Regulation of VEGF in Tumors by Ras, EGF and PTEN

描述（由申请人提供）：血管内皮生长因子（VEGF）是血管生成的关键介质，在癌症中经常过度表达。在许多体内模型中，抑制VBGF功能可以抑制肿瘤生长。虽然缺氧长期以来被认为是VEGF的有效诱导剂，但VEGF也可以在常氧环境中表达。最近的证据表明，在肿瘤肿块生长到足以容纳缺氧区域的大小之前，血管生成可以在肿瘤肿块中发生，这表明血管生成因子可能在常氧条件下由这些肿瘤表达。缺氧条件下VEGF rnRNA的诱导机制已知与缺氧诱导因子-1 （HIF-1）有关，而正常缺氧条件下VEGF的上调机制则知之甚少。该资助的总体目的是研究在正常氧合条件下，通过癌症中常见的改变（特别是表皮生长因子受体（EGFR）的激活和Ras和PTEN的突变），VEGF上调的机制。EGFR刺激可提高U87人胶质母细胞瘤细胞中VEGF mRNA水平和启动子活性。将野生型PTEN引入U87细胞后，PTEN失活，降低VEGF mRNA水平和启动子活性。特异性目标1将侧重于定义该途径中的元件，该途径似乎依赖于PI(3)激酶，但不依赖于HIF- 1。大鼠1成纤维细胞H-ras转化导致常氧条件下VEGF mRNA表达增加6倍。此外，在常氧Rat1-ras细胞中hif -1 α蛋白水平升高，这是一个意想不到的发现，因为hif -1 α传统上被认为只在缺氧条件下被诱导。特异性目的2的重点是确定在常氧条件下HIF- 1 α的增加是否导致VEGF表达的增加。目的2还将研究连接Ras激活、hif -1 α和VEGF表达的信号通路。这些实验将有助于更好地理解HIF-1 α的调控、肿瘤中VEGF过表达的机制、EGFR激活和Ras、PTEN突变对基因表达的影响。

DESCRIPTION (provided by applicant): Vascular endothelial growth factor (VEGF), a key mediator of angiogenesis, is often overexpressed in cancers. In many in vivo models, inhibition of VBGF function arrests tumor growth. While hypoxia has long been recognized to be a potent inducer of VEGF, VEGF can also be expressed in normoxia. Recent evidence indicates that angiogenesis can develop in tumor masses before they have grown to a size large enough to contain hypoxic regions, suggesting that angiogenic factors may be expressed by these tumors under normoxic conditions. In contrast to the induction of VEGF rnRNA under hypoxia whose mechanism is known to involve the hypoxia-inducible factor-1 (HIF-1), the upregulation of VEGF in normoxia is much less well understood. The overall aim of this grant is to study mechanisms of VEGF upregulation in normoxia by alterations commonly found in cancers: specifically, epidermal growth factor receptor (EGFR) activation and mutations in Ras and PTEN. VEGF mRNA levels and promoter activity in U87 human glioblastoma cells are increased by EGFR stimulation. Introduction of wild type PTEN into U87 cells, in which PTEN is inactivated, decreases VEGF mRNA levels and promoter activity. Specific Aim 1 will focus on defining the elements in this pathway, which appears to be PI(3) kinase dependent but independent of HIF- 1. H-ras transformation of Rat 1 fibroblasts leads to a six-fold increase in VEGF mRNA expression in normoxia. Furthermore, the level of HIF-1alpha protein is increased in normoxic Rat1-ras cells, an unexpected finding given that HIF-1alpha has traditionally been thought to only be induce under hypoxic conditions. The focus of Specific Aim 2 is to determine whether this increase in HIF- 1 alpha causes the increase in VEGF expression under normoxia. Aim 2 will also examine the signaling pathways that link Ras activation, HIF-1alpha and VEGF expression. These experiments will lead to a better understanding of HIF-1 alpha regulation, mechanisms of VEGF overexpression in cancers, and the effects of EGFR activation and Ras and PTEN mutations on gene expression.