Pam (Protein associated with Myc) functions as an E3 Ubiquitin ligase and regulates TSC/mTOR signaling
Pam (Protein associated with Myc) functions as an E3 Ubiquitin ligase and regulates TSC/mTOR signaling
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DOI：
10.1016/j.cellsig.2008.01.020
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发表时间：
2008-06-01
影响因子：
4.8
通讯作者：
Ramesh, Vijaya
中科院分区：
文献类型：
--
作者：
Han, Sangyeul;Witt, Rochelle M.;Ramesh, Vijaya
肿瘤抑制因子tuberin由恶性硬化复合物（TSC）基因TSC 2编码，负调控雷帕霉素靶蛋白（mTOR）通路，其在控制细胞生长和增殖中起关键作用。除了天然存在的突变之外，已知包括Akt、RSK 1和ERK的几种激酶磷酸化和磷酸化块茎蛋白。我们证明了一种新的机制，通过泛素化的块茎蛋白失活的帕姆，一个假定的环指含E3泛素（Ub）连接酶在哺乳动物细胞。我们发现，帕姆协会与E2泛素结合酶，和tuberin可以泛素化的帕姆通过其环指结构域。泛素化不依赖于Akt、RSK 1和ERK激酶的磷酸化。Pam也通过其RING指结构域自我泛素化。此外，与块茎蛋白形成异源二聚体的TSC 1蛋白错构蛋白保护块茎蛋白免受Pam的泛素化。然而，TSC 1不能保护TSC 2的疾病相关的错义突变体免受Pam的泛素化。此外，在大鼠原代神经元中通过RNA干扰（RNAi）敲低Pam提高了tuberin的水平，并随后抑制mTOR通路。我们的研究结果提供了新的证据表明，Pam可以作为一个E3 Ub连接酶对tuberin和调节mTOR信号，表明Pam可以反过来调节细胞的生长和增殖，以及神经元功能，通过TSC/mTOR途径在哺乳动物细胞。(C)2008年爱思唯尔公司All rights reserved.
The tumor suppressor tuberin, encoded by the Tuberous Sclerosis Complex (TSC) gene TSC2, negatively regulates the mammalian target of rapamycin (mTOR) pathway, which plays a key role in the control of cell growth and proliferation. In addition to naturally occurring mutations, several kinases including Akt, RSK1, and ERK are known to phosphorylate and inactivate tuberin. We demonstrate a novel mechanism of tuberin inactivation through ubiquitination by Pam, a putative RING finger-containing E3 ubiquitin (Ub) ligase in mammalian cells. We show that Pam associates with E2 ubiquitin-conjugating enzymes, and tuberin can be ubiquitinated by Pam through its RING finger domain. Tuberin ubiquitination is independent of its phosphorylation by Akt, RSK1, and ERK kinases. Pam is also self-ubiquitinated through its RING finger domain. Moreover, the TSC1 protein hamartin, which forms a heterodimer with tuberin, protects tuberin from ubiquitination by Pam. However, TSC1 fails to protect a disease-associated missense mutant of TSC2 from ubiquitination by Pam. Furthermore, Pam knockdown by RNA interference (RNAi) in rat primary neurons elevates the level of tuberin, and subsequently inhibits the mTOR pathway. Our results provide novel evidence that Pam can function as an E3 Ub ligase toward tuberin and regulate mTOR signaling, suggesting that Pam can in turn regulate cell growth and proliferation as well as neuronal function through the TSC/mTOR pathway in mammalian cells. (C) 2008 Elsevier Inc. All rights reserved.