Abstract 19105: β2 Integrin-Dependent HuR-Mediated mRNA Stabilization in Macrophages is Required for Lymphatic Vessel Formation in Inflammatory Lymphangiogenesis

Abstract

Macrophages play a central role in the response to acute and chronic tissue injuries including infection, ischemia, and atherosclerosis, where their effector functions in injured tissue include cytokine, growth factor, and matrix remodeling factor production. β2 integrin engagement promotes stabilization of labile mRNAs bearing adenylate-uridylate-rich elements (AREs) by inducing the rapid nuclear-to-cytoplasmic translocation of the RNA binding protein HuR. The secretory role of macrophages in lymphangiogenesis, together with predicted HuR binding sites in the VEGF-C 3’-UTR, led us to hypothesize that HuR regulates VEGF-C production in macrophages in response to integrin engagement. In bone marrow-derived macrophages from mice harboring a myeloid-specific deletion of HuR, we observed that VEGF-C production is impaired due to an increase in the rate of VEGF-C mRNA decay. A conserved ARE was the degradation target and was necessary to mediate HuR-dependent transcript stability that in turn resulted in increased VEGF-C protein. The HuR knockout mice exhibit an abnormal lymphangiogenic response to intraperitoneal LPS injection despite intact macrophage recruitment. Preliminary data indicates a functional interaction between the mRNA stabilizing effect of HuR and the destabilizing effect of microRNA recognition sequences in the 3’-UTR of VEGF-C and that of other integrin-induced lymphangiogenic gene products including cytokines and matrix remodeling proteins. VEGF-C likely acts in concert with these other factors to help guide vessel formation at sites of tissue injury. In conclusion, β2 integrin signaling through HuR promotes VEGF-C production as a central component of a post-transcriptional gene regulatory program essential for macrophage-directed lymphangiogenesis, a finding with implications for processes including tissue ischemia, wound repair, extracellular fluid trafficking, and atherosclerosis.