Vascular Endothelial Growth Factor Transcriptional Activation Is Mediated by Hypoxia-inducible Factor 1α, HDM2, and p70S6K1 in Response to Phosphatidylinositol 3-Kinase/AKT Signaling

Heath D Skinner,Jenny Z Zheng,Jing Fang,Faton Agani,Bing-Hua Jiang

doi:10.1074/jbc.m404097200

Abstract

Vascular endothelial growth factor (VEGF) expression is elevated in ovarian and other cancer cells. However, the mechanism that causes the increase in VEGF expression still remains to be elucidated. In this study, we demonstrated that activation of PI3K signaling mediated VEGF protein expression at the transcriptional level through hypoxia-inducible factor 1alpha (HIF-1alpha) expression in human ovarian cancer cells. We found that inhibition of PI3K activity by LY294002 decreased VEGF transcriptional activation and that forced expression of AKT completely reversed the inhibitory effect. HDM2 and p70S6K1 are two downstream targets of AKT that mediate growth factor-induced VEGF transcriptional activation and HIF-1alpha expression. The inhibition of PI3K by LY294002 inhibited p70S6K1 and HDM2 activity in the cells. Forced expression of p70S6K1 or HDM2 reversed LY294002-inhibited VEGF transcriptional activation and HIF-1alpha expression. This study identifies a potential novel mechanism responsible for increased VEGF expression in ovarian cancer cells. It also indicates the important role of VEGF and HIF-1 in ovarian tumorigenesis and angiogenesis, which is mediated by the PI3K/AKT/HDM2 and AKT/p70S6K1 pathways in ovarian cancer cells.

Highlights

Vascular endothelial growth factor (VEGF)1 is essential for both physiological and pathological angiogenesis and has been shown to play a critical role in ovarian cancer
We demonstrated that activation of PI3K signaling mediated VEGF protein expression at the transcriptional level through hypoxia-inducible factor 1␣ (HIF-1␣) expression in human ovarian cancer cells
We wanted to determine whether PI3K signaling regulates VEGF expression and transcriptional activation and to determine whether PI3K-mediated VEGF expression is regulated by HIF-1␣ expression in ovarian cancer cells

Summary

Introduction

Vascular endothelial growth factor (VEGF) is essential for both physiological and pathological angiogenesis and has been shown to play a critical role in ovarian cancer. HIF-1␤ is constitutively expressed in cells, whereas HIF-1␣ expression is up-regulated by hypoxia, as well as by a variety of growth factors and oncogenes (16 –23). PI3K signaling was shown to regulate HIF-1␣ expression in some cell systems in response to growth factors and hypoxia (20 – 23, 32, 33), whereas it was shown not to be involved in HIF-1␣ regulation in other cell lines [34]. Pharmacologic inhibition of PI3K decreased ovarian cancer cell proliferation and tumor growth in vivo and rendered ovarian cancer cells more sensitive to chemotherapy agents [35, 39, 40]. We wanted to determine whether PI3K signaling regulates VEGF expression and transcriptional activation and to determine whether PI3K-mediated VEGF expression is regulated by HIF-1␣ expression in ovarian cancer cells. We further investigated the possible mechanism by which PI3K signaling mediates VEGF and HIF-1␣ expression and identified potential signaling molecules for regulating VEGF and HIF-1␣ expression

Methods

Results

Conclusion