Responses of MHC Class I Genes to Exogeneous Stimuli

MHC I 类基因对外源刺激的反应

• 批准号: 9343561
• 负责人: Dinah S. Singer
• 金额: $ 8.54万
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/9343561
• 关键词: Acetyltransferase; Affect; Autoantigens; Autoimmune Diseases; B-Lymphocytes; Beryllium; Binding; Binding Sites; Biological Assay; Boxing; Bypass; Cell Surface Receptors; Characteristics; Complex; Critical Pathways; Data; Dependence; Disease; Elements; Employee Strikes; Enhancers; Failure; Frequencies; Gene Expression; Genes; Genetic Transcription; Goals; HIV; Hormonal; Hormones; Immune response; Immunologic Surveillance; Indium; Individual; Infection; Inflammation; Interferon Type II; Interferons; Lead; Link; Lymphocyte; MHC Class I Genes; MHC Class II Genes; Major Histocompatibility Complex; Mammalian Cell; Maps; Modeling; Molecular; Pathway interactions; Peptides; Phosphotransferases; Play; Process; Protein-Serine-Threonine Kinases; Proteins; RNA; Regulation; Regulatory Pathway; Reporter; Reporting; Research; Role; Signal Pathway; Signal Transduction; Specificity; Stimulus; Syndrome; TAF7 gene; TATA-Binding Protein Associated Factors; Tissues; Transcription Coactivator; Transcription Initiation; Transfection; Transgenic Mice; Tumor Antigens; Yeasts; base; carcinogenesis; cytokine; extracellular; hormone regulation; in vivo; mutant; neoplastic cell; novel; overexpression; pathogen; programs; promoter; response; single molecule; transcription factor; tumor

The TFIID components TAF7 and TAF1 regulate eukaryotic transcription initiation. TAF7 regulates transcription initiation of TAF1-dependent genes by binding to the acetyltransferase (AT) domain of TAF1 and inhibiting the enzymatic activity that is essential for transcription. TAF7 is released from the TAF1/TFIID complex upon completion of preinitiation complex assembly, allowing transcription to initiate. However, not all transcription is TAF1-dependent and the role of TAF7 in regulating TAF1-indepedent transcription has not been defined. The IFN-gamma--induced transcription factor CIITA is a coactivator and general transcription factor that regulates both MHC Class I and Class II gene transcription, and is thus critical to activated immune response. Known as the master regulator of Class II expression, CIITA is required for both Class II transcription and activated Class I expression. Its deficiency is linked to bare lymphocyte syndrome. Comparison of eukaryotic basal class I transcription and interferon-activated transcription initiation reveals similar preinitiation complex recruitment mechanisms, and striking parallels between their respective critical components, the TATA-binding protein (TBP)-associated factor 1 (TAF1) and CIITA. Both TAF1 and CIITA possess instrinsic acetyltransferase (AT) activity required to activate MHC transcription, which is regulated by TAF7. Moreover, CIITA can bypass the requirement for TAF1 to activate both the MHC class I and II promoters. TAF1 has two distinct kinase activities, located with its amino-terminal and carboxy-terminal domains. However, despite the striking functional parallels between CIITA and TAF1, no similar kinase activity has been reported for CIITA thus far. We have now identified the transcriptional coactivator CIITA as a novel atypical serine-threonine kinase whose substrates include various general transcription factors. We have characterized the kinase activity of the protein and mapped the putative kinase domains. We have proposed a model in which the kinase activity of CIITA serves a function similar to that of TAF1, in which it regulates TAF7 binding and release, and thus MHC transcription initiation. This may elucidate a novel role for CIITA in the regulation of activated transcription initiation and stimulated immune response during pathogenic infection. To further characterize regulation of class I gene expression, we have undertaken to characterize the role of core promoter elements in hormonal responses in vivo. The minimal class I core promoter has been localized to a segment between -65 bp and +14 bp. Contained within this segment are a canonical CCAAT box, a TATAA-like element, an Sp1 binding site (Sp1BS) and an Initiator (Inr). In past studies, we have reported that no single element is necessary for expression of a reporter in transient transfection assays. However, we have now examined the dependence of transcription on each of the core promoter elements in the context of the native gene in transgenic mice. Remarkably, all of the mutant promoters supported transcription. Each element contributed uniquely to tissue-specificity, hormonal responses or both. Whereas the WT, TATAA-like and CCAAT mutant promoters were activated by gamma-interferon, the Inr and Sp1 mutants were repressed, implicating these elements in regulation of hormonal responses. Transcription initiation is not a continuous process, but rather occurs in bursts which differ in amplitude and frequency. Although the roles of enhancers on the bursting characteristics of promoters in yeast and cultured mammalian cells have been described, the contributions of individual core promoter elements to bursting amplitude and frequency have not been assessed. Having demonstrated that the core promoter elements that constitute the MHC class I promoter all contribute to transcription initiation, we are examining whether interferon-activated transcription affects burst amplitude, frequency or bothand the role of the core promoter elements in determining these bursting characteristics in primary splenic B cells by single molecule RNA FISH.

TFIID组件TAF7和TAF1调节真核转录启动。 TAF7通过与TAF1的乙酰转移酶（AT）结合并抑制转录必不可少的酶促活性来调节TAF1依赖性基因的转录启动。 TAF7在完成前的复合体组装后从TAF1/TFIID复合物中释放出来，从而启动转录。但是，并非所有转录都是taf1依赖性的，并且尚未定义TAF7在调节TAF1内部转录中的作用。 IFN-GAMMA诱导的转录因子CIITA是调节MHC I类和II类基因转录的共激活因子和一般转录因子，因此对于激活的免疫反应至关重要。 CIITA被称为II类表达的主要调节剂，II类转录和激活的I类表达都需要CIITA。它的缺乏与裸露的淋巴细胞综合征有关。真核基础I类转录和干扰素激活的转录起始的比较揭示了相似的预处理复杂募集机制，以及它们各自的关键成分之间的显着性相似之处，即TATA结合蛋白（TBP）与之相关的因子1（TAF1）和CIITA。 TAF1和CIITA都具有激活MHC转录所需的辅助乙酰转移酶（AT）活性，该活性受TAF7调节。此外，CIITA可以绕过TAF1激活MHC I和II类启动子的要求。 TAF1具有两种不同的激酶活性，其氨基末端和羧基末端结构域。然而，尽管CIITA和TAF1之间的功能相似，但到目前为止，CIITA尚无类似的激酶活性。现在，我们已经将转录共激活因子CIITA确定为一种新型非典型丝氨酸 - 硫代激酶，其底物包括各种一般转录因子。我们已经表征了蛋白质的激酶活性，并映射了假定的激酶结构域。我们提出了一个模型，其中CIITA的激酶活性具有与TAF1相似的函数，在该函数中，它调节TAF7结合和释放，从而调节MHC转录起始。这可以阐明CIITA在调节活化转录起始和致病感染期间刺激免疫反应中的新作用。为了进一步表征I类基因表达的调节，我们已承诺表征核心启动子元素在体内激素反应中的作用。最小I类核心启动子已定位到-65 bp和+14 bp之间的细分市场。该段中包含的是一个规范的CCAAT框，类似Tataa的元素，SP1结合位点（SP1B）和一个引发剂（INR）。在过去的研究中，我们报告说，在瞬态转染测定中表达报告基因并不需要单一元素。但是，我们现在检查了转录对转基因小鼠中天然基因的背景下的转录对每个核心启动子元素的依赖性。值得注意的是，所有突变启动子都支持转录。每个元素都对组织特异性，激素反应或两者兼有贡献。尽管WT，TATAA样和CCAAT突变体的启动子被伽马互化剂激活，但抑制了INR和SP1突变体，这意味着这些元素在调节激素反应中。转录启动不是一个连续的过程，而是发生在振幅和频率不同的爆发中。尽管已经描述了增强子在酵母和培养的哺乳动物细胞中启动子爆发特征上的作用，但尚未评估单个核心启动子元素对爆发幅度和频率的贡献。在证明构成MHC I类启动子的核心启动子元素都会有助于转录开始，我们正在研究干扰素激活的转录是否会影响爆发幅度，频率，还是两者均和核心启动子元素在确定单分子rna Fish原代脾脏B细胞中这些爆发特性中的作用。