Regulation of Cell Growth by RNA Binding Proteins

描述（由申请人提供）：P21和一系列转录因子，CCAAT/增强子结合蛋白（C/EBP），在细胞生长和分化的调控中起着至关重要的作用。C/EBPalpha和p21是细胞增殖的强抑制剂，因为它们都能够与cdk2和cdk4结合并抑制它们的活性。尽管C/EBP蛋白和p21的表达主要在转录水平上受到调节，但最近的观察表明，RNA结合蛋白对C/EBPalpha翻译的抑制是白血病等肿瘤发展的关键事件。我们最近发现，一组特定的细胞质RNA结合蛋白与C/EBPalpha、C/EBPbeta和p21 mrna中富含gc的区域相互作用，并能够调节这些mrna的翻译。分离了其中两个RNA结合蛋白并对其进行了详细的表征。钙网蛋白（CRT）与C/EBPalpha、C/EBPbeta和p21 mrna中的茎环结构相互作用，抑制它们的翻译。我们还发现，一种RNA结合蛋白CUGBP1与C/EBPbeta和p21 mrna的5'区结合，这种相互作用增加了C/EBPbeta和p21的翻译。该应用的主要假设是RNA结合蛋白通过控制C/EBP蛋白和p21的翻译来调节细胞生长和分化。Three Specific Aims旨在使用多种生物模型，包括无细胞系统、培养细胞和动物模型来解决这一假设。特异性目的1研究了C/EBPalpha在细胞生长调节中的作用。特异性目的II研究了crt介导的p21调控在细胞衰老中的作用。具体来说，我们将验证一个假设，即衰老成纤维细胞中p21的升高需要释放依赖于crt的p21翻译抑制。在Specific Aim III中，我们将验证RNA结合蛋白调控p21和C/EBPbeta翻译的竞争决定细胞命运的假设。这一假设是基于我们的观察，显示CRT和CUGBP1结合到p21和C/EBPbeta mrna中的相同序列，但这些相互作用的结果是不同的。总之，这些研究将为了解特定RNA结合蛋白如何通过新发现的途径控制细胞分裂提供重要的见解。

DESCRIPTION (provided by applicant): P21 and a family of transcription factors, CCAAT/Enhancer Binding Proteins (C/EBP), play a crucial role in the regulation of cell growth and differentiation. C/EBPalpha and p21 are strong inhibitors of cell proliferation, since both are capable of binding to cdk2 and cdk4 and inhibiting their activities. Although the expression of C/EBP proteins and p21 are primarily regulated at the level of transcription, recent observations showed that the inhibition of translation of C/EBPalpha by RNA binding proteins is a key event in development of tumors such as leukemias. We have recently found that a specific group of cytoplasmic RNA binding proteins interact with GC-rich regions within C/EBPalpha, C/EBPbeta and p21 mRNAs and are able to regulate translation of these mRNAs. Two of these RNA binding proteins were isolated and characterized in detail. Calreticulin (CRT) interacts with stem-loop structures within C/EBPalpha, C/EBPbeta and p21 mRNAs and inhibits their translation. We also found that an RNA binding protein, CUGBP1, binds to 5' regions of C/EBPbeta and p21 mRNAs and that this interaction increases translation of C/EBPbeta and p21. The major hypothesis of this application is that RNA binding proteins regulate cell growth and differentiation by controlling translation of C/EBP proteins and p21. Three Specific Aims are designed to use a variety of biological models including a cell-free system, cultured cells and animal models address this hypothesis. Specific Aim I examines the role of CRT-dependent inhibition of C/EBPalpha in the regulation of cell growth. Specific Aim II investigates the role of CRT-mediated regulation of p21 in cellular senescence. Specifically, we will test the hypothesis that release of CRT-dependent inhibition of p21 translation is required for the elevation of p21 in senescent fibroblasts. In Specific Aim III, we will test the hypothesis that competition of RNA binding proteins for regulation of p21 and C/EBPbeta translation determines cell fate. This hypothesis is based on our observations showing that CRT and CUGBP1 bind to the same sequences within p21 and C/EBPbeta mRNAs, but the results of these interactions are different. Together, these studies will provide important insight into how particular RNA binding proteins function through newly discovered pathways to control cell division.