Role of MAT and SAMe in Colon Cancer Pathogenesis and Treatment

摘要 蛋氨酸腺苷转移酶(MAT)是催化S形成的一种必不可少的酶。 腺苷蛋氨酸(相同)。在哺乳动物中，MAT的催化亚单位由两个基因编码，MAT1a和MAT1a MAT2a，而第三个基因MAT2？，编码一个调节亚单位？它调节由MAT2A编码的酶。 Mat1a在肝脏中表达，而Mat2a在肝脏中广泛分布。在肝细胞中，MAT2A和MAT2？ 表达促进了生长。Same抑制肝细胞生长，在肝癌细胞中促凋亡，但抗 正常肝细胞中有细胞凋亡。MAT基因的调控以及MAT和MAT是否调节生长和 结肠癌细胞的死亡尚不清楚。我们发现MATA和MAT2升高了？切除的组织中的mRNA水平 结肠癌标本与邻近正常组织的比较。这是由于转录增加所致。 Min小鼠息肉中MAT2AmRNA水平也升高。EGF、IGF-1和瘦素--三种有丝分裂原 与结肠癌的发病机制和侵袭性有关，诱导Mat2a在结肠癌中的表达和生长 结肠癌细胞株RKO和HT29。通过RNAi降低MAT2A的表达抑制生长并阻断 这些生长因子的有丝分裂作用。Same及其代谢物甲硫腺苷(MTA)降低 并抑制生长因子诱导MAT2A和细胞增殖的能力。 此外，SAME和MTA通过诱导细胞凋亡来抑制结肠癌细胞的生长。一种新的靶子 确定的是cFLIP，它被Same和MTA下调。最后，过度表达增加，而 MAT2的表达减少？抑制生长并导致细胞凋亡。目前的提案将延长这些 在五个特定目标上的新观察：1.检测结肠癌中MAT2A的转录调控 我们将确定MAT2A在基线和生长反应中是如何转录调节的 2.阐明MAT2A和MAT2？的分子机制(S)。上调监管在 结肠癌我们将使用切除的结肠癌和正常组织标本来阐明其机制。 确定mat基因如何影响结肠癌细胞的生长和死亡。 我们将如何确定MAT2A和MAT2？调节生长和细胞凋亡；4.阐明其作用机制。 Same和MTA诱导结肠癌细胞凋亡的分子机制和 检查正常结肠上皮细胞是否受到影响；以及5.评估MAT表达的变化 肿瘤形成过程中的作用及其与MTA在肠道化学预防治疗中的作用 我们将检查SAME和MTA是否可以防止Min小鼠自发性息肉的形成，以及 停止进展和逆转已经建立的异常隐窝病灶在用偶氮甲烷治疗的小鼠中。 这些研究的成功完成，应可大大加深我们对旅游及旅游事务监察委员会角色的认识。 在结肠癌的发病机制上也是如此，并可能为这两种化学预防提供一种新的治疗方法 以及结肠息肉和癌症的治疗，这些都是与公共健康高度相关的话题。项目叙事 结肠癌仍然是西方世界最常见的癌症之一。目前有效的 缺乏无副作用的化学预防疗法。这个项目的目标是调查一个 结肠癌发展的新范式，看看S-腺苷蛋氨酸(SAME)，一种营养补充剂 广泛存在，其代谢产物甲硫腺苷(MTA)可有效地在化学预防和 结肠癌的治疗。

ABSTRACT Methionine adenosyltransferase (MAT) is an essential enzyme that catalyzes the formation of S- adenosylmethionine (SAMe). In mammals, the catalytic subunit of MAT is encoded by two genes, MAT1A and MAT2A, while a third gene MAT2?, encodes for a regulatory subunit ? that regulates MAT2A-encoded enzyme. MAT1A is expressed in liver while MAT2A is widely distributed. In hepatocytes, increased MAT2A and MAT2? expression increased growth. SAMe inhibits hepatocyte growth, is pro-apoptotic in liver cancer cells but anti- apoptotic in normal hepatocytes. Regulation of MAT genes and whether MAT and SAMe regulate growth and death in colon cancer cells are unknown. We found increased MAT2A and MAT2? mRNA levels in resected colon cancer specimens as compared to adjacent normal tissue. This occurred due to increased transcription. MAT2A mRNA levels are also increased in the polyps of Min mice. EGF, IGF-1 and leptin, three mitogens implicated in the pathogenesis and invasiveness of colon cancer, induced MAT2A expression and growth in colon cancer cell lines RKO and HT29. Lowering MAT2A expression by RNAi reduced growth and blocked the mitogenic effects of these growth factors. SAMe and its metabolite methylthioadenosine (MTA) lowered MAT2A expression and prevented the ability of growth factors to induce MAT2A and cell proliferation. Furthermore, SAMe and MTA inhibited growth of colon cancer cells by inducing apoptosis. A novel target identified is cFLIP, which is down-regulated by both SAMe and MTA. Finally, overexpression increased, while reduced expression of MAT2? inhibited growth and caused apoptosis. The current proposal will extend these novel observations in five specific aims: 1. Examine transcriptional regulation of MAT2A in colon cancer cell lines ¿ we will determine how MAT2A is transcriptionally regulated at baseline and in response to growth factors, SAMe and MTA; 2. elucidate the molecular mechanism(s) of MAT2A and MAT2? up-regulation in colon cancer ¿ we will use resected colon cancer and normal tissue specimens to elucidate the mechanisms of their up-regulation; 3. determine how MAT genes influence growth and death of colon cancer cells ¿ we will determine how MAT2A and MAT2? regulate growth and apoptosis; 4. elucidate the mechanisms of SAMe and MTA-induced apoptosis in colon cancer cells ¿ we will define the molecular mechanisms and examine whether normal colon epithelial cells are affected; and 5. Assess changes in MAT expression during tumor formation and efficacy of SAMe and MTA in chemoprevention and treatment of intestinal tumors ¿ we will examine whether SAMe and MTA can prevent spontaneous polyp formation in Min mice, and halt progression and reverse already established aberrant crypt foci in Min mice treated with azoxymethane. Successful completion of these studies should greatly enhance our understanding of the role of MAT and SAMe in colon cancer pathogenesis and may provide a novel therapeutic approach for both chemoprevention and treatment of colon polyps and cancer, topics that are highly relevant to public health. PROJECT NARRATIVE Colon cancer remains one of the most common cancers in the western world. At the present time effective chemopreventive therapy that is devoid of side effects is lacking. The goals of this project are to investigate a new paradigm in colon cancer development and see if S-adenosylmethionine (SAMe), a nutritional supplement widely available, and its metabolite methylthioadenosine (MTA) can be effective in the chemoprevention and treatment of colon cancer.