Abstract 8: RNA-binding Protein Quaking Maintains Endothelial Barrier Function Through β-catenin and VE-cadherin

Abstract

Endothelial barrier function plays a major role in the onset of atherosclerosis. This barrier is determined largely by adherens junctions. Remarkably little is known about their regulation at the post[[Unable to Display Character: ‐]]transcriptional level. We find that the RNA-binding protein Quaking (QKI), known for its function in embryonic blood vessel formation, is highly expressed in quiescent adult endothelial cells (EC) in vivo. In vitro, EC displayed increased levels of QKI when cultured under laminar atheroprotective flow. Using KLF2 overexpression and a human QKI promoter reporter gene, we found that KLF2 mediates this increase in QKI expression. Subsequently we aimed to investigate the role of QKI in EC vascular integrity. Silencing of QKI markedly impaired (0.65 fold ±0.13; p<0.05) the capacity to form a high resistance endothelial monolayer, as measured using Electric cell-substrate impedance sensing. To confirm a role for QKI in maintaining EC barrier function in vivo, we measured Bradykinin-induced vascular leakage in QKI viable mice (QKIv), which express decreased levels of the QKI protein. Indeed, QKIv mice displayed a 20% (p<0.05) increase in extravascular accumulation of Evans blue-labeled albumin compared to wild type littermates. Interestingly, the mRNA of both β-catenin and VE-cadherin, the prime adhesion proteins in EC adherens junctions, contain conserved QKI-binding sites. Moreover the targeted reduction of QKI resulted in a reduction of β-catenin and VE-cadherin protein expression. Importantly, we identified a direct role for QKI in regulating mRNA biology of β-catenin and VE-cadherin, as RNA immunoprecipitation and luciferase-reporter assays revealed that QKI can directly bind to the mRNA and induces transcript translation, respectively. This effects was perturbed upon reduced QKI expression. In conclusion, we show that QKI functions as a critical regulator of β-catenin and VE-cadherin in endothelial cells, and the modulation of QKI expression affects endothelial monolayer integrity, in vitro and in vivo. These studies provide novel insight into the importance of post-transcriptional regulation of components of the endothelial adherens junction, and may have wide ranging implications for the preservation of vascular integrity in disease.