限分裂的机理，这将有助于靶向癌症治疗。就细胞分裂而言，恶性肿瘤细胞打破了几乎所有规律。这种细胞在没有外部信号时，仍能分裂，这些细胞通过旁路而获得关于生长的外部信号，所以仍能增殖。关于癌细胞能无限分裂的机制，至今科学家们还不是很清楚。该研究的研究人员发现了两个关键因子的作用，就是c-Myc和SIRT1，在癌细胞中，前者能摆脱细胞内的控制机制，促使癌细胞分裂。他们发现高度聚集的c-Myc蛋白可激活一种抑制细胞衰老和死亡的酶SIRT1，而这种酶又可反作用于c-Myc蛋白，如此形成一个回路，令c-Myc蛋白和SIRT1酶越来越多，最终促使癌细胞无限分裂。之前的研究表明SIRT1蛋白在长寿，糖代谢，以及胰岛素分泌过程中扮演了重要角色。

【点评】
　　该研究揭示延伸细胞寿命与癌细胞生长之间的关联，也提出了一种治疗癌症的新靶标系统，未来有助于开发新型治疗方法。

【参考论文】
PNAS  2011, doi:10.1073/pnas.1105304109
The c-MYC oncoprotein, the NAMPT enzyme, the SIRT1-inhibitor DBC1, and the SIRT1 deacetylase form a positive feedback loop
Antje Menssen, Per Hydbring, Karsten Kapelle, et al.

Silent information regulator 1 (SIRT1) represents an NAD+-dependent deacetylase that inhibits proapoptotic factors including p53. Here we determined whether SIRT1 is downstream of the prototypic c-MYC oncogene, which is activated in the majority of tumors. Elevated expression of c-MYC in human colorectal cancer correlated with increased SIRT1 protein levels. Activation of a conditional c-MYC allele induced increased levels of SIRT1 protein, NAD+, and nicotinamide-phosphoribosyltransferase (NAMPT) mRNA in several cell types. This increase in SIRT1 required the induction of the NAMPT gene by c-MYC. NAMPT is the rate-limiting enzyme of the NAD+ salvage pathway and enhances SIRT1 activity by increasing the amount of NAD+. c-MYC also contributed to SIRT1 activation by sequestering the SIRT1 inhibitor deleted in breast cancer 1 (DBC1) from the SIRT1 protein. In primary human fibroblasts previously immortalized by introduction of c-MYC, down-regulation of SIRT1 induced senescence and apoptosis. In various cell lines inactivation of SIRT1 by RNA interference, chemical inhibitors, or ectopic DBC1 enhanced c-MYC-induced apoptosis. Furthermore, SIRT1 directly bound to and deacetylated c-MYC. Enforced SIRT1 expression increased and depletion/inhibition of SIRT1 reduced c-MYC stability. Depletion/inhibition of SIRT1 correlated with reduced lysine 63-linked polyubiquitination of c-Myc, which presumably destabilizes c-MYC by supporting degradative lysine 48-linked polyubiquitination. Moreover, SIRT1 enhanced the transcriptional activity of c-MYC. Taken together, these results show that c-MYC activates SIRT1, which in turn promotes c-MYC function. Furthermore, SIRT1 suppressed cellular senescence in cells with deregulated c-MYC expression and also inhibited c-MYC–induced apoptosis. Constitutive activation of this positive feedback loop may contribute to the development and maintenance of tumors in the context of deregulated c-MYC.