Department of Carcinogenesis, University of Texas M.D. Anderson Cancer Center, Smithville, Texas, United States of America.
PLoS One. 2010 Feb 16;5(2):e9239. doi: 10.1371/journal.pone.0009239.
Autosomal dominant polycystic kidney disease (ADPKD) is a commonly inherited renal disorder caused by defects in the PKD1 or PKD2 genes. ADPKD is associated with significant morbidity, and is a major underlying cause of end-stage renal failure (ESRF). Commonly, treatment options are limited to the management of hypertension, cardiovascular risk factors, dialysis, and transplantation when ESRF develops, although several new pharmacotherapies, including rapamycin, have shown early promise in animal and human studies. Evidence implicates polycystin-1 (PC-1), the gene product of the PKD1 gene, in regulation of the mTOR pathway. Here we demonstrate a mechanism by which the intracellular, carboxy-terminal tail of polycystin-1 (CP1) regulates mTOR signaling by altering the subcellular localization of the tuberous sclerosis complex 2 (TSC2) tumor suppressor, a gatekeeper for mTOR activity. Phosphorylation of TSC2 at S939 by AKT causes partitioning of TSC2 away from the membrane, its GAP target Rheb, and its activating partner TSC1 to the cytosol via 14-3-3 protein binding. We found that TSC2 and a C-terminal polycystin-1 peptide (CP1) directly interact and that a membrane-tethered CP1 protects TSC2 from AKT phosphorylation at S939, retaining TSC2 at the membrane to inhibit the mTOR pathway. CP1 decreased binding of 14-3-3 proteins to TSC2 and increased the interaction between TSC2 and its activating partner TSC1. Interestingly, while membrane tethering of CP1 was required to activate TSC2 and repress mTOR, the ability of CP1 to inhibit mTOR signaling did not require primary cilia and was independent of AMPK activation. These data identify a unique mechanism for modulation of TSC2 repression of mTOR signaling via membrane retention of this tumor suppressor, and identify PC-1 as a regulator of this downstream component of the PI3K signaling cascade.
常染色体显性多囊肾病（ADPKD）是一种常见的遗传性肾脏疾病，由 PKD1 或 PKD2 基因缺陷引起。ADPKD 与显著的发病率有关，是终末期肾衰竭（ESRF）的主要潜在原因。通常，当 ESRF 发展时，治疗选择仅限于高血压、心血管危险因素、透析和移植的管理，尽管几种新的药物治疗方法，包括雷帕霉素，在动物和人类研究中显示出早期的希望。证据表明，多囊蛋白-1（PC-1），PKD1 基因的产物，在调节 mTOR 途径中起作用。在这里，我们证明了多囊蛋白-1（CP1）的细胞内羧基末端尾巴通过改变结节性硬化复合物 2（TSC2）肿瘤抑制因子的亚细胞定位来调节 mTOR 信号的机制，TSC2 是 mTOR 活性的守门员。AKT 引起的 TSC2 第 S939 位磷酸化导致 TSC2 通过 14-3-3 蛋白结合从膜上分离出来，其 GAP 靶标 Rheb 及其激活伙伴 TSC1 到细胞质中。我们发现 TSC2 和一个 C 末端多囊蛋白-1 肽（CP1）直接相互作用，并且膜结合的 CP1 保护 TSC2 免受 AKT 第 S939 位磷酸化，将 TSC2 保留在膜上以抑制 mTOR 途径。CP1 降低了 14-3-3 蛋白与 TSC2 的结合，并增加了 TSC2 与其激活伙伴 TSC1 的相互作用。有趣的是，虽然 CP1 的膜结合对于激活 TSC2 和抑制 mTOR 是必需的，但 CP1 抑制 mTOR 信号的能力不需要初级纤毛，并且独立于 AMPK 激活。这些数据确定了一种通过这种肿瘤抑制因子的膜保留来调节 TSC2 对 mTOR 信号的抑制的独特机制，并确定 PC-1 是 PI3K 信号级联的这个下游成分的调节剂。
