Molecular concepts that monitor methionine metabolism

项目摘要 蛋氨酸在氨基酸中占有特殊的地位。这一现象最好地说明了这一点 被称为“癌症的蛋氨酸依赖”。这种癌症特有的代谢需求描述了 细胞在不含蛋氨酸但添加即刻蛋氨酸的培养基中的生长行为 代谢前体同型半胱氨酸。非致瘤细胞在体内保持增殖率 同型半胱氨酸，但绝大多数癌细胞，与其组织来源无关，诱导细胞 同型半胱氨酸培养时，细胞周期停滞，继而发生细胞凋亡。重要的是，蛋氨酸- 依赖性不仅存在于培养的癌细胞中。实体瘤和白血病也依赖于 高通量通过与蛋氨酸相连的代谢途径。此外，长寿是 这与饮食中蛋氨酸的摄取密切相关。众所周知，限制卡路里摄入会增加 许多生物体的寿命。这种效果是通过限制蛋氨酸在其他丰富的 节食。相反，用蛋氨酸补充低卡路里饮食会消除卡路里的益处 对寿命的限制。 这项建议旨在了解蛋氨酸水平波动对 细胞和组织生理学，以及对蛋氨酸依赖的解释 癌症。文献中的报告和我们的初步研究表明，蛋氨酸使用独特的 尚未在分子水平上研究的信号通路。我们发现，经典的 氨基酸和营养响应TOR通路不参与蛋氨酸的测量或信号传递 级别。此外，下游代谢产物S-腺苷蛋氨酸和S-腺苷-蛋氨酸- 同型半胱氨酸(SAH)-而不是蛋氨酸本身-似乎是这两种疾病的效应代谢物 对癌细胞增殖和寿命的影响。SAM是主要的细胞甲基供体，而 SAM/SAH比率通常被认为是细胞甲基化潜力的决定因素。就其本身而言 这些代谢物的理想位置是通过特定的甲基化来通知蛋氨酸水平。 事件。我们已经确定了RNA组和特定蛋白质上的甲基化事件是候选事件 将蛋氨酸水平与特定的细胞反应联系起来。这项提案的一个目标是确定 通过甲基化控制的关键RNA和蛋白质，表现出超敏反应 对蛋氨酸或SAM/SAH浓度波动的反应。对变化的敏感反应 甲基化使这些RNA和蛋白质触发信号，最终触发细胞通路， 将蛋氨酸代谢与细胞增殖和其他细胞功能联系起来。的第二个目标 因此，建议确定这些路径，并开始调查它们是如何连接的 代谢与细胞生理学在分子水平上。 理解将蛋氨酸代谢与其他细胞相结合的分子概念 功能预示着治疗癌症和其他与年龄相关的疾病的新治疗策略。 因此，这项提议旨在将分子洞察力发展到到目前为止的分子基础上 未被探索的，具有巨大治疗开发潜力的生物过程。

Project Summary Methionine occupies a special place among amino acids. This is best illustrated by the phenomenon called “methionine-dependence of cancer”. This cancer specific metabolic need describes the behavior of cells when grown in medium lacking methionine but supplemented with the immediate metabolic precursor homocysteine. Non-tumorigenic cells maintain their proliferation rate in homocysteine, but the vast majority of cancer cells, independent of their tissue origin, induce cell cycle arrest followed by apoptosis when cultured in homocysteine medium. Importantly, methionine- dependence is not only observed in cultured cancer cells. Solid tumors and leukemias also depend on high flux through the metabolic pathways connected to methionine. Furthermore, longevity is strikingly connected to dietary methionine uptake. Caloric restriction is well known to increase longevity in many organisms. This effect is mimicked by restricting methionine in an otherwise rich diet. Conversely, supplementing a low-calorie diet with methionine eliminates the benefits of caloric restriction for longevity. This proposal seeks understanding of the molecular effects that fluctuating methionine levels have on cellular and organismal physiology, as well as an explanation for the methionine dependence of cancer. Reports in the literature and our preliminary studies suggest that methionine uses unique signaling pathways that have not been explored at the molecular level. We find that the canonical amino acid and nutrient responsive TOR pathway is not involved in measuring or signaling methionine levels. Furthermore, the downstream metabolites S-adenosylmethionine (SAM) and S-adenosyl- homocysteine (SAH) — and not methionine itself — appear to be the effector metabolites for both the effects on cancer cell proliferation and longevity. SAM is the primary cellular methyl donor and the SAM/SAH ratio is generally considered the determinant of the cellular methylation potential. As such these metabolites are ideally positioned to signal methionine levels through specific methylation events. We have identified methylation events on groups of RNAs and specific proteins as candidates that link methionine levels to specific cellular responses. One goal of this proposal is to identify the critical RNAs and proteins that are controlled through methylation and show a hypersensitive response to fluctuations in methionine or SAM/SAH concentrations. The sensitive reaction to varying methylation allows these RNAs and proteins to trigger signals and ultimately cellular pathways that connect methionine metabolism to cell proliferation and other cellular functions. The second goal of the proposal is thus to identify these pathways and initiate investigation of how they connect metabolism with cell physiology at the molecular level. Understanding the molecular concepts that integrate methionine metabolism with other cellular functions promise new therapeutic strategies for treatment of cancer and other age-related disorders. Thus, this proposal aims to development molecular insight into a fundamental, so far molecularly unexplored, biological process with great potential for therapeutic exploitation.