FACTORS IMPORTANT IN BETA2 TARGETED ACTIVATION

BETA 2是独立分离的，其特征在于它能够 在转染的β细胞中激活胰岛素报告基因转录 （称为BETA2），和非洲爪蟾异位表达后的神经突形成 胚胎（称为NeuroD 1）。这种基本的螺旋-环-螺旋（bHLH）转录 将该因子称为BETA2。在胰岛中表达 内分泌细胞，肠，垂体和一个子集的神经元， 中枢和外周神经系统。有趣的是， BETA2-/-小鼠中表达胰岛素的β细胞严重减少， 剩余的内分泌细胞不能形成胰岛。这些动物进化出 早发性糖尿病并在围产期死亡神经系统似乎 在BETA2-/-小鼠中正常发育，可能是由于 补偿系数。总的来说，这些结果表明，BETA 2 在胰岛素基因的转录中起重要的调节作用 在胰岛β细胞中，以及对于胰岛所需的基因， 分化不幸的是，与肌源性或脂肪源性 系统，没有细胞系可用于研究胰岛细胞 分化然而，作为内分泌胰腺的祖细胞， 表达对神经外胚层和 和胰岛内分泌分化，包括ISL-1和PAX 6，我们推断 非洲爪蟾的神经发生试验可以提供对 BETA2在胰腺发育过程中的作用机制。作为 因此，我们一直在描述BETA2中的序列， 是刺激胰岛素基因转录和神经原性 分化我们的研究结果表明， 跨越bHLH（氨基酸100-155）和C-末端的保守序列 （氨基酸156-355）区域对于这两个过程都是重要的。 C-末端区域的缺失分析表明， 活化由BETA 2的两个独立且可分离的结构域介导， 其跨越氨基酸156-251和252-355。p300/CBP共激活剂是 显示与156-251和300-355个氨基酸区域相互作用， 贝塔二号此外，我们最近发现，BETA2：p300/CBP可以 激活编码细胞周期蛋白依赖性激酶的基因的表达 抑制剂p21，表明这一关键细胞周期上调 胰岛的正常进展可能需要调节剂 差异化方案下面提出的实验将测试 假设BETA 2介导的激活涉及募集 p300/CBP，一种增强重要调节因子活性的因子 细胞的增殖和分化。

BETA2 was independently isolated and characterized by its ability to activate insulin reporter gene transcription in transfected Beta cells (termed BETA2), and neurite formation upon ectopic expression in Xenopus embryos (termed NeuroD1). This basic helix-loop-helix (bHLH) transcription factor will be referred to as BETA2. It is expressed in pancreatic islet endocrine cells, the intestine, the pituitary, and a subset of neurons in the central and peripheral nervous system. Interestingly, the number of insulin-expressing Beta cells was severely reduced in BETA2-/- mice, and the remaining endocrine cells failed to form islets. These animals develop early-onset diabetes and die perinatally. The nervous system appears to develop normally in BETA2-/- mice, presumably due to the presence of a compensatory factor(s). Collectively, these results suggested that BETA2 played an important regulatory role in transcription of the insulin gene in islet Beta cells, as well as for gene(s) required for pancreatic islet differentiation. Unfortunately, in contrast to the myogenic or adipogenic systems, the are not cell lines available to study islet cell differentiation. However, as progenitors cells of the endocrine pancreas express transcription factors that are essential for both neuroectodermal and islet endocrine differentiation, including ISL-1 and PAX6, we reasoned that the neurogenesis assay in Xenopus could provide insight into the mechanisms utilized by BETA2 during pancreatic development. As a consequence, we have been characterizing the sequences within BETA2 that are required for stimulating insulin gene transcription and neurogenic differentiation. Our results have demonstrated that evolutionarily conserved sequences spanning the bHLH (amino acids 100-155) and C-terminal (amino acids 156-355) regions are important for both of these processes. Deletional analysis of the C-terminal region indicate that regulated activation is mediated by two independent and separable domains of BETA2, which span amino acids 156-251 and 252-355. The p300/CBP co-activator was shown to interact with the 156-251 and 300-355 amino acid regions of BETA2. In addition, we have recently shown that BETA2:p300/CBP can activate expression of the gene-encoding the cyclin-dependent kinase inhibitor p21, suggesting that up-regulation of this key cell cycle regulator may be required for normal progression of the islet differentiation program. The experiments proposed below will test the hypothesis that BETA2-mediate activation involves the recruitment of p300/CBP, a factor that potentiates the activity of important regulators of cellular proliferation and differentiation.