The regulation of protein synthesis in stem cells

摘要 为了维持造血，造血干细胞(HSCs)必须在一生中持续存在 再生的造血细胞由于正常的周转、出血和疾病而丧失。我们学到了很多 在过去的十年里，关于规范HSC维护的机制。这项工作有 证明细胞生理学的几个方面在造血干细胞中受到不同的调节。 其他造血细胞。这提出了一个根本的问题，即细胞生理学的所有方面 在干细胞中受到不同的调控，与受限的祖细胞相比，或者是否在某些方面 细胞生理学是一种“看家”功能，在干细胞中受到类似的调节并受到限制。 祖先。不幸的是，细胞生理学的许多方面在技术上很难用现有的 少量干细胞中的技术，因此尚未得到解决，留下了大片区域 未被探索的生物学。细胞生理学的一个这样的方面是蛋白质合成的调节。那里 几乎没有关于任何体细胞干细胞群体中翻译调控的数据，部分原因是 目前还没有开发出研究体内少量细胞翻译的方法。我们最近做了 开发了一种分析方法，使研究多肽合成的速度成为可能 活体中的单个细胞。使用这项测试，我们已经确定HSCs具有显著较低的 蛋白质合成比其他造血细胞更多，即使我们控制了细胞周期的差异 分发。我们的初步功能数据表明，HSC的维持依赖于高度调控 蛋白质合成的速度。这一发现可能解释了之前观察到的HSC自我更新的缺陷 没有在机械论的层面上被理解。例如，我们以前已经演示过删除 成人造血细胞中的PTEN肿瘤抑制因子增加了HSC中的PI3-K途径信号， 导致白血病发生和HSC衰竭。尽管已知PTEN缺陷的HSCs耗尽 依赖于mTORC1和mTORC2信号诱导的肿瘤抑制反应，它是未知的 MTOR信号升高如何增加肿瘤抑制基因的表达。在本申请中，我们建议 扩展我们的初步数据以测试成年HSC是否需要PTEN来维持异常低的水平 蛋白质合成水平及PTEN缺失后蛋白质合成增加是否诱发肿瘤 耗尽造血干细胞的抑制反应。这项工作有可能产生新的研究技术。 蛋白质在体内稀有细胞群合成中的作用及开辟新的研究领域 调节造血和干细胞功能中的蛋白质合成。蛋白质调控中的缺陷 合成可能会潜在地导致不同的和鲜为人知的血液系统疾病 系统。

ABSTRACT To sustain hematopoiesis, hematopoietic stem cells (HSCs) must persist throughout life, constantly regenerating hematopoietic cells lost to normal turnover, bleeding, and disease. Much has been learned over the past ten years regarding the mechanisms that regulate HSC maintenance. This work has demonstrated that several aspects of cellular physiology are regulated differently in HSCs as compared to other hematopoietic cells. This raises the fundamental question of whether all aspects of cellular physiology are regulated differently in stem cells as compared to restricted progenitors, or whether certain aspects of cellular physiology are "house-keeping" functions that are regulated similarly in stem cells and restricted progenitors. Unfortunately, many aspects of cellular physiology are technically difficult to study with existing techniques in small numbers of stem cells and therefore have not yet been addressed, leaving large areas of biology unexplored. One such aspect of cellular physiology is the regulation of protein synthesis. There are almost no data on the regulation of translation in any somatic stem cell population, partly because assays have not yet been developed to study translation in small numbers of cells in vivo. We have recently developed an assay that makes it possible to study the rate at which polypeptides are synthesized by individual cells in vivo. Using this assay we have determined that HSCs have significantly lower rates of protein synthesis than other hematopoietic cells even when we control for differences in cell cycle distribution. Our preliminary functional data suggest that HSC maintenance depends upon highly regulated rates of protein synthesis. This discovery may explain previously observed defects in HSC self-renewal that were not understood at a mechanistic level. For example, we have demonstrated previously that deletion of the PTEN tumor suppressor in adult hematopoietic cells increases PI3-kinase pathway signaling in HSCs, leading to leukemogenesis and HSC depletion. Although the depletion of PTEN deficient HSCs is known to depend upon a tumor suppressor response induced by mTORC1 and mTORC2 signaling, it is unknown how elevated mTOR signaling increases tumor suppressor expression. In this application we propose to extend our preliminary data to test whether PTEN is required in adult HSCs to maintain an unusually low level of protein synthesis and whether increased protein synthesis after PTEN deletion induces the tumor suppressor response that depletes HSCs. This work has the potential to yield new techniques to study protein synthesis in rare cell populations in vivo and to open new areas of inquiry related to the role of regulated protein synthesis in hematopoiesis and stem cell function. Defects in the regulation of protein synthesis could potentially contribute to diverse and poorly understood diseases of the hematopoietic system.