Role of TRAF2 and NCK Interacting Kinase (TNIK) in the Regulation of Innate Interferon Signaling and Suppression of Viral Infection in Endothelial Cells

Abstract

Endothelial cells (ECs) are the major cell types that govern vascular tone and homeostasis. Endothelial inflammation and activation are the first step in the initiation of atherosclerosis and several vascular dysfunctions. Interferon signaling (IFN Type I and II) are key inflammatory pathways in ECs and are implicated to be involved in the vascular complications associated with viral infections and systemic lupus erythematosus. Traf2 and Nck-interacting kinase (TNIK), is a serine/threonine-protein kinase (Ste20) family member of MAP kinase kinase kinase kinases (MAP4K). TNIK is reported to be involved in multiple biological functions such as regulation of actin dynamics, cell morphology, neuronal structure, and cellular proliferation. The underlying mechanisms of TNIK in EC functions and inflammation remains largely unknown. To identify the pathways and functions of TNIK in ECs, we performed next-generation RNA sequencing (RNA-seq) in ECs under TNIK depletion conditions (siTNIK). We found that TNIK affects several cellular pathways, but most significantly they were involved in the regulation of interferon (IFN) and hypercytokinemia/hyperchemokinemia pathways. Using molecular expression studies, we identified that TNIK depletion significantly downregulates several interferon molecules at both mRNA and protein expression levels. Further, to probe the regulatory effects induced by TNIK on the IFN pathway we used treatment of wildtype human adenovirus to ECs. Adenovirus have been previously shown to elicit strong interferon responses in many human cell types. We observed cytopathic effect (CPE) induced by wild type virus only under siTNIK condition but not in other controls. In addition, after the treatment of wildtype adenovirus, viral replication was observed only under TNIK depletion but not in other controls, suggesting that TNIK plays an important role in activation of IFN pathway and in the suppression of viral infection in ECs. In addition to elucidating the novel role of TNIK in activation of interferon pathway, our study supports the idea that ECs have innate immune functions manifested by strong interferon responses as a pro-survival mechanism. Our study will pave the way for the understanding of chronic vascular conditions under several inflammatory conditions and viral infections and be critical in the development of therapeutics targeting vascular dysfunctions.