ARF6

Medical researchers have found a peptide which, when administered intravenously, homes in on the new blood vessels that are forming in damaged tissue. The peptide has been used as a delivery vehicle for therapeutics targeted at regenerating tissues. A new study has discovered that the peptide activates the natural healing mechanism in the tissue, accelerating regeneration. The finding opens new opportunities to treat not only skin wounds, but also any injuries resulting from accidents and traumas, such as ruptured muscles and fractured bones. Professor Tero Järvinen has found a peptide which, when administered intravenously, homes in on the new blood vessels that are forming in damaged tissue. The peptide has been used as a delivery vehicle for therapeutics targeted at regenerating tissues. A new study led by professor Järvinen discovered that the peptide activates the natural healing mechanism in the tissue, accelerating regeneration. The finding opens new opportunities to treat not only skin wounds, but also any injuries resulting from accidents and traumas, such as ruptured muscles and fractured bones. One of the key goals of medical science is to speed up the healing of tissue injuries in a way that would not enable the forming of less functional scar tissue in the affected areas. Professor Tero Järvinen at Tampere University in Finland is leading research that is seeking solutions to achieve this goal. In an earlier study, Järvinen discovered a so-called homing peptide, a small piece of protein that specifically seeks tissue damage via the bloodstream. The homing peptide was named the CAR peptide after its amino acid composition. It was screened out of more than a billion peptides using the screening technology of in vivo phage display. The peptide was used to transport a scar reducing drug to the wounds via systemic administration. Recently, the research group showed that the CAR transport peptide is itself a therapeutic drug. CAR activates a natural healing pathway crucial for tissue regeneration and accelerates wound healing without the need to attach to any kind of drug. The study, reported in a recent issue of Nature Communications, confirmed that the CAR peptide activates the tissue regeneration mechanism that is critical for wound healing by entering the wound through the bloodstream. In the wound, the peptide binds to syndecan-4, a cell membrane receptor. This binding activates the intracellular cytohesin-2 factor, which in turn activates the Arf6 GTPase that triggers cell migration, i.e., the migration of regenerating cells across the damaged area in the wound. By this molecular mechanism, the skin wounds in mice receiving the CAR peptide healed significantly faster than without the therapy. The ensuing scars were also smaller than without treatment. As this syndecan-4 dependent cell migration-mechanism is crucial for the healing of multiple injuries, such as skeletal muscle ruptures and bone fractures, the CAR peptide has multiple clinically relevant indications not just for traumatology, but also surgery and sports medicine. "Syndecan-4-dependent tissue regeneration is a key factor in the healing of several other tissue injuries beyond skin wounds, including muscle ruptures and bone fractures. The CAR peptide we found, which activates this natural healing mechanism, opens completely new possibilities for treating traumas and injuries not only in traumatology but also in surgery and sports injuries. Because the drug molecule actively seeks tissue damage through the bloodstream, the treated injury can be in any part of the body and can be targeted by the CAR peptide therapy," Järvinen explains. Professor Tero Järvinen led the study in cooperation with Academician of Science Erkki Ruoslahti. The research was carried out at Tampere University, Sanford Burnham Prebys Medical Discovery Institute (La Jolla, CA, USA) and at the University of California Santa Barbara (UCSB, CA, USA). Researchers from the University of Liverpool (UK) and the Wellcome Trust Centre for Cell-Matrix Research at the University of Manchester (UK) also participated.

Root hairs represent a low-cost strategy to enhance nutrient uptake because they can significantly increase the nutrient-acquiring surface of plant roots. While primary and lateral roots are stimulated to elongate when plants grow under mild nitrogen deficiency, the existence of such a foraging response for root hairs and its underlying regulatory mechanism remain elusive. Now, researchers have revealed a framework composed of specific molecular players meditating auxin synthesis, transport and signaling that triggers root hair elongation for nitrogen acquisition. Root hairs represent a low-cost strategy to enhance nutrient uptake because they can significantly increase the nutrient-acquiring surface of plant roots. While primary and lateral roots are stimulated to elongate when plants grow under mild nitrogen deficiency, the existence of such a foraging response for root hairs and its underlying regulatory mechanism remain elusive. Now, an international research team led by IPK Leibniz Institute revealed a framework composed of specific molecular players meditating auxin synthesis, transport and signaling that triggers root hair elongation for nitrogen acquisition. The results have been published in the journal Current Biology. Plants have evolved diverse adaptive strategies to optimize the exploration of light and soil resources from their environments. One of the most prominent adaptive responses is the developmental plasticity of their root systems, which enables plants to efficiently forage nutrient pools that fluctuate in space and time. As a crucial component determining the active root surface, root hairs represent a powerful morphological trait to improve water and nutrient acquisition. Root hairs are extensions of epidermal cells that effectively enlarge the root surface area and facilitate soil exploration for water and nutrients. Root hair development starts with cell fate specification, which determines whether an epidermal cell becomes a hair-forming cell (trichoblast) or a hairless cell (atrichoblast). "In our study, we first showed that nitrogen deficiency strongly stimulates root hair elongation in the model species Arabidopsis thaliana and that this response is crucial for plant fitness under low nitrogen," explains Prof. Dr. Nicolaus von Wirén, head of the department "Physiology and Cell Biology" at IPK Leibniz Institute. "And we then integrated transcriptomics, molecular genetics and cell biology approaches to establish that low nitrogen-induced root hair elongation builds on a spatially coordinated auxin signaling cascade that enters the root hair developmental program via the epidermal transcriptional module RHD6-LRL3." The signaling cascade consists of three stages. Through upregulation of the enzymes TAA1 and YUCCA8, low nitrogen increases auxin accumulation in the root apex (step 1, synthesis). Auxin is then directed shootward to the root hair differentiation zone via the transporters AUX1 and PIN2 (step 2, transport). Upon arrival, auxin activates the transcription factors ARF6 and ARF8 to promote the transcriptional module RHD6-LRL3, which is confined to the epidermis and steers root hair elongation in response to low nitrogen (step 3, signaling). "Overall, our results suggest that root hair elongation represents an additional systemically-induced foraging response strategy to explore the soil for nitrogen, gaining even more relevance as nitrogen deficiency becomes more severe," says Dr. Zhongtao Jia, first author of the study. "These findings add a new feature to our understanding of root foraging responses in low-nutrient environments and expand the mechanistic framework of hormone-regulated nutrient sensing in plant roots." Since more abundant and longer root hairs represent a low-cost strategy for plants to bring roots in contact with soil nutrients, understanding how root hair development is regulated by nitrogen provides new breeding targets for developing crops with enhanced nitrogen-uptake efficiency.

摘 要：目前，新靶点的发现一直是实体瘤治疗的最有效途径之一，通过靶向给药，能更有针对性的摧毁实体瘤。DDR1是近年来受到广泛关注的明星靶点，可能在实体瘤治疗过程中发挥“双刃剑”作用，本文详细概述了DDR1的结构、生理功能，以及梳理了DDR1在癌症中的表达情况，DDR1与肿瘤发生机制和对癌症愈后价值，并讨论了靶向DDR的抗体药物应用前景。最后系统总结了未来设计更多DDR1靶向药物的前景，以期在实体瘤治疗中取得更好的效果。前 言实体瘤治疗是癌症治疗面临最大难点之一。免疫疗法为癌症治疗提供了新思路，但无论是近年来大热的ADC还是CAR-T疗法，都始终无法攻克实体瘤治疗难关。但换个思路来看，一旦攻克实体瘤治疗难点，将会为癌症患者带来巨大福音。DDR1是以胶原蛋白为配体的RTK家族成员。系列研究发现，DDR1在调节细胞形态发生、分化、增殖、黏附、迁移、侵袭和基质重塑等过程中起关键作用。而DDR1的异常激活通常与实体瘤发生发展密切联系。最近的一项研究发现，在三阴性乳腺癌中，DDR1蛋白会阻止免疫细胞进入肿瘤，从而影响杀瘤作用。DDR1基因一旦被敲除或被抗体抑制，就有望冲破三阴性乳腺癌防线。因此DDR1是一个很有前景的靶点。针对DDR1的药物的全球开发正在加速布局，如2022年11月10日，Parthenon Therapeutics公司与开发下一代放射性药物疗法（RPT）产品的ImaginAb公司达成合作，Parthenon公司将在评估其候选药物PRTH-101的I期临床研究中使用ImaginAb的CD8 ImmunoPET成像技术，该研究预计将于2023年启动。（引用自药研网）一、DDR结构和功能概述DDR来自“大名鼎鼎”的RTK家族（受体酪氨酸激酶），只有前三个含有KD的激酶活性受体是全长功能性受体，后两者由于截断或移码而没有激酶活性。DDR2只有一种异构体。DDR的分子结构由胞内激活区、跨膜区和胞外区组成（图1）图1 DDR1和DDR2的结构和亚型。DDR1a、b和c是激酶活性的，而DDR1d和e缺乏激酶结构域具体地说，它是位于胞外区的N-末端DS结构域，能与各种胶原蛋白结合，下方是DS样蛋白，再下方是EJXM域，其次是TM结构域，IJXM，紧随其后的是酪氨酸KD，最后是C末端的尾巴。DDR1和DDR2的表达分布也不同。过去研究发现，DDR1在上皮细胞中广泛表达，而DDR2主要在间充质细胞中表达，更具体来说，DDRs与胶原蛋白结合，而胶原蛋白是细胞外基质中含量最丰富的蛋白质之一，并刺激DDRs的磷酸化以激活激酶。以上是DDR最大的特点。这些结构特点让DDR能够顺利激活MAPK、整合素、转化生长因子-β、胰岛素受体和Notch信号通路。此外，DDR1在调节细胞形态发生、分化、增殖、黏附、迁移、侵袭和基质重塑方面起着关键作用。二、DDR1在人单个细胞中的表达谱为了全面了解DDR1在人类单细胞及其细胞系中的分布，使用集蛋白质组、转录组和系统生物学数据来绘制组织、细胞、器官等的HPA数据库，来进行进一步分析。如图2a所示。在单细胞型表达群中，以呼吸道上皮细胞-粘膜防御为主，此外，DDR1在免疫细胞中检测不到，在HaCaT、HBEC3-KT、RT4和T-47d中的表达会增加（图2B）图2 DDR1在人单个细胞中的分布。(A)DDR1在单细胞类型中的分布；(B)DDR1在细胞系中的表达三、DDR和人类实体瘤关系1DDR1在多种人类实体肿瘤中异常表达和肿瘤发生有关为了进一步明确DDR在癌症中的表达，使用TIMER2.0 数据库对其进行分析，分析发现与正常组织相比，DDR1在多种肿瘤组织中高表达，比如BLCA、BRCA、CHOL、ESCA、HNSC、HNSC−HPVpos、KICH、KIRC、KRIP、LIHC、LUAD、LUSC、PRAD、READ、STAD、THCA、UCEC（图3）。图3 基于TIMER2.0的DDR1基因表达分布分析(图显示基因表达水平的分布，差异表达的统计意义用Wilcoxon检验进行评估此外，通过检索文献，DDR1的异常表达可引起胃癌、肝癌、结肠癌、胰腺癌、乳腺癌、肺癌、卵巢癌、前列腺癌和胶质母细胞瘤等一系列肿瘤发生。2DDR1与实体瘤发生机制实体瘤组织由实质和间质组成。肿瘤实质部分主要是组织特异性肿瘤细胞。后文主要阐明DDR1通过影响肿瘤细胞及其肿瘤细胞微环境而促进肿瘤发生和发展的机制。DDR1与肿瘤细胞分化在生理条件下，DDR1主要在上皮细胞表达，具有维持细胞分化和组织动态平衡的功能。DDR1通过稳定E-钙粘附素（上皮分化的关键调节因子）促进细胞黏附，从而触发上皮细胞分化。在病理条件下观察DDR1对未分化的人甲状腺癌细胞IGF-2/IR-A环和细胞分化的影响。研究发现，DDR1沉默或下调会导致IR-A和IGF-2表达显著降低，分化标志物(NIS、TG、TSH、TPO)水平升高。DDR1与肿瘤细胞增殖细胞增殖是癌症的基本特征之一，目前DDR1在不同肿瘤中促进细胞增殖的作用不同。先前研究发现，在肝细胞癌中，DDR1的上调通过与SLC1A5(SLC转运体家族)相互作用来调节其稳定性，从而影响mTORC1信号通路，促进肝癌的增殖，及促进肝癌的异种移植，下调作用则相反。在肺癌细胞株A549和H1299中，TM4SF1通过调节DDR1及其下游靶蛋白Akt/ERK/mTOR通路的表达而部分促进肺癌细胞的增殖。此外，在卵巢癌中，姜黄素衍生物ST09调节miR-199a-5p/DDR1轴，并调节卵巢癌细胞的增殖。在结肠癌细胞中，LRP-1通过内吞作用调节细胞表面DDR1的表达。LRP-1介导的DDR1内吞通过促进细胞周期进入S期和减少细胞凋亡而促进细胞增殖。总的来说，DDR1影响癌细胞增殖的信号通路是不同的。因此，靶向DDR1的药物被设计成通过作用于不同的信号通路来抑制肿瘤细胞的增殖，从而达到治疗癌症的效果。DDR1与肿瘤细胞黏附：细胞间的黏附与癌细胞的扩散密切相关，DDR1在细胞间黏附中起关键作用。据报道，DDR1可以增加细胞表面E-钙粘附素的稳定性，促进MDCK细胞的聚集。从机制上讲，这是由DDR1/E-钙粘素复合体的形成所介导的。已发现和E-钙粘素之间的相互作用会以消极和黏附依赖性的方式调节DDR1活性和DDR1抑制细胞扩散。此外，先前对乳腺癌的研究发现，DDR1缺失可诱导CD90+和CD24+癌细胞分化，且基底细胞增多与肿瘤细胞有丝分裂有关。坏死区附近K14+细胞增多。简而言之，DDR1促进生长和黏附，有利于基底细胞的扩张，增强纤维化和坏死/缺氧情况。DDR1与肿瘤细胞的侵袭和迁移相关数据表明，DDR1可以影响肿瘤细胞的侵袭和迁移能力。先前的一项研究表明，DDR1过表达会促进膀胱癌细胞的体外迁移和侵袭。但经COL4A1-siRNA处理后，DDR1介导的RT4细胞的迁移和侵袭可以逆转。在肝癌中，DDR1会正向调节肝癌细胞的肺转移。这主要是因为DDR1与ARF6相互作用，并通过募集PSD4激活ARF6。ARF6的激活及其在肿瘤转移中的作用需要DDR1的激酶活性。总之，肿瘤细胞的侵袭和迁移是肿瘤转移的前提，而DDR1与肿瘤细胞的侵袭和迁移密切相关，靶向DDR1为预防肿瘤细胞转移提供了新思路。DDR1 和 EMTEMT在肿瘤起始到转移发展过程中发挥关键作用。但DDR1可能会影响EMT。研究发现，DDR1和STAT3正反馈调节会促进EMT和谷氨酰胺代谢，从而推动肝癌进程。而在前列腺癌中，通过siRNA方法下调DDR1在LNCaP-FGC和DU-145前列腺癌细胞中的表达。I型胶原会刺激DDR1，从而增强PYK2和MKK7信号分子磷酸化，诱导DU-145和LNCaP-FGC细胞发生EMT。相反，DDR1基因敲除后，PYK2和MKK7的EMT显著减弱。简而言之，未来针对DDR1的药物设计可以通过抑制上皮-间充质转化来发挥抗癌作用。DDR1与肿瘤细胞凋亡诱导肿瘤细胞凋亡是一种有效的抗肿瘤策略。在3D横纹肌肉瘤细胞培养中，使用不同硬度的胶原基质和类似体内的微结构，DDR1的激活具有促凋亡和整合素β1促生存的功能。从机制上讲，这是由于DDR1非依赖和DDR1依赖的TRPV4介导的机械限制的双重反应。设计针对DDR1的药物，有望通过诱导肿瘤细胞凋亡来达到抗癌效果。DDR1与肿瘤细胞能量代谢能量代谢异常是疾病发展的因素之一。肿瘤细胞的十个关键特征之一是能量代谢的重新编程。DDR1参与了多种癌症中能量代谢的重新编程。在肝细胞癌中，DDR1和STAT3正反馈调节通过促进谷氨酰胺代谢来提升肝癌发生率。在生成的乳腺癌MCF7 BC细胞中，DDR1沉默会导致总ATP产量显著下降，尤其会影响线粒体ATP的产生,此外，参与糖酵解和氧化磷酸化的关键分子也会下调。在结直肠癌中，DDR1a会促进LoVo细胞的增殖、线粒体功能和胞外酸化。四、DDR1是实体瘤预后的生物标志物本文总结了DDR1作为大多数实体肿瘤生物标志物的预后价值(表1)。表1：DDR1作为实体肿瘤标志物的价值。五、靶向DDR1的药物通过对上述DDR1的全面、系统的介绍，可以看出DDR1在维持人体正常生理功能和肿瘤的发生发展中发挥关键作用。接下来将介绍针对DDR1的全球药物和抗体开发的现状，并对未来靶向DDR1的药物设计进行假设。1全球针对DDR1的药物和抗体研究现状DDR1可能成为肿瘤免疫治疗的新靶点之一，因此，了解全球针对DDR1的药物和抗体的发展现状，对未来的临床治疗具有重要意义，在这里，使用PharnexCloud数据库搜索了针对DDR1的全球药物开发和临床试验(https://www.pharnexcloud.com/).大多数针对DDR1的药物治疗领域都在肿瘤学领域(表2)。此外，针对DDR1的8项全球临床试验中有4项是在实体肿瘤中进行的(表3)。还使用TAB(https://tabs.craic.com/users/sign_in))数据库来搜索针对DDR1D的抗体开发的现状。目前，世界上有8种基于DDR1的抗体处于临床前研究阶段(表4)。简而言之，这些研究都反映了针对DDR1的药物和抗体的开发正在加速，这些药物和抗体可能会给肿瘤患者带来新的希望。2以DDR1为靶点的未来药物设计随着人工智能和深度学习的快速发展，越来越多的DDR1激酶抑制剂被快速鉴定出来，这将极大地促进DDR1激酶抑制剂在实体肿瘤中的更大作用。此外，此前一项研究发现，抗DDR1单抗可抑制实体瘤的免疫排斥反应，为肿瘤免疫基质治疗开辟了新途径。未来有望通过释放细胞毒因子来杀伤癌细胞来制备针对DDR1的CAR-T细胞（图5）开发针对DDR1的CAR-T细胞来治疗实体瘤将是一项非常有趣和具有挑战性的任务。图5 杀癌靶向DDR1-CAR-T细胞基于DDR1在肿瘤中的独特作用，它很可能发挥出强大的抗肿瘤作用。总结与展望目前针对DDR1的药物不断被开发出来，并逐步走向临床，这或许会对实体瘤的治疗带来变革性的影响。同时，在实体瘤治疗的过程中立下汉马功劳的单抗也在不断发展，全人源抗体因免疫原性低等优势（详情参照：）提高了治疗效果。可以乐观预测，虽然靶点DDR1基因在实体瘤中的作用研究只是一小步，但却是一把在不久的将来将有力推动实体瘤治疗的“双刃剑”。参考文献：Tian, Y., Bai, F., & Zhang, D. (2022). New target DDR1: A "double-edged sword" in solid tumors. Biochimica et biophysica acta. Reviews on cancer, 1878(1), 188829. Advance online publication. https://doi-org.libproxy1.nus.edu.sg/10.1016/j.bbcan.2022.188829