Coordination of cell cycle, metabolism, and myeloid differentiation by lineage-specific transcription factors

生物学的一个中心问题是了解细胞和生物体如何调节细胞分裂以响应发育和环境线索。在血细胞发育期间，静止的造血干细胞产生快速增殖的祖细胞。随着祖细胞分化为成熟细胞，它们逐渐减慢细胞周期时钟的速率并诱导基因表达的变化。有新的证据表明，造血分化过程中的代谢变化是细胞周期时钟的重要输入。这种分化过程是在细胞类型特异性转录因子的控制下。关于细胞类型特异性转录因子协调细胞周期停滞与分化的机制，还有很多有待了解。 PU.1（由Spi1基因编码）是E26转化特异性（ETS）家族转录因子，是血细胞分化的浓度依赖性调节因子。巨噬细胞从骨髓祖细胞分化伴随着分化所需的PU.1浓度的5倍上调。由突变或抑制引起的PU.1表达减少导致未成熟骨髓祖细胞增殖增加和分化受损。PU.1表达减少与造血干细胞中细胞周期失调有关。这项研究计划的长期目标是确定细胞周期，代谢变化和髓样细胞的终末分化如何通过转录因子如PU.1协调。 我们建议使用我们实验室开发的PU.1诱导型BN细胞系系统以及体内自我更新的巨噬细胞群体来确定PU.1协调细胞周期停滞，代谢变化和分化的机制。我们的计划目标将解决四个问题：1）PU.1是否直接或间接控制由PU.1直接结合的基因编码的mRNA的下调？2)PU.1如何下调关键直接靶基因的mRNA水平？3)PU.1诱导的脂肪酸代谢相关基因编码的mRNA下调是否负责细胞周期阻滞，或者细胞周期阻滞是否控制脂肪酸代谢？4)PU.1水平在巨噬细胞群体的自我更新中发挥作用吗？ 这些实验有望详细了解PU.1如何调节骨髓分化和自我更新。

A central problem in biology is to understand how cells and organisms regulate cell division in response to developmental and environmental cues. During blood cell development, quiescent hematopoietic stem cells generate rapidly proliferating progenitor cells. As progenitor cells differentiate into mature cells, they gradually slow the rate of their cell cycle clock and induce changes in gene expression. There is emerging evidence that metabolic changes during hematopoietic differentiation are an important input into the cell cycle clock. This differentiation process is under the control of cell-type-specific transcription factors. Much remains to be learned about mechanisms by which cell type specific transcription factors coordinate cell cycle arrest with differentiation. PU.1 (encoded by the Spi1 gene) is an E26-transformation specific (ETS) family transcription factor that is a concentration-dependent regulator of blood cell differentiation. Differentiation of macrophages from myeloid progenitors is accompanied by a 5-fold upregulation of PU.1 concentration that is required for differentiation. Reduced PU.1 expression caused by mutation or repression leads to increased proliferation and impaired differentiation of immature myeloid progenitor cells. Reduced PU.1 expression is associated with deregulated cell cycle in hematopoietic stem cells. The long-term goal of this research program is to determine how cell cycle, metabolic changes, and terminal differentiation of myeloid cells are coordinated by transcription factors such as PU.1. We propose to use a PU.1-inducible BN cell line system developed in our laboratory as well as in vivo self-renewing macrophage populations to determine the mechanism of coordination of cell cycle arrest, metabolic changes and differentiation by PU.1. There are four questions that will be addressed by our program goals: 1) Does PU.1 directly or indirectly control the downregulation of mRNA encoded by genes that are directly bound by PU.1? 2) How does PU.1 downregulate mRNA levels for key direct target genes? 3) Is PU.1-induced downregulation of mRNAs encoded by genes involved fatty acid metabolism in charge of cell cycle arrest, or does cell cycle arrest control fatty acid metabolism? 4) Do PU.1 levels play a role in self-renewal of resident macrophage populations? These experiments are expected to result in a detailed understanding of how PU.1 regulates myeloid differentiation and self-renewal.