Regulation of apoptosis by menin

-描述(申请人提供)：多发性内分泌肿瘤I型(MEN1)是一种主要遗传的肿瘤综合征，其特征是肿瘤发生在多个内分泌器官，偶尔发生在非内分泌器官。在MEN1患者中，该基因发生突变，MEN1编码一种由610个氨基酸残基组成的蛋白质--薄荷素。在小鼠中靶向干扰MEN1还会导致一种内分泌肿瘤综合征，这种综合征与人类的MEN1非常相似，表明确实具有对脑膜素的肿瘤抑制功能。由于在脑膜素中没有明显的区域暗示任何生化功能，所以阐明脑膜素在肿瘤抑制中的关键作用的潜在机制一直是具有挑战性的，但也是令人兴奋的。最近，我们在了解脑膜素在肿瘤坏死因子-α介导的细胞凋亡中的重要作用方面取得了重大进展。我们发现，薄荷素对于最佳的肿瘤坏死因子-α诱导的细胞凋亡是必不可少的。此外，薄荷素直接与DNA结合，两个与MEN1疾病相关的突变体无法与DNA结合。此外，膜蛋白在caspase 8转录中起重要作用，并与内源性caspase 8启动子结合，而两个与MEN1相关的膜蛋白突变不能激活caspase 8的表达，也不能诱导肿瘤坏死因子-a诱导的细胞凋亡。其他最近的报告表明，薄荷素与组蛋白甲基转移酶有关，组蛋白甲基转移酶通常激活基因转录。综上所述，这些结果导致我们假设，Menin与DNA结合，并将其他转录调节因子招募到caspase 8基因的启动子，导致caspase 8转录上调和肿瘤坏死因子-α诱导的细胞凋亡，以及抑制MEN1的肿瘤形成。 为了检验这些假说，已经提出了三个具体目标。首先，我们将确定脑膜素中最小的DNA结合域，并研究脑膜素-DNA相互作用在调节caspase8表达和肿瘤坏死因子-α诱导的细胞凋亡中的作用。其次，我们将研究脑膜素、组蛋白甲基转移酶和其他脑膜素相互作用蛋白在半胱氨酸天冬氨酸蛋白酶8和肿瘤坏死因子-α诱导的细胞凋亡的转录调控中的作用。第三，脑膜素介导的caspase 8的表达在抑制MEN1肿瘤形成中的作用将在经典的和条件性的Man 1基因敲除小鼠中进行评估。这些独立但互补的研究结果可能会极大地促进我们对MEN1发展的分子回路的理解，并为改进MEN1和其他相关肿瘤的治疗干预措施提供帮助。

-DESCRIPTION (provided by applicant): Multiple endocrine neoplasia type I (MEN1) is a dominantly inherited tumor syndrome characterized by development of tumors in multiple endocrine organs and occasionally in non-endocrine organs. The gene mutated in MEN1 patients, Men1, encodes a protein of 610 amino acid residues, menin. Targeted disruption of Men1 in mice also leads to an endocrine tumor syndrome that closely mimics the human MEN1, indicating a bona fide tumor suppressing function for menin. Since there are no obvious domains in menin that suggest any biochemical functions, it has been challenging yet exciting to elucidate the mechanisms underlying the crucial role of menin in tumor suppression. Recently, we have made significant progress in understanding a vital role for menin in TNF-alpha-mediated apoptosis. We show that menin is essential for optimal TNF-alpha-induced apoptosis. Moreover, menin directly binds DNA, and two MEN1 disease-related mutants fail to bind DNA. Furthermore, menin plays an essential role in caspase 8 transcription and also binds the promoter of endogenous caspase 8, while two MEN1-related menin point mutants fail to activate caspase 8 expression and TNF-a-induced apoptosis. Other recent reports show that menin associates with histone methyltransferases that usually activates gene transcription. Together, these results lead us to hypothesize that menin binds to DNA and recruits other transcriptional regulators to the promoter of the caspase 8 gene, resulting in upregulation of caspase 8 transcription and TNF-alpha-induced apoptosis, as well as suppression of tumorigenesis in MEN1. Three Specific Aims have been proposed to test these hypotheses. First, we will identify the minimal DNA binding domain in menin and characterize the role of menin-DNA interaction in regulating caspase 8 expression and TNF-alpha-induced apoptosis. Second, we will examine the role of menin, histone methyltransferases and other menin-interacting proteins in the transcriptional regulation of caspase 8 and TNF-alpha-induced apoptosis. Third, the role of menin-mediated expression of caspase 8 in suppressing the MEN1 tumorigenesis will be evaluated in classic and conditional Men 1 knock out mice. Results from these independent yet complementary studies will likely significantly advance our understanding of the molecular circuitry of the MEN1 development and shed lights on improving therapeutic interventions for MEN1 and other related tumors.