Juncture of the cytoskeleton and innate immune signaling pathways: the role of Suppressor of IKK epsilon (SIKE)

The innate immune system rapidly responds to challenges by pathogens via activation of an inflammatory response. As a convergence point for multiple inflammatory and anti‐viral signaling pathways, TANK binding kinase 1 (TBK1) serves as a catalytic hub to initiate host defenses. Suppressor of IKK epsilon (SIKE) is a newly identified TBK1 substrate. The goal of this project was to identify the function of SIKE within the host's anti‐viral response. Co‐immunoprecipitation – tandem MS/MS analyses of the SIKE interaction network identified several interactions with cytoskeletal components. Immunofluorescence assays of endogenous SIKE with cytoskeletal markers and colocalization analyses indicated that SIKE colocalized with tubulin, actin, and a‐actinin. Reciprocal immunoprecipitation (RcIPs) studies confirmed the SIKE:tubulin and SIKE:a‐actinin interaction that appeared enhanced following dsRNA stimulation, a mimic of viral infection. ELISA assays were used to characterize the binding affinity between SIKE and the cytoskeletal proteins under unstimulated and simulated viral‐stimulated conditions. The SIKE:actin interaction was not detected by RcIP. In vitro immunoprecipitation assays mapped direct interactions between SIKE:tubulin and SIKE:a‐actinin and were used to further probe for a weak SIKE:actin interaction. Assays employed purified cytoskeletal proteins and full‐length (residues 1–207), N‐terminal (residues 1–112), C – terminal (residues 113–207) or a phosphomimetic (S6E) of a 6x‐His‐tagged SIKE construct. Together these studies establish an interaction between SIKE and cytoskeletal proteins that may provide a direct link between innate immune signaling and cytoskeletal components. Support or Funding Information This work was supported by NIH grant R21AI107447 and the University of San Diego SURE program.