The proton-coupled amino acid transporter PAT1 has been postulated to regulate the amino acid-stimulated mTORC1 through two different mechanisms, either it activates mTORC1 by sensing and transducing the lysosomal amino acid signal to mTORC1, or it inhibits mTORC1 by decreasing the signal level, as increased PAT1 has been shown to either activate or inactivate mTORC1 in the human embryonic kidney HEK293 cells. The current study aims to clarify the cause of these controversial observations, which is promoted by the recent discovery that the lysosomal PAT1 can be induced by starvation. Here, we show that under the normal culture condition, overexpression of PAT1 did not apparently change the mTORC1 activity in the fast proliferating cells. However when these cells were synchronized by starvation, followed by nutrient replenishment for a short period of time, the mTORC1 activity was decreased by PAT1 overexpression; if the nutrient stimulation lasted for longer time, the mTORC1 activities could be recovered in the PAT1-overexpressing cells. In addition, we showed the starvation-induced lysosomal PAT1 was gradually decreased during the nutrient replenishment. These results reveal that the influence of PAT1 on mTORC1 seems to be affected by the nutrient condition and the level of lysosomal PAT1. We further demonstrate that suppressing the transport activity of PAT1 abolished its inhibitory effect on mTORC1. Our data support a mechanism that PAT1 can negatively regulate mTORC1 by controlling the cellular nutrient signal level.

中文翻译：

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氨基酸转运蛋白PAT1以营养敏感的方式调节mTORC1，这需要其转运活性。

假定质子偶联的氨基酸转运蛋白PAT1通过两种不同的机制调节氨基酸刺激的mTORC1，要么通过将溶酶体氨基酸信号感应并将其转导到mTORC1来激活mTORC1，要么通过降低信号水平来抑制mTORC1，因为增加的PAT1已显示在人胚胎肾HEK293细胞中激活或灭活mTORC1。当前的研究旨在阐明这些有争议的观察结果的原因，这是由于最近发现饥饿引起的溶酶体PAT1的发现。在这里，我们表明，在正常培养条件下，PAT1的过表达并没有明显改变快速增殖细胞中的mTORC1活性。但是，当这些细胞因饥饿而同步时，随后在短时间内补充营养，PAT1过表达降低了mTORC1的活性。如果营养刺激持续更长的时间，则可以在过表达PAT1的细胞中恢复mTORC1活性。此外，我们显示了饥饿诱导的溶酶体PAT1在营养补充过程中逐渐减少。这些结果表明，PAT1对mTORC1的影响似乎受营养条件和溶酶体PAT1水平的影响。我们进一步证明抑制PAT1的运输活性消除了其对mTORC1的抑制作用。我们的数据支持PAT1可以通过控制细胞营养信号水平来负调控mTORC1的机制。可以在过表达PAT1的细胞中恢复mTORC1活性。此外，我们显示了饥饿诱导的溶酶体PAT1在营养补充过程中逐渐减少。这些结果表明，PAT1对mTORC1的影响似乎受营养状况和溶酶体PAT1水平的影响。我们进一步证明抑制PAT1的运输活性消除了其对mTORC1的抑制作用。我们的数据支持PAT1可以通过控制细胞营养信号水平来负调控mTORC1的机制。可以在过表达PAT1的细胞中恢复mTORC1活性。此外，我们显示了饥饿诱导的溶酶体PAT1在营养补充过程中逐渐减少。这些结果表明，PAT1对mTORC1的影响似乎受营养状况和溶酶体PAT1水平的影响。我们进一步证明抑制PAT1的运输活性消除了其对mTORC1的抑制作用。我们的数据支持PAT1可以通过控制细胞营养信号水平来负调控mTORC1的机制。这些结果表明，PAT1对mTORC1的影响似乎受营养条件和溶酶体PAT1水平的影响。我们进一步证明抑制PAT1的运输活性消除了其对mTORC1的抑制作用。我们的数据支持PAT1可以通过控制细胞营养信号水平来负调控mTORC1的机制。这些结果表明，PAT1对mTORC1的影响似乎受营养状况和溶酶体PAT1水平的影响。我们进一步证明抑制PAT1的运输活性消除了其对mTORC1的抑制作用。我们的数据支持PAT1可以通过控制细胞营养信号水平来负调控mTORC1的机制。