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Double-Stranded RNA-Binding Protein Regulates Vascular Endothelial Growth Factor mRNA Stability, Translation, and Breast Cancer Angiogenesis

Frank Vumbaca, Kathryn N. Phoenix, Daniel Rodriguez-Pinto, David K. Han, and Kevin P. Claffey^*

Center for Vascular Biology, University of Connecticut Health Center, Farmington, Connecticut 06030-3501

Received 7 November 2006/ Returned for modification 4 December 2006/ Accepted 1 November 2007

Vascular endothelial growth factor (VEGF) is a key angiogenic factor expressed under restricted nutrient and oxygen conditions in most solid tumors. The expression of VEGF under hypoxic conditions requires transcription through activated hypoxia-inducible factor 1 (HIF-1), increased mRNA stability, and facilitated translation. This study identified double-stranded RNA-binding protein 76/NF90 (DRBP76/NF90), a specific isoform of the DRBP family, as a VEGF mRNA-binding protein which plays a key role in VEGF mRNA stability and protein synthesis under hypoxia. The DRBP76/NF90 protein binds to a human VEGF 3' untranslated mRNA stability element. RNA interference targeting the DRBP76/NF90 isoform limited hypoxia-inducible VEGF mRNA and protein expression with no change in HIF-1-dependent transcriptional activity. Stable repression of DRBP76/NF90 in MDA-MB-435 breast cancer cells demonstrated reduced polysome-associated VEGF mRNA levels under hypoxic conditions and reduced mRNA stability. Transient overexpression of the DRBP76/NF90 protein increased both VEGF mRNA and protein levels synthesized under normoxic and hypoxic conditions. Cells with stable repression of the DRBP76/NF90 isoform showed reduced tumorigenic and angiogenic potential in an orthotopic breast tumor model. These data demonstrate that the DRBP76/NF90 isoform facilitates VEGF expression by promoting VEGF mRNA loading onto polysomes and translation under hypoxic conditions, thus promoting breast cancer growth and angiogenesis in vivo.

Published ahead of print on 26 November 2007.

Present address: The Feinstein Institute for Medical Research, Autoimmune Disease Center, 350 Community Drive, Manhasset, NY 11030.