Regulation of Hematopoiesis by Ribosomal Protein Paralogs

描述（由申请人提供）：核糖体病是由核糖体结构蛋白或促进核糖体生物发生的蛋白质突变引起的一系列疾病。人们普遍认为核糖体病的发育异常是由于核糖体生物发生或功能的普遍缺陷造成的。与此观点相反，我们假设核糖体蛋白（RP）具有在核糖体外结合细胞rna的能力，并且一些人类疾病实际上是由这种独特的“核糖体外”功能的破坏引起的。为了支持这一假设，我们已经发现了一对相似的rna结合RP， Rpl22及其相似的Rpl22-Like1 (Like1)，它们对核糖体的生物发生和功能都是必不可少的，但在造血中起着关键的调节作用。此外，尽管Rpl22和Like1具有高度的同源性（氨基酸序列相同70%），但我们证明它们具有不同的功能，即分别依赖p53在T淋巴细胞的发育中起作用，依赖smad1在驱动造血干细胞（HSC）出现中起作用。重要的是，Rpl22和Like1不仅执行不同的功能，而且这些功能也是相互拮抗的。实际上，通过消除Rpl22，可以挽救由Like1敲低引起的HSC出现障碍。事实上，Rpl22和Like1的RNA结合螺旋是相同的，这表明这些蛋白质结合了大量重叠的RNA靶标，但对这些靶标的活性有不同的影响。因此，我们现在试图了解这些高度同源的RP如何在造血的不同阶段发挥关键的拮抗功能。我们这样做有三个目的：1)确定Rpl22的系统性缺失是如何导致发育中的T细胞选择性阻滞的。2)阐明Rpl22和Like1拮抗作用的基础。3)了解Rpl22和Like1的拮抗平衡如何通过调节Smad1调控HSC的发生。

DESCRIPTION (provided by applicant): Ribosomopathies are a collection of diseases caused by mutations in the structural proteins of the ribosome or in proteins that facilitate ribosome biogenesis. It is widely held that the developmental abnormalities that characterize ribosomopathies result from a generalized defect in ribosome biogenesis or function. In contrast to this view, we postulate that ribosomal proteins (RP) have the capacity to bind cellular RNAs outside the context of the ribosome, and that some human diseases are in fact caused by disruption of such distinct, "extra-ribosomal" functions. In support of this hypothesis, we have identified a paralogous pair of RNA-binding RP, Rpl22 and its paralog Rpl22-Like1 (Like1), that are dispensable for both the biogenesis and function of ribosomes, yet perform critical regulatory roles in hematopoiesis. Furthermore, despite their high degree of homology (>70% identical in amino acid sequence), we demonstrate that Rpl22 and Like1 perform distinct functions, i.e., a p53-dependent role in development of �T lymphocytes and a Smad1-dependent role in driving hematopoietic stem cell (HSC) emergence, respectively. Importantly, not only do Rpl22 and Like1 perform distinct functions, but those functions are also mutually antagonistic. Indeed, the block in HSC emergence caused by knockdown of Like1 is rescued by eliminating Rpl22. The fact that the RNA binding helices of Rpl22 and Like1 are identical suggests that these proteins bind largely overlapping sets of RNA targets but have different effects on the activities of those targets. Thus, we now seek to understand how these highly homologous RP perform antagonistic functions that are critical at distinct stages of hematopoiesis. We will do so according to three aims: 1) To determine how systemic loss of Rpl22 causes a selective arrest of developing T cells. 2) To elucidate the basis for the antagonistic functions of Rpl22 and Like1. 3) To understand how the antagonistic balance of Rpl22 and Like1 controls HSC emergence by regulating Smad1.