Abstract 429: HuR and microRNA-128 Competitively Regulate Vascular Endothelial Growth Factor C to Modulate Inflammatory Lymphangiogenesis

Abstract

Macrophages respond to acute and chronic tissue injuries such as infection, ischemia, atherosclerosis, and tumor expansion with the production of cytokines, growth factors, and matrix remodeling factors. Many of these factors are encoded by mRNAs that, through interactions with RNA binding proteins and noncoding RNAs, are subject to signal-dependent post-transcriptional regulation. Macrophage recruitment and adhesion-triggered signaling, specifically by β2 integrin engagement, promotes stabilization of some mRNAs by inducing the nuclear-to-cytoplasmic translocation of the RNA binding protein HuR. HuR binds and stabilizes mRNAs bearing AU-rich elements that, when unbound by HuR, confer short mRNA half-life and limit protein production. By promoting stability and translation, HuR functionally opposes RNA degradation and translational repression by microRNAs. Lymphangiogenesis, largely mediated by VEGF-C’s engagement of its lymphatic endothelial cell receptor VEGFR3, plays a role in tissue edema clearance, cholesterol homeostasis, tumor metastasis, hypertension, and atherosclerosis. Here, we report competitive post-transcriptional regulation of VEGF-C in macrophages by HuR and miR-128. Translation of VEGF-C is repressed by the binding of miR-128 to its 3’-UTR. This binding and repression is abrogated by β2 integrin engagement in an HuR-dependent manner. Using an HuR conditional allele and a transgenic fluorescent marker of lymphatic endothelium, we show that macrophage-specific HuR deletion in mice leads to a reduction in lymphatic vessel proliferation and VEGF-C protein expression in an in vivo model of inflammatory lymphangiogenesis. Our data implicate the loss of HuR and consequent unopposed miR-128 activity in impaired VEGF-C production and lymphatic expansion in vivo. Our investigation includes transcriptome and RISC footprint profiling of activated primary macrophages to identify additional HuR regulated factors that act in concert with VEGF-C to drive lymphangiogenesis. In conclusion, this study describes a novel regulatory mechanism in which adhesion signaling in macrophages promotes growth factor expression necessary for lymphatic vascular expansion in response to inflammatory stimuli.