The Role of Methylthioadenosine Phosphorylase Loss in Tumorigenesis

描述（申请人提供）：甲基硫腺苷磷酸化酶（MTAP）是蛋氨酸回收途径中的关键酶，其功能是将5美分-脱氧-5美分-甲基硫腺苷（MTA）转化为蛋氨酸。MTAP的失活，通常是通过纯合缺失，在实体和血液系统恶性肿瘤中都有很高的频率。由于MTAP位于CDKN2A/ARF肿瘤抑制基因附近，因此尚不清楚MTAP的丢失是否在肿瘤发生中起主要作用，还是仅仅由于靠近CDKN2A/ARF而丢失。在已发表的工作和本文提供的初步数据中，我们表明将MTAP重新引入MTAP缺失的肿瘤细胞系可显著抑制致瘤性并影响细胞迁移和侵袭过程。我们还发现MTAP空等位基因（MtaplacZ）杂合的小鼠过早死于类似t细胞淋巴瘤的淋巴增生性疾病。综上所述，这些数据表明MTAP的缺失在癌症的发展中起着功能性的作用。这项提议的总体目标是确定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发生。我们将在MTAP杂合动物中充分表征淋巴增生性疾病，并确定它们是否患有完全成熟的淋巴瘤。我们还将在两种不同的小鼠模型中确定MTAP缺失是否会加速肿瘤的发生。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的药理学抑制是否会导致或增强小鼠的肿瘤发生。使用这种化合物，我们将验证抑制MTAP会加速正常和CDKN2A/ARF缺陷小鼠肿瘤发展的假设。在第三个目标中，我们将确定MTAP丢失对体内侵袭和转移的影响。我们将向SCID小鼠注射荧光标记的等基因细胞系，并使用最先进的体内全身成像技术来确定MTAP表达如何影响侵袭和转移。最后，在最后一个目标中，我们将验证mtap缺失通过抑制调节染色质和基因表达的甲基转移酶的MTA积累改变基因表达来影响肿瘤发生的假设。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，这些研究将确定“管家”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：甲基硫代腺苷磷酸化酶（MTAP）基因的缺失是在许多不同类型的人类肿瘤中观察到的最常见的遗传变化之一。这项拟议的研究与人类健康有关，因为将MTAP识别为肿瘤抑制基因可以识别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，可以选择性地靶向MTAP缺失的肿瘤细胞进行破坏。这可能与许多不同种类的人类癌症有关。

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.