THE ROLE OF FGFR2 IN PROTEIN SYNTHESIS DURING SKELETAL DEVELOPMENT

 描述(申请人提供)：骨骼异常影响人口的很大比例，发病率为每3000名新生儿中有1例。许多骨骼先天缺陷是由基因突变造成的，这些基因决定了骨骼祖细胞在发育过程中何时何地从自我更新状态转变为终末分化状态。成纤维细胞生长因子受体2(FGFR2)就是这样一种基因，它的突变导致了至少10种不同的疾病，这些疾病表现出颅面和四肢骨骼的异常。FGFR2通过调节骨祖细胞自我更新或分化的二元选择，在骨中起关键的信号转导作用。然而，FGFR2控制这些不同的细胞结果的机制并不完全清楚。这一建议的总体目标是通过揭示核FGFR2调控核糖体生物发生的机制来更具体地了解FGFR2如何调控骨骼发育。核糖体的丰度调节细胞的蛋白质合成能力；核糖体组成的异质性调节翻译的特异性。蛋白质的翻译是基因表达的真正终点，由于许多关键调控基因的mRNA和蛋白质水平之间存在差异，因此通过核糖体生物发生来控制翻译在调节细胞生长、增殖和分化方面至关重要。在发育中的骨骼中有强有力的证据表明这种控制作用，核糖体生物合成减少与骨骼异常的发病机制有关。我们发现了令人信服的证据表明，FGFR2紊乱的弯曲性骨发育不良综合征(BBDS)是由核糖体生物生成增加引起的。我们发现，BBDS中的突变增强了核仁中FGFR2的正常活性，在那里它激活了rDNA转录，这是构建核糖体的限速步骤。FGFR2介导的rDNA转录增加增加了核糖体的数量，并与以牺牲骨祖细胞分化为代价的增殖激增相一致。这一提议将检验核FGFR2通过核糖体生物发生调节蛋白质合成来调节骨骼祖细胞发育的假设。在目标1中，我们将区分核和膜FGFR2信号在骨形成过程中的确切作用。在目标2中，我们将定义核FGFR2如何调节骨骼祖细胞的核糖体合成。在目标3中，我们将通过调节产生的蛋白质的特性和数量来确定增加的rRNA对骨骼祖细胞发育的调节程度。这一贡献将产生重大而广泛的影响，因为它将1)从根本上促进我们对FGFR2引起的疾病和核糖体功能障碍(包括出生缺陷和癌症)的基础机制的了解，2)为针对核FGFR2的治疗策略创造新的机会，并从本质上纠正这些疾病中异常细胞的增殖和分化。

 DESCRIPTION (provided by applicant): Skeletal anomalies affect a significant proportion of the population, with an incidence rate of 1 case per 3000 births. Numerous skeletal birth defects arise as a consequence of mutations in genes that define when and where skeletal progenitor cells transition from a self-renewing state to one of terminal differentiation during development. Fibroblast Growth Factor Receptor 2 (FGFR2) is one such gene whose mutations are responsible for at least 10 distinct disorders that exhibit abnormalities within the craniofacial ad limb skeleton. FGFR2 acts as a key signaling node in bone by regulating the binary choice of osteoprogenitor cells to either self-renew or to differentiate. However, the mechanism by which FGFR2 controls these distinct cellular outcomes is not completely understood. The overall objective of this proposal is to understand with much greater specificity how FGFR2 regulates skeletal development by revealing the mechanism through which nuclear FGFR2 regulates ribosome biogenesis. The abundance of ribosomes regulates a cell's capacity for protein synthesis; heterogeneities in the composition of ribosomes regulate specificity in translation. Translation of mRNA into protein is the true endpoint of gene expression and because there is a discrepancy between mRNA and protein levels for many key regulatory genes, controlling translation through ribosome biogenesis is critical in regulating cell growth, proliferation, and differentiation. There is strong evidence for such control in the developing skeleton where decreased ribosome biogenesis is implicated in the pathogenesis of skeletal anomalies. We have uncovered compelling evidence that the FGFR2-disorder Bent Bone Dysplasia Syndrome (BBDS) is cause by increased ribosome biogenesis. We found that the mutations in BBDS enhance a normal activity for FGFR2 in the nucleolus where it activates rDNA transcription, the rate-limiting step in building ribosomes. FGFR2-mediated increase in rDNA transcription elevates the number of ribosomes and is coincident with an upsurge in proliferation at the expense of differentiation in osteoprogenitor cells. This proposal will test the hypothesis that nuclear FGFR2 regulates skeletal progenitor cell development by modulating protein synthesis via ribosome biogenesis. In Aim 1, we will distinguish the precise roles of nuclear and membrane FGFR2 signaling during bone formation. In Aim 2, we will define how nuclear FGFR2 regulates ribosome synthesis in skeletal progenitor cells. In Aim 3, we will determine the extent to which increased rRNA regulates development of skeletal progenitor cells by modulating the identity and amount of proteins produced. This contribution will have significant and broad impact because it will 1) fundamentally advance our understanding of the mechanisms underpinning diseases caused by FGFR2 and ribosome dysfunction, including birth defects and cancer, and 2) create new opportunities for therapeutic strategies that target nuclear FGFR2 and intrinsically correct aberrant cell proliferation and differentiation in these diseases.