Regulation of VEGF/HIF-1 by AKT: Implications for Radiotherapy

描述(申请人提供)：我们的长期目标是确定在人类癌症中普遍激活的PI3K/AKT通路增加血管内皮生长因子(VEGF)和缺氧诱导因子-1a(HIF-1a)表达的机制。我们也希望了解这在目前临床上使用的EGFR抑制剂的疗效中可能起到什么作用。血管内皮生长因子是血管生成的关键介质，在人类癌症中经常过度表达。长期以来，低氧被认为是通过转录因子HIF-1有效地诱导血管内皮细胞生长因子表达。我们发现，PI3K/AKT通路至少通过两种不同的机制在调节血管内皮生长因子中发挥重要作用。首先，PI3K/AKT途径通过增加转录因子Sp1与血管内皮生长因子近端核心启动子的结合来促进转录。其次，AKT途径可以增加HIF-1a的表达，这也可以导致血管内皮生长因子转录增加，特别是在低氧条件下。在具体目标1中，我们将探索AKT导致Sp1介导的血管内皮生长因子启动子反式激活增加的机制。在特定的目标2中，我们将研究AKT下游参与蛋白质翻译的靶点GSK-3J3在增加HIF-1a方面的潜在作用。一些药物目前正在临床测试中，可能部分通过上述机制发挥作用。EGFR抑制剂(如吉非替尼、厄洛替尼)可抑制PI3K/AKT信号转导，我们发现这些抑制剂还可降低HIF-1a和VEGF的表达。我们的初步数据表明，吉非替尼可能会增加肿瘤的氧合，这应该会导致放射增敏。因此，在特定的目标3中，我们将研究抑制EGFR对HIF-1α和VEGF表达的影响，以及对体内肿瘤氧合的影响，以及对放射敏感性的影响。我们将研究血管生长的重要介质--血管内皮生长因子在人类肿瘤中的表达是如何增加的。这些研究的临床重要性在于，目前临床上使用的EGFR抑制剂可能通过这些途径发挥作用，增加肿瘤的氧合。增加氧合应该会使肿瘤对辐射更敏感；因此，我们的研究可能有助于优化EGFR抑制剂与辐射的组合。

DESCRIPTION (provided by applicant): Our long-term goal is to determine mechanisms by which the PI3K/AKT pathway, which is commonly activated in human cancers, increases expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-la (HIF-la). We also wish to understand what role this may play in the efficacy of EGFR inhibitors, which are currently being used in the clinic. VEGF, a key mediator of angiogenesis, is often overexpressed in human cancers. Hypoxia has long been recognized to be a potent inducer of VEGF expression through the transcription factor HIF-1. We have found that the PI3K/AKT pathway plays an important role in VEGF regulation through at least two different mechanisms. First, the PI3K/AKT pathway increases transcription by increasing binding of the transcription factor Sp1 to the VEGF proximal core promoter. Secondly, the AKT pathway can increase the expression of HIF-1a, which can also lead to increased VEGF transcription, particularly in hypoxia. In Specific Aim 1 we will explore the mechanisms by which AKT leads to increased Sp1-mediated transactivation of the VEGF promoter. In Specific Aim 2 we will study the potential role of glycogen synthase kinase-3p (GSK-3J3), a downstream target of AKT involved in protein translation, on increasing HIF-1 a. A number of drugs are currently being tested in the clinic that may work in part through the mechanisms described above. EGFR inhibitors (e.g. gefitinib, erlotinib) decrease PI3K/AKT signaling and we have found that these inhibitors also decrease HIF-1a and VEGF expression. Our preliminary data suggest that gefitinib may increase tumor oxygenation, which should lead to increased radiosensitization. Therefore, in Specific Aim 3 we will study the effects of EGFR inhibition on HIF-1 a and VEGF expression and on tumor oxygenation in vivo and the effects on radiosensitivity. LAY SUMMARY: We will study how the expression of VEGF, an important mediator of blood vessel growth, is increased in human tumors. The clinical importance of these studies is that EGFR inhibitors currently being used in the clinic may work though these pathways to increase the oxygenation of tumors. Increased oxygenation should make tumors more sensitive to radiation; therefore, our studies may be important in helping to optimize the combination of EGFR inhibitors with radiation.