C-MYC PROTO-ONCOGENE TRANSCRIPTIONAL ELONGATION BLOCK

描述(摘自申请者摘要)：c-myc原癌基因， 它的表达与正常细胞的生长和分化有关， 在许多肿瘤状态中异常表达，包括淋巴瘤， 白血病和小细胞肺癌。黄曲霉的分子分析 C-myc基因在正常细胞和肿瘤细胞中的表达调控 发现了转录调控的新机制 真核基因的表达。控制c-myc表达的一个水平是 对转录的数量和比例进行调制，这些转录来自 两个c-myc启动子，P1和P2。第二种和新的转录模式 抑制转录延伸的控制区在正常情况下也受到调节。 细胞。这种机制最初是在人类c-myc中描述的。 基因和小鼠c-myc基因中，控制启动的量 延伸超过外显子1的3‘端的一个区块的转录 产生全长的c-myc转录本。C-myc延伸块运行 以启动子特有的和可调控的方式。转录 在P1启动子启动时组成地读出外显子1块， 而P2启动子的转录可以被调节为 要么通过，要么被挡住。在正常细胞中，P2是主要的启动子。 相比之下，在Burkitts淋巴瘤(BL)细胞中，这种细胞的特征是 C-myc和免疫球蛋白(Ig)序列并列的易位 是转录起始主要向P1启动子转移。 因此，在BL细胞中，伸长块被取消，导致高 C-myc RNA的水平和/或结构性合成。调查员 工作假说是终止或反终止的因素 以启动子特异性方式对RNA聚合酶II复合体的活性。 这些因素改变聚合酶复合体以识别或阅读 下行闭塞信号。在正常细胞中，这种联系是可调节的 在P2启动子，其中在P1启动子形成的复合体赋予 条件性的通读。在BL细胞中，向P1转录的转变可能 是由于抑制P2活性的反式作用因子的存在 和/或增加P1利用率，或由于顺式对启动子的影响 C-myc启动子与 作为易位的结果，IG序列。这样做的目的是 建议确定启动子特异的元件和反式因子 授予聚合酶II通读和“阻断”模式所必需的 转录c-myc基因的复合体，并确定其分子基础 C-myc伸长阻断和结构性表达的取消 Bl中c-myc基因的表达。

DESCRIPTION (Adapted from applicant's abstract): The c-myc proto-oncogene, whose expression is linked to growth and differentiation in normal cells, is expressed aberrantly in many neoplastic states, including lymphomas, leukemias and small cell lung carcinomas. Molecular analyses of the regulation of expression of the c-myc gene in normal and neoplastic cells have uncovered novel mechanisms for the transcriptional regulation of eukaryotic gene expression. One level of control of c-myc expression is modulation in the quantity and ratio of transcripts that initiate from the two c-myc promoters, P1 and P2. A second and novel mode of transcriptional control, a block to transcription elongation, is also regulated in normal cells. This mechanism, which was described originally in the human c-myc gene and in the murine c-myc gene, controls the amount of initiated transcription that elongates past a block at the 3' end of exon 1 to produce full length c-myc transcripts. The c-myc elongation block operates in both a promoter-specific and regulatable fashion. Transcription initiated at the P1 promoter constitutively reads through the exon 1 block, whereas transcription for the P2 promoter can be modulated to either read through or be blocked. In normal cells, P2 is the predominant promoter. In contrast, in Burkitts's lymphoma (BL) cells, which are characterized by translocation that juxtapose c-myc and immunoglobulin (Ig) sequences, there is a shift of transcription initiation predominantly to the P1 promoter. Thus, the elongation block is abrogated in BL cells, resulting in high levels and/or constitutive synthesis of c-myc RNA. The investigator working hypothesis is that factors confer termination or antitermination activities to RNA polymerase II complexes in a promoter-specific fashion. These factors modify the polymerase complex to recognize or read through downstream block signals. In normal cells, this association is regulatable at the P2 promoter, where as the complex formed at the P1 promoter confers constitutive read through. In BL cells, the shift to P1 transcription may be due to the presence of trans-acting factors that suppress P2 activity and/or increase P1 utilization, or due to cis effects on promoter utilization and strength imposed by the proximity of the c-myc promoters to Ig sequences as a consequence of the translocation. The goal of this proposal is to identify the promoter-specific elements and trans-factors essential in conferring the read-through and "block" modes to polymerase II complexes transcribing the c-myc gene, and to determine the molecular basis of the abrogation of the c-myc elongation block and constitutive expression of c-myc in BL.