VEGF regulation by the TSC2 tumor suppressor

描述(由申请人提供)： 结节性硬化症复合体2(TSC2)基因的功能突变导致结节性硬化症(TSC)，TSC是一种在许多组织中发生肿瘤的疾病。TSC2处于一条整合生长因子和营养物质的细胞外信号与蛋白质翻译装置的途径，但该途径对其肿瘤抑制功能的贡献尚不清楚。癌症易感综合征TSC和von Hippel-Lindau(由VHL肿瘤抑制基因突变引起)之间的相似性，使我假设TSC2和pVHL之间存在功能联系。我现在已经证明，TSC2的缺失，就像pVHL的缺失一样，会导致一个基因表达程序的激活，该程序赋予细胞选择性生长优势，受转录因子缺氧诱导因子(HIF)的调节(Brugarolas等人，2003年)。TSC2失活足以上调HIF，并且与野生型TSC2不同，用TSC2疾病相关突变体重建TSC2缺陷细胞不能恢复HIF调节，这表明这一功能对于肿瘤抑制是重要的。由于HIF水平通常受氧压变化的调节，而这种反应在TSC2缺乏的细胞中受到损害，因此我假设TSC2的功能也可能受到氧水平变化的调节。事实上，虽然野生型细胞在低氧条件下下调哺乳动物雷帕霉素靶标(MTOR)的功能，但TSC2缺失的细胞无法做到这一点，这表明在这些条件下需要TSC2来抑制mTOR。此外，暴露在低氧环境下会导致TSC2的快速磷酸化。这项提案中概述的实验旨在揭示TSC2功能受低氧调控的机制。进一步了解缺氧对TSC2的调控可能有助于深入了解其作为肿瘤抑制因子的功能。

DESCRIPTION (provided by applicant): Loss of function mutations in the Tuberous Sclerosis Complex 2 gene (TSC2) result in Tuberous Sclerosis Complex (TSC), a disease characterized by the development of tumors in many tissues.TSC2 is in a pathway that integrates extracellular signals from growth factors and nutrients with the protein translation apparatus but the contribution of this pathway to its tumor suppression function is unclear. Similarities between the cancer prone syndromes TSC and von Hippel-Lindau (resulting from mutations in the VHL tumor suppressor gene), led me to hypothesize the existence of a functional link between TSC2 and pVHL. I have now demonstrated that loss of TSC2, like loss of pVHL, results in the activation of a program of gene expression conferring a selective growth advantage to cells that is regulated by the transcription factor Hypoxia-lnducible Factor (HIF) (Brugarolas et al., 2003). TSC2 inactivation is sufficient to upregulate HIF and reconstitution of TSC2-deficient cells with a TSC2 disease-associated mutant, unlike with wild-type TSC2, fails to restore HIF regulation suggesting that this function is important for tumor suppression. Because HIF levels are normally regulated by changes in oxygen tension and this response is impaired in TSC2-deficient cells, I hypothesized that TSC2 function might also be regulated by changes in oxygen levels. Indeed, while wild-type cells downregulate mammalian Target of Rapamycin (mTOR) function in response to hypoxia, TSC2 deficient cells fail to do so, suggesting that TSC2 is required for mTOR inhibition under these conditions. Furthermore, exposure to hypoxia results in the rapid phosphorylation of TSC2. The experiments outlined in this proposal aim to unravel the mechanism whereby TSC2 function is regulated by hypoxia. A greater understanding of TSC2 regulation by hypoxia might provide insight into its function as a tumor suppressor.