Binding of the Andes Virus Nucleocapsid Protein to RhoGDI Induces the Release and Activation of the Permeability Factor RhoA

Abstract

Andes virus (ANDV) nonlytically infects pulmonary microvascular endothelial cells (PMECs) causing acute pulmonary edema termed hantavirus pulmonary syndrome (HPS). In HPS patients virtually every PMEC is infected, however the mechanism by which ANDV induces vascular permeability and edema remains to be resolved. The ANDV nucleocapsid (N) protein activates the GTPase, RhoA, in primary human PMECs causing VE-Cadherin internalization from adherens junctions and PMEC permeability. We found that ANDV N protein failed to bind RhoA, but co-precipitates RhoGDI (Rho GDP-dissociation inhibitor), the primary RhoA repressor that normally sequesters RhoA in an inactive state. ANDV N protein selectively binds the RhoGDI C-terminus (69-204) but fails to form ternary complexes with RhoA or inhibit RhoA binding to the RhoGDI N-terminus (1-69). However, we found that ANDV N protein uniquely inhibits RhoA binding to an S34D phosphomimetic RhoGDI mutant. Hypoxia and VEGF increase RhoA induced PMEC permeability by directing Protein Kinase C (PKC) phosphorylation of S34 on RhoGDI. Collectively, ANDV N protein alone activates RhoA by sequestering and reducing RhoGDI available to suppress RhoA. In response to hypoxia and VEGF activated PKC, ANDV N protein additionally directs the release of RhoA from S34-phosphorylated RhoGDI, synergistically activating RhoA and PMEC permeability. These findings reveal a fundamental edemagenic mechanism that permits ANDV to amplify PMEC permeability in hypoxic HPS patients. Our results rationalize therapeutically targeting PKC and opposing Protein Kinase A (PKA) pathways that control RhoGDI phosphorylation as a means of resolving ANDV induced capillary permeability, edema and HPS. ImportanceHPS causing hantaviruses infect pulmonary endothelial cells causing vascular leakage, pulmonary edema and a 35% fatal acute respiratory distress syndrome (ARDS). Hantaviruses dont lyse or disrupt the endothelium but dysregulate normal EC barrier functions and increase hypoxia directed permeability. Our findings reveal a novel underlying mechanism of EC permeability resulting from ANDV N protein binding to RhoGDI, a regulatory protein that normally maintains edemagenic RhoA in an inactive state and inhibits EC permeability. ANDV N sequesters RhoGDI and enhances the release of RhoA from S34 phosphorylated RhoGDI. These findings indicate that ANDV N induces the release of RhoA from PKC phosphorylated RhoGDI, synergistically enhancing hypoxia directed RhoA activation and PMEC permeability. Our data suggests inhibiting PKC and activating PKA phosphorylation of RhoGDI as mechanisms of inhibiting ANDV directed EC permeability and therapeutically restricting edema in HPS patients. These findings may be broadly applicable to other causes of ARDS.