Laboratory for Cellular and Molecular Thyroid Research, Division of Endocrinology and Metabolism, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
J Biol Chem. 2013 Mar 1;288(9):6511-21. doi: 10.1074/jbc.M112.399485. Epub 2013 Jan 15.
Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that regulates cell growth, proliferation, and survival. mTOR is frequently activated in human cancers and is a commonly sought anticancer therapeutic target. However, whether the human mTOR gene itself is a proto-oncogene possessing tumorigenicity has not been firmly established. To answer this question, we mutated evolutionarily conserved amino acids, generated eight mutants in the HEAT repeats (M938T) and the FAT (W1456R and G1479N) and kinase (P2273S, V2284M, V2291I, T2294I, and E2288K) domains of mTOR, and studied their oncogenicity. On transient expression in HEK293T cells, these mTOR mutants displayed elevated protein kinase activities accompanied by activated mTOR/p70S6K signaling at varying levels, demonstrating the gain of function of the mTOR gene with these mutations. We selected P2273S and E2288K, the two most catalytically active mutants, to further examine their oncogenicity and tumorigenicity. Stable expression of the two mTOR mutants in NIH3T3 cells strongly activated mTOR/p70S6K signaling, induced cell transformation and invasion, and remarkably, caused rapid tumor formation and growth in athymic nude mice after subcutaneous inoculation of the transfected cells. This study confirms the oncogenic potential of mTOR suggested previously and demonstrates for the first time its tumorigenicity. Thus, beyond the pivotal position of mTOR to relay the oncogenic signals from the upstream phosphatidylinositol 3-kinase/Akt pathway in human cancer, mTOR is capable potentially of playing a direct role in human tumorigenesis if mutated. These results also further support the conclusion that mTOR is a major therapeutic target in human cancers.
哺乳动物雷帕霉素靶蛋白（mTOR）是一种丝氨酸/苏氨酸蛋白激酶，可调节细胞生长、增殖和存活。mTOR 在人类癌症中经常被激活，是一种常见的抗癌治疗靶点。然而，人类 mTOR 基因本身是否是具有致癌性的原癌基因尚未得到确凿证实。为了回答这个问题，我们突变了进化上保守的氨基酸，在 HEAT 重复（M938T）和 FAT（W1456R 和 G1479N）以及激酶（P2273S、V2284M、V2291I、T2294I 和 E2288K）结构域中生成了八个突变体，并研究了它们的致癌性。在 HEK293T 细胞中的瞬时表达中，这些 mTOR 突变体显示出升高的蛋白激酶活性，并伴有不同水平的激活的 mTOR/p70S6K 信号，证明这些突变导致 mTOR 基因获得功能。我们选择了 P2273S 和 E2288K，这两个最具催化活性的突变体，进一步研究它们的致癌性和致瘤性。这两个 mTOR 突变体在 NIH3T3 细胞中的稳定表达强烈激活了 mTOR/p70S6K 信号，诱导细胞转化和侵袭，并且显著地，在转染细胞皮下接种后，迅速在无胸腺裸鼠中形成肿瘤并生长。这项研究证实了 mTOR 先前被提示的致癌潜力，并首次证明了其致瘤性。因此，除了 mTOR 在人类癌症中从上游磷脂酰肌醇 3-激酶/Akt 途径传递致癌信号的关键位置之外，如果发生突变，mTOR 有可能在人类肿瘤发生中发挥直接作用。这些结果还进一步支持了 mTOR 是人类癌症的主要治疗靶点的结论。
