Role of Hyperplasia Suppressor Gene (HSG) in cell growth.

我们最近发现Mfn 2过表达通过抑制Ras-Raf-MEK-ERK信号通路在多种细胞系中引起生长抑制。 为了研究Mfn 2的抗增殖特性的生理相关性，我们将我们的研究扩展到人外周血T细胞。 我们想知道在通过T细胞受体激活T细胞期间Mfn 2水平发生了什么。 我们的数据表明，激活诱导的降解Mfn 2细胞进入细胞周期之前。 阻断活化诱导的Mfn 2降解的药理学抑制剂（LY 294002，一种PI 3激酶抑制剂;雷帕霉素，一种mTOR抑制剂;和A443654，一种AKT抑制剂）也阻断了细胞周期。 Mfn 2降解的阻断不是细胞周期抑制的一般结果，因为晚期细胞周期阻断剂（阿非地霉素，一种S期阻断剂;和诺考达唑，一种G2/M期阻断剂）阻断了细胞周期，但没有阻止Mfn 2的降解。 这些数据表明，活化诱导的Mfn 2降解是细胞进入细胞周期的先决条件。 组成型活性AKT的过度表达导致Mfn 2的下调，这可以被蛋白酶体抑制剂阻断。 Akt介导的Mfn 2下调是通过mTORC 1途径，因为（i）这种下调被雷帕霉素阻断，（ii）mTOR的过度表达导致Mfn 2下调。 我们的数据表明，mTOR参与激活诱导的ROS产生，这反过来又激活p38 MAP激酶，导致Mfn 2的磷酸化和随后的降解。总的来说，我们的数据表明，PI 3 K-AKT-mTOR通路在活化诱导的Mfn 2下调和随后的静息T细胞增殖中起重要作用。 已知来自老年小鼠的T细胞在其增殖能力方面存在缺陷。 为了研究Mfn 2在来自老年小鼠的T细胞的增殖应答中的状态，通过T细胞受体将来自年轻和老年小鼠的初始和记忆CD 4 + T细胞活化3天，并且使用全细胞裂解物通过蛋白质印迹分析确定Mfn 2的状态。 激活诱导的Mfn 2降解的程度是少得多的记忆相比，幼稚的人口，这与减少增殖能力的记忆相比，幼稚的人口。 我们目前正在调查的机制，负责改变记忆人群中的Mfn 2的降解，无论他们的年龄。

We have shown recently that Mfn2 overexpression caused growth suppression in multiple cell lines by suppressing Ras-Raf-MEK-ERK signaling pathway. To investigate the physiological relevance of the anti-proliferative properties of Mfn2, we extended our studies to human peripheral blood T cells. We wanted to know what happens to the Mfn2 levels during T cell activation through T cell receptors. Our data have demonstrated that the activation-induced degradation of Mfn2 preceded the cells entry into the cell cycle. Pharmacological inhibitors (LY294002, a PI3 kinase inhibitor; rapamycin, an mTOR inhibitor; and A443654, an AKT inhibitor) that blocked the activation-induced degradation of Mfn2, also blocked the cell cycle. The blockage in Mfn2 degradation was not a general consequence of cell cycle inhibition, since late cell cycle blockers (aphidicolin, an S-phase blocker; and Nocodazole, a G2/M blocker) blocked the cell cycle without preventing the degradation of Mfn2. These data suggest that the activation-induced Mfn2 degradation is a pre-requisite for cells entry into the cell cycle. Over-expression of constitutively active AKT resulted in the downregulation of Mfn2, which can be blocked by a proteasome inhibitor. Akt-mediated downregulation of Mfn2 was via the mTORC1 pathway since (i) this downregulation was blocked by rapamycin, and (ii) over-expression of mTOR caused Mfn2 downregulation. Our data suggested that mTOR was involved in activation-induced ROS production, which in turn activated p38 MAP kinase resulting in the phosphorylation of Mfn2 and subsequent degradation. Collectively, our data suggest that PI3K-AKT-mTOR pathway plays an important role in activation-induced downregulation of Mfn2 and subsequent proliferation of resting T cells. It is known that T cells from aged mice have deficit in their proliferative capacities. To investigate the status of Mfn2 in the proliferative response of T cells from aged mice, naive and memory CD4+ T cells from young and old mice were activated through T cell receptor for 3 days, and the status of Mfn2 was determined by western blot analysis using whole cell lysates. The degree of activation-induced Mfn2 degradation was much less in memory as compared to nave populations, which correlated with the reduced proliferative capacities of memory as compared to naive populations. We are currently investigating the mechanisms responsible for the altered degradation of Mfn2 in memory populations irrespective of their age.