The regulation of protein synthesis in stem cells

描述（由申请人提供）：为了维持造血功能，造血干细胞（hsc）必须在整个生命中持续存在，不断再生因正常周转、出血和疾病而失去的造血细胞。在过去的十年里，关于调节HSC维持的机制已经学到了很多。这项工作已经证明，与其他造血细胞相比，造血干细胞中细胞生理学的几个方面受到不同的调节。这就提出了一个基本问题，即干细胞中细胞生理学的所有方面是否与限制性祖细胞相比受到不同的调节，或者细胞生理学的某些方面是否具有“管家”功能，在干细胞和限制性祖细胞中受到类似的调节。不幸的是，细胞生理学的许多方面在技术上难以用现有的技术在少量干细胞中进行研究，因此尚未得到解决，留下了大量的生物学领域未被探索。细胞生理学的一个这样的方面是蛋白质合成的调节。在任何体细胞干细胞群体中，几乎没有关于翻译调节的数据，部分原因是尚未开发出用于研究少量体内细胞翻译的检测方法。我们最近开发了一种测定方法，使研究体内单个细胞合成多肽的速率成为可能。通过这个实验，我们已经确定造血干细胞的蛋白质合成率明显低于其他造血细胞，即使我们控制了细胞周期分布的差异。我们的初步功能数据表明，HS的维持依赖于高度调节的蛋白质合成速率。这一发现可以解释先前观察到的HSC自我更新缺陷，这些缺陷在机制水平上不被理解。例如，我们之前已经证明，成人造血细胞中PTEN肿瘤抑制因子的缺失会增加造血干细胞中pi3 -激酶信号通路，导致白血病发生和造血干细胞耗竭。尽管已知PTEN缺陷hsc的消耗依赖于mTORC1和mTORC2信号诱导的肿瘤抑制反应，但尚不清楚mTOR信号的升高如何增加肿瘤抑制因子的表达。在这项应用中，我们建议扩展我们的初步数据，以测试成人造血干细胞是否需要PTEN来维持异常低水平的蛋白质合成，以及PTEN缺失后蛋白质合成的增加是否会诱导消耗造血干细胞的肿瘤抑制反应。这项工作有可能产生新的技术来研究体内稀有细胞群中的蛋白质合成，并为研究调节蛋白质合成在造血和干细胞功能中的作用开辟新的研究领域。在蛋白质合成的调节缺陷可能有助于多种和知之甚少的造血系统疾病。

DESCRIPTION (provided by applicant): 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 HS 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.