A novel regulation of VEGF expression by HIF‐1α and STAT3 in HDM2 transfected prostate cancer cells

Appu Rathinavelu,Praneetha Muthumani,Madhusudhanan Narasimhan

doi:10.1111/j.1582-4934.2011.01472.x

Abstract

On the basis of increasing roles for HDM2 oncoprotein in cancer growth and progression, we speculated that HDM2 might play a major role in hypoxia-induced metastatic process. For verification of this hypothesis, wild-type LNCaP prostate cancer cells and HDM2 transfected LNCaP-MST (HDM2 stably transfected) cells were studied. The data obtained from our experiments revealed that the HDM2 transfected LNCaP-MST cells possessed an ability to multiply rapidly and show distinct morphological features compared to non-transfected LNCaP cells. During exposures to hypoxia HDM2 expression in the LNCaP and LNCaP-MST cells was significantly higher compared to the normoxic levels. The LNCaP-MST cells also expressed higher levels of HIF-1α (hypoxia-inducible factor-1α) and p-STAT3 even under the normoxic conditions compared to the non-transfected cells. The HIF-1α and p-STAT3 expressions were increased several fold when the cells were subjected to hypoxic conditions. The HIF-1α and p-STAT3 protein expressions observed in HDM2 transfected LNCaP-MST cells were 20 and 15 folds higher, respectively, compared to the non-transfected wild-type LNCaP cells. These results demonstrate that HDM2 may have an important regulatory role in mediating the HIF-1α and p-STAT3 protein expression during both normoxic and hypoxic conditions. Furthermore, the vascular endothelial growth factor (VEGF) expression that is typically regulated by HIF-1α and p-STAT3 was also increased significantly by 136% (P < 0.01) after HDM2 transfection. The overall results point towards a novel ability of HDM2 in regulating HIF-1α and p-STAT3 levels even in normoxic conditions that eventually lead to an up-regulation of VEGF expression.

Highlights

Overexpression of HDM2 in cancer cells generally leads to constitutive inhibition of p53, which allows the tumour cells to escape from p53-induced cell cycle arrest and apoptosis [1]
The levels of HIF-1␣, STAT3 and vascular endothelial growth factor (VEGF) detected in HDM2 transfected LNCaP-MST cell lines during normoxia and hypoxia in our experiments presented us with an important finding related to tumour angiogenesis
It is recognized that HDM2 oncoprotein has profound effects on cell proliferation and tumour growth [3]

Summary

Introduction

Overexpression of HDM2 in cancer cells generally leads to constitutive inhibition of p53, which allows the tumour cells to escape from p53-induced cell cycle arrest and apoptosis [1]. Angiogenesis, the process of new blood vessels formation from a pre-existing vasculature, is considered to be essential for enhancing tumour growth and metastasis [8] This angiogenic process is tightly regulated by hypoxia through the transcriptional control of pro-angiogenic growth factors such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor, transforming growth factor, interleukin 8, etc. Loss of p53 activity in tumour cells enhances the levels of HIF-1␣ and STAT3 to augment gene transcription in response to hypoxia, including VEGF expression [11, 16]. The levels of HIF-1␣, STAT3 and VEGF detected in HDM2 transfected LNCaP-MST cell lines during normoxia and hypoxia in our experiments presented us with an important finding related to tumour angiogenesis. The preliminary results of these findings along with our hypothesis are presented

Methods

Results

Conclusion