FUNCTION OF THE RETINOBLASTOMA PROTEIN

正常细胞在肿瘤形成过程中会经历许多突变。其中一个 这一过程的特点是失去了对扩散的控制。 通常，这种缺失是两种基因突变的结果， 癌基因和肿瘤抑制基因。癌基因的产物通常 促进细胞分裂，这些基因的突变会导致 不合适的信号来划分。肿瘤的蛋白质产物 抑制基因的作用是限制正常细胞的增殖。在.期间 肿瘤发生这些基因通常通过突变而失活，而它 是肿瘤抑制基因产物的丢失导致 增加了扩散。最早的肿瘤抑制基因之一是 分离到视网膜母细胞瘤易感基因Rb-1。 视网膜母细胞瘤典型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，一个突变 等位基因是遗传的，其他等位基因在体细胞发育过程中发展 视网膜。在散发性视网膜母细胞瘤中，这两种突变都发生在 躯体发育。Rb-1基因突变也在广泛的 各种各样的其他人类肿瘤。这项工作得出的结论是 Rb-1基因的产物对许多 不同类型的细胞。 最近对Rb-1基因的蛋白产物(PRb)的研究已经 提供了有关其功能的第一条线索。它是一种核蛋白，其 正常的作用似乎是调节某些细胞 转录因子。PRB最具特色的合作伙伴是 转录因子E2F。E2F似乎调节转录 细胞增殖所必需的一组基因。 目前的证据表明，pRb抑制E2F介导的转录 从而有助于关键基因的调控。这种互动 似乎只是E2F监管的一个组成部分。有很强的 E2F活性也受其关联性调节的证据 与PRB相关蛋白p107结合。 PRb和p107有许多共同的性质。他们最初都是被确认的 通过它们与DNA肿瘤病毒癌蛋白的相互作用。病毒式传播 蛋白质，包括腺病毒E1a、SV40大T和人 乳头瘤病毒E7，都以pRb和p107为靶点，作为其 转化能力。在这些情况下，E1a、大T和E7处于停用状态 PRb和p107，从而模拟了pRb在人类肿瘤中的缺失。 这项拨款建议调查pRb、p107和E2F是如何结合在一起的 调节的反式激活并确定其生物学后果 在这些互动中。我们的近期目标有三个。首先，我们 需要了解PRB/E2F法规的细节。这项工作是 目前正在进行中，包括pRb/E2F的生物化学 监管、上游监管机构影响的确定和 对下游目标的分析。第二个主要目标是确定 P107如何影响E2F转录。所需的大多数试剂 这些研究现在已经完成，我们已经建立了基本的分析方法。 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是如何参与调节的 关于细胞增殖、分化和肿瘤形成的研究。

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.