FUNCTION OF THE RETINOBLASTOMA PROTEIN

正常细胞在肿瘤发生期间经历许多突变。 之一 这一过程的特点是扩散失控。 通常这种损失是两种类型基因突变的结果， 癌基因和肿瘤抑制基因。 癌基因的产物通常 促进细胞分裂，这些基因的突变导致 不适当的信号来划分。 肿瘤蛋白产物 抑制基因的作用是限制正常细胞的增殖。 期间 这些基因通常通过突变失活， 是肿瘤抑制基因产物的丢失， 增加扩散。 第一个肿瘤抑制基因之一， 分离的是视网膜母细胞瘤易感基因RB-1。 视网膜母细胞瘤特征性地包含两个限速突变， RB-1的每个等位基因中有一个。 在家族性视网膜母细胞瘤中， 一个等位基因是遗传的，另一个是在体细胞发育过程中发育的。 视网膜 在散发性视网膜母细胞瘤中，这两种突变都发生在 体细胞发育 RB-1突变也在广泛的 其他各种人类肿瘤。 这项工作得出的结论是， RB-1基因的产物负调节许多 不同类型的细胞。 最近对RB-1基因的蛋白质产物（pRB）的研究表明， 为它的功能提供了最初的线索。 它是一种核蛋白， 正常的作用似乎是调节某些细胞 转录因子 pRB的最佳特征伴侣是 转录因子E2 F。 E2 F似乎调节转录， 一组基因，其表达是细胞增殖所必需的。 目前的证据表明，pRB抑制E2 F介导的转录 从而有助于调节关键基因。 这种相互作用 这似乎只是E2 F监管的一个组成部分。 有强有力 证据表明E2 F的活性也受其关联的调节， pRB相关蛋白p107 pRB和p107共享许多特性。 他们两人最初都被确认为 通过它们与DNA肿瘤病毒癌蛋白的相互作用。 病毒 蛋白质，包括腺病毒E1 A、SV 40大T和人 乳头瘤病毒E7均靶向pRB和p107，作为其部分 转化能力。 在这些情况下，E1 A、大T和E7 pRB和p107，从而模拟人肿瘤中pRB的缺失。 这项资助计划研究pRB、p107和E2 F如何联合收割机， 调节反式激活，并确定生物学后果 这些互动。 我们的近期目标有三个方面。 一是 需要了解pRB/E2 F调节的细节。 这项工作是 目前正在进行中，包括pRB/E2 F的生物化学 调节，确定上游调节器的影响， 下游目标分析。 第二个主要目标是确定 p107如何影响E2 F转录。 大多数试剂需要 这些研究现已完成，我们已建立了基本的化验方法。 这些相互作用的生物学后果是我们的第三个目标。 在这里，我们将确定这些蛋白质如何有助于调节 细胞增殖、分化和肿瘤发生的过程。

A normal cell undergoes many mutations during tumorigenesis. One of the features of this process is the loss of control over proliferation. Typically this loss is the result of mutations in two types of genes, oncogenes and tumor suppressor genes. The products of oncogenes normally act to promote cell division, and mutation of these genes leads to inappropriate signals to divide. The protein products of tumor suppressor genes act to limit the proliferation of a normal cell. During tumorigenesis these genes are often inactivated through mutation, and it is the loss of tumor suppressor gene products that contributes to increased proliferation. One of the first tumor suppressor genes to be isolated was the retinoblastoma susceptibility gene, RB-1. Retinoblastomas characteristically contain two rate limiting mutations, one in each allele of RB-1. In familial retinoblastomas, one mutant allele is inherited and the other develops during somatic development of the retina. In sporadic retinoblastomas, both mutations occur during somatic development. RB-1 mutations have also been found in a wide variety of other human tumors. This work leads to the conclusion that the product of the RB-1 gene negatively regulates proliferation of many different types of cell. Recent studies of the protein product of the RB-1 gene (pRB) have provided the first clues to its function. It is a nuclear protein whose normal role appears to be the regulation of certain cellular transcription factors. The best characterized partner for pRB is the transcription factor E2F. E2F appears to regulate the transcription of a set of genes whose expression is required for cell proliferation. Current evidence suggests that pRB represses E2F-mediated transcription and thereby contributes to the regulation of key genes. This interaction appears to be only one component of E2F regulation. There is strong evidence that the activity of E2F is also regulated by its association with the pRB-related protein p107. pRB and p107 share many properties. They both were originally identified through their interactions with DNA tumor virus oncoproteins. Viral proteins, including adenovirus E1A, SV40 large T, and human papillomavirus E7, all target pRB and p107 as a portion of their transforming ability. In these cases, E1A, large T, and E7 inactivate pRB and p107, thus mimicking the loss of pRB in human tumors. This grant proposes to investigate how pRB, p107 and E2F combine to give regulated transactivation and to determine the biological consequences of these interactions. Our immediate goals are threefold. First, we need to understand the details of pRB/E2F regulation. This work is currently underway and encompasses the biochemistry of pRB/E2F regulation, the determination of the effects of upstream regulators and the analysis of downstream targets. The second main goal is to determine how p107 affects E2F transcription. Most of the reagents needed for these studies are now available and we have established the basic assays. The biological consequences of these interactions are our third goal. Here, we will determine how these proteins contribute to the regulation of cell proliferation, differentiation, and oncogenesis.