Role of menin in islet cell biology and tumorigenesis

描述（由申请人提供）：多发性内分泌瘤，I型（MEN1），是一种以多发肿瘤为主累及内分泌腺为特征的遗传性癌症。MEN1的基因是一种典型的肿瘤抑制基因，它编码一种叫做menin的核蛋白。受影响个体的肿瘤发生在失去野生型等位基因后，遵循经典的肿瘤抑制模型。尽管许多相互作用的蛋白质已经提供了对menin的功能见解，但尚不清楚menin的缺失是如何导致肿瘤形成的。我们最近为MEN1开发了小鼠模型。这些小鼠发育的内分泌肿瘤谱忠实地概括了相应的人类状况，因此是追求与Men1肿瘤抑制基因作用有关的三个目标的优秀资源。在Specific Aim 1中，我将确定在Men1基因敲除小鼠胰腺内分泌肿瘤中替换menin的结果。这一目的将通过在诱导启动子控制下含有Men1基因的转基因小鼠来解决。虽然有几项研究表明，逆转一个或多个激活的癌基因可导致肿瘤消退，但到目前为止，还没有人报道在癌症中重新表达缺失的肿瘤抑制基因的后果。在Specific Aim 2中，我将深入了解MEN1（一种普遍表达的基因）的缺失如何仅在一组特定的组织中引起肿瘤。为了做到这一点，我对小鼠进行了基因工程改造，使其肝脏中MEN1蛋白纯合为零，而肝脏中MEN1蛋白通常不容易产生肿瘤。有趣的是，Men1-null的肝脏看起来完全正常，并且在整个成年期都没有肿瘤。为了深入了解MEN1中组织特异性肿瘤表型的悖论，我将比较肝脏中野生型和MEN1 -null表达谱与内分泌胰腺中产生的表达谱，内分泌胰腺是MEN1中易发生肿瘤的组织。我推测，鉴定在MEN1缺失的肝脏和内分泌胰腺中显示表达差异的基因将为MEN1的组织特异性提供重要线索。在Specific Aim 3中，我将利用染色质免疫沉淀与微阵列技术（ChlP-chip）相结合的方法来鉴定受menin转录共调节的基因。重要的是，我提供了初步数据，其中包含> 18000个基因启动子的微阵列被用来鉴定与menin结合的>50个启动子。这些结果不仅说明了这种方法的力量和可行性，而且为menin提供了新的机制见解。一种鉴定menin共同调控的其他基因的综合方法不仅将增加我们对menin如何调节细胞增殖的理解，正如在Aim 1中所研究的那样，而且还将通过提供MEN1中组织特异性肿瘤表型悖论的线索，很好地补充Aim 2。

DESCRIPTION (provided by applicant): Multiple endocrine neoplasia, type I (MEN1), is a form of inherited cancer characterized by multiple tumors primarily involving the endocrine glands. The gene for MEN1 is a classic tumor suppressor gene that encodes a nuclear protein called menin. Tumors in affected individuals occur after loss of the wild-type allele, following the classic tumor suppressor model. Although a number of interacting proteins have provided functional insights to menin, it is not clear how the loss of menin causes tumor formation. We recently developed mouse models for MEN1. These mice develop an endocrine tumor spectrum that faithfully recapitulates the corresponding human condition, and therefore are excellent resources to pursue three aims pertaining to the action of the Men1 tumor suppressor gene. In Specific Aim 1, I will determine the consequence of replacing menin in pancreatic endocrine tumors of Men1 knockout mice. This aim will be addressed using transgenic mice containing the Men1 gene under the control of an inducible promoter. Although there are several studies suggesting that the reversal of one or more activated oncogenes can cause tumor regression, so far no one has reported the consequences of re-expressing a deleted tumor suppressor gene in cancer. In Specific Aim 2,1 will gain insights into how the loss of MEN1, a ubiquitously expressed gene, gives rise to tumors only in a defined set of tissues. To do this, I have engineered mice that are homozygous null for menin in liver, a tissue not normally predisposed to developing tumors in MEN1. Interestingly, Men1-null livers appear entirely normal and remain tumor free throughout adulthood. To gain insights to the paradox of the tissue-specific tumor phenotype in MEN1, I will compare wild-type and Men1-null expression profiles from liver to those generated from endocrine pancreas, a tissue that is susceptible to developing tumors in MEN1. I hypothesize that the identification of genes that show expression differences in Men1-null livers and endocrine pancreas will provide vital clues to tissue specificity in MEN1. In Specific Aim 3,1 will take advantage of an approach that couples chromatin immunoprecipitation with microarray technology (ChlP-chip) to identify genes that are transcriptionally co-regulated by menin. Importantly, I present preliminary data in which microarrays containing >18,000 gene promoters were used to identify >50 promoters bound by menin. These results not only illustrate the power and feasibility of this approach, but also provide new mechanistic insights to menin. A comprehensive approach to identify additional genes that are co-regulated by menin will not only increase our understanding of how menin regulates cell proliferation, as studied in Aim 1, but will also nicely complement Aim 2 by providing clues to the paradox of tissue-specific tumor phenotype in MEN1.