Poster abstracts

Poster number 142 submitted by Peng Yao

Mechanism and Function of a 3-Element mRNA Switch in the VEGFA 3'UTR

Peng Yao (Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland Clinic), Alka A. Potdar (Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland Clinic), Partho Sarothi Ray (Department of Biology, Indian Institute of Science Education and Research, Kolkata, India), Paul L. Fox (Department of Cellular and Molecular Medicine, Lerner Research Institute, Cleveland Clinic)

Abstract:
Cell regulatory circuits integrate diverse and conflicting environmental cues to generate appropriate condition-dependent responses. Here, we elucidate the components and mechanisms driving a protein-directed RNA switch in the 3'UTR of vascular endothelial growth factor (VEGF)-A [1]. We describe a novel HILDA (hypoxia-inducible hnRNP L–DRBP76–hnRNP A2/B1) complex that coordinates a three-element RNA switch, enabling VEGFA mRNA translation during combined hypoxia and inflammation. In addition to binding the CA-rich element, heterogeneous nuclear ribonucleoprotein (hnRNP) L regulates switch assembly and function. hnRNP L undergoes two condition-dependent post-translational modifications: IFN-γ induces prolyl hydroxylation and von Hippel-Lindau (VHL)-mediated proteasomal degradation; whereas, hypoxia stimulates hnRNP L phosphorylation at Tyr359, inducing binding to hnRNP A2/B1 which stabilizes the protein. Phospho-hnRNP L recruits DRBP76 (double-stranded RNA binding protein 76) to the 3'UTR where it binds an adjacent AU-rich stem-loop element, “flipping” the RNA switch by disrupting the GAIT (Gamma-interferon Activated Inhibitor of Translation) element, preventing GAIT complex binding, and driving robust VEGFA mRNA translation. We exploited a genome-wide analysis of hypoxia-induced RNA switches that suggest a widespread posttranscriptional regulon that might contribute to tumorigenesis. We show that halofuginone (HF), a derivative from a Chinese herbal-based medicine, can enhance GAIT-mediated translational silencing activity and reverse GAIT-dependent RNA switches. Also, we demonstrate that CA-rich miR-574-3p acts as a decoy of hnRNP L, which binds CA-rich regions of mRNAs, and prevents HILDA binding of target mRNAs and reduces translation of the entire pool of HILDA-directed RNA switch transcripts. Our studies reveal novel molecular mechanisms, biological significance, and therapeutic potential of stress-responsive HILDA-directed RNA switches.

References:
1. Peng Yao, Alka A. Potdar, Partho Sarothi Ray, Sandeepa M. Eswarappa, Andrew C. Flagg, Belinda Willard, and Paul L. Fox. The HILDA complex coordinates a conditional switch in the 3’-untranslated region of the VEGFA mRNA. Plos Biology 2013(11): e1001635

Keywords: RNA switch, VEGF-A, miRNA