一個名為mTOR的酵素在細胞的生長代謝扮演樞紐的角色，舉凡生長因子、營養、能量供給都會透過此蛋白質/酵素使細胞得以存活、生長。在細胞中，mTOR會與不同的蛋白聚合，形成兩類型的複合體：mTOR蛋白複合體I與II。mTOR蛋白複合體I中主要由mTOR、mLST8與Raptor所組成。它會受到生長因子等外來刺激活化活性，透過磷酸化下游分子4EBP1與S6K1影響蛋白質的合成。另一個由mTOR、mLST8、mSIN1與Rictor聚合形成的mTOR蛋白複合體II，相較於mTOR蛋白複合體I，mTOR蛋白複合體II相關研究就少了許多。根據過去實驗室的結果發現，有一個蛋白質因為能與Rictor結合，暫命名為RICAP且和肌肉分化有關。因此，此研究欲探討Rictor/RICAP的下游分子及RICAP如何調節肌肉細胞的分化與型態。我們發現Akt、SGK1而不是PKCζ是位於Rictor/RICAP複合體作用的下游；進一步的研究發現FoxO1、FoxO3的磷酸化在Rictor或RICAP蛋白量降低的肌肉細胞株中有相似的下降，表示FoxO1/3可能是SGK1分子作用的下游；利用Small GTPase活性分析法得知Rac1亦可能牽涉在因RICAP蛋白量降低而使肌肉細胞不能分化的訊息傳遞中。總而言之，RICAP/Rictor/mTORC2在肌肉細胞分化中扮演角色，其機轉可能是透過SGK1/FoxO/分化，並與Rac1有關。

The serine/threonine kinase, mammalian target of rapamycin (mTOR), plays a crucial role in growth factor, nutrition, and energy supplement by which it controls cellular process such as survival, growth, and metabolism. Through associating with different components in cells, mTOR forms two complexes, named mTORC1 and mTORC2. mTORC1, consisted of mTOR, mLST8 and Raptor, affects protein synthesis via phosphorylation of 4EBP1 and S6K1. mTORC2 is comprised mTOR, mLST8, mSin1, and rictor. Compared to mTORC1, the detail molecular mechanism and signaling transduction regarding of mTORC2 are much less known. A novel protein, named temporarily Rictor associated protein (RICAP), was previously found in a Rictor immunoprecipitation assay and related to muscle differentiation. Hence, this study tends to dissect the downstream signaling of Rictor/RICAP and how RICAP regulates muscular differentiation. We find Akt and SGK1, but not PKCζ, are the downstream proteins of Rictor/RICAP complex. Furthermore, the decrease of FoxO1 phosphorylation is similar in C2C12 containing Rictor or RICAP RNAi. Such a phenomenon was also observed in terms of FoxO3. It means both FoxO1 and FoxO3 are downstream proteins of SGK1. By utilizing GTPase activity assay, Rac1 activity was decreased in either Rictor RNAi or RICAP RNAi cells. Taken together, Rictor/RICAP/mTORC2 plays a crucial role in muscular differentiation by which the mechanism could mediate SGK1/FoxO and possibly relate to Rac1 as well.

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