Novel Role of Importins in Endothelial Permeability and Inflammation

Abstract

Endothelial cell (EC) permeability and inflammation are central events in the pathogenesis of many inflammatory diseases including acute lung injury (ALI). Although importins (α and β) have been implicated in mediating the activation of NF‐kB, a master regulator of inflammation in epithelial and cancer cell, their role in regulating EC inflammation and barrier disruption remains unclear. In this study, we addressed the role of importins α4 and α3, adaptor molecules that interact with nuclear localization signal (NLS)‐containing proteins and importin β1, a carrier protein, which mediates the docking of the cargo/importin α complex to the nuclear pore to promote their translocation across the nuclear envelope, in the mechanism of EC permeability and inflammation. Exposure of EC to thrombin, a procoagulant and proinflammatory mediator, resulted in activation of the transcription factor NF‐κB and expression of its target genes VCAM‐1 and IL‐6. RNAi‐mediated knockdown of α4, α3 and β1 inhibited these responses. Further mechanistic analysis revealed that knockdown of α4, α3 or β1; each inhibited thrombin‐induced DNA binding activity of RelA/p65 as well as its phosphorylation at Ser536, a critical event that controls transcriptional capacity of RelA/p65 bound to DNA. Intriguingly, knockdown of α3, α4 or β1, each protected against thrombin‐induced EC barrier disruption. Together these studies identify a novel role of α3, α4 and β1 in EC inflammation and permeability associated with intravascular coagulation.Support or Funding InformationNIH (HL096907 and HL130870)