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Asian Journal of Andrology (2012) 14, 745–751; doi:10.1038/aja.2011.197; published online 18 June 2012
Vascular endothelial growth factor A, secreted in response to transforming growth factor-β1 under hypoxic conditions, induces autocrine effects on migration of prostate cancer cells
Eric Darrington*, Miao Zhong*, Bao-Han Vo and Shafiq A Khan*
Center for Cancer Research and Therapeutic Development, Clark Atlanta University, Atlanta, GA 30314, USA
Correspondence: Dr SA Khan, (skhan@cau.edu)
* These authors contributed equally to this work.
Received 8 September 2011; Revised 18 November 2011; Accepted 20 December 2011
Advance online publication 18 June 2012.
| Abstract |
Hypoxia and transforming growth factor-β1 (TGF-β1) increase vascular endothelial growth factor A (VEGFA) expression in a number of malignancies. This effect of hypoxia and TGF-β1 might be responsible for tumor progression and metastasis of advanced prostate cancer. In the present study, TGF-β1 was shown to induce VEGFA165 secretion from both normal cell lines (HPV7 and RWPE1) and prostate cancer cell lines (DU145 and PC3). Conversely, hypoxia-stimulated VEGFA165 secretion was observed only in prostate cancer cell lines. Hypoxia induced TGF-β1 expression in PC3 prostate cancer cells, and the TGF-β type I receptor (ALK5) kinase inhibitor partially blocked hypoxia-mediated VEGFA165 secretion. This effect of hypoxia provides a novel mechanism to increase VEGFA expression in prostate cancer cells. Although autocrine signaling of VEGFA has been implicated in prostate cancer progression and metastasis, the associated mechanism is poorly characterized. VEGFA activity is mediated via VEGF receptor (VEGFR) 1 (Flt-1) and 2 (Flk-1/KDR). Whereas VEGFR-1 mRNA was detected in normal prostate epithelial cells, VEGFR-2 mRNA and VEGFR protein were expressed only in PC3 cells. VEGFA165 treatment induced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in PC3 cells but not in HPV7 cells, suggesting that the autocrine function of VEGFA may be uniquely associated with prostate cancer. Activation of VEGFR-2 by VEGFA165 was shown to enhance migration of PC3 cells. A similar effect was also observed with endogenous VEGFA induced by TGF-β1 and hypoxia. These findings illustrate that an autocrine loop of VEGFA via VEGFR-2 is critical for the tumorigenic effects of TGF-β1 and hypoxia on metastatic prostate cancers.
Keywords: cell migration; hypoxia; prostate cancer; transforming growth factor-β1 (TGF-β1); vascular endothelial growth factor A (VEGFA) |
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