The Role of Methylthioadenosine Phosphorylase Loss in Tumorigenesis

说明(申请人提供)：甲硫腺苷磷酸化酶(MTAP)是蛋氨酸回收途径中的一个关键酶，其功能是将5美分脱氧-5美分甲硫腺苷(MTA)转化为蛋氨酸。MTAP失活，通常是纯合子缺失，在实体和血液系统恶性肿瘤中被发现的频率很高。由于MTAP位于CDKN2A/ARF抑癌基因附近，目前尚不清楚MTAP的缺失是否在肿瘤的发生中起主要作用，还是仅仅因为靠近CDKN2A/ARF而丢失。在已发表的工作和这里提供的初步数据中，我们表明将MTAP重新引入MTAP缺失的肿瘤细胞系显著抑制了肿瘤的致瘤性，并影响了涉及细胞迁移和侵袭的过程。我们还发现，MTAP零等位基因杂合子(MtaplacZ)的小鼠因类似T细胞淋巴瘤的淋巴增殖性疾病而过早死亡。综上所述，这些数据表明MTAP缺失在癌症的发生发展中起着重要作用。这项提案的总体目标是确定MTAP缺失如何直接促进癌症的发展。有四个具体目标。在第一个目标中，我们将确定MTAP的种系突变是否会加速小鼠的肿瘤形成。我们将充分描述MTAP杂合子动物的淋巴增殖性疾病的特征，并确定它们是否患有完全成熟的淋巴瘤。我们还将确定MTAP缺失是否会加速两种不同小鼠模型的肿瘤发生。在第二个目标中，我们将使用最近开发的过渡状态抑制剂MT-DAD-Me-IMMA来确定MTAP的药物抑制是否可以导致或增强小鼠的肿瘤形成。使用这种化合物，我们将检验这样的假设，即抑制MTAP将加速正常和CDKN2A/ARF缺陷小鼠的肿瘤发展。在第三个目标中，我们将确定MTAP缺失对体内侵袭和转移的影响。我们将把荧光标记的等基因细胞系注射到SCID小鼠体内，并使用体内最先进的全身成像技术来确定MTAP的表达如何影响侵袭和转移。最后，在最后一个目标中，我们将检验MTAP缺失通过MTA的积累改变基因表达来影响肿瘤发生的假说，MTA抑制了调节染色质和基因表达的甲基转移酶。这些研究意义重大，因为了解MTAP缺失在肿瘤发生中的作用可能会导致MTAP缺失肿瘤的新治疗策略。此外，这些研究还将确定“看家”代谢酶如何作为肿瘤抑制基因发挥新的作用。公共卫生相关性：甲硫腺苷磷酸化酶(MTAP)基因缺失是在许多不同类型的人类肿瘤中观察到的最常见的基因变化之一。这项拟议的研究与人类健康相关，因为确认MTAP是一种肿瘤抑制基因可以识别出癌症风险增加的个体。此外，了解MTAP缺失促进肿瘤发生的机制可能会导致新的策略，选择性地针对MTAP缺失的肿瘤细胞进行破坏。这可能与许多不同类型的人类癌症有关。

DESCRIPTION (provided by applicant): Methylthioadenosine phosphorylase (MTAP) is a key enzyme in the methionine salvage pathway whose function is to convert 5cent-deoxy-5cent-methylthioadenosine (MTA) into methionine. Inactivation of MTAP, generally by homozygous deletion, is found in both solid and hematologic malignancies at a high frequency. Because MTAP is located near the CDKN2A/ARF tumor suppressor gene, it is unclear if loss of MTAP plays a primary role in tumorigenesis or if it is lost simply due to proximity to CDKN2A/ARF. In published work and preliminary data presented here, we show that reintroduction of MTAP into MTAP-deleted tumor cell lines significantly suppresses tumorigenicity and affects processes involved in cell migration and invasion. We also found that mice heterozygous for a MTAP null allele (MtaplacZ) die prematurely of lymphoproliferative disease resembling T-cell lymphoma. Taken together, these data suggest that MTAP loss plays a functional role in the development of cancer. The overall goal of this proposal is to determine how MTAP loss contributes directly to the development of cancer. There are four specific aims. In the first aim, we will determine if germline mutations in MTAP accelerate tumorigenesis in mice. We will fully characterize the lymphoproliferative disease in MTAP heterozygous animals and determine if they have full fledged lymphoma. We will also determine if MTAP loss can accelerate tumorigenesis in two different mouse models. In the second aim we will determine if pharmacologic inhibition of MTAP can cause or enhance tumorigenesis in mice using the recently developed transition state inhibitor MT-DAD-Me-ImmA. Using this compound we will test the hypothesis that inhibition of MTAP will accelerate the development of tumors both in normal and CDKN2A/ARF deficient mice. In the third aim we will determine the effect of MTAP loss on invasion and metastasis in vivo. We will inject fluorescently labeled isogenic cell lines into SCID mice and use state-of-the-art in vivo whole body imaging to determine how MTAP expression affects invasion and metastasis. Finally in the last aim we will test the hypothesis that MTAP-loss affects tumorigenesis by altering gene expression via accumulation of MTA that inhibits methyltransferase enzymes regulating chromatin and gene expression. These studies are significant because an understanding of the role that MTAP deletion plays in tumorigenesis may lead to novel therapeutic strategies for MTAP-deleted tumors. In addition, these studies will establish how a "house-keeping" metabolic enzyme can have a novel role as a tumor suppressor gene. PUBLIC HEALTH RELEVANCE: Deletion of the gene for methylthioadenosine phosphorylase (MTAP) is one of the most frequent genetic changes observed in many different types of human tumors. The proposed study is relevant to human health because the identification of MTAP as a tumor suppressor gene could identify individuals at increased risk of cancer. In addition, understanding of the mechanism by which MTAP deletion contributes to tumorigenesis may lead to novel strategies that can selectively target MTAP-deleted tumor cells for destruction. This would potentially have relevance to many different kinds of human cancer.